Untitled - International Rice Research Institute

Contents 

Foreword 

Preface 

v 

vi 

INTRODUCTION 1 

FUNCTIONS OF SEED HEALTH TESTING 3 

Cataloguing pathogens of crops 3 

Detection methods 3 

Post introduction measures 5 

THE MISSING LINK 6 

Epidemiology 6 

Disease and infection cycles 7 

Seed transmission 8 

Relationship between seedborne inoculum and 9 

disease development in the field 

Inoculum level and inoculum thresholds 9 

Risk analysis 10 

Microorganisms associated with seed 11 

SEED HEALTH MANAGEMENT FOR CROP PRODUCTION 12 

IDENTIFICATION OF FUNGI DETECTED ON RICE SEED 13 

Seedborne fungi causing foliage diseases in rice 14 

Alternaria padwickii 14 

Bipolaris oryzae 17 

Cercospora janseana 21 

Microdochium oryzae 24 

Pyricularia oryzae 27 

Seedborne fungi causing stem, leaf sheath, and root diseases in rice 31 

Fusarium moniliforme 31 

Sarocladium oryzae 35 

Seedborne fungi causing grain and infloresence diseases in rice 38 

Curvularia sp. 38 

Fusarium solani 42 

Nigrospora sp. 44 

Phoma sorghina 47 

Pinatubo oryzae 51 

Tilletia barclayana 53 

Other fungi detected on rice seeds 57 

Acremoniella atra 58 

Acremoniella verrucosa 58 

iii

Alternaria longissima 59 

Alternaria tenuissima 59 

Aspergillus clavatus 60 

Aspergillus flavus-oryzae 60 

Aspergillus niger 61 

Chaetomium globosum 61 

Cladosporium sp. 62 

Curvularia eragrostidis 62 

Dreclslera hawaiiensis 63 

Epicoccum purpurascens 63 

Fusarium avenaceum 64 

Fusarium equiseti 65 

Fusarium larvarum 66 

Fusarium nivale 66 

Fusarium semitectum 67 

Gilmaniella humicola 67 

Memnoniella sp. 68 

Microascus cirrosus 68 

Monodictys putredinis 69 

Myrothecium sp. 70 

Nakataea sigmoidea 70 

Nectria haematococca 71 

Papularia sphaerosperma 71 

Penicillium sp. 72 

Pestalotia sp. 73 

Phaeoseptoria sp. 74 

Phaeotrichoconis crotolariae 74 

Pithomyces sp. 75 

Pyrenochaeta sp. 75 

Rhizopus sp. 76 

Septogloeum sp. 76 

Sordaria fimicola 77 

Spinulospora pucciniiphila 77 

Sterigmatobotrys macrocarpa 78 

Taeniolina sp. 78 

Tetraploa aristata 79 

Trichoderma sp. 79 

Trichothecium sp. 81 

Tritirachium sp. 81 

Ulocladium botrytis 80 

REFERENCES 82 

iv

Introduction 

The purpose of seed health testing is to assure the 

safe movement of seed of different crops, for research 

or trade. It is premised on the hypothesis that 

many harmful organisms are carried by and moved 

together with the seed, and that these organisms have 

the potential to cause severe damage to crop production 

and crop seed for international trade once they 

are introduced. Seed health testing information reveals 

the organisms carried by the seed and the level 

of infection, or infestation, that will be introduced to 

another region or country. The information, although 

useful, does not indicate the importance of organisms 

carried by the seed. For most plant diseases, this information 

is not available. Such information comes 

from experiments or surveys under field conditions 

where the seed is grown. 

Seed health testing can also be a means of quality 

control to improve seeding stocks for crop production 

by farmers. It is also useful for seed certification 

used by seed growers and public seed suppliers to 

farmers. Seed health testing is often done in the context 

of seed movement or trade for phytosanitary 

certification to meet plant quarantine regulations. The 

testing information, however, can also be applied to 

improve farmers’seed stocks for planting for crop 

management. In developing countries where farmers 

have to save their own seed for planting, knowledge 

of seed health can be very important to crop and pest 

management. It is a service that agricultural extension 

could provide. Farmers can acquire this knowledge 

through training. Seed health testing applied to 

seed certification would establish the standard for 

quality control. When the seed is put on the market, 

pest incidence is minimized and productivity of crop 

varieties is enhanced. 

Rice seed, like seeds of other crops, carries 

many organisms. Among them, fungi, bacteria, and 

nematodes are the most commonly detected microorganisms. 

These seedborne organisms can be 

pathogens and saprophytes. Many of the bacteria or 

fungi carried by rice seed are potential biological 

control agents against other rice pathogens. Some of 

them also promote seed germination and seedling 

vigor. The ecological relationship between these beneficial 

microorganisms and the pathogens or between 

pathogenic forms and nonpathogenic forms on rice 

seed needs further investigation. Very little research 

on this subject is published in scientific literature. 

Seedborne pathogens often serve as barriers to 

seed movement. Misunderstanding often arises because 

of insufficient biological and epidemiological 

data to guide the development of plant quarantine 

regulations. In scientific literature, research on 

seedborne pathogens focuses on developing methods 

for accurate and reliable detection of pathogens on or 

in the seed. Many importing countries need seed 

health information to determine whether the seed 

carries targeted pathogens important to quarantine. 

Without epidemiological data on the disease that the 

pathogen causes, we cannot establish the standard 

and level of importance of the disease. We know 

very little about crop damage and yield losses caused 

by pathogens carried by seed. Equally lacking is information 

about disease establishment in the field 

and the effect of seedborne pathogens on crop production. 

Not every pathogen carried by rice seed, for 

instance, is transmitted to the field when the seed is 

grown. Transmission varies from one pathogen to 

another and the same pathogen may react differently 

when the seed is sown in different growth conditions. 

These are important topics for further research. In 

this publication, we provide information on fungi 

commonly detected from rice seed during routine 

seed health testing. We also review briefly the missing 

links in information on seedborne pathogens and 

the seed as a source of inoculum for disease development 

in the field. 

Microorganisms carried by seeds can be classified 

as pathogens, nonpathogens, and nonpathogens 

with biological control properties. From the viewpoint 

of plant quarantine regulations, seed-carried microorganisms 

can be distinguished into either “hazard” or 

“common organisms” (Kahn and Mathur 1999). 

“Hazard” organisms involve those pathogens that 

have never been introduced into an area and can 

cause serious damage to crop production. Information 

on the level of damage caused by seedborne 

pathogens is not always available. The quarantine 

decision is often conservative to avoid any untoward 

consequences. Whether serious crop damage or 

yield losses would occur is a matter of speculation 

and not necessarily based on experimental results, 

1

which take into account various production situations 

and ecology. In reality, it is not possible or desirable 

to obtain seed lots free from any organism (Mew 

1997). 

From a plant pathologist’s point of view, there 

are missing links in documented information on 

seedborne pathogens. McGee (1995) pointed out the 

need for accurate information on seed transmission 

of some key seedborne pathogens. We need to study 

the epidemiology of seedborne pathogens in relation 

to disease development in the field. We need yield 

loss data to estimate the risk of seedborne pathogens. 

Furthermore, we need to study the role of seed health 

testing to improve farmers’ pest management and 

crop production. To know whether common pathogens 

carried by the seed pose a threat to crop production, 

we need to understand disease epidemiology. 

Conventional seed health testing provides adequate 

information about the frequency of detection from the 

seed and levels of seed infection. We need to assess 

whether these pathogens, upon detection, could be 

transmitted to the field when the seed is sown and if 

the disease that develops causes damage or injury to 

effect yield loss. In scientific literature, this information 

is not readily available or it needs to be confirmed. 

Very little research has been done in this 

area. Because of the increasing concern about 

seedborne pathogens, we need to understand their 

epidemiology. The initial inoculum is the key to understanding 

what causes an epidemic in a plant quarantine 

context. The threshold inoculum carried by a 

seed lot has to be defined in terms of its effect on 

transmission and disease establishment. Detection 

methods and the potential role of nonpathogenic microorganisms, 

especially those possessing biological 

control properties, must be studied and taken into 

account. 

2

Functions of seed health testing 

Seed health testing is done to determine microbial 

infection or contamination for quarantine purposes 

(e.g., international seed exchange or movement). It 

identifies the cause of seed infection that affects the 

planting value of seed lots for seed certification by 

seed growers to supply seed to farmers. Seed testing 

affects policies on seed improvement, seed trade, 

and plant protection. Neergard (1979) brought out the 

importance of pathogens carried by seeds and the 

disease potential assigned to pathogens. 

Several routine activities are undertaken during 

seed health testing. These include dry seed inspection, 

the standard blotter test for seed infection and 

contamination, postentry planting for field inspection 

of undetected plant diseases of seedborne and seedcontaminated 

pathogens, and certification. In seed 

multiplication for export, crop inspection prior to seed 

harvest offers an additional means to link seedborne 

pathogens and diseases of mother plants. All these 

activities provide preventive measures to eliminate 

the introduction of undesirable pathogens into a region 

or country. Seed health testing offers a powerful 

tool for documenting microorganisms associated with 

seeds. Information on microorganisms, however, 

needs to be associated with a database on yield loss 

and information on pathogens that cause diseases. 

Catalouging pathogens of crops 

For rice, seed health testing has been done on more 

than 500,000 seed lots following International Seed 

Testing Association (ISTA) rules (1985). A total of 

more than 80 fungi were detected on rice seeds 

(Table 1). The detection frequency varied. About 20 

species of fungal pathogens were detected from rice 

seed at any one time. Not all of them cause notable 

diseases in the field and it was not ascertained 

whether diseases were all seed-transmitted and, if so, 

what their transmission efficiency was. The role of a 

rice seed in a fungus life cycle is not clear. 

Pyricularia oryzae, the rice blast pathogen, although 

considered a very important rice pathogen, 

has the lowest detection frequency. The level varied 

according to seed source. Except Fusarium 

moniliforme, the seedborne inoculum of the other 

pathogens may not serve as an important source of 

secondary inoculum in the field. The infection level 

of P. oryzae is likely to be higher in temperate or 

subtropical environments than in tropical environments. 

The data set provides insights into the occurrence 

of rice fungal pathogens. The detection frequency 

and infection level are very high for Alternaria 

padwickii (80–90%) (Fig. 1). In tropical Asia, 

stackburn, the disease it causes, is hardly observed in 

the field. 

Detection methods 

Many detection methods have been developed over 

the years for various seedborne pathogens. We found 

the blotter test to be a common but efficient method 

of detecting seedborne fungal pathogens in rice seed. 

Following ISTA rules, the method involves plating 

400 seeds on some layers of moistened filter paper. 

Below is a list of the different detection methods used 

in routine seed health testing. Descriptions of these 

methods can be found in the references listed (see 

page 82). 

Seed health testing procedures involve techniques 

such as 

• Direct examination of dry seeds 

• Examination of germinated seeds 

• Examination of organisms removed by washing 

• Examination after incubation (both blotter and 

agar plates) 

• Examination of growing plants (for example, 

the seedling symptom test) 

• Embryo count methods 

• Molecular and serological techniques 

Other methods include a selective medium for 

specific pathogens. With advances in molecular 

techniques, emphasis in fungal identification and 

taxonomy has changed from a morphological approach 

(for example, spore size and spore shape) to 

a more functional approach based on aspects of the 

life cycle, mechanisms of spore production and release, 

DNA relationships, and physiological attributes. 

DNA analysis techniques such as the polymerase 

chain reaction (PCR), and random amplified 

polymorphic DNA (RAPD) analysis are the most 

commonly used tools. 

These are powerful techniques for detecting and 

for establishing the relationship between the inocu- 

3

Table 1. Fungi detected on rice seeds, IRRI Seed Health Unit (SHU) data (1983-97). 

Species Incidence a Species Incidence 

Alternaria padwickii +++ 

Bipolaris oryzae +++ 

Curvularia lunata +++ 

C. oryzae +++ 

Fusarium semitectum +++ 

F. moniliforme +++ 

Microdochium oryzae +++ 

Phoma spp. +++ 

Sarocladium oryzae +++ 

Alternaria longissima ++ 

Aspergillus clavatus ++ 

A. flavus-oryzae ++ 

A. niger ++ 

Curvularia affinis ++ 

C. oryzae ++ 

Cladosporium sp. ++ 

Epicoccum purpurascens ++ 

Nakataea sigmoidea ++ 

Nigrospora oryzae ++ 

Penicillium sp. ++ 

Pinatubo oryzae ++ 

Pithomyces maydicus ++ 

Rhizopus sp. ++ 

Tilletia barclayana ++ 

Ustilaginoidea virens ++ 

Acremoniella atra + 

Alternaria tenuissima + 

Annellophragmia sp. + 

Botrytis cinerea + 

Cephalosporium sp. + 

Cercospora janseana + 

Chaetomium globosum + 

Chramyphora sp. + 

Colletotrichum sp. + 

Corynespora sp. + 

Cunninghamella sp. + 

Curvularia cymbopogonis + 

C. eragrostidis + 

C. inaequalis 

C. intermedia + 

C. ovoidea + 

C. pallescens + 

C. stapeliae + 

Cylindrocarpon sp. + 

Darluca sp. + 

Diarimella setulosa + 

Diplodia sp. + 

Drechslera cynodontis + 

D. dematioideum + 

D. halodes + 

D. hawaiiensis + 

D. longistrata + 

D. maydis + 

D. rostrata + 

D. sacharri + 

D. sorokiniana + 

D. turcica + 

D. tetramera + 

D. victoriae + 

Fusarium avenaceum + 

F. decemcellulare + 

F. equiseti + 

F. fusarioides + 

F. graminearum + 

F. larvarum + 

F. longipes + 

F. nivale + 

F. solani + 

F. tumidum + 

Gilmaniella humicola + 

Graphium sp. + 

Leptoshaeria sacchari + 

Masoniomyces claviformis + 

Melanospora zamiae + 

Memnoniella sp. + 

Microascus cirrosus + 

Monodictys levis + 

M. putredinis + 

Nectria haematococca + 

Nigrospora sphaerica + 

Papularia sp. + 

Penicillifer pulcher + 

Periconia sp. + 

Pestalotia sp. + 

Phaeoseptoria sp. + 

Phaeotrichoconis crotolariae + 

Phyllosticta sp. + 

Phyllosticta glumarum + 

Pyrenochaeta oryzae + 

Pyricularia grisea + 

Septogloeum sp. + 

Septoria sp. + 

Sordaria fimicola + 

Spegazzinia deightonii + 

Spinulospora pucciniiphila + 

Stemphylium sp. + 

Sterigmatobotrys macrocarpa + 

Taeniolina sp. + 

Tetraploa aristata + 

Trichoderma sp. + 

Trichosporiella sp. + 

Trichothecium sp. + 

Trichosporiella sp. + 

Tritirachium sp. + 

Ulocladium sp. + 

Verticillium albo-atrum + 

a 

+++ = frequent, ++ = moderate, + = low. 

4

% infected seed lots 

100 

80 

60 

40 

20 

Alternaria padwickii 

Sarocladium oryzae 

Fusarium moniliforme 

Bipolaris oryzae 

Pyricularia grisea 

Tilletia barclayana 

0 

1989 1990 1991 1992 1993 1994 1995 1996 1997 

Year 

Fig. 1. Detection of common seedborne fungal pathogens of rice from exported seeds at IRRI, 1989-97. 

Table 2. Level of fungal pathogens detected from seeds, field observations on seed planted in the field after 

treatment, disease incidence, and level of fungal infection detected from harvested seeds (24 entries; 1996 dry 

season). 

Field inspection for disease 

Fungal pathogen RSHT a at receipt (%) Disease % 

Entries infected RSHT at harvest 

Alternaria padwickii 15.7 Stackburn 0 A. padwickii 10.7 

Curvularia spp. 5.4 Black kernel 0 Curvularia spp. 9.0 

Sarocladium oryzae 0.8 Sheath rot 2 (8.3%) S. oryzae 2.7 

Gerlachia oryzae 2.7 Leaf scald 2 (8.3%) G. oryzae 0.2 

Fusarium moniliforme 0.2 Bakanae 0 F. moniliforme 3.8 

Bipolaris oryzae 1.7 Brown spot 0 B. oryzae 0.4 

Pyricularia grisea 0 Blast 1 (4.1%) P. grisea 0 

Phoma sp. 1.6 Glume blight 0 Phoma sp. 4.6 

Tilletia barclayana 0.3 Kernel smut 0 T. barclayana 0 

Disease-free 19 entries (79%) 

a 

RSHT = routine seed health test. Seed treatment applied: hot water, 52–57°C for 15 min plus Benlate and Dithane M-45 at 0.1% by seed weight. 

lum of seedborne pathogens and diseases in the field. 

Postintroduction measures 

“Damage control” often refers to actions taken to 

minimize damage after it has happened. The concept 

can be applied to seedborne fungal pathogen management 

by relating it to postquarantine treatment. 

There is always concern that if a pathogen is unintentionally 

introduced into a country or region, it may 

cause potential damage to the crop. The entry of infected 

seeds when seed lots are brought into a country 

is unavoidable. However, it is still not clear 

whether the infected seed being introduced will begin 

an infection of the crop in the field. It is desirable to 

limit the probability of infection. Several 

postquarantine treatments can be applied to control 

such damage. Many of these postquarantine treatments 

provide measures to counteract the introduction 

of undesirable pathogens (Table 2). 

Seed health testing is important to assure the 

safe movement of seed on the one hand and to control 

the spread of seedborne diseases through seed 

movement on the other hand. 

Seed treatment and seed health testing to eliminate 

potential pathogens are damage control steps 

intended to avoid the introduction of key pathogens. 

Currently available information or control measures 

in place may not be adequate. Some control measures, 

such as seed treatment, successfully check the 

movement of pathogens from the seed. 

5

The missing link 

Epidemiology 

There is little doubt that many pathogens are 

seedborne. Questions arise, however, on whether the 

introduction of seedborne inoculum of these pathogens 

would lead to the establishment of a disease in 

the field or whether the field population of a fungal 

pathogen is derived from the seedborne inoculum. 

Pathogens of significance to quarantine suggest 

the potential of seed transmission. They also relate to 

the potential damage or yield loss caused by diseases 

derived from the seedborne inoculum of the pathogen. 

However, there is very little accurate information 

about yield loss caused by rice diseases, and 

diseases derived from seedborne inoculum. Yield 

loss caused by a pest outbreak or a disease epidemic 

is important in determining pathogens with quarantine 

significance. There are very few comprehensive 

studies or databases on yield losses caused by pests 

or pathogens in scientific literature. Studies conducted 

and documented by Savary et al (1996, 1997, 

1998, 2000a,b), Savary and Willocquet (1999), and 

Willocquet et al (1999a,b) are some of the most comprehensive 

ones on rice diseases. Using both survey 

and experimental data, they developed pest and 

pathogen profiles for different rice production situations 

(PS). Production situations refer to the set of 

environmental conditions—climatic, technical, social, 

economic, and biological—under which agricultural 

production takes place. These were then related 

to yield losses with individual pests and pathogens, 

and also pest and pathogen profiles. 

Savary et al (1996, 1997, 1998, 1999) believe 

that by using such a systems approach combined 

with different statistical analyses, all these factors 

could be captured by a limited number of variables, 

such as those that describe patterns of cropping practices, 

for example, method of crop establishment, 

amount of chemical fertilizer used, type of weed 

control, and rice cultivar type (with or without disease 

resistance). In reality, farmers’ practices are, to a 

large extent, reflections of, or adaptations to, social, 

physical, and biological environments. Injury profiles 

refer to the sequence of harmful organisms that may 

occur during the crop cycle. Many such organisms 

affect rice. The number of processes by which a pest 

or pathogen may affect rice, however, is limited to 

less than 10, and injuries are often associated with 

one another. On this basis, yield losses caused by 

individual injuries as well as by injury profiles establish 

the importance of rice pests and diseases in specific 

PS at the regional level (Savary et al 2000a,b). 

The database identified sheath blight caused by 

Rhizoctonia solani AG1 and brown spot caused by 

Bipolaris oryzae as the two most important diseases 

in rice in Asia, each responsible for 6% yield loss, 

whereas blast caused by Pyricularia grisea and bacterial 

blight caused by Xanthomonas oryzae pv. 

oryzae account for 1–3% and 0.1% yield losses, respectively. 

However, most rice cultivars planted by 

Asian farmers are resistant to these two diseases. If 

cultivars possess no resistance to these two diseases, 

yield losses are likely to be higher than current estimates. 

Other diseases, such as sheath rot, stem rot, 

and those known as sheath rot complex and grain 

discoloration (Cottyn et al 1996a,b), are responsible 

for rice yield losses ranging from 0.1% to 0.5%. All 

other diseases alone or in combination would not 

cause more than 0.5–1% yield losses based on estimates. 

Projected yield losses cause by various rice 

diseases under different production situations are 

given in Table 3. 

In seed health testing, detection frequency 

means the number of pathogens detected in a seed 

lot. Infection frequency refers to the number of seeds 

(based on 400 seeds tested) within a seed lot which 

are infected (Mew and Merca 1992) and is equivalent 

to the inoculum level. In the epidemiological 

sense, no information is available to correlate detection 

frequency and infection frequency to seed transmission 

and disease establishment in the field. Still, 

there are other questions related to seedborne pathogens 

that must be answered. In rice, in which most 

fungal pathogens can be seedborne, and for which 

current farmer cultural practices have done little to 

improve quality (a result of farm labor shortage and 

short turnaround time), what is introduced to the field 

with seeds when the rice crop is planted? In seed 

production fields, it is necessary to practice disease 

management to produce disease-free seed? 

6

Table 3. Pathogen profiles closely associated with rice production situations (PS) and potential yield losses caused 

by rice diseases (adapted and modified from Savary et al 1998, Savary and Willocquet 1999). 

PS1 PS2 PS3 PS4 PS5 PS6 Yield loss 

(%) 

Actual yield (t ha –1 ) 4.8 4.6 3.5 6.7 3.8 3.9 

Disease 

Blast a L L M M 1–3 

Bacterial blight L L L L L 0.2 

Bakanae VL 0.0 

Brown spot L L VH H H 6.6 

Sheath blight VH VH M VH H H 6.4 

Sheath rot complex M M H M 0.5 

Grain discoloration M M H M 0.1 

Characteristics of environments 

Mineral fertilizer m l l h m h 

Fallow period l l m s m s 

Drought stress l l h l h m 

Water stress l l l h h h 

Crop establishment tr tr tr ds ds ds 

Herbicide use m l l m l l 

Insecticide use m m m m m m 

Fungicide use l l l h h h 

Previous crop rice rice w/b w/b rice rice 

a 

In the surveys, rice varieties possessing resistance to blast and bacterial blight diseases. For characteristics of environments, m = moderate, h = 

high, l = low, tr = transplanted rice, ds = direct-seeded rice, s = short, w/b = wheat or barley. For diseases and grain discoloration, L = low, M = medium, 

H = high, VH = very high. 

Disease and infection cycles 

Figure 2 shows how seedborne inoculum reinfects 

the seed during the development of a disease epidemic: 

seedborne inoculum → disease establishment 

→ disease development in the field (infection cycle) 

→ crop damage or yield loss (effect of seedborne 

inoculum) → reinfection of infestation of seed (potential 

dissemination to other fields, regions, or countries). 

There is voluminous information on seedborne 

pathogens of various crops derived from routine seed 

health testing for either certification or issuance of 

phytosanitary certificates. Information on transmission 

of the pathogen from the infected or infested 

seed to disease development in the field is scarce. 

Various factors that affect the infection cycle are 

weather conditions, cropping practices, resistance or 

susceptibility of the variety, virulence of the pathogen, 

and amount of incoculum produced for secondary 

spread and efficiency of the inoculum. 

It is often assumed that, for a pathogen to be 

seedborne, it must be seed-transmitted. McGee 

(1995) indicated that in only very few seedborne 

pathogens is the transmission clearly established. 

When conditions in the nursery bed and the 

ecosystem where rice is grown re taken into account, 

there is inadequate documentation on plant 

quarantine to guide decision making. It is not 

known under what specific conditions seedborne 

pathogens are transmitted to the crop at the seedling 

stage. Blast caused by P. oryzae and bakanae 

caused by F. moniliforme, are two of the better 

known diseases (Ou 1985). Once a disease is established 

in a crop, its intensity will depend on factors 

that influence the infection cycle. Climatic 

conditions and crop management practices are 

crucial to disease development. 

In rice, the infection frequency of P. oryzae is 

very low, yet the disease potential under a conducive 

environment (e.g., upland, subtropical, and 

temperate) is very high. Once seedlings are infected 

from seedborne inoculum, even at a low 

infection rate, millions of conidia are produced for 

secondary infection. On the other hand, seedborne 

F. moniliforme often induces bakanae with only 

one cycle of infection. Therefore, the initial inocu- 

7

Seedborne 

inoculum 

Reinfection/ 

infection of seed 

Transmission 

(Establishment) 

Infected 

seed 

Crop damage/ 

Injury (Impact) 

Inoculum 

production 

Disease 

development 

Infection 

efficiency 

Climatic 

conditions 

Cropping 

environments 

Fig. 2. Diseases and infection cycles of a seedborne fungal disease and its effect. 

lum for F. moniliforme is important. Once the 

seedborne inoculum is minimized, the disease is 

likely to be controlled. 

Changes in crop cultivation methods and cultural 

practices affect seedborne diseases. In traditional 

methods of cultivation, rice seedlings are raised in a 

seedbed with a saturated water supply. Because of 

the reduction in arable land and the decreasing productivity 

of available agricultural land, new methods 

of cultivation are being developed. These new methods 

are conducive to the transmission and development 

of seedborne diseases previously considered 

minor. 

In epidemiological research, seed transmission 

and establishment of disease derived from seedborne 

inoculum should be considered. These data are essential 

for assessing the importance of seedborne 

pathogens. 

Seed transmission 

McGee (1995) indicated that one of the missing links 

in seed health testing is the lack of information on 

seed transmission. Based on postquarantine planting, 

one of the difficulties encountered is distinguishing 

between a disease that developed from inoculum 

derived from the seed and that from other sources. 

Polymerase chain reaction (PCR) DNA technology 

is useful in this regard. Based on DNA fingerprinting, 

patterns of a pathogen population can be distinguished 

from those of the pathogen manifesting a 

disease on the crop grown from the seed. This 

would establish the transmission of the seedborne 

inoculum and its relation to the disease on the crop 

in the field. In routine disease monitoring of field 

crops such as rice or other nursery crops, identifying 

disease foci in nursery beds may be an alternative. 

For rice, this appears feasible at the seedling 

stage in the seedbed. A disease focus is a patch of 

crop with disease limited in space and time 

(Zadoks and van den Bosch 1994) and is likely to 

have been caused by the initial source of inoculum. 

In Japan, the seedbox nursery for rice provides an 

ideal means to identify the disease foci of single or 

different seedborne pathogens. The paper towel 

method, a very common method for testing seed 

germination, resulted in more seedling mortality 

and thus less germination than the seedbed method 

(seedbed with field soil) used in crop production 

(Table 4). The method used for assessing the effect 

of seedborne fungal pathogens on seed germination 

varies. 

8

Table 4. Germination (%) of untreated and treated seeds using paper towel and in-soil germination methods (400 

seeds each; randomized complete block design). 

Normal a Abnormal Dead seeds 

Varieties Paper In-soil Paper In-soil Paper In-soil 

towel test towel test towel test 

Untreated 

IR62 79.7 ab 91.7 a 16.0 a 5.3 a 4.3 a 3.0 b 

SARBON 65.3 b 75.7 ab 20.3 a 12.0 a 14.3 a 12.3 ab 

C22 94.0 a 84.0 ab 4.3 b 10.3 a 1.7 a 5.7 ab 

BS1-10 68.0 b 72.7 b 18.3 a 11.0 a 13.7 a 16.3 a 

Hot-water treatment 

IR62 86.7 a 85.3 a 5.0 b 7.7 b 8.3 b 7.0 b 

SARBON 46.3 b 50.3 c 19.7 a 10.3 b 34.0 a 39.3 a 

C22 92.3 a 94.3 a 5.0 b 4.0 b 2.7 b 1.7 b 

BS1-10 76.3 a 67.7 b 13.7 ab 25.0 a 10.0 a 7.3 b 

a 

In a column under each treatment, means followed by a common letter are not significantly different at the 5% level by Duncan’s multiple range 

test. 

Relationship between seedborne inoculum 

and disease development in the field 

In determining the importance of a seedborne pathogen, 

it is essential to relate inoculum production and 

the efficiency of the secondary spread to the inoculum 

threshold and disease severity after establishment. 

For a monocyclic disease, initial infection 

should be closely related to the initial inoculum provided 

by the seed. For a polycyclic disease, a low 

level of seedborne inoculum is adequate to begin 

infection from the seedbed to the main field, and increase 

disease intensity if climatic or crop-growing 

conditions are favorable. For instance, in rice blast 

caused by P. oryzae with low detection and infection 

frequencies, seed-carried inoculum is more important 

in temperate or subtropical environments than in 

a tropical lowland environment. In the former environments, 

the likelihood of seed-carried inoculum 

beginning an infection and producing a sufficient 

amount of inoculum for secondary infection is higher 

(Ou 1985). 

Inoculum level and inoculum thresholds 

In seed health testing for certification, the inoculum 

threshold of seedborne pathogens is defined as the 

amount of seed infection or infestation that can cause 

a disease in the field under conducive conditions and 

lead to economic losses (Kuan 1988). We believe 

that this should mean a minimal amount of seed infection 

or infestation. In principle and as Gabrielson 

(1988) indicated, one infected seed may give rise to 

one infected plant, but, under field conditions, this is 

hardly the case. The values of the inoculum threshold 

for different crop-pathogen combinations in different 

countries vary widely (Gabrielson 1988). 

Our experience with rice has shown that the 

potential of a seedborne pathogen to cause a disease 

is determined by the type of pathogen in relation to 

the crop growth environment. Under conditions in a 

wet-bed nursery for rice seedlings, the likelihood of a 

fungal pathogen beginning an infection appears less 

than under tropical conditions. Perhaps this is because 

of the microbial competition or antagonism. 

On the other hand, if the level of seedborne inoculum 

is high (we have not had it quantified), then the probability 

of it causing infection is also high. As one infected 

seed begins one disease focus and this focal 

point expands, the probability of infection increases. 

In reality, disease establishment is affected by inoculum 

density and the crop cultivation environment. 

The more infected seeds there are (inoculum level), 

the higher the probability of having an infection. 

We have monitored detection levels of seedborne 

fungal pathogens from imported seed lots by 

planting them in the field after seed treatment for 

postentry plant quarantine observation. Diseases observed 

were not related to seedborne pathogens 

(Table 2). Pathogens from harvested seeds from 

these plants were detected, but we are not sure 

whether these fungal pathogen populations were the 

same as those carried by the original seed or if they 

came from other sources in the field. 

9

For other fungal pathogens, there is a close relation 

between seed infection and infected plants 

grown from these seeds. An example is blackleg of 

crucifer caused by Phoma lingam (Leptosphaeria 

maculans) (Gabrielson1983). The classical example 

from Heald (1921) indicated that the sporeload of 

seeds was highly correlated to the percentage of 

smut appearing in the field. 

Inoculum thresholds vary according to cultural 

environments. In Japan, for instance, after rice cultivation 

became mechanized and seedlings were 

raised indoors in seedboxes, the occurrence of many 

seedborne fungal and bacterial pathogens increased. 

This is because the indoor conditions—high temperature 

and high humidity with artificial light—are very 

favorable for seedling disease development. As a 

result, the inoculum threshold is lower than that of 

seedlings raised outdoors under a field nursery. The 

inoculum becomes more efficient under certain conditions. 

Inoculum efficiency is determined by various 

factors. The type of disease and crop-growing environments 

are important. Gabrielson (1988) cautioned 

that thresholds must be developed for average environmental 

conditions of crop growth because they 

are influenced by all factors affecting the epidemiology 

of each host-parasite combination. It is difficult 

to use a single threshold of a single disease for all 

cropping environments. There is no clear definition 

on levels of threshold for the different pathogens detected 

from the seed. In rice, different fungal pathogens 

are detected from the seed (Table 1) and all of 

them are distributed throughout the rice-growing 

countries worldwide. Disease potential, however, 

depends on the rice ecosystem (upland, rainfed, irrigated, 

tropical, subtropical, and temperate environments, 

and deepwater and tidal coastal areas), cultural 

conditions, and types of crop management and 

production. Whether there is a need to treat all diseases 

the same way or differently for different ecosystems 

and production levels needs careful study. 

There is a general agreement that the threshold level 

for a disease is zero in an area if it has not been reported 

there. 

Risk analysis 

Risk analysis should serve an important basis for 

developing plant quarantine regulations. Risk analysis 

based on seed health testing needs to consider the 

following factors: 

1. type of pathogens 

2. role of seed in the life cycle of the 

pathogen 

3. disease or epidemic potential 

4. genetic variability of the pathogen 

5. type or site of initial infection 

6. kind of crop production environment (Mew 

1997) 

The risk of infection from seedborne pathogens 

is a function of risk probability and risk magnitude. 

Furthermore, risk probability is determined by introduction 

risk, that is, the probability that a pathogen 

enters a region or a field through the seed, the epidemiological 

risk, the probability that the pathogen establishes 

infection through seedborne inoculum. Risk 

magnitude is the potential consequence of an epidemic 

caused by the pathogen. Consequences are 

considered from the viewpoint of yield loss. Seed 

health testing results provide actual data on a pathogen 

that could potentially be introduced into a region 

or a field. The risk magnitude can be computed from 

a yield loss database or from modeling. In rice, this 

kind of database is available at IRRI. The yield loss 

database provides an estimate of losses and “hazards” 

caused by a pathogen once the infection is established 

through seedborne inoculum. 

However, data are lacking on the transmission 

efficiency of seedborne inoculum of many rice 

seedborne pathogens. A concerted effort is needed to 

compile this information through international collaboration. 

Research on seed pathology provides the 

basis for setting seed health testing policy, while information 

on pest or pathogen risk provides a starting 

point for seed health testing on target organisms for 

plant quarantine regulations. Very limited or no financial 

support is available for this important area of 

activities. 

A yield loss database can estimate the “hazards” 

of a pathogen once an infection is established 

through the introduction of a seedborne inoculum. 

However, data on inoculum levels and thresholds are 

also needed to develop realistic assessment or measurement 

procedures for some important seedborne 

pathogens. Data on seed transmission of many 

pathogens and transmission efficiency of seedborne 

inoculum are currently not available. 

Although conventional seed health testing provides 

adequate information on detection frequency 

and infection levels of some pathogens, we need to 

assess whether these pathogens cause any real injury 

to effect yield loss. In scientific literature, this information 

is not readily available. 

10

Microorganisms associated with seed 

Not all microorganisms associated with seed are 

pathogens. Some microorganisms possess biological 

control properties. The occurrence of nonpathogenic 

Xanthomonas has further complicated the issue of 

seedborne bacterial pathogens. Cottyn et al (2001) 

and Xie et al (2001) proved that seedborne antagonistic 

bacteria are present in rice and promote seed germination 

and seedling vigor, and also suppress disease 

with an inoculum from the seed. Microflora 

associated with the seed may be roughly categorized 

into pathogens and nonpathogens. The study by 

Cottyn et al (2001), supported by the Belgium 

Adminstration for Development Cooperation, and 

Xie et al (2001) showed that rice seed carries many 

bacteria belonging to 17 genera and over hundreds of 

species. Predominant were Enterobacteriacae 

(25%), Bacillus spp. (22%) and Pseudomonas spp. 

(14%). Other bacteria regularly present were 

Xanthomonas spp., Cellulomonas flavigena, and 

Clavibacter michiganense. We found that about 4% 

of the total bacterial population possesses biological 

control properties against most seedborne pathogens. 

Also, seedling vigor was enhanced after soaking 

seeds in bacterial suspension. These studies show 

that rice seed not only carries pathogens but also 

abundant microorganisms that act as biological control 

agents. Whether they play a bigger role in crop 

production and disease management needs further 

research. More support should be given to this research 

area, which is a vital part of a farmers’ internal 

resource management for sustainable crop production 

and disease management. 

11

Seed health management for crop production 

In tropical Asia, the productivity of newly released 

modern rice cultivars declines rapidly because of 

seed health problems associated with the continuous 

use of the seed without adequate seed health management. 

At IRRI, we have conducted research on 

seed health management since the early 1990s. The 

research effort has focused on understanding farmers’ 

seed health problems in relation to crop management 

and production. By improving farmers’ seed 

health management, rice yield could be increased by 

5–20%. Increasing farmers’ yields generates more 

income and profit. The marginal cost-benefit ratio 

was estimated at 5, and even 10, depending on the 

quality of the farmers’ original seed stock for planting 

(T.W., unpubl. data). 

Seed health management is an important way of 

reducing pest damage and weed infestation in the 

field. By employing sound seed health management, 

farmers not only minimize the use of harmful agrochemicals, 

they also maximize the genetic yield potential 

of these modern rice cultivars. We found that 

the productivity of foundation seed is reduced by 1 t 

ha –1 in three crop seasons using current farmers’ 

seed health management practices (L. Diaz, M. 

Hossain, V. Merca, and T.W. Mew, unpubl. data). 

Yield changes according to the level of “high-quality 

seed” in seed stock used by farmers. When the level 

of high-quality seed reached 90% of the seed stock 

for planting, the yield increase was not significant. 

In rice seed health testing, little information exists 

on pathogen detection frequency on seed and on 

which part of the seed an organism is likely to be 

located. This handbbok contains information on rice 

seed health testing that we have been carrying out for 

the past 20 years. We hope to offer seed health testing 

technicians, college or graduate students, and 

teachers in plant pathology or seed technology a useful 

guide. Information on seed health testing can also 

be an important means of improving crop production 

practices of farmers. The information contained in 

this handbook is based on IRRI’s rice seed health 

testing activities on both incoming and outgoing 

seeds. Thus, the material provides a reference for 

many seed health testing laboratories. In view of the 

increasing interest in international trade in rice, the 

handbook also serves as a basis for establishing plant 

quarantine guidelines for individual countries. 

12

Identification of fungi detected on rice seed 

The standard detection method used in identifying 

fungi on rice seed at IRRI is given below. Figure 3 

shows the parts of a rice seed attacked by fungi. 

With this method, numerous fungi have been detected 

on rice seed. The profile of each fungus detected 

is presented in the following pages. 

Methods and conditions of rice seed incubation 

for microorganism detection are listed below. 

The International Rules for Seed Testing recommend 

the blotter test for detecting seedborne fungi. 

The procedure involves these steps: 

1. Prepare materials (9.5-cm plastic petri dish, 

marking pencil, round blotter paper, distilled 

water, sampling pan, forceps, seed sample). 

2. Label plates accordingly using a marking 

pencil. 

3. Place 2–3 pieces of moistened round blotter 

paper in labeled plastic petri dishes. 

4. Sow 25 seeds per plate making sure that 

seeds are sown equidistantly with 15 seeds on 

the outer ring, 9 seeds at the inner ring, and 1 

seed in the middle. 

5. Incubate seeded plates at 21 °C under a 12-h 

light and 12-h dark cycle. Light sources can 

be near ultraviolet (NUV) light or daylight 

fluorescent tubes. The NUV light source can 

be a 320–400 nm lamp, preferably Philips 

TLD 36W/08 or GE F 40 BL. Daylight fluorescent 

tubes can be Philips TL 40W/54 day 

light or its equivalent. 

6. Examine each of the seeds after 5–7 d of 

incubation for fungal growth. 

Partition between 

lemma and palea 

Lemma 

Awn 

Sterile lemmas 

Palea 

Fig. 3. Parts of a rice seed. 

13

Seedborne fungi causing foliage diseases in rice 

Alternaria padwickii (Ganguly) Ellis 

syn. Trichoconis padwickii Ganguly 

Trichoconiella padwickii (Ganguly) Jain 

Disease caused: stackburn 

a. Symptoms 

On leaves—large oval or circular spots with a 

pale brown center and distinct dark brown margin. 

Color of center eventually becomes white and 

bears minute black dots. 

On grains—pale brown to whitish spots with black 

dots at the center and dark brown border. 

Roots and coleoptile of germinating seedlings— 

dark brown to black spots that eventually coalesce. 

Small, discrete, and black bodies are 

formed on the surface of the darkened area as 

decay proceeds. 

b. Occurrence/distribution 

Stackburn disease is widespread in most of the 

rice-growing countries worldwide (Fig. 4). 

c. Disease history 

The disease was first reported in the U.S. It resembles 

black rust of wheat on rice leaves, but 

only sclerotia and mycelium were observed. 

Later the fungus was observed in and on rice 

seeds. 

d. Importance in crop production 

Stackburn leaf spot disease is not considered to 

be of economic importance. However, seed infection 

results in grain discoloration, which may 

reduce germination and lower grain quality. The 

disease potential of stackburn is very low and the 

yield loss caused by A. padwickii in literature 

may be overestimated. The effect of infected 

seed on seed germination is not yet properly assessed. 

Detection on seed 

a. Incubation period on blotter 

A. padwickii is easily observed on seeds using the 

blotter method 5 d after seeding on moistened 

blotter and incubated under NUV at 21 °C. The 

detection frequency is about 67.1% on seeds 

coming from different regions (Fig. 5a,b). 

b. Habit character 

Seed infected with A. padwickii after incubation 

shows abundant aerial mycelia, hairy to cottony, 

profusely branched, grayish or hyaline when 

Fig. 4. Occurence of stackburn (Ou 1985, Agarwal and Mathur 1988, EPPO 1997). 

14

Detection frequency (%) 

100 

80 

60 

40 

20 

0 

Detection level (%) 

100 

80 

East Asia 

Europe 

Latin America 

South Asia 

Southeast Asia 

Sub-Saharan Africa 

60 

40 

20 

0 

1990 1991 1992 1993 1994 1995 1996 1997 

Year 

Fig. 5. Detection level (a) and frequency (b) of Alternaria padwickii from imported untreated seeds, 1990-97. 

young, becoming creamy yellow when mature; 

pinkish to light violet pigmentation is produced on 

the blotter; conidia are borne singly per conidiophore; 

darker than mycelia; sterile appendage 

prominent (Fig. 6a-c). 

c. Location on the seed 

A. padwickii is most often observed growing over 

the entire seed surface (36%) (Fig. 7). 

Microscopic character 

a. Mycelia—septate, profusely branched; hyaline 

when young, becoming creamy yellow when mature; 

branches arising at right angles from the 

main axis (Fig. 6d). 

b. Conidiophore—simple, not sharply distinguishable 

from mature hyphae, often swollen at the apex, 

hyaline when young, becoming creamy yellow 

when mature (Fig. 6e). 

c. Conidia—straight, shape varies from fusiform to 

obclavate and rostrate or in some cases 

elongately fusoid; with long sterile appendage; at 

first hyaline, becoming straw-colored to golden 

brown; thick-walled; 3–5 septate; constricted at 

the septum; 4- to 5-celled, second cell from the 

base larger than the rest of the cells (Fig. 6f). 

Measurements: 81.42–225.40 µ long including 

appendage; 11.96–23.46 µ wide at the broadest 

part and 2.99–5.52 µ wide at the center of the appendage 

(PSA); 83.95–203.78 µ long including 

appendage; 9.66–17.48 µ wide in the broadest part 

and 3.45–5.75 µ wide at the middle of the appendage. 

Colony characters on culture media (Fig. 8) 

Colonies on potato dextrose agar (PDA) incubated at 

ambient room temperature (ART) (28–30 °C) grow 

15

→ 

a 

b 

→ 

e 

f 

→ 

f 

→ 

c 

d → 

→ 

Fig. 6. Habit character of Alternaria padwickii (Ganguly) Ellis on (a) whole seed (8X) and on sterile lemmas at (b) 

12.5X and (c) 25X. Photomicrograph of A. padwickii showing (d) mycelia, (e) conidiophore, and (f) conidia at 40X 

and stained with lactophenol blue. 

Observed frequency (%) 

40 

30 

20 

10 

0 

Sterile 

lemmas 

Awn 

Partition 

bet. lemma 

and palea 

Seed part 

Entire 

seed 

Lemma/ 

palea 

only or 

both 

Fig. 7. Observed frequency of Alternaria padwickii 

occurrence on seed part. 

Fig. 8. Plate culture of Alternaria padwickii Ellis showing 

colony growths on potato dextrose agar (PDA), potato 

sucrose agar (PSA), and malt extract agar (MEA) 

incubated at ambient room temperature (ART), 21 °C, 

and 28 °C at 15 d after inoculation. 

16

moderately fast and attain a 4.32-cm diam in 5 d. 

They are slightly zonated, thickly felted, and grayish, 

becoming light outward. On the reverse side of the 

agar plate, the colony is azonated, black, and lighter 

outward. At 21 °C under alternating 12-h NUV light 

and 12-h darkness, colonies grow moderately fast 

and attain a 4.14-cm diam in 5 d. They are azonated, 

becoming markedly zonated outward, felted, yellowish 

to greenish gray, with a 0.5-cm sterile white margin. 

On the reverse side of the agar plate, the colony 

appears zonated and black and light outward. At 28 

°C under alternating 12-h light and 12-h darkness, 

colonies grow moderately fast and attain a 4.33-cm 

diam in 5 d. They are zonated, felted, and greenish 

gray. On the reverse side of the agar plate, the colony 

is zonated and black and yellowish brown outward. 

Colonies on potato sucrose agar (PSA) incubated 

at ART (28–30 °C) grow moderately fast and 

attain a 4.18-cm diam in 5 d. They are deeply felted, 

zonated with an even margin, and gray. The colony 

appears zonated and black on the reverse side of the 

agar plate. At 21 °C under alternating 12-h NUV and 

12-h darkness, colonies grow moderately fast and 

attain a 4.36-cm diam in 5 d. They are slightly zonated 

with a light gray submerged advancing margin, 

felted, and dark greenish gray. The colony appears 

slightly zonated, black, and lighter outward on the 

reverse side of the agar plate. At 28 °C under alternating 

12-h light and 12-h darkness, colonies grow 


They are zonated, felted with a sinuate margin, yellowish 

to greenish gray, and lighter at the margins. 

The colony appears zonated and black, and yellowish 

brown outward on the reverse side of the agar 

plate. 

Colonies on malt extract agar (MEA) incubated 

at ART (28–30 °C) grow moderately fast and attain a 

4.53-cm diam in 5 d. They are zonated, felted, and 

light gray to gray. The colony appears zonated and 

black on the reverse side of the agar plate. At 21 °C 

under alternating 12-h NUV and 12-h darkness, colonies 

grow moderately fast and attain a 4.47-cm diam 

in 5 d. They are azonated, becoming markedly zonated 

outward, and white to yellowish gray and becoming 

gray outward. The colony appears zonated 

and black with a light gray margin on the reverse side 

of the agar plate. At 28 °C under alternating 12-h 

fluorescent light and 12-h darkness, colonies grow 


They are zonated, felted, and greenish gray, becoming 

gray at the margins. The colony appears slightly 

zonated and black on the reverse side of the agar 

plate. 

Bipolaris oryzae (Breda de Haan) Shoem. 

syn. Drechslera oryzae (Breda de Haan) Subram. & Jain 

Helminsthosporium oryzae 

teleomorph: Cochliobolus miyabeanus (Ito & Kurib) 

Disease caused: brown spot (brown leaf spot or 

sesame leaf spot) 

Helminsthosporium blight 

a. Symptoms 

On leaves—small and circular dark brown or 

purple brown spots eventually becoming oval 

(similar to size and shape of sesame seeds) and 

brown spots with gray to whitish centers, evenly 

distributed over the leaf surface; spots much 

larger on susceptible cultivars. A halo relating to 

toxin produced by the pathogen often surrounds 

the lesions. 

On glumes—black or brown spots covering the 

entire surface of the seed in severe cases. Under 

favorable environments, conidiophore and conidia 

may develop on the spots, giving a velvety appearance. 

Coleoptile—small, circular, or oval brown spots. 


Brown spot is distributed worldwide and reported 

in all rice-growing countries in Asia, America, 

and Africa (Fig. 9). It is more prevalent in rainfed 

lowlands and uplands or under situations with abnormal 

or poor soil conditions. 


This fungus was first described in 1900 and 

named as Helminthosporium oryzae. In Japan, the 

teleomorph was found in culture and was named 

Ophiobolus miyabeanus. However, Drechsler 

decided it belonged to Cochliobolus and renamed 

17

Fig. 9. Occurrence of brown spot (Ou 1985, Agarwal and Mathur 1988, EPPO 1997). 

it Cochliobolus miyabeanus. Because of the bipolar 

germination of the conidia, the anamorph of C. 

miyabeanus was changed to Bipolaris oryzae. 


Bipolaris oryzae causes seedling blight, necrotic 

spots on leaves and seeds, and also grain discoloration. 

Severely infected seeds may fail to germinate. 

Seedling blight is common on rice in both 

rainfed lowlands and uplands. Under these rice 

production situations, brown spot can be a serious 

disease causing considerable yield loss. In history, 

the Bengal famine of 1942 is attributed to brown 

spot. 



B. oryzae is easily observed on seeds using the 

blotter method 5 d after seeding on moistened 

blotter incubated under NUV light at 22 °C. The 

detection frequency is about 56.7% on seeds coming 

from different regions (Fig. 10a,b). 


There are two types of fungal detection on rice 

seed: type I shows less conidia and abundant 

aerial mycelia, fluffy to cottony; gray, greenish 

gray to black; conidiophores are usually slender 

and hard to distinguish from main mycelia; 

conidia are darker than mycelia, borne singly on 

the terminal portion of the hyphae. 

Type II shows abundant conidia and aerial 

mycelia are either absent or scanty. Conidiophores 

are straight or flexuous, relatively long; 

simple, brown to dark brown, arising directly from 

seed surface either solitary or in small groups 

bearing conidia at the end and/or on the sides, 

usually with 3–5 conidia per conidiophore (Fig. 

11a-c). 

c. Location on seed 

B. oryzae is often observed on the entire seed 

surface (about 32%) or on sterile lemmas (about 

29%) (Fig. 12). 


a. Mycelium—gray to dark greenish gray, septate. 

b. Conidiophores—septate, solitary, or in small 

groups; straight or flexuous, sometimes geniculate 

(bent like a knee); simple; pale to mid-brown; 

bearing conidia at the end and on sides (Fig. 11d). 

c. Conidia—dark brown to olivaceous brown, 

obclavate, cymbiform, naviculart, fusiform, 

straight, or curved (slightly bent on one side). The 

largest conidia may have 13 pseudosepta with a 

prominent hilum or basal scar (Fig. 11e). Measurements: 

5–9 septate, 39.56–101.89 µ × 11.96– 

18


120 

100 

East Asia 

Europe 

Latin America 

South Asia 



80 

60 

40 

20 

0 


100 

80 

60 

40 

20 

0 

1990 1991 1992 1993 1994 1995 1996 1997 

Year 

Fig. 10. Detection frequency (a) and level (b) of Bipolaris oryzae from imported untreated seeds, 1990-97. 

16.10 µ (PDA); 4–11 septate, 43.47–101.43 µ × 

12.19–16.10 µ (PSA); and 5–11 septate, 59.80– 

106.03 µ × 10.12–16.33 µ (MEA). 


Colonies on PDA at ART (28–30 °C) grow slowly 

and attain a 3.38-cm diam in 5 d. They are azonated 

with sinuate margins, hairy at the center, becoming 

cottony toward the margin, yellowish gray at the center 

and gray toward the margin, and becoming grayish 

olive with age. The colony appears azonated and 


under alternating 12-h NUV light and 12-h darkness, 

colonies grow very slowly and attain a 2.38-cm diam 

in 5 d. They are fluffy, azonated with uneven margins, 

with olive gray aerial mycelia, becoming dark 

olive gray outward. The colony on the reverse side of 

the agar plate appears azonated and black. At 28 °C 

under alternating 12-h fluorescent light and 12-h 

darkness, colonies grow very slowly and attain a 

2.53-cm diam in 5 d. They are fluffy with nil to 

scanty aerial mycelia, azonated with uneven margins, 

and olive black with 3.0-mm light gray advancing 

mycelia. The colony appears azonated and black 

with light gray margins on the reverse side of the 

agar plate. 

Colonies on PSA incubated at ART (28–30 °C) 

grow moderately fast and attain a 4.48-cm diam in 5 

d. They are fluffy, azonated with sinuate margins, 

and grayish yellow at the center, becoming dark olive 

gray outward. The colony appears azonated and olive 

black to black on the reverse side of the agar 

19

→ 

d 

e 

a 

e 

b 

d 

e 

d 

d 

e→ 

c 

Fig. 11. Habit character of Bipolaris oryzae (Breda de Haan) Shoem. on (a) whole seed (10X), (b) sterile lemmas 

(40X), and (c) awn portion (40X). Photomicrograph of B. oryzae showing (d) conidiophore and (e) conidia at 10X and 

40X. 


40 

30 

20 

10 

0 

Sterile 

lemmas 

Awn 

Partition 

bet. lemma 

and palea 

Entire 

seed 

Lemma/ 

palea 

only or 

both 

Seed part 

Fig. 12. Observed frequency of Bipolaris oryzae 

occurrence on the seed. 

Fig. 13. Plate cultures of Bipolaris oryzae (Breda de 

Haan) Shoem. showing colony growths on PDA, PSA, 

and MEA incubated at ART, 21 °C, and 28 °C at 15 d 

after inoculation. 

plate. At 21 °C under alternating 12-h NUV light and 

12-h darkness, colonies spread moderately fast and 

attain a 4.62-cm diam in 5 d. They are fluffy, zonated 

with sinuate margins, and dark olive gray with olive 

gray mycelial tufts and 4-mm grayish advancing 

mycelia. The colony appears slightly zonated to zonated, 

black, and becomes dark olive gray outward on 

the reverse side of the agar plate. At 28 °C under 

alternating 12-h fluorescent light and 12-h darkness, 

colonies grow fast and attain a 5.10 cm diam in 5 d. 

20

They are feathery to slightly fluffy, zonated with 

even to slightly uneven margins, and alternating olive 

yellow and dark olive with 5-mm light yellow margins. 


appears azonated to slightly zonated, black, and becomes 

dark greenish gray to olive black toward the 

margin. 

Colonies on MEA at ART (28–30 °C) grow very 

slowly and attain a 2.29-cm diam in 5 d. Colonies are 

scanty with fluffy aerial mycelia, azonated with uneven 

margins, and olive gray with grayish yellow 

aerial mycelia. The colony appears azonated and 

olive black on the reverse side of the agar plate. At 

21 °C under alternating 12-h NUV light and 12-h 

darkness, colonies are restricted in growth and attain 

a 1.71-cm diam in 5 d. They are azonated with 

crenate margins, velvety, and olive black with white 

to dark olive mycelial tufts. The colony appears zonated 

and olive black to black on the reverse side of 

the agar plate. At 28 °C under alternating 12-h fluorescent 

light and 12-h darkness, colonies are restricted 

in growth and attain a 1.71-cm diam in 5 d. 

They are azonated with crenate margins, velvety 

with slightly fluffy centers, and dark greenish gray to 

olive black. The colony on the reverse side of the 

agar plate appears azonated and black. 

Cercospora janseana (Racib.) Const. 

syn. Cercospora oryzae Miyake 

teleomorph: Sphaerulina oryzina Hara 

Disease caused: narrow brown leaf spot 

a. Symptoms 

Short, linear, brown lesions most common on 

leaves but also occur on leaf sheaths, pedicels, 

and glumes. 


The disease has worldwide distribution (Fig. 14). 


The disease was first observed in North America 

before 1910 but its detailed description was re- 

Fig. 14. Occurrence of narrow brown leaf spot (Ou 1985, Agarwal and Mathur 1988, EPPO 1997). 

21

ported in 1910 in Japan. The causal fungus was 

named Cercospora oryzae. In 1982, the fungus 

was renamed as C. janseana. 


The disease reduces effective leaf area of the 

plant and causes premature senescence of infected 

leaves and sheaths. Together with leaf 

scald, it may cause 0.1% yield loss across all rice 

production situations in Asia. 


a. Incubation on blotter 

Using the blotter test, C. janseana can be observed 

on rice seed 7 d after incubation in NUV 

light at 21 °C. The frequency of detection is


120 

100 

80 

60 

40 

20 

0 

Sterile 

lemmas 

Awn 

Partition 

bet. lemma 

and palea 

Entire 

se ed 

Lemma/ 

palea 

only or 

both 

Seed part 

Fig. 16. Observed frequency of Cercospora janseana 


Fig. 17. Plate cultures of Cercospora janseana (Racib) 

Const. showing colony growths of PDA, PJA, and VJA 

incubated at ART, 21 °C, and 28 °C at 15 d after 

inoculation. 


Colonies on PDA at ART (28–30 °C) grow very 

slowly and attain a 2.40-cm diam in 17 d. They are 

azonated, plane to slightly felted, with sinuate margins, 

slightly radial furrows, and dark gray. The 

colony appears azonated with radial wrinkles and 




in 17 d. They are zonated, plane to felted, with sinuate 

margins and radial furrows, and gray and light 

gray at the margins. The colony appears azonated 

with radial wrinkles and black on the reverse side of 

the agar plate. At 28 °C under alternating 12-h fluorescent 

light and 12-h darkness, colonies are restricted 


They are zonated, felted, with even to sinuate margins 

and deep radial furrows, and light gray. The 

colony appears azonated with wrinkles and black on 

the reverse side of the agar plate. 

Colonies on prune juice agar (PJA) at ART (28– 

30 °C) grow very slowly and attain a 2.40-cm diam in 

17 d. They are azonated, plane, powdery to granular 

with slightly radial furrows and even margins, and 

dark gray to gray and becoming light at the margins. 

The colony on the reverse side of the agar plate appears 

azonated and black. At 21 °C under alternating 

12-h NUV light and 12-h darkness, colonies grow 


slightly zonated, plane, granular, and gray with 0.5- 

cm white margins. The colony on the reverse side of 

the agar plate appears azonated and black with orange 

coloration. At 28 °C under alternating 12-h fluorescent 

light and 12-h darkness, colonies grow slowly 

and attain a 3.20-cm diam in 17 d. They are plane, 

zonated with radial furrows and sinuate margins, and 

light gray to gray. The colony on the reverse side of 

the agar plate appears azonated with radial wrinkles 

and black. 

Colonies on V-8 juice agar (VJA) at ART (28–30 

°C) are restricted in growth and attain a 2.20-cm 

diam in 17 d. They are zonated, felted, with sinuate 

margins and deep radial furrows, and light gray to 

gray with dark gray margins. The colony on the reverse 

side of the agar plate appears azonated with 

wrinkles and black. At 21 °C under alternating 12-h 

NUV light and 12-h darkness, colonies grow very 


zonated, felted, with even to sinuate margins and 

deep radial furrows, and light gray to dark gray. The 

colony on the reverse side of the agar plate appears 

azonated with wrinkles and black. At 28 °C under 



in 17 d. They are zonated with deep radial furrows 

and sinuate margins, felted, and brownish gray. The 

colony on the reverse side of the agar plate is 

azonated with radial wrinkles and black. 

23

Microdochium oryzae (Hashioka & Yokogi) Samuels & Hallett 

syn. Gerlachia oryzae (Hashioka & Yokogi) W. Gams. 

Rhychosporium oryzae Hashioka & Yokogi 

teleomorph: Monographella albescens (Thumen) Parkinson, Sivanesan & C. Booth 

syn. Metasphaeria albescens Thum. 

Metasphaeria oryzae-sativae Hara 

Micronectriella pavgii R.A. Singh 

Griposphaerella albescens (Thumen) Von Arx 

Disease caused: leaf scald 

a. Symptoms 

Lesions are usually observed on mature leaves. 

Characteristic symptoms include zonated lesions 

that start at leaf edges or tips. The lesion shape is 

more or less oblong with light brown halos measuring 

1–5 cm long and 0.5–1 cm wide. Individual 

lesions enlarge and eventually coalesce. As lesions 

become old, zonations fade. 


Leaf scald has been reported in all rice-growing 

countries worldwide (Fig. 18). 


Leaf scald was first reported in 1955 in Japan, 

and the causal organism was named as 

Rhynchosporium oryzae. However, the disease 

was known under different names. The causal 

fungus was confused with Fusarium nivale as the 

anamorph and with Micronectriella nivalis as the 

teleomorph. Later it was proved that the leaf scald 

fungus is not F. nivale. The anamorph and 

teleomorph of the leaf scald fungus have undergone 

many changes and are now known as 

Gerlachia oryzae and Monographella albescens, 

respectively. 


Leaf scald is very common on rice in tropical 

Asia. It is considered a relatively minor problem 

causing little yield loss alone in rice production. 



Using the blotter test, M. oryzae can be observed 

on rice seeds 7 d after seeding and incubation 

under NUV light at 21 °C. The detection frequency 

is about 28.2% on seeds coming from 

different regions (Fig. 19a,b). 


Aerial mycelia are absent; light pinkish or light 

orange to bright orange irregular masses 

Fig. 18. Occurrence of leaf scald (Ou 1985, Agarwal and Mathur 1988). 

24

Frequency level (%) 

120 

100 

East Asia 

Europe 

Latin America 

South Asia 



80 

60 

40 

20 

0 


50 

40 

30 

20 

10 

0 

1990 1991 1992 1993 1994 1995 1996 1997 

Year 

Fig. 19. Detection frequency (a) and level (b) of Microdochium oryzae from imported untreated seeds, 1990-97. 

(pionnotes) varying in size and thickness are scattered 

on seed surface (Fig. 20a-c). 


M. oryzae is most likely observed growing on 

sterile lemmas of the rice seed (about 55%) (Fig. 

21). 


Conidia (epispore)—borne on superficial stromata 

arising on lesions, bow-shaped; single-celled when 

young, 2-celled when mature; one septum; occasionally 

2–3 septate; not considered at septum; thinwalled, 

hyaline, pink in mass, hyaline under the microscope 

(Fig. 22d). Measurements: 8.97–17.48 µ × 

2.53–5.98 µ (PDA); 8.51–18.17 µ × 6.21–8.51 µ 

(PSA); and 10.36–15.64 µ × 2.30–5.52 µ (MEA). 


Colonies on PDA at ART (28–30 °C) grow moderately 

fast, thinly spreading, and attain a 4.20-cm diam 

in 5 d. They are evenly zonated with uneven margins, 

orange with scanty, white aerial mycelia, and 

somewhat pressed to the media. Colonies appear wet 

at the center, spreading outward with age. The 


evenly zonated and light orange. At 21 °C under alternating 

12-h NUV light and 12-h darkness, colonies 

are thinly spreading, grow moderately fast, and attain 

25

a 

b 

c 

d 

Fig. 20. Habit character of Microdochium oryzae (Hashioka and Yokogi) Sam. and Hal. showing orange pionnotes 

on the seed surface at (a) 8X, (b) 12.5X, and (c) 20X. cPhotomicrograph of M. oryzae showing lunar-shaped conidia d 

(40X). 


60 

50 

40 

30 

20 

10 

0 

Sterile 

lemmas 

Awn 

Partition 

bet. lemma 

and palea 

Entire 

se ed 

Lemma/ 

palea 

only or 

both 

Seed part 

Fig. 21. Observed frequency of Microdochium oryzae 


Fig. 22. Plate cultures of Microdochium oryzae 

(Hashioka and Yokogi) Samuels and Hallet showing 

colony growths on PDA, PSA, and MEA incubated at 

ART, 21 °C, and 28 °C at 5 d after inoculation. 

26

a 4.90-cm diam in 5 d. They are evenly zonated, 

orange with white aerial mycelia that appear to be 

pressed to the media, and wet at the center. The 


slightly zonated and orange to light orange outward. 

At 28 °C under alternating 12-h fluorescent light and 


attain a 5.0-cm diam in 5 d. They are orange without 

aerial mycelia. Colonies appear wet and slightly 

zonated with radial furrows and even margins. The 


slightly zonated with radial wrinkles and orange, 

becoming light outward. 

Colonies on PSA at ART (28–30 °C) are thinly 

spreading, grow moderately fast, and attain a 4.87- 

cm diam in 5 d. They are azonated with even margins 

and light orange with scarce white aerial mycelia. 

White mycelial tufts are produced as colonies 

age. The colony on the reverse side of the agar 

plate appears azonated and light orange. At 21 °C 


colonies are thinly spreading, grow moderately fast, 

and attain a 4.48-cm diam in 5 d. They are slightly 

zonated at the center, with even margins, and light 

orange with scarce white aerial mycelia that are 

pressed to the media. The colony on the reverse 

side of the agar plate is slightly zonated at the center 

and light orange. At 28 °C under alternating 12-h 

fluorescent light and 12-h darkness, colonies grow 


They are zonated at the center with about 1.5-cm 

submerged advancing mycelia and sinuate margins. 

Colonies are orange with white, densely floccose 

aerial mycelia. The colony on the reverse side of the 

agar plate appears zonated at the center and orange. 

Colonies on MEA at ART (28–30 °C) are thinly 

spreading, grow moderately fast, and attain a 4.93- 

cm diam in 5 d. They are zonated, with even margins, 

and orange with scarce white aerial mycelia 

that are somewhat pressed to the media. The colonies 

appear wet. The colony on the reverse side of 

the agar plate is zonated and orange, At 21 °C under 

alternating 12-h NUV light and 12-h darkness, colonies 

are thinly spreading, grow moderately fast, and 

attain a 5.67-cm diam in 5 d. They are zonated, with 

few radial furrows and even margins, and orange 

with scarce white aerial mycelia that are somewhat 

pressed to the media. The colonies appear wet at the 

center and spread outward with age. The colony on 

the reverse side of the agar plate appears zonated 

with few radial wrinkles and orange. At 28 °C under 


colonies are thinly spreading, grow fast, and attain a 

6.03-cm diam in 5 d. They are zonated with serrated 

margins, orange with scarce white aerial mycelia 

that are somewhat pressed to the media, especially at 

the center, and become wet with age. The colony on 

the reverse side of the agar plate appears zonated 

with few radial wrinkles and orange. 

Pyricularia oryzae Cav. 

syn. Pyricularia grisea (Cooke) Sacc. 

Pyricularia grisea 

Pyricularia oryzae Cavara 

Dactylaria oryzae (Cav.) Sawad 

Trichothecium griseum Cooke 

teleomorph: Magnaporthe grisea (Hebert) Barr 

Ceratospaeria grisea Hebert 

Phragmoporthe grisea (Hebert) Monod 

Disease caused: blast 

a. Symptoms 

The fungus can infect rice plants at any growth 

stage although it is more frequent at the seedling 

and flowering stage. 

On the leaves—Initially, lesions appear as small 

whitish or grayish specks that eventually enlarge 

and become spindle-shaped necrotic spots with 

brown to reddish brown margins. The size, shape, 

and color of the spots vary depending upon the 

susceptibility of the variety and environmental 

conditions. 

On the panicle base—Infected tissue shrivels and 

turns black. It breaks easily at the neck and hangs 

down. 

On the nodes—Infected nodes rot and turn black. 

27

. Occurrence/distribution 

Rice blast is widely distributed in all rice-growing 

countries (Fig. 23). It is most prevalent in temperate 

subtropical environments and also in rice 

grown in upland conditions. 


Records of this disease can be traced back to as 

early as 1637 in China. It was reported in 1704 in 

Japan, in 1828 in Italy, and in 1907 in South Carolina, 

USA. In India, it was first recorded in 1913. 

Its causal fungus, Pyricularia oryzae, was named 

in 1891 in Italy. It was recently renamed P. grisea 

but P. oryzae has widespread usage. 


Blast is generally considered as the principal disease 

of rice because of its wide distribution and 

destruction in causing crop failure and epidemics. 

The epidemic potential is very high under favorable 

conditions where susceptible cultivars are 

planted. Blast may cause total crop failure but, 

because resistant cultivars are grown widely in 

major rice production environments, it accounts 

for 1–3% yield loss across all rice production situations 

in Asia. 



Using the blotter test, P. oryzae can be observed 

on rice seeds 3–4 d after incubation in NUV light 

at 21 °C. The detection frequency is about 9.9% 

on seeds coming from different regions (Fig. 

24a,b). 


Aerial mycelia are rarely present or in most cases 

absent. If present, mycelia are branched, hyaline 

to olivaceous. If aerial mycelium is absent, conidiophores 

arise directly from the seed surface singly 

or in small groups or bundles. They are moderately 

long, simple, and light brown. Conidia are 

hyaline, pale olive or grayish, and borne 

sympodially (Fig. 25a-c). 


P. oryzae is observed mostly on sterile lemmas of 

the seed (91%) (Fig. 26). 

Microscopic characters 

a. Mycelium—septate, branched, and hyaline. 

b. Conidiophores—simple to rarely branched, moderately 

long, septated, light brown, slightly thickened 

at the base with denticles at the apex (Fig. 

25d). 

c. Conidia (sympodulosphores)—pyriform to 

obclavate, hyaline to pale olive; usually 2 septate, 

rarely 1 or 3 septate (observed in PJA); apex narrow, 

base rounded with a prominent appendage or 

hilum (Fig. 25e). Measurements: 15.64–22.54 µ × 

7.82–10.81 µ (PDA); 16.56–31.97 µ × 8.51–12.42 

µ (PJA); and 15.18–25.76 µ × 7.13–10.81 µ(VJA). 

Fig. 23. Occurrence of blast (Ou 1985, CMI 1981). 

28


90 

80 

East Asia 

Europe 

Latin America 

South Asia 



70 

60 

50 

40 

30 

20 

10 

0 


35 

30 

25 

20 

15 

10 

5 

0 

1990 1991 1992 1993 1994 1995 1996 1997 

Year 

Fig. 24. Detection frequency (a) and level (b) of Pyricularia oryzae from imported untreated seeds, 1990-97. 


Colonies on PDA at ART (28–30 °C) grow very 


azonated, slightly felted, with aerial mycelia that are 

white with brownish gray portions, even margins, and 

with about 1-mm advancing mycelia submerged. 

Saltation of colonies is observed in some plates. The 

colony on the reverse side of the agar plate is zonated 

and black, turning light outward. At 21 °C under 

alternating 12-h NUV light and 12-h darkness, colonies 

grow very slowly and attain a 2.17-cm diam in 5 

d. They are zonated, slightly felted with even margins, 

and brownish gray. The colony on the reverse 

side of the agar plate appears zonated and black with 

a lighter color outward. At 28 °C under alternating 

12-h fluorescent light and 12-h darkness, colonies 

grow very slowly and attain a 2.78-cm diam in 5 d. 

They are azonated and become zonated toward the 

margin, floccose to slightly felted. Aerial mycelia are 

white with brownish gray portions. The colony on the 

reverse side of the agar plate is azonated and becomes 

zonated near the margins, and appears white 

with greenish gray centers. 

Colonies on PJA at ART (28–30 °C) grow very 


azonated, becoming zonated toward the margins, 

velvety, becoming granular with age, with 0.8-cm 

submerged advancing mycelia, gray to light gray 

29

→ 

a 

b 

c 

d 

e 

e 

→→ 

e 

→ 

→ 

Fig. 25. Habit character of Pyricularia oryzae Cav. On sterile lemmas at (a) 10X, (b) 40X, and (c) 50X. Photomicrograph 

of P. oryzae showing (d) conidiophore and (e) conidia at 40X. 


100 

80 

60 

40 

20 

0 

Sterile 

lemmas 

Awn 

Partition 

bet. lemma 

and palea 

Seed part 

Entire 

seed 

Lemma/ 

palea 

only or 

both 

Fig. 26. Observed frequency of Pyricularia oryzae 


Fig. 27. Plate cultures of Pyricularia oryzae showing 

colony growths on PDA, PJA, and VJA, incubated at ART, 

21 °C, and 28 °C at 15 d after inoculation. 

near the margins. The colony on the reverse side of 

the agar plate appears azonated and dark purplish 

gray. At 21 °C under alternating 12-h NUV light and 

12-h darkness, colonies grow very slowly and attain a 

2.50-cm diam in 5 d. They are zonated, velvety with 

0.5-cm submerged advancing mycelia, and gray, 

becoming dark gray outward. The colony on the reverse 

side of the agar plate is zonated and dark purplish 

gray, becoming lighter outward. At 28 °C under 


colonies grow very slowly and attain a 3.17- 

cm diam in 5 d. They appear slightly zonated and 

30

gray, becoming dark near the margins with 1-cm submerged 

advancing mycelia. The colony on the reverse 

side of the agar plate is slightly zonated and 

dark purplish gray, becoming lighter outward. 

Colonies on VJA incubated at ART (28–30 °C) 

grow very slowly and attain a 2.96-cm diam in 5 d. 

They appear azonated, felted with even margins, and 

white with light gray portions. The colony on the reverse 

side of the agar plate appears azonated and 

brown-purple. At 21 °C under alternating 12-h NUV 

light and 12-h darkness, colonies grow very slowly 

and attain a 2.04-cm diam in 5 d. They appear zonated, 

slightly floccose to felted with radial furrows, 

and gray, becoming light gray toward the margins. 

The colony on the reverse side of the agar plate is 

zonated with radial wrinkles and brown-purple, 

becoming lighter toward the margin. At 28 °C under 


colonies grow very slowly and attain a 2.96-cm 

diam in 5 d. They appear azonated, becoming 

slightly zonated toward the margin, slightly felted 

with radial furrows and even margins, and gray, 

becoming lighter outward. The colony on the reverse 

side of the agar plate is azonated, becoming 

zonated toward the margins, with radial wrinkles 

and brown-purple, becoming lighter outward. 

Seedborne fungi causing stem, leaf sheath, and root diseases in rice 

Fusarium moniliforme Sheld. 

syn. Fusarium heterosporum Nees 

Fusarium verticillioides (Sacc.) Nirenberg 

Lisea fujikuroi Sawada 

teleomorph: Gibberella fujikuroi (Sawada) S. Ito 

Gibberella moniliformis Wineland 

Gibberella moniliforme 

Disease caused: bakanae, foot rot 

a. Symptoms 

The most conspicuous and common symptoms 

are the bakanae tillers or seedlings—an abnormal 

elongation of seedlings that are thin and yellowish 

green. These can be observed in the seedbed and 

in the field. In mature crops, infected plants may 

have a few tall, lanky tillers with pale green flag 

leaves; leaves dry up one after the other from 

below and eventually die. If the crop survives, 

panicles are empty. 


The disease is widely distributed in all rice-growing 

countries (Fig. 28). The pathogen detected in 

Africa is closely associated with that from maize 

and sorghum. 


This disease has been known since 1828 in Japan. 

In India, the disease was described as causing 

foot rot in 1931. Fujikuroi found the teleomorph 

and the fungus was placed in the genus 

Gibberella as G. fujikuroi with Fusarium 

moniliforme as its anamorph. 


The disease can be observed in seedbeds and in 

the field. Infected seedlings are either taller than 

normal seedlings or stunted. Infected mature 

plants eventually wither and die. When such 

plants reach the reproductive stage, they bear 

empty panicles. Across different rice production 

situations, bakanae can cause 0.01% yield loss in 

Asia. 



Using the blotter test, F. moniliforme can be observed 

on rice seeds 5 d after incubating seeds 

under NUV light at 21 °C. The detection frequency 

is about 28.1% on seeds coming from 



There are abundant aerial mycelia, floccose to 

felted, with loose and abundant branching, dirty 

white to peach. The conidiophores terminate in 

false heads and dirty white to peach pionnotes 

may be present (Fig. 30a-c). 

31

Fig. 28. Occurrence of bakanae (Ou 1985, Agarwal and Mathur 1988, EPPO 1997). 


F. moniliforme is most likely observed on the entire 

rice seed (about 57%) (Fig. 31). 


a. Mycelia—hyaline, septated (Fig. 30d). 

b. Microconidiophore—single, lateral, subulate 

phialides formed from aerial hyphae, tapering 

toward the apex (Fig. 30e). 

c. Macroconidiophore—consisting of a basal cell 

bearing 2–3 phialides that produce macroconidia. 

d. Microconidia—hyaline, fusiform, ovate or clavate; 

slightly flattened at both ends; one- or twocelled; 

more or less agglutinated in chains, and 

remain joined or cut off in false heads (Fig. 30f). 

Measurements: 2.53–16.33 µ × 2.30–5.75 µ 

(PDA); 5.06–14.26 µ × 1.61–4.83 µ (PSA); and 

4.60–10.35 µ × 1.61–4.83 µ (OA, oatmeal agar). 

e. Macroconidia—hyaline, inequilaterally fusoid; 

slightly sickle-shaped or almost straight; thinwalled; 

narrowed at both ends, occasionally bent 

into a hook at the apex and with a distinct foot cell 

at the base; 3–5 septate, usually 3 septate, rarely 

6–7 septate; formed in salmon orange 

sporodochia or pionnotes (Fig. 30g). Measurements: 

18.86–40.71 µ × 2.76–4.60 µ (PDA); 

16.10–35.42 µ × 2.07–4.60 µ (PSA); and 21.39– 

39.56 µ × 2.53–4.60 µ (OA). 


Colonies on PDA at ART (28–30 °C) grow moderately 

fast and attain a 5.20-cm diam in 5 d. They are 

slightly zonated; floccose to slightly felted, and become 

powdery with age; white tinged with pink at the 

center. The colony appearance on the reverse side of 

the agar plate is slightly zonated and white with a purplish 

center. At 21 °C under alternating 12-h NUV 

light and 12-h darkness, colonies grow slowly and attain 

a 3.72-cm diam in 5 d. They are slightly zonated, 

cottony to slightly felted with submerged advancing 

margins and pink. The colony on the reverse of the 

agar plate appears slightly zonated and dark pink and 

light toward the margin. At 28 °C under alternating 12- 

h fluorescent light and 12-h darkness, colonies grow 


They are zonated and appear cottony to slightly felted 

with sinuate margins, purplish at the center and light 

outward. Saltation of colonies is occasionally observed 

in some plates. The colony on the reverse side 

of the agar plate is zonated and purple and light purple 

outward. 

32


100 

80 

East Asia 

Europe 

Latin America 

South Asia 



60 

40 

20 

0 


60 

50 

40 

30 

20 

10 

0 

1990 1991 1992 1993 1994 1995 1996 1997 

Year 

Fig. 29. Detection frequency (a) and level (b) of Fusarium moniliforme from imported untreated seeds, 1990-97. 

Colonies on PSA at ART (28–30 °C) are spreading 

and grow moderately fast, attaining a 5.30-cm 

diam in 5 d. They are azonated, floccose with serrate 

margins, and white tinged with pink at the center. 

The colony on the reverse side of the agar plate is 

slightly zonated and white with a purplish tinge at the 

center. At 21 °C under alternating 12-h NUV light 

and 12-h darkness, colonies grow moderately fast 

and attain a 5.34-cm diam in 5 d. They are slightly 

zonated, floccose to slightly felted with serrate margins, 

and purplish at the center and light purple outward. 

The colony on the reverse side of the agar 

plate appears slightly zonated and white to creamy. 



attain a 5.90-cm diam in 5 d. They are slightly zonated, 

densely floccose with serrate margins, and 

white; they later become creamy at the center. The 

colony on the reverse side of the agar plate is slightly 

zonated and white to creamy. 

Colonies on OA at ART (28–30 °C) grow moderately 

fast and attain a 5.78-cm diam in 5 d. They 

are azonated and floccose to deeply felted with even 

to slightly sinuate margins. Colonies are white and 

become purple at the center. The colony on the reverse 

side of the agar plate appears azonated and 

white with dark purple centers. At 21 °C under alternating 

NUV light and 12-h darkness, colonies grow 


zonated, slightly felted with even margins, and white 

to purple. Saltation of colonies was observed in some 

plates. The colony on the reverse side of the agar 

33

a 

b 

→ 

d 

→ 

→ 

→ 

→ 

f 

→→ 

e 

g 

→ 

→→ 

→ 

c 

Fig. 30. Habit character of Fusarium moniliforme Sheld. on (a) whole seed (10X) and (b) awn portion (17X). (c) 

Mycelial growth of F. moniliforme showing false heads (49X). Photomicrograph of F. moniliforme showing (d) 

mycelia, (e) microconidiophores, (f) microconidia, and (g) macroconidia at 40X and stained with lactophenol blue. 

→ 


120 

100 

80 

60 

40 

20 

0 

Sterile 

lemmas 

Awn 

Partition 

bet. lemma 

and palea 

Seed part 

Entire 

seed 

Lemma/ 

palea 

only or 

both 

Fig. 31. Observed frequency of Fusarium moniliforme 


Fig. 32. Plate cultures of Fusarium moniliforme Sheld. 

showing colony growths on PDA, PSA, and oatmeal agar 

(OA) incubated at ART, 21 °C, and 28 °C at 15 d after 

inoculation. 

plate is zonated and white to dark purple. At 28 °C 


darkness, colonies grow moderately fast and attain a 

5.73-cm diam in 5 d. They are slightly zonated, floccose 

with even margins, and white with light purplish 

coloration at the center. The colony on the reverse 

side of the agar plate appears slightly zonated and 

dark purple and lighter outward. 

34

Sarocladium oryzae (Sawada) W. Gams & D. Hawks. 

syn. Acrocylindrium oryzae Saw. 

Sarocladium attenuatum W. Gams & D. Hawks. 

Disease caused: sheath rot 

a. Symptoms 

Lesions start at the uppermost leaf sheath enclosing 

young panicles as oblong or irregular spots, 

with brown margins and gray center or brownish 

gray throughout. Spots enlarge and coalesce covering 

most of the leaf sheath. Panicles remain 

within the sheath or may partially emerge. Affected 

leaf sheaths have abundant whitish powdery 

mycelium. The pathogen infects rice plants 

at all growth stages, but it is most destructive after 

the booting stage. 


Sarocladium oryzae is present in all rice-growing 

countries worldwide (Fig. 33). Sheath rot has become 

more prevalent in recent decades and is 

very common in rainfed rice or rice during the 

rainy season. 


Sawada first described sheath rot of rice in 1922 

from Taiwan. He named the causal organism as 

Acrocylindrium oryzae. In 1975, Gams and 

Hawksworth reclassified the causal organism as 

Sarocladium oryzae after comparing their isolates 

with those of Sawada. 


Densely planted fields and those infested by stem 

borers are susceptible to S. oryzae infection. The 

fungus tends to attack leaf sheaths enclosing 

young panicles, which retards or aborts the emergence 

of panicles. Seeds from infected panicles 

become discolored and sterile, thereby reducing 

grain yield and quality. 



Using the blotter test, S. oryzae can be observed 

on rice seeds 7 d after seeding and incubated under 

NUV light conditions at 21 °C. The detection 

frequency is about 21.3% on seeds coming from 



The mycelia are white, sparsely branched, septated, 

scanty to moderate, creeping close to the 

Fig. 33. Occurrence of sheath rot (Ou 1985, EPPO 1997). 

35


120 

100 

East Asia 

Europe 

Latin America 

South Asia 



80 

60 

40 

20 

0 


35 

30 

25 

20 

15 

10 

5 

0 

1990 1991 1992 1993 1994 1995 1996 1997 

Year 

Fig. 34. Detection frequency (a) and level (b) of Sarocladium oryzae from imported untreated seeds, 1990-97. 

seed surface, rarely becoming aerial. Conidiophores 

are very short with conidia collected in a 

slime drop that are globose and shiny (Fig. 35a-c). 


S. oryzae is mostly observed on the entire seed 

(about 46%) and on the lemma and/or palea 

(about 31%) (Fig. 36). 


a. Mycelia—white, sparsely branched, septate (Fig. 

35d). 

b. Conidiophores—slightly thicker than the vegetative 

hyphae, simple, or branched either once or 

twice; terminal branches tapering at the tip (Fig. 

35e). 

c. Conidia—hyaline, smooth, single-celled, cylindrical 

with rounded ends; straight, sometimes slightly 

curved, formed singly (Fig. 35f). Measurements: 

2.07–8.74 µ × 1.15–3.68 µ (PDA); 4.14–8.28 µ × 

1.38–3.68 µ (PSA); and 4.14–7.13 µ ×1.38–3.91 µ 

(MEA). 


Colonies on PDA at ART (28–30 °C) are restricted in 

growth and attain a 4.33-cm diam in 15 d. They are 

azonated, plane, velvety with even margins, and pale 

36

a 

b 

c 

e 

f 

d 

f 

Fig. 35. Habit character of Sarocladium oryzae (Sawada) W. Gams. and D. Hawks. on (a) whole seed (10X), (b) awn 

portion (32X), and (c) sterile lemmas (50X) showing minute, shiny, and globose false heads. Photomicrograph of S. 

oryzae showing (d) mycelia, (e) conidiophores, and (f) conidia at 40X and stained with lactophenol blue. 


50 

40 

30 

20 

10 

0 

Sterile 

lemmas 

Awn 

Partition 

bet. lemma 

and palea 

Entire 

se ed 

Lemma/ 

palea 

only or 

both 

Seed part 

Fig. 36. Observed frequency of Sarocladium oryzae 


Fig. 37. Plate cultures of Sarocladium oryzae (Sawada) 

W. Gams and D. Hawks. showing colony growths on 

PDA, PSA, and MEA incubated at ART, 21 °C, and 28 °C 

at 15 d after inoculation. 

37

orange. On the reverse side of the agar plate, the 

colony looks azonated and yellowish brown. At 21 °C 


colonies are restricted in growth and attain a 3.96-cm 

diam in 15 d. They are azonated, plane, velvety with 

even to slight sinuate margins, pale orange, and 

moisture is produced with age. The colony on the 

reverse side of the agar plate appears azonated and 

yellowish brown. At 28 °C under alternating 12-h 

fluorescent light and 12-h darkness, colonies are restricted 


They are zonated, plane, velvety with sinuate margins, 

and pale orange. On the reverse side of the agar 

plate, the colony appears slightly zonated and yellowish 

brown. 

Colonies on PSA at ART (28–30 °C) are restricted 


They are slightly zonated, slightly felted with sinuate 

margins, and pale orange. The colony on the reverse 

side of the agar plate appears slightly zonated and 

pale yellow-orange. At 21 °C under alternating 12-h 

NUV light and 12-h darkness, colonies are restricted 

in growth and attain a 4.21-cm diam in 15 d. They 

are azonated, plane, slightly velvety, with a few 

slight radial furrows, sinuate margins, and pale orange. 

The colony appears azonated, with a few radial 

wrinkles and pale yellow-orange on the reverse 

side of the agar plate. At 28 °C under alternating 12-h 

fluorescent light and 12-h darkness, colonies are restricted 


They are slightly zonated, slightly felted with a few 

slight radial furrows in some plates, with slightly sinuate 

to even margins, and pale orange; moisture is 

produced with age. The colony appears slightly zonated 

with a few slight radial wrinkles and pale yellow-orange 

on the reverse side of the agar plate. 

Colonies on MEA at ART (28–30 °C) are restricted 


They are slightly zonated, plane, velvety, and pale 

orange. The colony appears slightly zonated and dull 

orange with pale yellow-orange margins on the reverse 

side of the agar plate. At 21 °C under alternating 

12-h NUV light and 12-h darkness, colonies are 

restricted in growth and attain a 4.37-cm diam in 15 

d. They are zonated, felted with slight sinuate margins, 

and pale orange. On the reverse side of the agar 

plate, the colony appears azonated and dull orange 

with pale yellow-orange margins. At 28 °C under 


colonies are restricted in growth and attain a 4.47-cm 

diam in 15 d. They are plain to felted, zonated at the 

center, and become azonated toward the margins, 

with slight radial furrows and slight sinuate margins. 

Colonies are pale orange and whitish toward the margins. 


appears zonated with a few radial wrinkles and dull 

orange with pale yellow-orange margins. 

Seedborne fungi causing grain and inflorescence diseases in rice 

Curvularia sp. 

Disease caused: black kernel 

a. Symptoms 

Black discoloration on grains. 


Curvularia sp. is frequently isolated from discolored 

rice grains. Several species have been reported 

on rice from different countries (Fig. 38), 

but C. lunata and C. geniculata are the most common 

ones. 

c. Importance in crop production 

Curvularia sp. causes little or no yield loss under 

normal rice production situations. Infected grains, 

after being polished, may produce black kernels, 

thus reducing their market value. 



On blotters incubated under NUV light at 21 °C, 

the fungus can be observed growing on rice seed 

7 d after seeding. The detection frequency is 

about 70.6% on seeds coming from different regions 

(Fig. 39a,b). 


Aerial mycelia are scanty or absent; if present, 

they are light brown to brown with abundant 

branching. Conidiophores are solitary or in groups; 

dark brown; straight, sometimes bent; simple; 

arising directly from the seed surface. Conidia are 

borne more or less at the tip in a whorl or in thick 

panicles (Fig. 40a-c). 

38

Fig. 38. Occurrence of black kernel (Ou 1985, CABI/EPPO 1997). 


Curvularia sp. is observed most often on the 

lemma and/or palea (about 66%) of the seed (Fig. 

41). 


a. Mycelia—septated, branched, subhyaline to light 

brown, in some cases dark brown (Fig. 40d). 

b. Conidiophores—dark brown, unbranched, septate, 

sometimes bent and knotted at the tip (Fig. 40e). 

c. Conidia—dark brown, boat-shaped, rounded at the 

tip, mostly a little constricted at the base; with 

hilum scarcely or not at all protuberant, smoothwalled, 

light to dark brown, with three septa; the 

2nd cell is larger than the 1st, 3rd, and 4th cells; 

bent on the 2nd cell; borne at the tip, arranged in a 

whorl one over another or more or less spirally 

arranged or in thick panicles (Fig. 40f). Measurements: 

16.33–24.84 µ × 7.36–13.34 µ (PDA); 

17.48–27.37 µ × 8.28–13.11 µ (PSA); and 15.64– 

26.91 µ × 7.36–12.65 µ (MEA). 


Colonies on PDA at ART (28–30 °C) grow fast and 

attain an 8.40-cm diam in 5 d. Colonies are zonated 

and felted; the conidial area is greenish gray with a 3- 

mm sterile advancing margin and abundant grayish 

mycelial tufts. The colony appearance on the reverse 

side of the agar plate is zonated and gray. At 21 °C 



diam in 5 d. They are cottony to slightly felted with 

slight radial furrows and 5-mm even, sterile margins, 

zonated, and black, becoming gray toward the margins. 

The colony appearance on the reverse side of 

the agar plate appears zonated and black at the center 

and lighter outward. At 28 °C under alternating 


grow very fast and attain an 8.30-cm diam in 5 d. 

Colonies are zonated, hairy to slightly felted, and the 

conidial area is olive gray to greenish gray with a 2- 

mm sterile white margin. The colony appearance on 

the reverse side of the agar plate is slightly zonated 

and black. 

Colonies on PSA at ART (28–30 °C) grow very 

fast and attain an 8.50-cm diam in 5 d. They are 

slightly zonated, slightly cottony, and somewhat depressed 

to the media. The conidial area is black with 

3-mm sterile white margins becoming black as 

conidia are produced. The colony on the reverse side 

of the agar plate appears zonated and slightly black. 

At 21 °C under alternating 12-h NUV light and 12-h 

darkness, colonies grow fast and attain a 6.91-cm 

diam in 5 d. They are zonated, slightly cottony, with a 

39


120 

100 

East Asia 

Europe 

Latin America 

South Asia 



80 

60 

40 

20 

0 


100 

80 

60 

40 

20 

0 

1990 1991 1992 1993 1994 1995 1996 1997 

Year 

Fig. 39. Detection frequency (a) and level (b) of Curvularia sp. from imported untreated seeds, 1990-97. 

black conidial area with 3-mm sterile white margins. 

The colony on the reverse side of the agar plate appears 

zonated, black, and light outward. At 28 °C 


darkness, colonies grow very fast and attain a 9.0-cm 

diam in 5 d. They are zonated, slightly cottony, and 

the conidial area is black with 5-mm sterile white 

margins turning black as conidia are produced. The 


slightly zonated, black, and light outward. 


fast and attain an 8.17-cm diam in 5 d. They are 

markedly zonated, felted, and greenish gray. The 


zonated and black. At 21 °C under alternating 12-h 

NUV light and 12-h darkness, colonies grow moderately 


zonated, brown, and light outward. The colony on the 

reverse side of the agar plate appears zonated and 

brown, becoming lighter outward. At 28 °C under 


colonies grow very fast and attain an 8.23-cm diam 

in 5 d. They are zonated, slightly felted, olivaceous 

brown, and become light outward with 2-mm sterile 

white margins. The colony on the reverse side of the 

agar plate appears slightly zonated and black. 

40

a 

b 

d 

→ 

→ 

→ 

e 

→ 

f 

→ 

f 

→ 

d 

→ 

c 

Fig. 40. Habit character of Curvularia sp. on (a) whole seed (10X), (b) sterile lemmas (20X), and (c) lemma (32X). 

Photomicrograph of Curvularia sp. showing (d) mycelia, (e) conidiophores, and (f) conidia at 40X. 


70 

60 

50 

40 

30 

20 

10 

0 

Sterile 

glumes 

Awn 

Partition 

bet. lemma 

and palea 

Seed part 

Entire 

seed 

Lemma/ 

palea 

only or 

both 

Fig. 41. Observed frequency of Curvularia sp. occurrence 

on the seed. 

Fig. 42. Plate cultures of Curvularia lunata (Wakker) 

Boedijin showing colony growths on PDA, PSA, and MEA 

incubated at ART, 21 °C, and 28 °C at 15 d after 

inoculation. 

41

Fusarium solani (Mart.) Sacc. 

syn. Fusisporium solani Martius 

Fusarium javanicum Koorders 

Fusarium solani var. martii (Apel & Wollenw.) Wollenw. 

Fusarium solani var. striatum (Sherbakov) Woellenw. 

teleomorph: Hyphomyces solani 

Nectria haematococca var. brevicona (Wollenw.) Gerlach 

Disease caused: none reported in rice 

a. Occurrence/distribution 

F. solani is a rice seedborne pathogen that occurs 

in low frequency. The fungus may be involved in 

grain discoloration. However, it is detected on 

seed coming from different regions and rice ecosystems. 



Using the blotter test, F. solani can be observed 

on rice seeds 5 d after incubation in NUV light at 

21 °C. The detection frequency is

d 

a 

b 

e 

→ 

→ 

→ 

→ 

→ 

f 

c 

g 

h 

Fig. 43. Habit character of Fusarium solani (Mart.) Sacc. on (a) whole seed (11X) and sterile lemmas at (b) 21X and 

(c) 40X showing (d) pionnotes and (e) false heads. Photomicrograph of F. solani showing (f) conidiophore, (g) 

macroconidia, and (h) microconidia at 40X stained with lactophenol blue. 


70 

60 

50 

40 

30 

20 

10 

0 

Sterile 

glumes 

Awn 

Partition 

bet. lemma 

and palea 

Seed part 

Entire 

seed 

Lemma/ 

palea 

only or 

both 

Fig. 44. Observed frequency of Fusarium solani 


Fig. 45. Plate cultures of Fusarium solani (Mart.) Sacc. 

showing colony growths on PDA, PSA, and OA incubated 

at ART, 21 °C, and 28 °C at 15 d after inoculation. 

43

verse side of the agar plate is zonated. The color is 

dark reddish brown. At 21 °C under alternating 12-h 

NUV light and 12-h darkness, colonies spread relatively 


azonated; aerial mycelia are nil to scanty, slightly 

pressed to the media, powdery, becoming creamy 

with age, and light yellow at the center, becoming 

dull reddish brown n with light gray margins. The 


azonated and dull reddish brown. At 28 °C under 


colonies spread relatively fast and attain a 5.28-cm 

diam in 5 d. They are zonated with even margins and 

aerial mycelia are scanty and hairy, with 6-mm submerged 

advancing mycelia. The color is dull brown 

to brown, becoming lighter toward the margin. The 


zonated with a dull reddish brown color. 

Nigrospora sp. 

teleomorph: Khushia oryzae Huds. 

Disease caused: minute leaf and grain spot 

a. Symptoms 

Presence of numerous minute black pustules 

(

Fig. 46. Occurrence of minute leaf and grain spot (EPPO 1997). 


120 

100 

East Asia 

Europe 

Latin America 

South Asia 



80 

60 

40 

20 

0 


60 

50 

40 

30 

20 

10 

0 

1990 1991 1992 1993 1994 1995 1996 1997 

Year 

Fig. 47. Detection frequency (a) and level (b) of Nigrospora sp. from imported untreated seeds, 1990-97. 

45

a 

b 

→→ 

f 

→ 

→ 

c 

e 

→ 

d 

→ 

Fig. 48. Habit character of Nigrospora sp. on (a) whole seed (10X), (b) sterile lemmas (32X), and (c) plea (32X) 

showing shiny, black, and globose conidia. Photomicrograph of Nigrosopra sp. showing (d) mycelia, (e) conidiophore, 

and (f) conidia at 40X. 


70 

60 

50 

40 

30 

20 

10 

0 

Sterile 

lemmas 

Awn 

Partition 

bet. lemma 

and palea 

Seed part 

Entire 

seed 

Lemma/ 

palea 

only or 

both 

Fig. 49. Observed frequency of Nigrospora sp. occurrence 

on the seed. 

Fig. 50. Plate cultures of Nigrospora sp. showing colony 

growths on PDA, PSA, and MEA incubated at ART, 21 

°C, and 28 °C at 15 d after inoculation. 

46

of the agar plate appears slightly zonated and 

black. 

Colonies on PSA at ART (28–30 °C) grow 


They are slightly zonated and densely floccose 

with sinuate margins, black, and later become light 

toward the margins. The colony on the reverse side 

of the agar plate appears slightly zonated and 

black. At 21 °C under alternating 12-h NUV light 

and 12-h darkness, colonies grow fast and attain a 

7.78-cm diam in 5 d. They are slightly zonated, 

densely floccose, black, and lighter toward the 

margins. The colony on the reverse side of the agar 

plate appears zonated and black. At 28 °C under 


colonies grow fast and attain a 7.56-cm diam 

in 5 d. They are slightly zonated, densely floccose, 

black, and become lighter outward with sinuate 

margins. The colony of the reverse side of the agar 

plate appears slightly zonated and black. 


fast and attain an 8.00-cm diam in 5 d. They are zonated, 

slightly floccose to felted, grayish to black, and 

become lighter outward. The colony on the reverse 

side of the agar plate appears zonated and black. At 

21 °C under alternating 12-h NUV light and 12-h 

darkness, colonies grow moderately fast and attain a 

6.53-cm diam in 5 d. They are zonated, slightly 

felted, and alternating white and light gray. The 

colony of the reverse side of the agar plate appears 

zonated, dark gray, and light toward the margins. At 

28 °C under alternating 12-h fluorescent light and 12- 

h darkness, colonies spread fast and attain a 9.00-cm 

diam in 5 d. They are zonated, felted, and alternating 

gray and light gray. The colony on the reverse side of 

the agar plate appears zonated and dark gray. 

Phoma sorghina (Sacc.) Boerema et al 

teleomorph: Mycosphaerella holci Tehon 

Disease caused: glume blight 

a. Symptoms 

Lesions are initially small, oblong, and brown, 

then gradually enlarge and coalesce, becoming 

whitish with small black dots. 

The fungus infects glumes during the second or 

third week following emergence of panicles. 

When infection occurs early, no grain is formed. 

On the other hand, when infection is late, grains 

are partially filled or become discolored and 

brittle. 


This is a disease of the grain. It is widely distributed 

and the pathogen is often detected on rice 

seed from different regions and rice production 

ecosystems (Fig. 51). 


The disease was first reported in the U.S. and 

Japan and later reported in other rice-growing 

areas as well. The fungus P. sorghina has been 

reported under different names, including 

Phyllosticta glumarum (Ell. & Tracy) Miyake, 

Ph. oryzina Padw., and Ph. glumicola (Speg.) 

Hara, and Phoma oryzicola Hara with 

Trematosphaerella oryzae (Miyake) Padw. as its 

teleomorph. 


The disease is a relatively minor problem of rice. 

Together with other diseases of the grain, the loss 

is

Fig. 51. Occurrence of glume blight (EPPO 1997). 

b. Pycnidia—dark brown, globose or subglobose 

with protruding ostioles (Fig. 53d). 

c. Conidia—oblong to ovoid, hyaline to slightly pigmented, 

single-celled (Fig. 53e). Measurements: 

2.99–6.21 µ × 1.84–3.68 µ (PDA); 3.68–8.74 µ × 

1.84–7.59 µ (PSA); and 3.45–6.67 µ × 1.38–4.60 µ 

(MEA). 


Colonies on PDA at ART (28–30 °C) spread very 


slightly zonated with even margins, thickly felted, 

and brownish gray. The colony on the reverse side of 

the agar plate appears zonated and is brownish gray 

with brownish black spots. At 21 °C under alternating 

12-h NUV light and 12-h darkness, colonies spread 

very fast and attain a 7.73-cm diam in 5 d. They are 

zonated with even margins, felted, dull yellowish 

brown at the center, and greenish gray outward with 

4-mm light brownish gray advancing margins. The 


zonated and dark reddish brown at the center and 

reddish orange outward. At 28 °C under alternating 


grow very fast and attain an 8.11-cm diam in 5 d. 

They are zonated, cottony to felted with even margins, 

and grayish olive and light gray outward. On the 

reverse side of the agar plate, the colony appears 

zonated and alternating brownish black and dull yellow-orange. 

Colonies on PSA at ART (28–30 °C) spread 


azonated and fluffy to slightly floccose with even 

margins. The color is grayish yellow-brown at the 

center, becoming dark grayish yellow to grayish yellow. 


appears slightly zonated to zonated and is dull yellowish 

brown to brownish black with dull yelloworange 

margins. At 21 °C under alternating 12-h 

NUV light and 12-h darkness, colonies spread very 


azonated to slightly zonated, felted to cottony with 

even margins, and grayish yellow and gray outward. 

On the reverse side of the agar plate, the colony appears 

zonated, black at the center, and alternating 

dark olive and grayish olive outward. At 28 °C under 


colonies spread very fast and attain a 7.70-cm diam 

in 5 d. They are azonated with even margins, cottony 

to fluffy, and olive black, becoming light gray outward. 

On the reverse side of the agar plate, colony 

appears zonated. The color is black, becoming 

brownish black to dull yellow brown toward the margins. 

Colonies on MEA at ART (28–30 °C) spread 


48


120 

100 

East Asia 

Europe 

Latin America 

South Asia 



80 

60 

40 

20 

0 


70 

60 

50 

40 

30 

20 

10 

0 

1990 1991 1992 1993 1994 1995 1996 1997 

Year 

Fig. 52. Detection frequency (a) and level (b) of Phoma sp. from imported untreated seeds, 1990-97. 

azonated and loosely floccose to hairy with even 

margins. Aerial mycelia are pressed to the media, 

olive black at the center, and become grayish olive to 

olive yellow outward. On the reverse side of the agar 

plate, the colony appears zonated. It is dark olive at 

the center and becomes grayish olive to olive yellow 

toward the margins. At 21 °C under alternating 12-h 

NUV light and 12-h darkness, colonies are thin but 

spread very fast and attain a 6.89-cm diam in 5 d. 

They are azonated with even margins. Aerial mycelia 

are pressed to the media. The color is dark olive 

green at the center and grayish olive outward. On the 


azonated. The color is olive black at the center and 

dark olive outward. At 28 °C under alternating 12-h 

fluorescent light and 12-h darkness, colonies spread 

thinly but very fast and attain a 7.10-cm diam in 5 d. 

They are azonated to slightly zonated, hairy to 

loosely floccose with even submerged margins, and 

grayish olive. On the reverse side of the agar plate, 

the colony appears slightly zonated and is dark olive, 

becoming lighter outward. 

49

a 

b 

e 

c 

e 

→ 

d 

Fig. 53. Habit character of Phoma sorghina (Sacc.) on (a) whole seed (10X), (b) palea and lemma (25X), and (c) 

sterile lemmas (40X) showing dark, globose to subglobose, ostiolate pycnidia. Photomicrograph of P. sorghina 

showing (d) pycnidia and (e) conidia at 40X. 


40 

30 

20 

10 

0 

Sterile 

lemmas 

Awn 

Partition 

bet. lemma 

and palea 

Seed part 

Entire 

seed 

Lemma/ 

palea 

only or 

both 

Fig. 54. Observed frequency of Phoma sp. occurrence 

on the seed. 

Fig. 55. Plate cultures of Phoma sp. showing colony 

growths on PDA, PSA, and MEA incubated at ART, 21 

°C, and 28 °C at 15 d after inoculation. 

50

Pinatubo oryzae Manandhar & Mew 

Disease caused: seed rot 

a. Symptoms 

Gray lesions on plumules. 


Pinatubo oryzae is frequently encountered in rice 

seed grown in the Philippines and other countries 

occurring on both germinated and nongerminating 

seeds (Fig. 56). 


This fungus was previously identified as Verticillium 

cinnabarinum and re-identified as Pinatubo 

oryzae in 1996. It has been detected from rice 

seeds since 1982. It is highly probable that the 

organism was already present earlier but there are 

no literatures to document any efforts to identify 

the fungus. 


This fungus is a rice grain pathogen. It is minor in 

importance to rice production. 

→ 



Using the blotter test, P. oryzae can be observed 

on rice seeds 5 d after incubation in NUV light at 

21 °C. The detection frequency is about 25.2% on 

rice seeds coming from different regions. 


Aerial mycelia are sparse to abundant and white 

with loose and abundant branching. Conidia are 

borne terminally and arranged in a flower-like 

manner. Pionnotes present on the seed surface 

are wet and creamy to pink or they hang under a 

thin cover of aerial hyphae (Fig. 57 a-c). 


P. oryzae is most often observed over the entire 

seed surface (about 46%) (Fig. 58). 


a. Mycelia—hyaline, septate (Fig. 57d). 

b. Conidiophore—simple or branched, short, septate 

with denticles at the terminal portion (Fig. 57e). 

c. Conidia—elongately oval, single- to 2-celled, 

very rarely 3-celled; pointed at the basal portion 

and rounded at the apical portion, hyaline (Fig. 

57f). Measurements: 5.06–10.81 µ × 2.70–6.21 µ 

(PDA); 5.75–12.88 µ × 2.76–5.98 µ (PSA); and 

5.75–11.73 µ × 2.53–5.06 µ (MEA). 


Colonies on PDA at ART (28–30 °C) grow relatively 

fast and attain a 5.02-cm diam in 5 d. They are zonated 

with even margins, floccose, and reddish or- 

Fig. 56. Occurrence of Pinatubo oryzae on rice seed from different countries received at IRRI (IRRI-SHU unpublished 

data 1990-97). 

51

a 

b 

→ 

→ 

→ 

f 

e 

f 

c 

d 

Fig. 57. Habit character of Pinatubo oryzae Manandhar and Mew on (a) whole seed (12X), (b) sterile lemmas (50X), 

and (c) awn portion (50X). Photomicrograph of P. oryzae showing (d) mycelia, (e) conidiophore, and (f) conidia at 

40X and stained with lactophenol blue. 


60 

50 

40 

30 

20 

10 

0 

Sterile 

lemmas 

Awn 

Partition 

bet. lemma 

and palea 

Entire 

seed 

Lemma/ 

palea 

only or 

both 

Seed part 

Fig. 58. Observed frequency of Pinatubo oryzae 


Fig. 59. Plate cultures of Pinatubo oryzae Manandhar 

and Mew showing colony growths on PDA, PSA, and 

MEA incubated at ART, 21 °C, and 28 °C at 15 d after 

inoculation. 

52

ange with orange. The pionnotes are wet. On the 


slightly zonated and becomes azonated toward the 

margins. The color is orange to light yellow-orange 

toward the margins. At 21 °C under alternating 12-h 

NUV light and 12-h darkness, colonies grow fast and 

attain a 6.26-cm diam in 5 d. They are azonated with 

even margins and pale orange to grayish red. 

Pionnotes are wet and appear as reddish orange 

small dots. The colony appears azonated to slightly 

zonated on the reverse side of the agar plate. The 

color is orange interspersed with dull reddish brown. 


12-h darkness, colonies grow relatively fast and attain 

a 5.20-cm diam in 5 d. They are zonated with 

even margins, floccose, and alternating pale orange 

and orange with pale orange mycelial tufts. The 

colony appears slightly zonated to zonated and is 

alternating orange and light yellow in color on the 

reverse side of the agar plate. 

Colonies on PSA at ART (28–30 °C) grow relatively 


slightly zonated with even margins, slightly felted, 

and orange to light yellow-orange, becoming reddish 

brown with age. The colony appears slightly zonated 

on the reverse side of the agar plate. The color is 

orange to bright reddish brown, becoming light yellow-orange 

toward the margins. At 21 °C under alternating 

12-h NUV light and 12-h darkness, colonies 

grow relatively fast and attain a 5.70-cm diam in 5 d. 

They are azonated with even margins and slight radial 

furrows, felted, and pale orange with shiny reddish 

orange pionnotes. The colony appears 

azonated to slightly zonated and alternating yelloworange 

and orange on the reverse side of the agar 

plate. At 28 °C under alternating 12-h fluorescent 

light and 12-h darkness, colonies grow relatively 


azonated to slightly zonated with even margins, 

slightly felted to fluffy, becoming wet with age, and 

pale orange to orange. The colony appears slightly 

zonated and orange on the reverse side of the agar 

plate. 

Colonies on MEA at ART (28–30 °C) grow 


They are azonated with even margins, floccose, 

and light yellow-orange, becoming powdery with 

age. On the reverse side of the agar plate, the 

colony appears slightly zonated and pale yellow to 

yellow. At 21 °C under alternating 12-h NUV light 

and 12-h darkness, colonies grow relatively fast and 

attain a 5.18-cm diam in 5 d. They are azonated 

with even margins and thin aerial mycelia that are 

pressed to the media. The color is pale orange. The 

colony appears azonated and dull yellow-orange on 

the reverse side of the agar plate. At 28 °C under 



diam in 5 d. They are zonated with even margins. 

Aerial mycelia are thin and pressed to the media. 

The color is pale orange and becomes powdery 

with age. On the reverse side of the agar plate, the 

colony appears slightly zonated to zonated and the 

color is pale orange. 

Tilletia barclayana (Bref.) Sacc. & Syd. 

syn. Neovossia barclayana Bref. 

Tilletia horrida Tak. 

Neovossia horrida (Tak.) Padw. & Kahn 

Disease caused: kernel smut (bunt) 

a. Symptoms 

Infected grains show very small black pustules or 

streaks bursting through the glumes. When infection 

is severe, rupturing glumes produce a short 

beak-like outgrowth or the entire grain is replaced 

by powdery black mass of smut spores. 


The disease is known to occur in many countries 

worldwide (Fig. 60). 


In 1986, the causal fungus of this disease was 

originally called Tilletia horrida. Later it was 

identified as Neovossia barclayana. Further studies 

made placed it in the genus Tilletia; it is now 

known as Tilletia barclayana. 


The disease can be observed in the field at the 

mature stage of the rice plant. It is considered 

economically unimportant, causing stunting of 

53

seedlings and reduction in tillers and yield when 

smutted seeds are planted. 


a. Dry seed inspection 

Infection on seeds can be detected by direct inspection 

using a stereo binocular microscope (Fig. 

61a,b). 


Aerial mycelia absent. Dull black and globose 

teliospores scattered on seed surface and cotyledon 

(Fig. 62a-c). 

c. Microscopic character 

Teliospores are globose to subglobose, light to 

dark brown with spines, and measure 22.5–26.0 µ 

× 18.0–22.0 µ (Fig. 62d). 

Fig. 60. Occurrence of kernel smut (Ou 1985, CMI 1991). 

54


70 

60 

East Asia 

Europe 

Latin America 

South Asia 



50 

40 

30 

20 

10 

0 


100 

80 

60 

40 

20 

0 

1990 1991 1992 1993 1994 1995 1996 1997 

Year 

Fig. 61. Detection frequency (a) and level (b) of Tilletia barclayana from imported untreated seeds, 1990-97. 

55

a 

b 

c 

d 

Fig. 62. Habit character of Tilletia barclayana (Bref.) Sacc. and Syd. (Duran and Fischer) on (a) whole seed (16X), 

(b) palea (40X), and (c) cotyledon and portion of lemma (40X). Photomicrograph of T. barclayana showing (d) 

teliospores (40X). 

56

Other fungi detected on rice seeds 

Other fungi are detected on rice seeds from different countries. Some, such as Nakataea sigmoidea, the 

conidial state of Sclerotium rolfsii, cause stem rot, which is important in specific ecosystems. However, most 

of these “other fungi” are not known to cause diseases of economic importance. These fungi are listed in 

Table 5 and photomicrographs of their habit and microscopic characters are shown. 

Table 5. List of other fungi detected on rice seeds. 

Fungi Incidence a 

Acremoniella atra + 

Acremoniella verrucosa + 

Alternaria longissima ++ 

A. tenuissima + 

Aspergillus clavatus + 

A. flavus-oryzae ++ 

A. niger ++ 

Chaetomium globosum + 

Cladosporium sp. ++ 

Curvularia eragrostidis + 

Drechslera hawaiiensis + 

Epicoccum purpurascens + 

Fusarium avenaceum + 

F. equiseti + 

F. larvarum + 

F. nivale + 

F. semitectum +++ 

Gilmaniella humicola + 

Memnoniella sp. + 

Microascus cirrosus + 

Monodictys putredinis + 

Myrothecium sp. + 

Nakataea sigmoidea ++ 

Nectria heamatococca + 

Papularia sphaerosperma + 

Penicillium sp. ++ 

Pestalotia sp. + 

Phaeoseptoria sp. + 

Phaeotrichoconis crotolariae + 

Pithomyces sp. ++ 

Pyrenochaeta sp. + 

Rhizopus sp. ++ 

Septogloeum sp. + 

Sordaria fimicola + 

Spinulospora pucciniiphila + 

Sterigmatobotrys macrocarpa + 

Taeniolina sp. + 

Tetraploa aristata + 

Trichoderma sp. + 

Trichothecium sp. + 

Tritirachium sp. + 

Ulocladium botrytis + 

a 

+ = low, ++ = moderate, +++ = frequent. 

57

a 

b 

e 

e 

d 

e 

f 

c 

f 

Fig. 63. Habit character of Acremoniella atra (Corda) Sacc. on (a) whole seed (10X) and palea at (b) 25X and (c) 40X. 

Photomicrograph of A. atra showing (d) mycelia, (e) conidiophores, and (f) conidia at 10X and stained with 

lactophenol blue. 

a 

b 

d 

→ 

→ 

→ 

e 

c 

d 

Fig. 64. Habit character of Acremoniella verrucosa Tognini on (a) whole seed (12X) and awn area at (b) 25X and (c) 

50X. Photomicrograph of A. verrucosa showing (d) conidiophores and (e) conidia at 40X. 

58

a 

b 

e 

c 

d 

Fig. 65. Habit character of Alternaria longissima Deighton & MacGarvie on (a) whole seed (10X), (b) lemma (40X), 

and (c) awn (40X). Photomicrograph of A. longissima showing (d) conidiophore and (e) conidia at 40X. 

a 

b 

c 

d 

Fig. 66. Habit character of Alternaria tenuissima (Kunze ex Pers.) Wiltshire on awn area at (a) 9X, (b) 25X, and (c) 

50X. Photomicrograph of A. tenuissima showing (d) conidia (40X). 

59

a 

b 

→ 

→ 

e 

c 

d 

Fig. 67. Habit character of Aspergillus clavatus Desmazieres on palea and lemma at (a) 10X, (b) 25X, and (c) 40X. 

Photomicrograph of A. clavatus showing (d) conidiophore and (e) conidial head at 40X and stained with lactophenol 

blue. 

a 

b 

f 

c 

d 

e 

Fig. 68. Habit character of Aspergillus flavus-oryzae Thom & Raper on (a) whole seed (8X) and lemma at (b) 16X and 

(c) 30X. Photomicrograph of A. flavus-oryzae showing (d) conidiophore, (e) conidial head showing sterigmata, and 

(f) conidia at 40X. 

60

a 

d 

d 

b 

c 

Fig. 69. Habit character of Aspergillus niger van Tiegh. showing black conidial heads on whole seed at (a) 9X and 

(b) 25X. Photomicrograph of A. niger showing (c) portion of conidiophore and (d) conidial head showing sterigmata 

and conidia at 40X. 

a 

b 

d 

c 

Fig. 70. Habit character of Chaetomium globosus Kunze. Fr. showing dark, ostiolate, sub-globose perithecium 

with brown flexuous hairs at (a) awn area (40X) and (b) sterile lemma (50X). Photomicrograph of C. globosum 

showing (c) perithecium with hairs (40X) and (d) mature ascospores (10X). 

61

→ 

→ 

→ 

→ 

a 

b 

→ 

d 

→ 

→ 

e 

→ 

a 

Fig. 71. Habit character of Cladosporium sp. on (a) embryonal area (10X) and sterile lemmas at (b) 40X and (c) 50X. 

Photomicrograph of Cladosporium sp. showing portion of (d) conidiophores and (e) conidia at 40X. 

a 

b 

d 

d 

d 

→ 

→ 

e 

e 

→ 

c 

Fig. 72. Habit character of Curvularia eragrostidis (P. Henn.) Meyer on (a) whole seed (9X) and lemma at (b) 25X and 

(c) 50X. Photomicrograph of C. eragrostidis showing (d) conidiophore and (e) conidia at 40X. 

62

→ 

→ 

→ 

a 

b 

f 

f 

e 

d 

e 

e 

c 

f 

Fig. 73. Habit character of Drechslera hawaiiensis Subram. & Jain on (a) whole seed (9X) and lemma at (b) 25X and 

(c) 50X. Photomicrograph of D. hawaiiensis showing (d) mycelia, (e) conidiophores, and (f) conidia at 40X. 

a 

→ 

b 

d 

→ 

→ 

c 

Fig. 74. Habit character of Epicoccum purpurascens Ehrenb. ex Schlect. on sterile lemmas showing sporodochia 

at (a) 10X, (b) 25X, and (c) 50X. Photomicrograph of E. purpurascens showing (d) golden brown conidia (40X). 

63

a 

b 

c 

Fig. 75. Habit character of Fusarium avenaceum (Corda ex Fr.) Sacc. on whole seed at (a) 12X and (b) 40X showing 

white floccose aerial mycelia with pionnotal-like sporodochia. Photomicrograph of F. avenaceum showing (c) 

conidia (40X) stained with lactophenol blue. 

64

a 

b 

a 

Fig. 76. Habit character of Fusarium equiseti (Corda) Sacc. showing light orange pionnotes on (a) whole seed (10X) 

and (b) sterile lemmas and palea and lemma (25X). Photomicrograph of F. equiseti showing (c) falcate conidia 

(40X) stained with lactophenol blue. 

65

a 

→ 

→ 

→ 

→ 

→ 

→ 

a 

f 

→ 

d 

b 

→ 

f 

c 

e 

→ 

Fig. 77. Habit character of Fusarium larvarum Fuckel on embryonal area showing slimy yellowish pionnote at (a) 

10X, (b) 18X, and (c) 35X. Photomicrograph of F. larvarum showing (d) mycelia, (e) conidiophore, and (f) conidia 

(40X) stained with lactophenol blue. 

→ 

→ 

a 

b 

c 

d 

Fig. 78. Habit character of Fusarium nivale Ces. showing sporodochia on embryonal area at (a) 12X, (b) 25X, and 

(c) 40X. Photomicrograph of F. nivale showing (d) conidia (40X) stained with lactophenol blue. 

66

a 

b 

d 

c 

d 

e 

e 

Fig. 79. Habit character of Fusarium semitectum Berk. & Rav. on (a) whole seed (10X), (b) awn portion (25X), and 

(c) lemma (50X). Photomicrograph of F. semitectum showing (d) conidiophores and (e) macroconidia at 40X and 

stained with lactophenol blue. 

a 

b 

d 

c 

d 

Fig. 80. Habit character of Gilmaniella humicola Barron on sterile lemmas at (a) 9X, (b) 25X, and (c) 50X. 

Photomicrograph of G. humicola showing (d) conidia at 40X. 

67

→ 

a 

b 

f 

→ 

→ 

→ 

f 

→ 

e 

→ 

→ 

e 

d 

c 

→ 

d 

Fig. 81. Habit character of Memmoniella sp. on sterile lemmas at (a) 10X, (b) 25X, and (c) 40X. Photomicrograph 

of Memmoniella sp. showing (d) conidiophores, (e) phialides, and (f) conidia at 40X. 

a 

b 

e 

c 

d 

Fig. 82. Habit character of Microascus cirrosus showing dark, globose, ostiolate, with cylindrical neck ascoma on 

(a) whole seed (8X) and lemma and sterile lemmas at (b) 19X and (c) 40X. Photomicrograph of M. cirrosus showing 

(d) portion of ascoma and (e) mature ascopores at 40X. 

68

a 

b 

c 

→ 

→ 

→ 

d → 

Fig. 83. Habit character of Monodictys putredinis (Wallr.) Hughes showing blackish brown aerial mycelia and 

almost black conidia on whole seed at (a) 10X and (b) 50X. Photomicrograph of M. putredinis showing (c) 

conidiophore and (d) conidia at 40X. 

69

→ 

→ 

→ 

→ 

→ 

→ 

→ 

→ 

→ 

→ 

→ 

→ 

a 

b 

→ 

c 

d 

Fig. 84. Habit character of Myrothecium sp. on palea and lemma at (a) 10X, (b) 25X, and (c) 50X showing cushionlike 

sporodochia with marginal hyaline setae. Photomicrograph of Myrothecium sp. showing (d) elongately ovoid 

conidia (40X) stained with lactophenol blue. 

a 

d 

b 

c 

Fig. 85. Habit character of Nakataea sigmoidea Hara on sterile lemmas and pedicel at (a) 8X and (b) 50X. 

Photomicrograph of N. sigmoidea showing (c) conidiophore and (d) conidia at 40X. 

70

→ 

→ 

→ 

a 

b 

d 

c 

Fig. 86. Habit character of Nectria haematococca Berk. & Broome showing superficial, red-orange, globose 

ascoma at (a) 20X and (b) 40X. Photomicrograph of N. haematococca showing (c) cross section of ascoma (10X) 

and (d) ascopores (40X) stained with lactophenol blue. 

a 

b 

d 

c 

Fig. 87. Habit character of Papularia sphaerosperma (Pers.) Hohnel. showing minute, black, round conidia at (a) 

8X, (b) 25X, and (c) 50X. Photomicrograph of P. sphaerosperma showing (d) conidia (63X). 

71

a 

b 

f 

e 

c 

d 

Fig. 88. Habit character of Penicillium sp. on (a) whole seed (10X), (b) sterile lemmas and lemma (18X), and (c) awn 

(50X). Photomicrograph of Penicillium sp. showing (d) branched conidiophore, (e) phialides, and (f) conidia at OIO. 

72

a 

b 

c 

Fig. 89. Habit character of Pestalotia sp. showing subepidermal acervuli with conidial mass on sterile lemmas at 

(a) 12X and (b) 30X. Photomicrograph of Pestalotia sp. showing (c) septated conidia with 2–3 hyaline appendages 

(40X). 

73

→ 

→ 

→ 

→ 

→ 

a 

b 

→ 

d 

e 

c 

Fig. 90. Habit character of Phaeoseptoria sp. on sterile lemmas at (a) 10X, (b) 25X, and (c) 50X. Photomicrograph 

of Phaeoseptoria sp. showing (d) portion of pycnidia and (e) conidia at 40X. 

a 

b 

d 

c 

e 

Fig. 91. Habit character of Phaeotrichoconis crotalariae (Salam & Rao) Subram. on (a) palea and lemma (25X), (b) 

sterile lemmas (40X), and (c) awn area (40X). Photomicrograph of P. crotalriae showing (d) portion of conidiophore 

(40X) and (e) conidia with large dark brown scar at the base (40X). 

74

a 

b 

d 

c 

e 

Fig. 92. Habit character of Pithomyces sp. on (a) whole seed (9X) and palea and lemma at (b) 18X and (c) 40X. 

Photomicrograph of Pithomyces sp. showing (d) mycelia and (e) conidia at 40X. 

b 

a 

f 

e 

c 

d 

Fig. 93. Habit character of Pyrenochaeta sp. showing dark and globose pycnidia with bristles on (a) whole seed 

(9X) and palea at (b) 25X and 40X. Photomicrograph of Pyrenochaeta sp. showing portion of (d) pycnidia, (e) 

bristles, and (f) 1-celled conidia at 40X. 

75

→ 

a 

g 

→ 

→ 

f 

g 

→ 

→ 

b 

→ 

e 

→ 

c 

d 

Fig. 94. Habit character of Rhizopus sp. showing gray sporangia on (a) whole seed (9X), (b) lemma (25X), and (c) 

embryonal area (40X). Photomicrograph of Rhizopus sp. showing (d) rhizoids, (e) sporangiophores, (f) sporangium, 

and (g) sporangiospores (10X). 

→ 

→ 

→ → 

→ 

a 

→ 

b 

→ 

→ 

c 

d 

Fig. 95. Habit character of Septogloeum sp. on sterile lemmas at (a) 10X, (b) 25X, and (c) 50X. 

Photomicrograph of Septogloeum sp. showing (d) conidia at 40X. 

76

→ 

→ 

→ 

→ 

a 

b 

e 

f 

→ 

c 

d 

Fig. 96. Habit character of Sordaria fimicola (Roberge ex Desmaz.) Ces. at (a) 9X, (b) 25X, and (c) 50X. 

Photomicrograph of S. fimicola showing (d) perithecium and (e) ascus with ascospores at 10X. (f) Ascus with 

ascospores at 40X. 

a 

b 

d 

c 

Fig. 97. Habit character of Spinulospora pucciniiphila Deighton on (a) whole seed (10X), (b) sterile lemma area 

(25X), and (c) embryonal side (50X). Photomicrograph of S. pucciniiphila showing (d) bulbils (40X). 

77

→ 

→ 

→ 

→ 

a 

b 

c 

d 

Fig. 98. Habit character of Sterigmatobotrys macrocarpa (Corda) Hughes on (a) whole seed (10X), (b) portion of 

sterile lemmas (40X), and (c) awn portion (40X). Photomicrograph of S. macrocarpa showing (d) conidia at 40X. 

→ 

a 

b 

c 

d 

Fig. 99. Habit character of Taeniolina sp. on sterile lemmas at (a) 12X, (b) 25X, and (c) 40X. Photomicrograph of 

Taeniolina sp. showing (d) multiseptate conidia (40X). 

78

a 

b 

c 

d 

Fig. 100. Habit character of Tetraploa aristata Berk. & Br. on (a) whole seed (12X), (b) palea and lemma (25X), and 

(c) palea (50X). Photomicrograph of T. aristata showing (d) conidia with septate appendages (40X). 

a 

b 

c 

d 

Fig. 101. Habit character of Trichoderma sp. on sterile lemma and palea and lemma at (a) 10X, (b) 25X, and (c) 40X. 

Photomicrograph of Trichoderma sp. showing (d) conidia borne in small terminal clusters (40X). 

79

a 

b 

e 

c 

e 

d 

Fig. 102. Habit character of Trichothecium sp. on (a) whole seed (9X), (b) embryonal area (25X), and (c) lemma 

(50X). Photomicrograph of Trichothecium sp. showing (d) conidiophore and (e) conidia at 40X and stained with 

lactophenol blue. 

a 

b 

→→ 

e 

c 

d 

Fig. 103. Habit character of Tritirachium sp. on (a) whole seed (10X), (b) palea and lemma (18X), and (c) awn (50X). 

Photomicrograph of Tritirachium sp. showing (d) branched conidiophore and (e) conidia at 40X. 

80

→ 

→ 

→ 

→ 

→ 

→ 

a 

→ 

→ 

→ 

b 

d 

d 

c 

Fig. 104. Habit character of Ulocladium botrytis Preuss. at (a) 30X and (b) 50X. Photomicrograph of U. botrytis 

showing (c) conidiophores and (d) conidia at 40X. 

81

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83

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