Sexual recombination within the “Kranich” race of the yellow rust fungus Puccinia striiformis f.sp. tritici on Berberis vulgaris

An isolate of the “Kranich” race of the basidiomycete Puccinia striiformis f.sp. tritici (Pst), which causes yellow (stripe) rust on wheat, was selfed on Berberis vulgaris, the alternate (sexual) host for several rust fungi infecting cereals and grasses. Since 2011, the “Kranich” race has been detected in several European countries and it has contributed to the replacement of the pre-existing European Pst population. A sexual origin of the “Kranich” race has been suggested due to the high capacity of teliospore production and the genetic similarity to the populations in the centre of diversity of Pst in the near-Himalayan region. For the completion of the sexual life cycle, B. vulgaris was inoculated with basidiospores derived from germinating teliospores. Pycnia appeared on the adaxial side of the leaves 8 days after inoculation (dai) and subsequent fertilization resulted in the development of aecia on the abaxial side of the leaves from 15 dai. Inoculation of wheat seedlings with aeciospores from bulked aecia resulted in 124 progeny isolates. Twenty-three of these were randomly selected and genotyped using 19 simple sequence repeat (SSR) markers, which confirmed the parental origin of the progeny isolates. Eight heterozygous markers in the parental isolate revealed segregation in the progenies resulting in 18 novel multilocus genotypes, confirming recombination following sexual reproduction. This study demonstrated a high sexual capacity of the “Kranich” race, which highlights the risks associated with sexual reproduction under suitable conditions for rust development.