Overwintering of Wheat Stripe Rust Under Field Conditions in the Northwestern Regions of China.

Stripe rust, caused by Puccinia striiformis f. sp. tritici Erikss., is an important disease of wheat worldwide. Identification of pathogen survival hot spots is important for predicting disease onset and subsequent spread to other regions, and such understanding is essential for developing integrated management strategies. We conducted field studies to determine the relationship of P. striiformis f. sp. tritici overwintering potential to winter temperatures in 10 sites in the northwest of China in three growing seasons (2011-12, 2012-13, and 2013-14). The fungus survived better in wheat cultivars with stronger winter hardiness than in those with weaker winter hardiness. Windowpane analysis suggested that P. striiformis f. sp. tritici winter survival is related to temperatures in the coldest period from mid-December to late January. β Regression showed that P. striiformis f. sp. tritici winter survival was negatively related to the number of days with daily average temperature <-2°C for cultivars with weak winter hardiness and <-4°C for cultivars with both moderate and strong winter hardiness. Models developed under constant temperature experiments greatly underestimate the P. striiformis f. sp. tritici overwinter potential under field conditions. This underestimation probably results from the possibility that P. striiformis f. sp. tritici in wheat tissues may have increased tolerance to low temperatures because of acclimation to gradual temperature changes under field conditions. The present models can be used to predict quantitative risks of P. striiformis f. sp. tritici overwintering in winter-wheat-growing regions for timely implementation of regional disease management strategies.