Susceptibility in oats to stem rust induced by co-infection with leaf rust

Abstract

Induction of susceptibility in oats to a normally avirulent pathotype of Puccinia graminis f. sp. avenae was studied in the presence of different pathotypes of P. coronata f.sp. avenae. Induction occurred on seedlings only in the presence of a virulent culture of P. coronata avenae and was not dependent on time or order of inoculation of either pathogen. This phenomenon was restricted to seedlings of lines possessing the Pg-a source of oat stem rust resistance. The specificity of induced susceptibility can be used as a valuable bioassay for screening and identifying Pg-a. Induced susceptibility occurred only at the seedling stage, and apparently provides no obstacle to the use of Pg-a as a source of stem rust resistance in oats.