Identification of Genes on Wheat Chromosomes 2BS and 2BL Conferring Resistance to Stem Rust Fungus Race Ug99

Bread wheat lines ‘Yaye#1’ and ‘Huhwa#1’ showed resistance to stem rust fungus race Ug99 in wheat seedlings as well as adult plants. Cacuke#1 is known to be susceptible for Ug99. Recombinant inbred lines (RILs) populations- Yaye#1/ Cacuke#1 and Huhwa#1/Cacuke#1 were phenotyped with Ug99 to detect the presence or absence of resistance associated with low seedling infection types ranging between 2 and 2+ in greenhouse and moderately resistant infection response in field condition. RILs in each population confirmed a -1 homozygous resistant: 1 homozygous susceptible segregation ratio, indicating monogenic resistance. Selective genotyping with a set of 44 RILs with DArT markers was carried out. Two resistance genes were mapped; one on chromosome 2BS contributed by Yaye#1 and other on chromosome 2BL contributed by Huhwa#1. Selected individuals were bulked and genotyped with chromosome 2B specific SSR markers. Further whole population was genotyped with polymorphic SSR markers. Markers linked to gene on chromosome 2BS were Xbarc200 and Xwmc770; whereas, markers linked to the gene on chromosome 2BL were Xgwm388 and Xwmc332. The infection type pattern and map location of gene on chromosome 2BS clearly indicated that it is novel Ug99 resistance gene. The gene mapped on chromosome 2BL contributed by Huhwa#1 also collocated with previously reported Ug99 resistance genes and test of allelism as well as marker haplotyping is underway to determine the novelty of this gene. Identified genes in the study can be utilized in breeding Ug99 resistant wheat varieties preferably in combination with other resistance genes to enhance their durability.