| Abstract:
| Common wheat line 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. Present study was conducted to identify genetic loci that confer resistance in Arula and to understand their interactions for rust resistance. A recombinant inbred line (RIL) population (190 lines) 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 stem rust (Ug99) during the off and main seasons of 2015 in Kenya. The RIL population and parents were genotyped with Sr2/Yr30-linked simple sequence repeat (SSR) marker gwm533 and two sequence tagged site (STS) markers (Lr34/Yr18/Sr57-csLV34 and Lr68-csGS) in addition to genotyping using Illumina iSelect 90K SNP array. A genetic map of 2,634 polymorphic markers (2,631 SNPs, 1 SSR and 2 STS markers) was constructed to locate the resistance loci. Composite interval mapping (CIM) was conducted to identify quantitative trait loci (QTL) associated with rust resistance using phenotypic and genotypic data in Windows QTL cartographer version 2.5. 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 CIM. Based on presence or absence of identified genes/QTLs, lines were classified into different groups and t-tests were used to compare the mean relative area under disease progress curve (relAUDPC) over years of different gene combinations. RILs carrying both Lr34/Yr18/Sr57 and Lr68 showed significantly higher APR to LR showing the benefit of gene combination Lr34/Yr18/Sr57 + Lr68. 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. |
