Fungicide Application on Alternate Host Barberry has Significant Roles in Declining Population Genetic Diversity and the Risk of Emerging New Races of Puccinia striiformis f. sp. tritici.

Puccinia striiformis f. sp. tritici (Pst) is a destructive pathogen renowned for its dual reproductive modes, asexual stage on wheat and sexual stage on barberry (Berberis) that makes wheat cultivars vulnerable to newly emerging races. However, little has been known impact of treatment on barberry plants on declining population genetic diversity and race composition. In this study, we selected six barberry-wheat coexisting sites in which Pst occurs sexually, as treatment and control group for experimental purpose. The treatment group were treated with triadimefon fungicides on barberry at early pycnial stage to suppress the sexual reproduction. Conversely, the control group represented sexual reproduction without fungicide application. Pst populations from wheat fields closed to barberry with/without fungicide treatment were phenotype on Chinese differentials and genotype using a DNA microarray. The results showed treatment population displayed a lower heterozygosity level (F_hom = -0.36945, Tajima's D = 0.285033), and a lower genetic diversity (π = 0.000156053) compared to control population (F_hom = -0.41745, Tajima's D = 0.955451, π = 0.000184483), and a significant difference was observed between both populations (P < 0.001; P < 0.05). Treatment population was identified 17 new races and 3 known races, and control population was identified 46 new races and 8 known races. Treatment population (α = 4.644) showed the standard races diversity lower than control population (α = 5.194) based on a set of 25 Yr-single gene lines. Our results showed a significant impact of fungicide application on barberry to minimize emergence of new races and the level of genetic diversity. It provided guidance to growers, emphasizing the importance of timely fungicide application on barberry to ensure the long-term resistance durability of wheat cultivars against stripe rust.