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Yr36 Confers Partial Resistance at Temperatures Below 18°C to U.K. Isolates of Puccinia striiformis

Wheat yellow (stripe) rust, caused by the obligate biotrophic fungus Puccinia striiformis f. sp. tritici, is a continual threat to wheat fields worldwide. New isolates with increased virulence have recently emerged driving breeding efforts to incorporate disease resistance genes which confer potentially more durable, albeit partial, resistance. Yr36 is one such locus which was recently cloned (WKS1) and described as a high-temperature adult-plant gene being effective only at temperatures above 25°C. We examined the potential use of Yr36 at temperatures below 25°C. Field experiments in the United Kingdom across 2 years show that lines carrying Yr36 provide slow rusting resistance to the yellow rust pathogen. Juvenile and adult Yr36 isogenic lines showed partial resistance at temperatures below 18°C under control environment conditions in tetraploid and hexaploid genetic backgrounds, but not at seedling stage, when inoculated with U.K. P. striiformis isolates. This partial resistance phenotype was similar to that observed previously at temperatures ≥25°C. Transgenic complementation tests and ethyl methanesulfonate mutants showed that the low-temperature partial resistance was due to the WKS1 gene. This study indicates that Yr36 has the potential to be an effective source of partial resistance in temperate wheat growing regions.