B. Zimowska
30
Biodiversity of fungi colonizing and damaging selected parts of
motherwort (Leonurus cardiaca L.)
BEATA ZIMOWSKA
Department of Plant Pathology
Agricultural University
Leszczyńskiego 7
20-069 Lublin, Poland
e-mail: beata.zimowska@ar.lublin.pl
Summary
Studies on biodiversity of fungi colonizing and damaging selected plant parts were conducted in 2004–2006. They were performed on productive plantations of motherwort
(Leonurus cardiaca L.) grouped in south-eastern Poland. Fungi were isolated from superficially disinfected roots, stem bases and leaves by means of a mineral medium. Fungi from
Fusarium spp., Phoma spp. and Rhizoctonia solani were obtained from the roots showing necrosis and tissue disintegration. Phoma nepeticola was commonly obtained from the leaves
and stems with symptoms of small, regular, necrotic spots. This is reported for the first
time in Poland.
Key words: motherwort, Leonurus cardiaca, fungi, biodiversity
INTRODUCTION
In recent years, in south-eastern Poland the spice and medicinal plants from the
species of the family Labiateae, e.g. motherwort (Leonurus cardiaca L.) have been
cultivated. Grouping of herbaceous plants in this region causes their frequent return to the same field which contributes to the accumulation of fungi decreasing
the quality and quantity of the yield [1-5].
As it is known from literature, saprophytic species, facultative parasites and
specific pathogens of this plant are found among the fungi occurring on the plants
of motherwort in the United States [6]. The first group includes, among others,
Phoma exigua var. exigua, while the second comprises Cercospora leonuri, Ascochyta
leonuri and Septoria lamiicola, the species causing leaf spot of motherwort [6].
Biodiversity of fungi colonizing and damaging selected parts of motherwort (Leonurus cardiaca L.)
31
The present paper discusses the results of three-year-long studies on fungi colonizing and damaging the underground and aboveground parts of motherwort
plants cultivated in south-eastern Poland.
MATERIAL AND METHODS
The studies were conducted in 2004–2006 on three productive plantations of
motherwort in the second year of cultivation, at Fajsławice in Dziecinin commune
(the Lublin district). Each year the percentage of plants with necrotic symptoms
on the stems and leaves was determined twice during the vegetation period.
Plants with visible disease changes were analyzed in the laboratory. The presence
of fungi was assumed on the basis of etiological signs observed on the infected
parts of plants and on the basis of the mycological analysis. Fungi were isolated
from the roots, the stems up to the height of 25 cm from the base and the leaves
disinfected on the surface. A 10% solution of sodium hypochlorite was used to
disinfect the material, while a mineral medium was used to isolate the fungi [4].
Monospore cultures were identified as the species on the medium used for isolations or on standard medium [7-13].
RESULTS
Two types of disease symptoms in the form of necrotic spots were observed on
the leaves of motherwort. Some of them were formed on the tops and edges of
the leaf blade. Those were of irregular shape, extensive, occupying greater part
of the leaf at full vegetation (fig. 1). Apart from such symptoms, smaller, regular spots of 3–5 mm diameter were observed. They were situated on the whole
surface of the leaf blade (fig. 2). Intensification of these disease symptoms was
observed at full vegetation, in second half of July. At that time, yellowing of such
leaves and their earlier falling were observed (fig. 3). Similar small, necrotic, regular spots occurred on the stems. They were most frequently formed at the height
of 5 to 20 cm from the base. Besides, the symptoms of necrosis and tissue softening were observed on the roots and lower parts of the stems up to the height
of 5–7 cm. Conidia typical of Altenaria alternata were found on the leaves with
the symptoms of extensive, irregular spots. On the other hand, on the leaves and
stems with small regular spots perithecia (fig. 4) with asci- and ascopores typical
for genus Leptosphaeria (fig. 5), and conidia typical of Phoma spp. were found out
(fig. 6). Conidia of features typical fot Fusarium spp. were found on the roots and
lower stem parts.
The above-described symptoms occurred in 10–20% of plants at the beginning
of vegetation and on 25–40% of plants at full vegetation.
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Figure 1. Necrotic irregular spots of the leaves from which Alternaria alternata was isolated. Photo:
B. Zimowska
Figure 2. Regular necrotic spots from which Phoma nepeticola was isolated. Photo: E. Zalewska
Biodiversity of fungi colonizing and damaging selected parts of motherwort (Leonurus cardiaca L.)
33
Figure 3. Yellowing of the diseased leaves. Photo: B. Zimowska
Figure 4. Perithecia of Leptosphaeria rubicunda. Photo: E. Zalewska
Vol. 54 No 2 2008
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Figure 5. Asci and ascospores of Leptosphaeria rubicunda (640 x). Photo: B. Zimowska
Figure 6. Conidia of Phoma nepeticola (640 x). Photo: B. Zimowska
Biodiversity of fungi colonizing and damaging selected parts of motherwort (Leonurus cardiaca L.)
35
In total, 2933 isolates of fungi represented by 30 species were obtained from
the analyzed parts of motherwort plants (tab.1). The cultures of A. alternata, Phoma
nepeticola and Botrytis cinerea were most frequently obtained from the leaves, and
their proportion was, 72.24%, 8.57% and 5.20%, respectively of all fungi obtained
from this organ (fig. 7). The above-mentioned fungi species were also isolated from
the motherwort stems. They coustituted 25.44, 11.74 and 4.21% of the cultures obtained from this part of plants, respectively (fig. 7). However, species from Fusarium
genus were isolated from the stems most frequently, since those fungi constituted
as much as 36.60% of the cultures obtained from this organ (fig. 7). Fusarium spp.
was also isolated from the roots of motherwort most frequently, and the cultures of
these fungi constituted almost half of all isolates obtained from this part of plants
(fig. 7). The cultures of Phoma spp., including P. exigua var.exigua, Rhizoctonia solani,
A. alternata, Cylindrocarpon spp., Trichoderma spp. and Gliocladium spp. were obtained
from the roots with much less frequency (tab.1, fig. 7).
Ta b l e 1 .
Fungi isolated from motherwort plants (Leonurus cardiaca L.) in 2004–2006
fungus species
Alternaria alternata (Fr.) Keissler
Botrytis cinerea Pers.
Chaetonium globosum Kunze
Cladosporium cladosporioides (Fres. De Vries)
Cylindrocarpon heteronema (Berk. et Br.)
Cylindrocarpon didymum (Harting) Wollenw.
Cylindrocarpon obtusisporum (Cooke et Harkness) Wollenw.
Epicoccum purpurascens Ehrenberg
Fusarium avenaceum (Fr.) Sacc.
Fusarium culmorum (W.G.Sm.) Sacc.
Fusarium equiseti (Corda) Sacc.
Fusarium oxysporum Schlecht.
Fusarium solani (Mart.) Appel et Wollenw. Snud et Marasas
Gliocladium catenulatum Gilman et Abbott
Gliocladium roseum Bainier
Penicillium decumbens
Phoma exigua Desm. var. exigua
Phoma glomerata (Corda) Wollenw&Hochapfel
Phoma labilis Sacc.
Phoma nemophilae Neerg.
Phoma nepeticola (Melnik) Dorenb.& de Gruyter
Phoma septicidalis Boerema
Phoma subglomerata Boerema
Rhizoctonia solani Küchn
Talaromyces flavus
Trichotecium roseum
Trichoderma aureoviride Rifai
Trichoderma harzianum Rifai
Trichoderma koningii Oud.
Trichoderma polysporum (Link ex Pers. Rifai)
total
roots
143
8
10
14
26
94
76
127
92
10
5
25
1
26
13
15
3
31
3
41
4
2
24
22
55
3
873
number of isolates
stems
leaves
260
781
43
54
1
14
22
1
4
81
137
103
51
2
42
2
2
4
2
14
46
9
26
120
8
13
11
1
1
15
22
39
1
1022
4
3
89
11
5
2
2
12
1038
total (%)
1184 (40.37)
97 (3.31)
1 (0.03)
44 (1.50)
10 (0.35)
14 (0.48)
27 (0.92)
46 (1.57)
177 (6.03)
215 (7.33)
234 (7.98)
145 (4.94)
12 (0.41)
5 (0.17)
39 (1.31)
5 (0.17)
75 (2.56)
22 (0.75)
41 (1.39)
3 (0.10)
209 (7.13)
50 (1.70)
16 (0.55)
52 (1.77)
5 (0.17)
8 (0.27)
41 (1.39)
46 (1.57)
106 (3.61)
4 (0.14)
2933
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Figure 7. Means of some fungi isolated from examined organs of motherwort in 2004-2006
DISCUSSION
The studies pointed to big diversity of fungi occurring in the studied, cultivated
plants of motherwort. They included the species from Fusarium, Phoma and R. solani genera, which are known as facultative parasites of plants [5, 12, 14, 15]. The
occurrence of necrosis starting with the roots and the softening of lower parts of
stems may suggest that the soil-borne fungi caused the disease [4, 16]. Results of
the mycological analysis showed that those fungi were colonized by a complex of
fungi, the most important of which were the species from genera Fusarium, Phoma
and R. solani. Much attention was devoted to the role of fungi of Fusarium spp. in
the soil and the problem of their colonization of the underground parts of plants,
including the spices and medicinal ones [3, 5, 17-19]. The saprophytic forms of
fungi living in the soil are pathogenic of different degrees and may cause an infection in favorable conditions [10].
R. solani also belongs to facultative species isolated in the present studies. The
fungus is known to induce the symptoms of rot, and then dying-out of the roots,
stems and even leaves of different species of plants [4, 20-22].
Documented in the present differentiation of species from Phoma spp. occurring in the cultivated environment of motherwort studies deserves attention. The
commonly occurring saprophytes developing on different substrates include the
species isolated in the present studies, namely: P. glomerata, P. subglomerata and
P. septicidalis, with the latter also causing the necrosis of plants from the family of
Gramineae [23-25]. The fact that P. labilis isolates were obtained from the roots and
the stems of motherwort points to the presence of this species in the cultivated
Biodiversity of fungi colonizing and damaging selected parts of motherwort (Leonurus cardiaca L.)
37
environment of the examined plants. Cultures of the fungus were earlier obtained
from the soil and the aboveground parts of herbaceous and lignified plants in
Italy, Turkey and Israel. This species is considered as a frequently occurring necrotroph, especially in the regions of warm climate [13]. Probably, this fungus found
suitable conditions for growth and development during vegetation periods observed in recent years in Poland, characterized by fairly high temperatures, which is
testified to be the obtained isolates.
The fact that the species P. nepeticola (Ascochyta nepeticola, A. nepetae) was obtained from the leaves and stems with symptoms of small, regular necrotic spots
deserves special attention. The fungus is described in the literature as a commonly occurring pathogen of catmint (Nepeta cataria) and other species from the
Nepeta genus [12]. A monograph on fungi of Ascochyta genus prepared by Mel’nik
in 1977 includes information that species discussed may infect other plants from
the Labiateae family, for example motherwort and peppermint (Mentha piperita)
[12, 13, 26]. On the synonyms list of P. nepeticola species provided by Mel’nik one
is found under the name of Ascochyta leonuri, which could point to pathogenic
relation of this species with Leonurus cardiaca [13, 16]. Common isolation of P.
nepeticola from the leaves and stems of motherwort showing the characteristic
disease symptoms in the form of regular, necrotic spots, and the information from
the literature presented above suggest that such symptoms could have been the
consequence of the pathogenic effect of the obtained isolates of the fungus. However, in order to confirm this hypothesis it is necessary to carry infection tests
according to the postulates by Koch.
The occurrence of perithecia and ascopores of Leptosphaeria rubicunda on
motherwort stems [6,27] led to the supposition that his species may be a teleomorph of the obtained Phoma cultures. However, after a thorough procedure based on the present principles of classifying the taxons of Phoma spp., the obtained
isolates were marked as P. nepticola, whose teleomorph belongs to Didymella genera [11,12]. It is known from the literature that L. rubicunda commonly occurs
on the stems of common teasel (Dipsacus sylvestris), purple loosestrife (Lythrum
salicaria), elder (Sambucus nigra) and motherwort [6, 28]. No information on the
pathogenicity of the discussed species was found in the available literature. It is
only known that ascospores of L. rubicunda are spread by winter or with raindrops,
and the fungus overwinters on plant residues [28]. However, other species of Leptosphaeria genus are described as dangerous pathogens of cultivated plants. Dying
out of the raspberry, blackberry and rose stems is caused by L. coniothyrium [29].
L. maculans belongs to most important plant pathogens of the Cruciferae family
[30]. In Africa, Australia and India, L. leucadendri causes leaf spot of plants from the
Proteaceae family [31].
The fact that the cultures of P.exigua var. exigua were obtained from the roots
and the lower parts of stems of the studied motherwort plants may indicate the
participation of this species in causing disease symptoms on those organs. Such a
conclusion is justified by numerous reports from the literature and experimentally
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proved harmfulness of the isolates of the fungus towards the sprouts and seedlings of garden thyme and lemon balm [32].
On the basis of the mycological analysis and the etiological signs occurring on
plants, the cause of the necrotic irregular spots formed on the leaves was determined as the species A. alternata. Reports from literature on the occurrence of the
fungus on different species of herbaceous plants [22, 23] as well as earlier information given by the author on the harmfulness of A. alternata constitute the basis
to consider this fungus as an economically important species in herb production
[5, 22, 34].
Botrytis cinerea should be included to species that may have a negative effect on
the quality of the raw material of Herba Leonuri cardiaceae. Such a conclusion was
justified by the fact of isolating the fungus cultures from the studied motherwort
plants and information from literature on the pathogenic effect of the fungus on
different species of spice and medicinal plants [5, 35, 36].
Present studies pointed to biodiversity of the species of fungi occurring in the
cultivated environment of the examined plants of motherwort. They contributed
to discovering species that had not been noted in Poland so far, namely P. nepeticola, which considerably lowers size and quality of Herba Leonuri cardiaceae raw material. Besides, the obtained results draw attention to the danger resulting from
the common colonization of leaves and stems of motherwort by toxin-forming
species of A. alternata.
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BIORóżNORODNOść GRZYBóW ZASIEDLAJąCYCH I USZKADZAJąCYCH WYBRANE
ORGANY SERDECZNIKA POSPOLITEGO (LEONuRuS CARDiACA L.)
BEATA ZIMOWSKA
Katedra Fitopatologii
Akademia Rolnicza
ul. Leszczyńskiego 7
20-069 Lublin
e-mail: beata.zimowska@ar.lublin.pl
Streszczenie
W latach 2004–2006 na plantacjach produkcyjnych serdecznika pospolitego (Leonurus
cardiaca L.) zgrupowanych w południowo-wschodniej Polsce przeprowadzono badania
nad grzybami zasiedlającymi i uszkadzającymi wybrane organy roślin. Grzyby izolowano
metodą sztucznych kultur z powierzchniowo odkażonych korzeni, łodyg oraz liści przy
zastosowaniu pożywki mineralnej. Z korzeni oraz dolnych części łodyg z objawami nekrozy i dezintegracji tkanek izolowano grzyby z rodzaju Fusarium, Phoma oraz Rhizoctonia
solani. Z łodyg oraz liści z symptomami drobnych regularnych plam uzyskano nie notowany
wcześniej w Polsce gatunek Phoma nepeticola.
Słowa kluczowe: serdecznik pospolity, Leonurus cardiaca, grzyby, bioróżnorodność
Beata Zimowska