Genetic characterization of slow rusting resistance to leaf rust in durum wheat cv. Bairds

The CIMMYT durum Bairds is susceptible to leaf rust (LR) at the seedling stage but shows an adequate level of slow rusting adult plant resistance (APR) in Mexican field environments. A recombinant inbred line (RIL) population developed from a cross of Bairds and the susceptible parent Atred#2 was phenotyped for LR response at Ciudad Obregon, Mexico, during 2013, 2014 and 2015 under artificial epidemics created with Pt race BBG/BP. Genetic analysis indicated that 3-4 additive genes conferred LR resistance. The RILs and parents were also genotyped with the 50K diversity arrays technology (DArT) sequence system and 93 SSR markers. A genetic map comprising 1,150 markers was used to map the resistance loci. Inclusive composite interval mapping analysis detected four quantitative trait loci (QTL) on chromosomes 1BL, 2BC (centromere region), 5BL and 6BL. These QTL, designated as QLr.cim-1BL, QLr.cim-2BC, QLr.cim-5BL and QLr.cim-6BL, explained 20.1-60.7%, 6.4-13.1%, 4.3-11.2%, and 7.1-28.0%, respectively, of the variation in leaf rust severity. QLr.cim-1BL was close to the previously reported APR gene Lr46, whereas QLr.cim-6BL, detected in all three seasons, is a new resistance locus in durum wheat. The four QTL combined showed a significant additive effect on resistance with a disease severity of 18-20%, whereas RILs carrying the individual QTL showed mean leaf rust severities ranging from 56 to 98%. Three QTL, except for QLr.cim-2BC, were derived from Bairds. The final LR severity of Bairds ranged from 15-25% across three years. This cultivar can be used as a source for complex APR in durum wheat breeding.

International Maize and Wheat Improvement Center (CIMMYT), México
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