Genetic Analysis Reveals Relationships Among Populations of Puccinia striiformis f. sp. tritici from the Longnan, Longdong and Central Shaanxi Regions of China

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most important diseases of wheat worldwide. In China, Longnan (LN) and Longdong (LD), in the south and east of Gansu province, are important PST over-summering areas and are a source of PST inoculum for the major wheat-growing regions in eastern China. Central Shaanxi (CS) is a wheat-growing region that acts as an important bridge zone for stripe rust epidemic development between LN and LD in the west, and the Huanghuai wheat-growing region in the east, and thus plays an essential role in PST epidemics in China. To study the relationships among PST populations in the three regions (LN, LD and CS), we sampled 284 isolates from different geographic locations. Based on 10 SSR markers, the results demonstrated high genetic diversity in all three regions although diversity did vary between region with LN > LD > CS. Genetic differentiation was lower with more extensive gene flow between LD and CS. PST populations in the CS region were genetically closer to those from LD than from LN, which may be due to geographical proximity and topography. A positive and significant correlation existed between linearized FST and the log of geographical distances among all subpopulations. Linkage disequilibrium analysis showed that subpopulations of PST from Qinzhou, Qincheng, Beidao, and Maiji from LN, and Qianyang and Longxian from CS were in equilibrium (P > 0.05), suggesting somatic hybridization and/or sexual reproduction may exist in these subpopulations.