Characterization of Stem Rust Resistant Genes in Wild Tetraploids

1. C
Characterization of Stem Rust Resistant
t
Genes in Wild Tetraploids
Alwan E1,2, Ogbonnaya FC2*, Ayele B3, Nazari K2, Abdalla O2, Yahyaoui A4, and Hakim SH1 CGIAR
1
Aleppo University, Faculty of Agriculture, Aleppo, Syria. 2
ICARDA, PO Box 5466, Aleppo, Syria
3
Ethiopian Institute of Agricultural Research, Box 2003, Addis Ababa, Ethiopia. ICARDA-CIMMYT Wheat Improvement Program, PO Box 5466, Aleppo, Syria
4
*Corresponding author: F.Ogbonnaya@cgiar.org
Abstract 200
A total of 73 wild tetraploid wheat accessions showing adult plant resistance (APR)
were analyzed using molecular markers linked reportedly to wheat stem rust race
Ug99 resistance genes. The wheat accessions were identified based on seedling and 150
adult plant test under heavy Ug99 inoculation conducted at Debre Zeit, Ethiopia. The
accessions were haplotyped for stem rust resistance genes Sr2, Sr22, Sr26, Sr36,
Sr40 using linked microsatellite (SSR) and diagnostic sequence tagged sites (STS).
Of the accessions tested, 2 accessions showed the diagnostic fragment associated
Sr2 Sr2 120 bp
with Sr2-linked SSR markers; while 1, 7, and eight accessions possessed the DNA
Control
Marker
fragment associated with Sr22, Sr36, and Sr40 resistance genes respectively . About
75% of the wild tetraploid accessions do not possess either SSR or STS haplotypes
associated with the currently mapped Ug99 effective genes that we investigated. Our Figure 1. PCR amplification of wild tetraploids with Sr2 linked marker.
preliminary results indicate that wild tetraploid accessions could provide potentially
new sources of durable stem rust resistance in wheat.
Introduction 250
Sr22
235
Stem rust (caused by Puccinia graminis f. sp. tritici Eriks. & E. Henn) is one of the
200
deadliest fungal diseases of wheat, which until the mid 1950s posed a tremendous threat
Diffrential
to wheat production worldwide. The disease was brought under control through the Control 150 bp
deployment of genetic resistance using mostly major genes transferred from cultivated Marker
rye and wild relatives of wheat until recently. However, the threat was renewed by the Figure 2. PCR amplification of wild tetraploids with Sr22 linked marker.
emergence of a new race commonly known as Ug99 designated “TTKS” (Singh et al.
2006), virulent on most of the widely used genes, with reported yield losses in Kenya
and Ethiopia ranging from to 20-50%. One accession of T. turgidium subsp dicoccoides with the phenotype SS/AMR also
Use of molecular markers would enhance the effective deployment of resistance genes. possessed the DNA fragment linked to Sr22 (Fig. 2).
Currently, about 50 stem rust resistance Sr genes have been identified and mapped to
specific chromosome (McIntosh et al. 2008). Amongst the mapped Sr genes, molecular Additionally, six accessions of T.timopheevii var. timopheevii, and one of T. turgidium
markers have been identified linked to some Ug99 effective resistance genes. The subsp dicoccoides which displayed seedling susceptibility and adult plant resistance
objective of this study was to determine the frequency of the DNA markers linked with (SS/AR) possessed the SSR haplotype linked to Sr36. Further, three accessions of T.
TTKS effective resistance genes, Sr2, Sr22, Sr26, Sr36, and Sr40 in wild tetraploids, turgidium subsp dicoccon, two of T. turgidium subsp dicoccoides, two of T.timopheevii
in order to identify those carrying genes likely different from those previously reported. var. timopheevii and one accession of T. turgidium subsp turanicum possessed the
SSR fragment linked to Sr40 gene. However, none of the tested accessions showed
the presence of the DNA fragment linked to Sr26.
Materials and Methods
In total, about 75% of the wild tetraploid accessions do not possess either SSR or
The wild tetraploid wheat accessions used in this study consisted of the following
STS haplotypes associated with the currently mapped Ug99 effective genes that we
accessions:
investigated. The results indicate that wild tetraploids of wheat could provide potentially
T. turgidum subsp. dicoccoides 28 T. turgidum subsp. carthlicum 6
new sources of durable stem rust resistance in wheat. These are further being genotyped
T. turgidum subsp. dicoccon 18 T. turgidum subsp. turanicum 4
as more markers become available to ensure that only those with new APR genes are
T. timopheevii subsp. timopheevii 10 T.timopheevii var araraticum 4
used in germplasm enhancement of durum and bread wheat.
T. turgidum subsp. polonicum 1 T. turgidum subsp. turgidum 2
Eight linked and diagnostic SSR and STS markers were chosen for haplotyping five
Table 2. Distribution of diagnostic markers linked to stem rust resistance
major stem rust resistance genes located on A and
genes Sr2, Sr22, Sr26 and Sr36 in wild Triticum species
B genomes (Table 1). PCR reaction was carried
out as previously reported by the authors. A group Gene
of monogenic lines having the above-mentioned Species sr2 sr22 sr26 sr36 sr40 No. of lines
major genes in addition to some lines previously T. turgidium subsp dicoccon 3 3
characterized and known to possess Sr genes were
T. turgidium subsp dicoccoides 2 1 1 1 5
used as checks in this study.
T. turgidium subsp turgidium 1 1
Results and Discussion T. turgidium subsp turanicum 1 1
Table 2 summarizes the results of charactering wild T.timopheevii var timopheevii 6 2 8
Triticum species with Sr linked and/or diagnostic
Total 18
markers. Among 73 accessions, two accessions (T.
turgidium subsp dicoccoides and T. turgidium subsp
turgidium) which displayed seedling susceptibility
and adult plant moderate resistance (SS/AMR)
showed the Sr2 haplotype (Fig. 1).
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Acknowledgments
T. timopheevii ssp.
Sr40 Xgwm344 2BS Yu et al., 2009 Staff of ICARDA’s biotechnology and genetic resources units, Ethiopian Institute for Agricultural Research,
armeniacum Durable Rust Resistance in Wheat Project, Cornell University.