Genes Sr2/Yr30 and Lr34/Yr18/Sr57 interact to confer enhanced adult plant resistance to the three rust diseases of common wheat
Common wheat Arula displays an acceptable level of adult plant resistance (APR) to stripe rust (YR), leaf rust (LR) and stem rust (SR) in Mexico, and to SR (Ug99 races) in Kenya. A recombinant inbred line (RIL) population developed from the cross of Arula with susceptible parent Apav was phenotyped under artificially created epidemics of the three rusts in 2014, 2015 and 2016 in Mexico and for SR during the off and main seasons of 2015 in Kenya. The RIL population and parents were genotyped using an iSelect 90K SNP array and 3 gene-linked markers (Sr2/Yr30-gwm533; Lr34/Yr18/Sr57-csLV34; Lr68-csGS), and a genetic map of 2,634 markers was constructed to locate the resistance loci. Two consistent QTL contributed by Arula were detected on chromosomes 3BS and 7DS, which corresponded to the previously known APR genes Sr2/Yr30 and Lr34/Yr18/Sr57, respectively. Sr2/Yr30 explained 1.1-14.7% and 41.0-61.5% of the phenotypic variation for YR and SR, respectively; whereas Lr34/Yr18/Sr57 accounted for 22.5-78.0%, 40.0-84.3% and 13.8-24.8% of the phenotypic variation for YR, LR and SR, respectively. Arula was also found to carry the positive allele for marker csGS closely linked to gene Lr68 on chromosome 7BL, although this gene was not detected using composite interval mapping. Our results show that RILs possessing both Sr2/Yr30 and Lr34/Yr18/Sr57 had significantly enhanced APR to all three rusts in field trials conducted in Mexico and Kenya. Strategic utilization of these two pleiotropic, multi-pathogen resistance genes with other minor genes is recommended to develop durable rust resistant wheat cultivars.