Barberry plays a role in spreading inoculums to wheat fields to cause stripe rust in China

Wheat stripe rust, caused by basidiomycete fungus Puccinia striiformis f. sp. tritici (Pst), is a damaging disease worldwide. The recent discovery demonstrated the fungus depends on living wheat and aecial hosts, mainly barberry (Berberis) species, to complete its life cycle. In China, we determined that, under natural conditions, the sexual cycle of Pst occurs based on collections of Pst isolates from the diseased barberry in the past three years. However, no direct evidence to support whether barberry plays a role in spreading inoculums to wheat field to cause stripe rust was detected. In the present study, we recovered 103 Pst samples from natural-infected B. shensiana in the western Shaanxi in spring 2016, and also collected 107 Pst isolates from neighboring wheat fields. Phenotype and genotype of the two Pst populations were tested using a set of Chinese differential hosts for Pst and SSR markers, respectively. The phenotype tests showed that 57 race types produced from the barberry-derived Pst populations, consisting of 58 known races, such as CYR 34, CYR32, G22-14, and Su11-14-3, and 45 new races. Many of the two Pst populations shared the same race types. The genotype tests indicated the barberry-derived Pst population produced a rich genotype, obviously higher than the wheat-derived Pst populations. The seven same genotypes were found on 40 isolates of the former and 26 of the latter. Our results provide evidence to support that sexual cycle of Pst occurs regularly in nature in China and that barberry provides inoculums to neighboring wheat fields, triggering stripe rust infections in the spring. This could be a reason why the Chinese Pst populations represent extreme genetic diversity.