Identification of a Major QTL for High-Temperature, Adult-Plant Resistance to Stripe Rust (Puccinia striiformis f. sp. tritici) in the Spring Wheat Cultivar Louise (Triticum aestivum L.).

Over the past decade, many single, all-stage resistance genes to stripe rust (Puccinia striiformis f. sp. tritici) have been circumvented in wheat (Triticum aestivum L.) by race changes in the pathogen.  All-stage resistance genes are desirable as they protect the plant during seedling and adult plant stages, but are often not durable.  In contrast, high-temperature, adult-plant resistance (HTAP), which provides resistance only during the adult-plant stage, has provided excellent and durable protection against stripe rust.  Our objective was to identify major quantitative trait loci (QTL) for HTAP resistance to stripe rust in the spring wheat cultivar ‘Louise’.  The mapping population consisted of 188 recombinant inbred lines (RIL) from Louise (resistant) by ‘Penawawa’ (susceptible).  F_5:6 lines were evaluated under natural inoculation in replicated field trials for resistance response at five locations in the Pacific Northwest and New Zealand in 2007.  Infection type (IT) (0-9 with 0= no disease symptoms) and disease severity (percent leaf area infected per plot) were recorded for each RIL three times at each location.  Mean area under the disease progress curve (AUDPC) IT values were 52 and 143 for Louise and Penawawa, respectively.  Mean AUDPC values over all locations ranged from 39-169.  Distribution of trait values was bimodal, indicating a major single gene affecting the trait.  The parents and entire RIL population were evaluated with 255 polymorphic simple sequence repeat (SSR) markers.  Genetic linkage map construction and QTL analysis were performed using MAPMAKER and QTL CARTOGRAPHER.  One major QTL associated with HTAP resistance in Louise was detected on chromosome 2BS (LOD scores from 3.4 to 63.0 across locations) within a 19.7 cM region flanked by Xwmc474 and Xgwm148.  SSRs associated with this QTL can be used in marker-assisted selection to transfer this source of HTAP resistance into regionally adapted wheat cultivars, thereby improving the durability of resistance.