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Title: Evaluation of Pakistan wheat germplasms for stripe rust resistance using molecular markers

Author
item TABASSUM, SOBIA - Pakistan University Of Agriculture
item ASHRAF, MUHAMMAD - Pakistan University Of Agriculture
item Chen, Xianming

Submitted to: Science China Life Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2009
Publication Date: 9/1/2010
Citation: Tabassum, S., Ashraf, M., Chen, X. 2010. Evaluation of Pakistan wheat germplasms for stripe rust resistance using molecular markers. Science China Life Science. 53(9):1-12.

Interpretive Summary: Wheat production in Pakistan is seriously constrained due to rust diseases, especially stripe rust. The first objective of present study was to evaluate 100 Pakistan wheat cultivars that were grown in over the past 60 years. These cultivars were inoculated in the seedling stage with two U.S. isolates and two Pakistan isolates of the stripe rust pathogen. None of the wheat cultivars were resistant to all tested isolates, while 16 cultivars were susceptible to the four isolates at seedling stage. Most of the Pakistan cultivars showed resistance against PST-127 but were susceptible to PST-116. The second objective was to evaluate the 100 Pakistan wheat cultivars for stripe rust resistance under natural epidemics in Pakistan and Washington State U.S.A. Of the 100 cultivars, 14 were highly resistant at all locations and 30 were found to patentially have high-temperature adult-plant (HTAP) resistance. The third objective was to determine the genetic diversity and presence of certain resistance genes in Pakistan wheat using resistance gene analog polymorphism, simple sequence repeat and sequence tagged site markers. Ten had the Yr9 marker and seven had the Yr18 marker. No marker band was detected for Yr5, Yr8 and Yr15, indicating the absence of these genes in the tested Pakistan wheat cultivars. The resistant genotypes identified in this study should be useful in developing new wheat cultivars with stripe rust resistance.

Technical Abstract: Wheat production in Pakistan is seriously constrained due to rust diseases. Stripe (yellow) rust, caused by Puccinia striiformis f. sp. tritici is one of these diseases that can limit yields in the area. Thus developing and cultivating genetically diverse and resistant varieties is the only sustainable solution. The first objective of present study was to evaluate 100 Pakistan wheat cultivars that were grown in over the past 60 years. These cultivars were inoculated in the seedling stage with two U.S. isolates and two Pakistan isolates of the pathogen. None of the wheat cultivars were resistant to all tested stripe rust isolates. In contrast, 16 (16%) lines were susceptible to the four isolates at seedling stage. The reaction data indicated that none of the Pakistan wheat cultivars have either the Yr5 or Yr15 genes that are considered to be effective against most P. striiformis f. sp. tritici races in the world. Most of the Pakistan cultivars showed resistance against PST-127 but were susceptible to PST-116, indicating the presence of Yr10 in these cultivars as the PST-127 is avirulent and PST-116 is virulent to Yr10. It is also possible that these cultivars may have other previously unidentified genes or gene combinations. The second objective was to evaluate the 100 Pakistan wheat cultivars for stripe rust resistance under natural epidemics in Pakistan and Washington State U.S.A. Of the 100 cultivars, 14 (14%) were highly resistant at all locations, 23 (23%) were resistant at both U.S. locations; 26 (26%) were resistant at one location and intermediate at another location; 22 (22%) were susceptible at both U.S locations; and the remaining 29 (29%) were susceptible at one location and either resistant or intermediate at another location and 2 (2%) were susceptible at all locations. Thirty genotypes were found to have potential HTAP resistance. The third objective was to determine the genetic diversity in Pakistan wheat germplasms using molecular markers. This study was based on DNA fingerprinting using resistance gene analog polymorphism (RGAP) marker analysis. The highest polymorphism detected with RGAP primer pairs were 40%, 50% and 57% with mean polymorphism of 36%. A total of 22 RGAP markers were obtained in this study. RGAP, simple sequence repeat (SSR) and sequence tagged site (STS) markers were used to determine the presence and absence of some important stripe rust resistance genes, such as Yr5, Yr8, Yr9, Yr15 and Yr18. Ten (17%) cultivars showed a RGAP marker band for Yr9 and seven (12%) cultivars showed the Yr18 marker band, indicating that these have Yr9 and Yr18, respectively. No marker band was detected for Yr5, Yr8 and Yr15, indicating the absence of these genes in the tested Pakistan wheat cultivars. Cluster analysis based on molecular and stripe rust reaction data is useful in identifying considerable genetic diversity among Pakistan wheat cultivars. The resistant germplasms identified with 22 RGAP markers and from the resistance evaluations should be useful in developing new wheat cultivars with stripe rust resistance.