Analysis of the primary sources of quantitative adult plant resistance to stripe rust in U.S. soft red winter wheat germplasm

Abstract

Stripe rust, or yellow rust (Puccinia striiformis Westend. f. sp. tritic), is a disease of wheat (Triticum aestivum L.) historically causing significant economic losses in cooler growing regions. Novel isolates of stripe rust with increased tolerance for high temperatures were detected in the United States circa 2000. This increased heat tolerance puts geographic regions, such as the soft red winter wheat (SRWW) growing region of the southeastern United States, at greater risk of stripe rust induced losses. In order to identify sources of stripe rust resistance in contemporary germplasm, we conducted genome‐wide association (GWA) studies on stripe rust severity measured in two panels. The first consisted of 273 older varieties, landraces, and some modern elite breeding lines and was evaluated in environments in the U.S. Pacific Northwest and the southeastern United States. The second panel consisted of 588 modern, elite SRWW breeding lines and was evaluated in four environments in Arkansas and Georgia. The analyses identified three major resistance loci on chromosomes: 2AS (presumably the 2NS:2AS alien introgression from Aegilops ventricosa Tausch; syn. Ae. caudata L.), 3BS, and 4BL. The 4BL locus explained a greater portion of variance in resistance than either the 2AS or 3BS loci in southeastern environments. However, its effects were unstable across different environments and sets of germplasm, possibly a result of its involvement in epistatic interactions. Relatively few lines carry resistance alleles at all three loci, suggesting that there is a pre‐existing reservoir of enhanced stripe rust resistance that may be further exploited by regional breeding programs.

Physiological specialization of Puccinia triticina and genome-wide association mapping provide insights into the genetics of wheat leaf rust resistance in Iran

“…terization of novel resistance sources is the prerequisite and most important strategy for controlling rust diseases in wheat and pyramiding these genes for durable resistance 33,34 . The rapid evolution of pathogens due to fungicide application, environmental conditions and also narrow genetic base of resistance genes in improved wheat genotypes can easily lead to the breakdown of the resistance genes 17,35 . In this study, 185 wheat genotypes comprising Iranian cultivars and landraces from diverse world geographical origins were evaluated for resistance against 10 Pt races at seedling stages.…”

“…Association analysis for each Pt race was conducted using the FarmCPU model 35,79 . Association results of the FarmCPU model were compared with association models like as GLM, MLM, CMLM and Super-MLM models and finally, this model provided a robust model for association mapping of resistance genes against Pt races, which effectively controls both false positives and false negatives 80 .…”