Genetic variation in Puccinia graminis collected from oats, rye, and barberry.

Puccinia graminis, the causal agent of stem rust, was collected from its alternate host barberry (Berberis spp.) and two different uredinial hosts, oats (Avena sativa) and rye (Secale cereale). The samples were analyzed using 11 polymorphic simple sequence repeat (SSR) markers. There were large differences between fungal populations on oats (P. graminis f. sp. avenae) and rye (P. graminis f. sp. secalis), and the genetic variation within the different formae speciales was also high. It was possible to distinguish between the two formae speciales on barberry. Additional genotypic groups not present in the field samples from oats and rye were also identified on barberry. Our results confirm the importance of barberry in maintaining the populations of P. graminis in Sweden and the importance of the sexual stage for the survival of the pathogen.