|Rouse, Matthew - Matt|
|BHAVANI, SRIDHAR - International Maize & Wheat Improvement Center (CIMMYT)|
|WANYERA, RUTH - Kenya Agricultural And Livestock Research Organization|
|NEWCOMB, MARIA - University Of Arizona|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2016
Publication Date: 2/9/2017
Citation: Babiker, E.M., Gordon, T.C., Chao, S., Rouse, M.N., Jin, Y., Bhavani, S., Wanyera, R., Newcomb, M., Bonman, J.M. 2017. Genetic loci conditioning adult plant resistance to the Ug99 race group and seedling resistance to races TRTTF and TTTTF of the stem rust pathogen in wheat landrace CItr 15026. Plant Disease. 101(3):496-501.
Interpretive Summary: Stem rust is the most important disease of wheat worldwide. A key problem in rust disease management is that new resistant cultivars often become susceptible over time due to the evolution of new pathogen races. A new race of the stem rust pathogen with virulence to the widely deployed stem rust resistance gene Sr31, originally designated as race TTKS and commonly referred to as ‘Ug99’, was reported in Uganda in 1999. One means to overcome this problem is to deploy new adult plant resistance (APR) in wheat cultivars. Wheat landrace CItr 15026 previously showed adult plant resistance (APR) to the Ug99 stem rust race group in Kenya and seedling resistance to Puccinia graminis f. sp tritici (Pgt) races QFCSC, TTTTF, and TRTTF. Recently, only five APR genes to Ug99 have been identified. The objective of this study was to elucidate the inheritance of APR to Ug99 race group in a wheat landrace accession CItr 15026. The recently developed wheat molecular markers, called single nucleotide polymorphisms (SNPs), were used to ‘genotype’ the population of plants developed by crossing the resistant accessions CItr 15026 with susceptible lines. With this method we found that there is a major locus for APR to Ug99 race group on chromosome arm 6AS. The TRTTF resistance loci located to chromosome 6AS and 6DS, whereas the TTTTF and QFCSC resistance locus located to the same region on 6DS as the TRTTF resistance. Based on race specificity and the mapping results, the APR locus in CItr 15026 was hypothesized to be novel. The SNP markers identified in this study could be used in marker assisted selection to combine the APR gene in CItr 15026 with other effective Sr genes. These results will help US wheat breeders develop new cultivars with better stem rust resistance.
Technical Abstract: Wheat landrace CItr 15026 previously showed adult plant resistance (APR) to the Ug99 stem rust race group in Kenya and seedling resistance to Puccinia graminis f. sp tritici (Pgt) races QFCSC, TTTTF, and TRTTF. CItr 15026 was crossed to susceptible accessions LMPG-6 and Red Bobs, and 180 DH lines and 140 recombinant inbred lines (RILs) were developed respectively. The 90K wheat iSelect SNP platform was used to genotype the parents and populations. Parents and 180 DH lines were evaluated in the field in Kenya for three seasons. A major QTL for APR was consistently detected on chromosome arm 6AS. This QTL was further detected in the RIL population screened in Kenya for one season. Parents, F1 seedlings, and the two populations were tested against races TRTTF and TTTTF. Whereas, the DH populations was tested against race QFCSC. Goodness-of-fit tests indicated that the TRTTF resistance in CItr 15026 was controlled by two complementary genes whereas the TTTTF and QFCSC resistance was conditioned by one dominant gene. The TRTTF resistance loci mapped to chromosome arms 6AS and 6DS, whereas the TTTTF and QFCSC resistance locus mapped to the same region on 6DS as the TRTTF resistance.