Genetic Analysis of Adult Plant Stripe Rust Resistance in Australian Wheat Cultivar Sentinel

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a devastating disease of wheat globally. Emergence of new virulent pathotypes continues to render resistance genes ineffective. Deployment of combinations of rust resistance genes is essential to achieve durable control of stripe rust. The common wheat cultivar Sentinel was observed to be resistant to stripe rust under field conditions and genetic basis of resistance is unknown. Sentinel was crossed with stripe rust susceptible genotype Nyabing 3 (NYB3) and a set of 109 F6 RILs were developed. RILs and parental genotypes showed susceptible responses at the seedling stage when inoculated with Pst pathotype 134E16A+Yr17+Yr27. The entire RIL population was grown in the field as 10 seed hill plots and artificially inoculated with Pst pathotype 134E16A+Yr17+Yr27. Adult plant stripe rust assessments were made using 1 to 9 scale, where 1 equals very resistant and 9 very susceptible and population was categorized as homozygous resistant (HR) and homozygous susceptible (HS). 55, 28, 14 and 12 RILs produced adult plant responses 2 to 3, 4 to 5, 6 to 7 and 8 to 9, respectively. Chi-squared analysis of adult plant stripe rust response variation conformed to segregation at three independent loci (97 HR : 12 HS, χ²_7:1 = 0.22, non-significant at P=0.05 and 1 d.f.). Genotyping of parents with Yr18-linked STS marker csLV34 and Yr29-linked SNP marker indicated the absence of Yr18 and presence of Yr29 in Sentinel. Yr29-linked SNP marker was genotyped on the entire RIL population and showed monogenic segregation. F6 RILs are currently being evaluated in the field and will be genotyped using 90K SNP platform to identify genomic locations of the remaining two adult plant stripe rust resistance genes carried by Sentinel.