Occurrence of Tapesia yallundae apothecia on field and laboratory‐inoculated material and evidence for recombination between isolates

Abstract

Tapesia yallundae was observed in early July on wheat straws, which had been inoculated with isolates of Pseudocercosporella herpotrichoides (W‐type) 9 months previously and placed in plots of winter wheat, to act as inoculum in a resistance screen. A perfect state was not observed on straws inoculated with R‐type isolates in the same experiment. One hundred and thirty‐four single‐ascospore isolates were obtained and observations on morphology in culture, pathogenicity to wheat and rye seedlings, resistance to benomyl and the pattern of restriction fragment length polymorphisms demonstrated that all isolates were W‐type, although some grew at half the expected rate on agar, and at least two isolates were involved in the production of apothecia. Apothecia were produced in vitro on straws inoculated with single isolates of P. herpotrichoides only when they were incubated in contact with other straws similarly inoculated with certain other isolates. No apothecia were produced on straws with only isolate present, suggesting the need for at least two strains, possibly representing different mating types, for apothecium formation. Apothecia of T. yallundae were produced in vitro on straw pieces which had been inoculated individually with W‐type isolates, 14‐16 weeks after straws of different isolates were mixed. Evidence for genetic recombination between isolates was obtained when single‐ascopore colonies were analysed for resistance to benomyl in culture and for restriction‐length polymorphisms (RFLPs).