Analysis of population genetic structure of Puccinia striiformis f. sp. tritici from central Gansu and the surrounding areas Analysis of population genetic structure of Puccinia striiformis f. sp. tritici in Shaanxi Province, China Interactions between wheat cultivars and yellow rust races QUANTITATIVE EFFECTS OF THE CONCENTRATIONS OF FUNGICIDES WITHIN WHEAT LEAVES ON DISEASE COMPONENTS OF YELLOW RUST EXPERT SYSTEM OF RICE-WHEAT DISEASE FORECAST IN YUNNAN PROVINCE