Expression of high-temperature adult-plant (HTAP) resistance against stripe rust (Puccinia striiformis f. sp tritici) in Pakistan wheat landraces

Stripe rust (Puccinia striiformis f. sp. tritici, Pst) is an important disease of wheat in the United States and Pakistan. Genetic resistance in wheat is a cost-effective and convenient control measure. In the present study, resistance testing of 115 wheat landraces from Pakistan was carried out initially at the seedling stage with seven races of the pathogen, four from the USA and three from Pakistan. The germplasm showed a general lack of effective seedling resistance. Only two genotypes (PI 210916, PI 219752) were resistant against all races. Adult plants of the wheat genotypes were also tested at high temperatures under greenhouse conditions and at two field locations in Washington State. In the test with US Pst race PST-127, 28 (32%) of the landraces had seedling resistance and 41 (52%) had high-temperature adult-plant (HTAP) resistance. When tested with Pakistan isolate PK07-2, 14 (13%) of the wheat genotypes had seedling resistance and 61 (53%) had HTAP resistance. In the test with Pakistan isolate PK07-6, 32 (40%) had seedling resistance and 38 (48%) had HTAP resistance. In field tests, 94 (86%) genotypes were resistant and four (4%) were intermediate at Pullman, Washington; and 72 (89%) were resistant and none was intermediate at Mount Vernon, Washington. The greenhouse and field tests revealed that the majority of the wheat landraces possess HTAP resistance against stripe rust. These landraces should be useful genetic resources for developing stripe rust resistant cultivars in regions where climatic conditions are suitable for the expression of the durable type of resistance.