Inheritance of stem rust (Puccinia graminis Pers. F. Sp. Tritici ericks and E. Hen) resistance in bread wheat (Triticum aestivum L.) lines to TTKST race

Int. J. Agri. & Agri. R.
Kosgey et al.
Page 1
RESEARCH PAPER OPEN ACCESS
Inheritance of stem rust (Puccinia graminis Pers. F. Sp. Tritici
ericks and E. Hen) resistance in bread wheat (Triticum aestivum
L.) lines to TTKST race
Zennah Kosgey1*
, James O. Owuoche1
, Michael A. Okiror1
, Peter N. Njau2
1
Egerton University (Njoro Campus), P.O. Box 536, Egerton, Kenya
3
Kenya Agricultural and Livestock Research Organization (KALRO), P.O. Private Bag -20107,
Njoro, Kenya
Article published on October 12, 2015
Key words: Duplicate recessive epistasis, Inheritance, Stem rust, TTKST isolate Wheat.
Abstract
Stem rust disease caused by Puccinia graminis f.sp. tritici (Pgt) is currently one of the major biotic constraints in
wheat (Triticum aestivum) production worldwide. Therefore, objectives of this study were (i) to identify resistant
wheat lines with both adult plant resistance (APR) and seedling plant resistance (SPR), and (ii) to determine the
kind of resistance to stem rust in KSL18, PCB52, PCB62 and PCB76 wheat lines. A collection of 100 wheat lines
was evaluated in the field and greenhouse for stem rust resistance. The following four lines- KSL18, PCB52,
PCB62 and PCB76 were identified as resistant and were crossed with known susceptible cultivars Kwale and
Duma. The resulting F1 hybrids and F2 populations alongside the parents were then tested in the greenhouse for
response to the stem rust race TTKST. The selected wheat lines exhibited infection types ‘;’ to ‘2’ depicting
resistance while Kwale and Duma depicted infection type ‘3+’ to TTKST. In the F2 populations evaluations that
derived from Kwale × PCB52 indicated that the resistance is conferred by a single dominant gene. However, all
other F2 populations showed that the resistance was conferred by two genes complementing each other (duplicate
recessive epistasis) thus the ratios 9R: 7S. These identified resistant lines could be evaluated for other qualities
and passed as potential varieties or used as sources of valuable stem rust resistance.
* Corresponding Author: Zennah Kosgey
International Journal of Agronomy and Agricultural Research (IJAAR)
ISSN: 2223-7054 (Print) 2225-3610 (Online)
http://www.innspub.net
Vol. 7, No. 4, p. 1-13, 2015

Kosgey et al.
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Introduction
The sources and inheritance of resistance genes to
stem rust (Puccinia graminis f.sp tritici) (Pgt) in
wheat (Triticum aestivum L.) is important to all
wheat breeders in their endeavor to develop resistant
varieties. Increased and sustainable productivity of
this crop both locally and globally will be achieved
largely if resistance to the rusts (yellow rust caused by
Puccinia striformis; leaf rust caused by Puccinia
tauschii; and stem rust caused by Puccinia graminis
f.sp tritici) that have often reduced yields in Kenya
and other wheat growing regions worldwide by as
much as 100% in susceptible varieties are adopted
(Leonard, 2001; Njau et al., 2010). The resurgence of
stem rust has received high attention from breeders
and pathologists in wheat breeding programs due to
the yield losses incurred worldwide (Singh et al.,
2011). Spraying with fungicides against stem rust is
expensive, hazardous and a short term solution to the
damage caused by this foliar disease. The foreseeable
and feasible best option is bioresistance (Singh et al.,
2006; Singh et al., 2008). A number of novel sources
of resistance to stem rust have been reported.
However, little is reported on the kind and mode of
the resistances they carry. Such information is very
important to all breeders wishing to design breeding
strategies for its use. The mode of action of such
genes is either dominant or recessive; single
(monogenic) or multigenic (polygenic); autosomal or
sex-linked (Bahadur et al., 2002; Odeny et al., 2009).
Inheritance studies on barley (Hordeum vulgare), oat
(Avena sativa), beans (Phaseolus vulgaris), rye
(Secale cereal) and pigeon pea (Cajanus cajan) have
shown that major genes and/or modifying genes are
vital in conferring resistance to various pathogens at
the various growth stage i.e seedling and adult plant
stages. For example, resistance to Puccinia coronata
avenae in spring oats is mainly conferred by major
genes and wheat lines possessing Lr28 gene showed
dominant genes governing resistance to leaf rust
races 77-1, 77-2 and 77-5 (Bansal et al., 2008; Staletic
et al., 2009) . However, the resistance to stem rust in
wheat with Tr129 background to race MCCF is
conditioned by two dominant genes (Ghazvini et al.,
2012). In barley, resistance to isolate 76-32-1335 of
Puccinia graminis f. sp. secalis is conferred by one
recessive gene (Steffenson et al., 1985). With such an
array of resistances to stem rust, it is proposed that
pyramiding these genes may offer even a more
lasting, durable and broad based resistance. To
achieve this, it is essential that the breeder is
equipped with knowledge on the kind of gene action
in such genes. Thus, the objectives of this study were
one, to select resistant lines at adult plant and
seedling stages, and two, to determine the nature and
number of genes conferring this resistance in selected
wheat lines
Materials and methods
Screening for resistance in recombinant inbred
wheat lines
Field screening
(a) Experimental site
This study was conducted at Kenya Agricultural and
Livestock Research Organization (KALRO) (- 0º 20
2 N 35º 56’ 40” E) Njoro centre-Kenya. The area
experiences an average annual rainfall of 939.3 mm
(average of 60 years) (Kenya Metereological Station
Identification Number 9031021) and average
temperatures of 9 ºC (minimum) and 24 ºC
(maximum). The soils are predominantly mollic
phaeozems with a pH of 7.0.
(b) Genotypes
A hundred semi dwarf recombinant inbred wheat
lines that originated from CIMMYT; Parcela Chica
(small plots) Bread Wheat Rainfed Lines (PCBWR)
and Kenyan Selected Lines (KSL) were evaluated for
stem rust resistance under field conditions over two
seasons (2012 and 2013) against stem rust Pgt race
Ug 99 and its variants.
(c) Experimental procedure
Evaluation was done in the field that was previously
under soyabean (Glycine max) crop. The field was
prepared by first spraying it with a non selective
herbicide, round up (glyphosate) at the rate of 360g
ha-1 and three weeks later, disc ploughed and
harrowed to a fine tilth suitable for wheat planting.

Kosgey et al.
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Each entry was planted to two 1.5m rows spaced 0.5m
apart. The susceptible cultivar Caccuke was planted
after every 20 entries for disease build up monitoring.
Several other cultivars susceptible to TTKST and
TTKSK races were used as spreaders and planted
perpendicular to all entries to supply adequate rust
inoculum. Di-ammonium phosphate fertilizer was
applied at planting at the rate of 125 kg ha-1 to supply
an equivalent rate of 22.5 kg ha-1 of N and 25 kg ha-1 of
P. Calcium ammonium nitrate (CAN) fertilizer was
applied at growth stage (GS) 20-29 at the rate of
100kg ha-1 to provide 33 kg N ha-1. Pre-emergence
herbicide, Buctril MC (Bromoxynil octanoate, 225 g
ha-1 and MCPA Ethyl Hexyl Ester, 225 g ha-1) was
applied at GS 20-29 (Zadoks et al., 1974) to further
control annual broad leaved weeds. Also, Bulldock
(beta-cyfluthrin), a systemic insecticide was sprayed
at the rate of 31 g ha-1 to control both sucking and
chewing pests.
(d) TTKST and TTKSK pathogen build up.
Epidemics were induced through artificial inoculation
with inoculants prepared from spreader row plants.
Rusted stems of these plants were harvested and
chopped into small pieces and soaked in a few drops
of tween 20 and water to provide concentration of
4×106 spores ml-1. The spreaders were inoculated
using a syringe at the stage GS 30-49 (Zadoks et al.,
1974) late in the evening. To enhance humidity, these
plants were repeatedly irrigated thereby enhance
stem rust infection and spread.
(e) Data collection
Evaluation was based on pustule size and the
associated necrosis. Disease severities were observed
as R= resistant (small uredinia surrounded by
necrosis), MR= moderately resistant (medium-sized
uredinia surrounded by necrosis), MS= moderately
susceptible (medium-sized uredinia without
necrosis), S= susceptible (large uredinia without
necrosis), MSS= moderately susceptible to
susceptible (medium to large-sized uredinia without
necrosis) and MRMS= infection response that overlap
the MR and MS categories (Roelfs et al., 1992). Stem
rust severity scoring begun when the spreader rows
had attained 50% infection based on modified Cobbs
scale where 0%= immune (no uredinia or any other
sign of infection) and 100%= completely susceptible
(large uredinia without necrosis) (Peterson et al.,
1948). Disease was evaluated three times at an
interval of 10 days between heading (GS 50-69) and
plant maturity (GS 70-89) (Zadoks et al., 1974).
Seedling screening in the greenhouse
The hundred inbred wheat lines were also screened
under glasshouse conditions. Ten seeds of each line
were planted in square 6 × 6 cm plastic pots in two
batches. Infected wheat plant stems were collected
from screening nurseries, chopped into small pieces
and suspended in light mineral oil (Soltrol 170). The
spore suspension was adjusted with more oil to obtain
a spore concentration of 4×106 spores ml-1. At growth
stage 12, the seedlings were inoculated by atomizing
spores solution using a hand sprayer. The plants were
then air dried for 30 minutes in an inoculation
chamber, then placed in a dew chamber set at 16 -18
ºC and about 100 RH for 48 hours and finally
transferred to a greenhouse bench maintained at 20
ºC. After 14 days, seedlings were evaluated for
infection types based on a 0 to 4 scale (Stakman et al.,
1962). Evaluation was based on uredinia size and
presence or absence of necrotic regions. In this scale,
‘0’= no uredinia or any other sign of infections, ‘; -
fleck’= presence of hypersensitive necrotic flecks but
no uredinia, ‘1’= small uredinia surrounded by
necrotic regions, ‘2’= small to medium size uredinia
surrounded by necrosis, ‘3’= medium sized uredinia
without necrosis and ‘4’= large uredinia without
necrosis. Infection types ‘0’, ‘;’, ‘1’ and ‘2’ were
categorized as resistant whereas ‘3’ and ‘4’ as
susceptible. Infection types were confirmed by re-
evaluating another set of the lines for the second time.
Genetics of resistance to TTKST race
(a) Parental stock and development of F1 and F2
populations
From the screening above, four resistant lines; KSL18,
PCB52, PCB62 and PCB76 were identified. These and
two adapted susceptible cultivars Kwale and Duma
were used in this study (Table 2). KSL18, PCB52,

Kosgey et al.
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PCB62 and Kwale are hard white spring wheat while
Duma and PCB76 are hard red spring wheats. Also,
KSL18, PCB62 and PCB76 are early maturing while
PCB52, Kwale and Duma are medium in maturing. F1
and F2 populations were derived from straight crosses
between the selected resistant recombinant inbred
lines and the susceptible cultivars Kwale and Duma.
(b) Preparation of TTKST pure race of stem rust.
Spores of the race TTKST were purified on a universal
susceptible wheat cultivar Kenya Mwamba. Five
seeds of cultivar K. Mwamba were each sown in ten 6
cm-diameter plastic pots filled with approximately
60g of vermiculite. At growth stage GS 12, seedlings
thereof were inoculated with spores collected from
Sr24 spreader wheat plants. Inoculum was prepared
and seedlings of Kenya Mwamba inoculated as in the
glasshouse experiment above. After 14 days, a single
pustule was collected into a capsule using automizer
machine. This pustule was then dissolved in soltrol oil
and atomized on seedlings of Kenya Mwamba for the
spore multiplication. The purified spores were then
bulk-collected, packed in capsules and stored at -20
°C to ensure their viabilities.
(c) Glasshouse screening of F1 and F2 populations
Five seeds of each purified inbred parents and their
F1s and a hundred and fifty seeds of each F2
population of the eight crosses were planted in 6 × 6
cm plastic pots set up in the greenhouse. At the GS 12,
inoculations were made by suspending the purified
TTKST spores in light mineral soltrol oil and spraying
the seedlings. These seedlings were handled and
evaluated after 14 days as above mentioned in the
greenhouse experiment.
(c) Data analysis of F2 populations
The infection types observed on parents, F1 and F2
genotypes were categorized into resistant (‘0’, ‘;’, ‘1’,
‘2’, ‘2-’ ‘2+’) and susceptible (‘3’, ‘3-’, ‘3+’, ‘4’). The data
of the F2 populations were analyzed using SAS version
9.4 (SAS, 2012) for a fit into the 3:1 ratio or other
ratios as follows:
Where χ2 = Chi Square value, ∑ = Summation, O =
Observed numbers in each category and E = Expected
numbers in the corresponding category according to
hypothesis
Phenotypic correlation was performed between
seedling infection types observed on F2 populations
that conformed to 9:7 and 3:1 resistant: susceptible
ratio using SAS version 9.4 (SAS, 2012) basing on the
following formula:
Where r = Pearson correlation coefficient, x = values
in set of infection type data from one population, y =
values in the set of infection type data from the next
population and n = Total number of values (Ott and
Longnecker, 2001).
Results
wheat lines
Among the wheat lines evaluated for Pgt, severity in
the field and greenhouse showed that there was
genotypic variability for both adult and seedling
resistance (Table 2). In the field, seasonal variations
affected the severity of stem rust in the wheat lines as
most lines were heavily infested in the 2013 season
compared to the 2012 season (Table 2). The hard
white spring wheat lines KSL 18, PCB52, PCB 62 and
PCB 76 had low disease severities (10 MR to 30 MR)
in 2013 than in 2012 and exhibited resistant seedling
infection types ‘2’ to ‘2+’ in the greenhouse. Thus,
based on their adult and seedling reactions to Pgt
infections, the four above mentioned lines were
selected as a valuable source of resistance to stem
rust. They were therefore used in crossings with
known susceptible cultivars Kwale (40 MSS, adult
plant resistance (APR); ‘3’, seedling infections) and
Duma (40 MSS, APR); ‘3’, seedling infections)
(Table 2). The reactions of the other lines pointed to
susceptibility for instance, lines PCB 34 and PCB 35
were rated 15 MSS and 20MSS, respectively in the
field (adult) and ‘3+’ and ‘4’, respectively in the
greenhouse (seedling stage) (Table 2). Also lines PCB

Kosgey et al.
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65 and PCB 66, that are sister lines reacted
differently. PCB 65 was susceptible to stem rust at
seedling stage with infection type ‘3+’ but responded
to field infection with susceptibility severity of 60 S.
However, PCB 66 was resistant at seedling stage with
infection types ‘;’, ‘1+’ (Table 2). There was differential
resistance observed between PCB 76 and PCB 77 that
are sister lines. The virulence of TTKST on lines KSL
3, PCB 29, PCB 37, PCB 65, PCB 69, PCB 71, PCB 77
and PCB 7 at seedling was low (‘;1’ to ‘2+’) despite
the fact that the severity of 20M to 40MSS were
observed in the field (Table 2). This suggests that
these lines have seedling resistance genes to Pgt but
are devoid of adult resistance genes.
Table 1. Mean temperatures and rainfall experienced during the evaluation period of 2012 and 2013 at KALRO-
Njoro.
Season January February March April May
2012
Min. Temp. °C (Mean) 10.0 16.0 18.0 14.0 12.0
Max. Temp. °C (Mean) 23.0 18.0 22.0 24.0 22.0
Mean rainfall (mm) 0.0 13.6 11.0 295.0 183.7
2013 August September October November December
Min. Temp. °C (Mean) 8.0 9.0 10.0 10.0 10.0
Max. Temp. °C (Mean) 22.0 23.0 21.0 22.0 23.0
Mean rainfall (mm) 110.6 173.3 73.9 60.6 137.5
Min. = Minimum, Max. = Maximum, Temp. = Temperature, mm= Millimeters.
Table 2. Field and greenhouse evaluation of 28% Recombinant inbred wheat lines from KALRO-Njoro stem rust
screening nursery for resistance to predominant Ug99 races.
Genotype Pedigree
Stem rust severity
20122013
Seedling
infection
type
KSL1 SSERI1/CHIBIA/4/BAV92//IRENA/KAUZ/3/HUITES 30MSS 50MSS 3+
KSL2 WBLL1*2/4/SNI/TRAP#1/3/KAUZ*2/TRAP//KAUZ/5/PFAU/
WEAVER//BRAMBLING/6/BAV92
20MSS 30MSS
3+
KSL18 WBLL1*2/KURUKU/4/BABAX/LR42//BABAX*2/3/KURUKU 20MR 10MR 2+
PCB5 WBLL1*2/BRAMBLING/3/KIRITATI//PBW65/2*SERI.1B 20M 30MSS 2-
PCB27 WBLL1*2/KUKUNA/4/WHEAR/KUKUNA/3/C80.1/3*BATAVI
A//2*WBLL1
40M 50MSS
3+
KSL3 BAV92//IRENA/KAUZ/3/HUITES*2/4/CROC_1/AE.SQUARR
OSA (224)//KULIN/3/WESTONIA
20 MSS 40MSS
2+
PCB4 WAXWING/4/SNI/TRAP#1/3/KAUZ*2/TRAP//KAUZ/5/KIRIT
ATI//ATTILA*2/PASTOR
30M 40MSS
3+
PCB7 FRANCOLIN #1/MESIA//MUNAL #1 25 M 25MSS 4
PCB9 ALTAR84/AE.SQUARROSA(221)//3*BORL95/3/URES/JUN//
KAUZ/4/WBLL1/5/KACHU/6/KIRITATI//PBW65/2*SERI.1B
30M 5MSS
3+
PCB29 KISKADEE #1//KIRITATI/2*TRCH 20M 40MSS 2+
PCB30 MUNAL/3/HUW234+LR34/PRINIA//PFAU/WEAVER 40M 30MSS 4
PCB31 PBW65/2*PASTOR/3/KIRITATI//ATTILA*2/PASTOR/4/DAN
PHE #1
30M 60MSS
3+
PCB34 ATTILA/3*BCN//BAV92/3/PASTOR/4/TACUPETO 10M 15MSS 3+

Kosgey et al.
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Genotype Pedigree
Stem rust severity
20122013
Seedling
infection
type
F2001*2/BRAMBLING/5/PAURAQ
PCB35 ATTILA/3*BCN//BAV92/3/PASTOR/4/TACUPETO
F2001*2/BRAMBLING/5/PAURAQ
15M 20MSS
4
PCB36 KACHU/BECARD//WBLL1*2/BRAMBLING 20M 30MSS 3+
PCB37 PFAU/SERI.1B//AMAD/3/WAXWING*2/4/TECUE #1 40 M 20M 2+
PCB40 PCAFLR/KINGBIRD #1//KIRITATI/2*TRCH 30 M 30M 3+
PCB41 MUNAL*2//WBLL1*2/BRAMBLING 25M 30MSS 3-
PCB52 MUU/KBIRD 5RMR 20MR 2+
PCB62 CHIBIA//PRLII/CM65531/3/SKAUZ/BAV92*2/4/QUAIU 30MR 30MR 2
PCB44 ND643/2*TRCH//BECARD/3/BECARD 40M 60MSS 3+
PCB65 ND643//2*ATTILA*2/PASTOR/3/WBLL1*2/KURUKU/4/WBL
L1*2/BRAMBLING
40 M 50M
;1
PCB66 ND643//2*ATTILA*2/PASTOR/3/WBLL1*2/KURUKU/4/WBL
L1*2/BRAMBLING
40M 60MSS
3+
PCB69 KIRITATI//ATTILA*2/PASTOR/3/AKURI 30 M 20M ;1+
PCB71 HUIRIVIS #1/MUU//WBLL1*2/BRAMBLING 10MR 20M ;1
PCB76 BABAX/LR42//BABAX*2/3/TUKURU*2/4/HEILO 50MR 30MR 2+
PCB77 BABAX/LR42//BABAX*2/3/TUKURU*2/4/HEILO 20MR 40M 2+
PCB79 PICUS/3/KAUZ*2/BOW//KAUZ/4/KKTS/5/T.SPELTA
PI348530/6/2*FRANCOLIN #1
20M 40MSS
2+
KWALE KAVKAZ/ TANORI-71/3/MAYA-74(SIB)//BLUEBIRD/INIA-66 30MS 40MSS 3
DUMA
AURORA/UP301//GALLO/SUPER
X/3/PEWEE/4/MAIPO/MAYA 74//PEWEE
30MSS 40MSS
3
IT (Infecton types) are based on 0 to 4 scale as described by Stakman et al. (1962). Field disease response and
severities are based on Roelfs et al. (1992) and Peterson et al. (1948).
In the determination of the genetics of resistance in
the identified four resistant lines, it was found that all
the F1s from the eight crosses were resistant (Table 3).
Hybrids from Kwale × PCB52, Kwale × KSL 18,
Kwale × PCB 76 and Kwale × PCB62 crosses with
resistant genes placed in Kwale background showed
infection types ‘;1+’, ‘2’ from PCB 52, ‘2’, ‘2+’ from
KSL18, ‘; 1+’ from PCB 76 and ‘; 1+’, ‘2’ from PCB 62. F1
genotypes derived from a cross that Duma was used
as recipient parent of the gene exhibited ‘2’ to ‘2+’
infection types compared to ‘; 1+’, ‘2’ infection types
observed on the F1 genotypes derived from crosses
involving susceptible cultivar Kwale. The F2
population derived from Kwale × PCB 52 fitted
segregating ratio of 3:1 (R: S) (χ2= 0.6881). In this
cross, 72% of the progenies exhibited ‘0’ to ‘2’
infection types. Among the resistant genotypes, 39%
of the progenies showed resistant reactions of ‘0’ and
‘;’ infection types, whereas 28% showed susceptible
reaction of ‘3’ to ‘4’ infection types (Fig. 1).
The F2 genotypes derived from Kwale × KSL18,
Kwale × PCB 76 and Kwale × PCB 62 crosses showed
infection types that conformed to :7 (χ2- 0.9900,
0.6796, 0.3608, respectively) ratio of resistance to
susceptible. From these three crosses, 61, 56 and 59%
of the genotypes fall in resistant class of ‘0’ to ‘2’
infection types, respectively (Fig. 1). Considering ‘0’
and ‘;’ infection types, 30, 27 and 18% of the
individuals, respectively, were considered highly
resistant. All the F2 progenies that involved Duma as
the female parent (Duma × PCB 52, Duma × KSL 18,
Duma × PCB 76 and Duma × PCB 62) conformed to

Kosgey et al.
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:7 ratio of resistance to susceptible, (χ2 - 2.3179,
0.1668, 2.6840 and 1.3593), respectively (Fig. 1). The
crosses showed the proportions of 63, 58, 64 and
55%, respectively, of resistant genotypes with the
infection types ranging from ‘0’ to ‘2’ (Fig. 1). The
progenies of the cross Duma × PCB 52 had 16% of the
genotypes exhibiting ‘0’ and ‘;’ infection types, while
37% of the genotypes were susceptible (Fig. 1).
Progenies of the cross Duma × KSL 18 had the least
proportion ( %) of the genotypes exhibiting ‘0’ and ‘;’
infection types while 42% were susceptible (Fig. 1). F2
progenies developed from Duma × PCB 76 progenies
had 16% showing ‘0’ and ‘;’ infection types and 30% of
the genotypes were susceptible exhibiting ‘3’ to ‘4’
infection types (Fig. 1). The progenies of the cross
Duma × PCB62 had 11% of the genotypes exhibiting
‘0’ and ‘;’ infection types and the highest proportion
of 36% showed a ‘3’ infection type (Fig. 1).
Table 3. Infection types (IT) of parents, F1 plants and segregation in F2 populations to pathotype Pgt-TTKST of
Puccinia graminis f.sp. tritici at seedling stage.
Parents
Observed
Infection types
Resistant Susceptible
Observed
ratio (R:S)
Chi-square
(χ2)
p- value
Kwale 3+
Duma 3+
PCB52 2+
KSL18 2+
PCB76 ;1
PCB62 2+
Crosses with Kwale as susceptible parent
F1 (Kwale × PCB52) ;1+, 2
F2 (Kwale × PCB52) 78 31 3:1 0.6881 0.4068
F1 (Kwale × KSL18) 2, 2+
F2 (Kwale × KSL18) 77 50 9:7 0.9900 0.3197
F1 (Kwale × PCB76) ;1+
F2 (Kwale × PCB76) 61 47 9:7 0.6796 0.4097
F1 (Kwale × PCB62) ;1+, 2
F2 (Kwale × PCB62) 62 48 9:7 0.3608 0.5481
Crosses with Duma as susceptible parent
F1 (Duma × PCB52) 2+
F2 (Duma × PCB52) 68 39 9:7 2.3179 0.1279
F1 (Duma × KSL18) 1+, 2, 2+
F2 (Duma × KSL18) 64 46 9:7 0.1668 0.6830
F1 (Duma × PCB76) 2, 2+
F2 (Duma × PCB76) 62 49 9:7 2.6840 0.1014
F1 (Duma × PCB62) 2
F2 (Duma × PCB62) 61 40 9:7 1.3593 0.2437
Infection type (IT) was based on the scale described by Stakman et al. (1962) with ITs ; 1, 2 considered resistant
and 3 considered susceptible. Positive (+) = larger uredinia than the normal size and negative (-) = smaller
uredinia than the normal size.

Kosgey et al.
Page 8
Fig. 1. Proportion of seedling infection types of F2 wheat (Triticum aestivum) populations developed from eight
crosses and evaluated in the greenhouse for Puccinia graminis f. sp. tritici race TTKST (category: resistant= 0, ;,
1, 2; susceptible= 3 and 4.

Kosgey et al.
Page 9
Table 4. Correlation among observed seedling infection types on F2 populations evaluated for resistance to race
TTKST.
Kwale
× PCB62
Duma
× PCB62
Duma
× PCB76
Kwale
× PCB76
Kwale
× KSL18
Duma
× KSL18
Duma
× PCB52
Kwale
× PCB52
Kwale × PCB62 0.888 * 0.811 * 0.753 0.842* 0.847* 0.786 0.215
Duma × PCB62 0.920** 0.481 0.564 0.912* 0.716 -0.190
Duma × PCB76 0.239 0.369 0.876* 0.701 -0.023
Kwale × PCB76 0.979 *** 0.453 0.531 0.246
Kwale × KSL18 0.527 0.586 0.354
Duma × KSL18 0.925 ** -0.065
Duma × PCB52 0.169
Kwale ×PCB52
*, **, *** = significant at 0.05, 0.01 and 0.001, respectively.
Discussion
wheat lines
Stem rust severity on evaluated wheat lines in the
field varied between the seasons having most of the
lines severely infected in 2013 compared to the 2012
season. The genotypic variation for Pgt severity
between the two seasons was due to weather related
factors that favored infection. The ideal temperatures
for the germination of the urediniospores (minimum,
2 °C; optimum, 15 - 24 °C and maximum is 30 °C)
whereas 5 °C, 30 °C and 40 °C are the minimum,
optimum and maximum, respectively, for the
sporulation of the spores (Hogg et al., 1969, Roelfs et
al., 1992). The temperatures in this study were within
the favorable range for the establishment and
development of Pgt pathogen in both years (Table 1).
The effects of varying temperature levels on
expression of genes influence either compatibility or
incompatibility of the host genotypes and pathogens
(Luig and Rajaram, 1972; Steffenson et al., 1985).
Effects of temperatures on expression of these genes
under controlled environments were not within the
scope of this study. In addition to the ideal
temperatures, rust develops in the presence of heavy
dews and high humidity (Todorovska et al., 2009;
Murray et al., 2010) hence the high precipitation
experienced in the second year seems to have
contributed and favored Pgt severity (Table 1).
Infection of diseases such as net blotch (Pyrenophora
teres Drechs.) in barley (Hordeum vulgare), is often
favored by high rainfall experienced during the
growing seasons (Steffenson and Webster, 1992).
Because of high severity observed in the second
season, the data from this season formed the basis of
selection of lines showing field resistance to Pgt.
The genotypic variability observed in the field
evaluation indicated that lines KSL 18, PCB 52, PCB
62 and PCB 76 were resistant to Pgt. The presence of
adult plant and seedling resistance genes against race
Ug99 in wheat are often beneficial to farmers. In this
study, low severity at adult plant and seedling stages
suggested that these four lines possess both seedling
and adult resistance genes that could be used for
improvement of adapted varieties. Unfortunately, the
identification and location of these Pgt genes in wheat
genomes have not yet been identified. The occurrence
of adult and seedling resistance for tanspot
(Pyrenophora tritici-repentis Drechs), leaf rust and
stripe rust (Puccinia striiformis) on the same
background has benefited wheat breeders in most
parts of the world (Park and Pathan, 2006; Park et
al., 2008;Tadesse et al., 2011). The virulence of Pgt
race TTKST on related lines PCB 34 and PCB 35
clearly indicated that these genotypes do not posses
adult and seedling resistance genes (Table 2). Neither
cultivar Kwale nor Duma possessed adult or seedling
resistance genes to Pgt hence used for inheritance
studies. The variation between sister lines PCB 65 and
PCB 66 suggested that PCB 65 has a gene for seedling
resistance but none of them has adult resistance
genes (Table 2). This difference may be attributed to
the recombination of genes during development of
the recombinant inbred lines. Avirulence of TTKST on
lines KSL 3, PCB 29, PCB 37, PCB 65, PCB 69, PCB 71,
PCB 77 and PCB 79 at seedling stage indicate that
these lines posses major genes for resistance.

Kosgey et al.
Page 10
Unfortunately, these lines did not have genes for
adult resistance and this may not be useful for field
resistance (Table 2).
All the male parental genotypes and hybrids were
resistant to Pgt race TTKST. Resistance depicted by
low infection types on F1 and segregation of F2
genotypes is an indication that the resistance at F1 is
conferred by major gene(s). The resistant infection
types observed on PCB 52, KSL 18, PCB 76 and PCB
62 at seedling stage suggested that these lines posses
resistant genes that could be useful for improvement
of wheat varieties. The segregation ratios for
resistance to Pgt suggested that major genes that are
modified due to epistatic effect are involved in
conferring resistance to race TTKST. Nevertheless,
apart from the Kwale × PCB 52 cross whose
segregation ratio conformed to 3:1 (R:S), the 9:7 ratio
observed on the other crosses demonstrated that
modifying genes that influenced the resistance genes
to Pgt TTKST may be due to duplicate recessive
epistasis (Staletic et al., 2009). The observed 9R:7S
ratio in this study was also depicted by barley F2
progenies derived from the Steptoe × Q 21861 cross
when they were screened against stem rust Pgt MCC
and QCC races (Jin et al., 1994). However, double
recessive genes (9S:7R) conferred resistance to head
bug in populations developed from different sorghum
genotypes (Aladele and Ezeaku, 2003).
Other than the resistance to Pgt in wheat lines noted
in this study, a single dominant gene also conferred
resistance to leaf rust and powdery mildew (Blumeria
graminis f.sp hordei) in barley, chocolate spot
(Botrytis fabae) in faba bean (Vicia faba L.), leaf rust
in wheat cultivars and Asian soybean rust
(Phakopsora pachyrhizi) in soybean (Glycine max)
(Abbassi et al., 2004; Charan et al., 2006; Ghazvini et
al., 2012; Naghavi et al., 2002). In addition, two
dominant independent (15R:1S) and three dominant
genes (63S:1S) conferred resistance to leaf rust races
0R9 (106), 29 R23 (104B), 109 R31-1 (77-2), HD
2285, Vaishali and HD 2189 in wheat (Bahadur et al.,
2002; Charan et al., 2006). Crosses that involved
Kwale cultivar (Kwale × PCB 62, Kwale × PCB 76
and Kwale × KSL 18) have more or less the same
frequencies of ‘0’ infection type in the resistant
categories, an indication that a major/dominant gene
was expressed in these crosses (Fig. 1). When
infection types of Kwale × PCB 76 and Kwale ×
KSL18 populations were correlated, positive
associations were noted between the infection types
in all categories (Fig. 1, Table 4). This showed that the
effect of resistant and modifying genes were the same
in the Kwale background because of the expression of
9:7 ratios in F2 population. The infection types in
Kwale × PCB 62 and Kwale × KSL18 crosses were
also positively correlated (Table 4) and this
association indicated that mode of gene action was
the same because the proportion of infection types in
the resistant (‘;’, ‘1’, ‘2’) and susceptible (‘3’, ‘4’)
categories were more or less the same.
Crosses that involved cultivar Duma (Duma × KSL
18, Duma × PCB 76 and Duma × PCB 62) had less
number of resistant categories (‘0’, ‘;’, ‘1’, ‘2’)
compared to susceptible categories (‘3’, ‘4’) (Fig.ure 1)
and this suggests probably some recessive genes were
involved in the modification of the resistance genes.
However, single recessive genes (3S:1R) conferred
resistance to Pgt races (ND8702 and ND89-3) in
barley, resistance to fusarium wilt in pigeon pea and
head bug resistance in sorghum (Aladele and Ezeaku,
2003; Karimi et al., 2010). Among the crosses, only
Kwale × PCB 52 exhibited 3:1 ratio without modifying
effects. In addition, there were more infection types in
the resistant category (‘0’,’;’,’1’,’2’) compared to those
in the susceptible category (‘3’, ‘4’) in Kwale × PCB 52
cross. This was an indication that PCB 52 donated a
major gene for resistance to Pgt at seedling stage. A
single dominant gene also conferred resistance to Pgt
f.sp. hordei in barley and wheat populations derived
from four resistant and one susceptible bread wheat
cultivars against three different leaf rust races; 0R9
(106), 29R23 (104B) and 109R31-1 (77-2) (Charan et
al., 2006).

Kosgey et al.
Page 11
Conclusion
The inheritance of resistance in the wheat lines to
Puccinia graminis f.sp tritici was conditioned by a
single major gene due to the observed 3R:1S ratio in
Kwale × PCB 52 cross and epistatic effect of two
interacting major genes (9R:7S) in crosses derived
from PCB62, PCB76 and KSL 18 lines. Duma cultivar
could be having recessive modifying genes for Pgt
resistance. It would be advisable to locate these genes
in the wheat genome and furthermore lines that
showed both adult and seedling resistance could be
used for the improvement of Pgt resistance in
adapted wheat varieties in the breeding programs.
Acknowledgment
The financial and technical support from Kenya
Agricultural and Livestock Research Organization
(KALRO) through Durable Rust Resistance in Wheat
(DRRW) project is highly acknowledged.
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Inheritance of stem rust (Puccinia graminis Pers. F. Sp. Tritici ericks and E. Hen) resistance in bread wheat (Triticum aestivum L.) lines to TTKST race

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Inheritance of stem rust (Puccinia graminis Pers. F. Sp. Tritici ericks and E. Hen) resistance in bread wheat (Triticum aestivum L.) lines to TTKST race