Mapping Quantitative Trait Loci for Slow-Rusting Traits in Wheat

Leaf rust of wheat is caused by Puccinia triticina. Slow rusting is an important component of durable resistance to leaf rust and often expressed in the form of long latent period, and low infection type and severity. Deployment of slow rusting resistance genes is an effective approach to improve durability of rust resistance in wheat cultivars. CI13227 is a U.S. winter wheat germplasm that shows slow rusting. The objective of this study was to identify quantitative trait loci (QTLs) associated with the slow rusting traits in CI13227 using DNA markers. A population of double haploid (DH) lines developed from the cross of CI13227/Lakin was evaluated for latent period (LP), final rust severity (FRS), area under disease progress curve (AUDPC), and infection type (IT) in greenhouse experiments at Kansas State University, Manhattan, KS. A total of 3468 polymorphic SNP markers derived from 92K SNP chip and 42 simple sequence repeat (SSR) were scored in the DH population. The frequency distributions for these slow rusting traits were continuous, and significant correlations (r = 0.41 to 0.62, p<0.001) were observed for all the traits between the two greenhouse experiments (2012 and 2013). Two QTLs on chromosome 7B and 2B were consistently detected for all slow rusting traits measured. The percentages of phenotypic variances explained by each QTL varied with experiments and traits, ranging from 10.2 to 27.8% for LP, 12.1 to 30.3% for FRS, 11.3 to 29.6% for AUDPC, and 10.6 to 35.4% for IT. This study confirmed the two QTLs on chromosome 2B and 7B reported in a previous study conducted using a recombinant inbred population from CI13227/Suwon92 and identified new markers closer to the QTLs than previously reported markers. SNPs closely linked to the QTLs have been converted to KASP SNP markers that can be easily used in marker-assisted selection for slow rusting traits from CI13227 in breeding.