Genetic Structure and Asymmetric Migration of Wheat Stripe Rust Pathogen in Western Epidemic Areas of China

Puccinia striiformis f. sp. tritici causes severe global epidemics of wheat stripe rust primarily by airborne urediniospores. Understanding long-distance migration patterns of P. striiformis f. sp. tritici is critical for disease forecasting and management. Although the western epidemic areas in China have been considered as the source of inoculum spread eastward across the country, migration pathways among different populations within the western epidemic areas are poorly understood. In this study, we investigated the population genetics of 200 P. striiformis f. sp. tritici isolates from western epidemic areas using amplified fragment length polymorphism and simple sequence repeat markers. A coalescent approach was also used to calculate the migration rates among populations. Data analyses with both marker systems indicated high genetic diversity in each regional population. The Mantel test revealed significant positive correlation between genetic and geographic distances. Both discriminant analysis of principal components and STRUCTURE analysis supported moderate population structure shaped by seasonality and geography. The calculated migration rates indicated the presence of asymmetric migration between major populations in western epidemic areas, with greater migration rates from high elevation, oversummering areas to low elevation, overwintering areas. Sichuan Basin, one of the low elevation, overwintering areas, sampled in both fall and spring, was inferred as a recipient in fall but a donor in spring. Migration among P. striiformis f. sp. tritici populations may be partly attributable to terrace fanning and prevailing wind direction in different seasons. Our study provides a better understanding of fine-scale population structure and the interregional migration pattern of P. striiformis f. sp. tritici in northwestern China and will inform future rust management.