Genetic structure and exchange of <i>Blumeria graminis</i> f. sp. <i>tritici</i> populations in China

Wheat powdery mildew caused by the obligate airborne biotrophic pathogen Blumeria graminis f. sp. tritici (Bgt), is one of the most important diseases in wheat production in China. Understanding the genetic structure and genetic exchange in Bgt populations in China is important to understand epidemics and develop management strategies for wheat powdery mildew. The genetic diversity and genetic structure of 412 Bgt isolates, grouped into twelve populations which were collected from 13 wheat-producing regions, covering almost all the major wheat growing areas of China, were analyzed by microsatellite molecular markers (SSR). The results showed that a total of 370 multilocus genotypes were detected, which revealed a high genetic diversity of Bgt populations. Distance-based redundancy analysis (db-RDA) using Bruvo's genetic distance revealed a significant but weak isolation-by-distance pattern, with geographic distance explaining only 2.5% of total genetic variation, supporting gene flow limitation with increasing distance over the studied areas. The Bgt populations from Yunnan (YN) was clearly separated from other Bgt populations. Gene flow exists between the Shaanxi (SX) and Hubei (HuB) populations, with transmission likely occurring from SX to HuB. Furthermore, the genetic differentiation between the high elevation Gansu (GS) population and the low elevation Sichuan (SC) population suggests that gene flow may be limited along the elevational gradient. There were gene flows among Bgt populations from Shandong (SD), Hebei (HB) and Henan (HN) and migration was mainly from HN to SD and HB. Furthermore, it was inferred that the source of inoculum in Jiangsu was mainly from Anhui. Similarly, the pathogen population of Jiangsu-Zhejiang (JZ) and Beijing (BJ) might share the same sources of inoculum. These results were valuable to understand wheat powdery mildew epidemics and to develop effective disease management strategies.