Studies on asexual variation in the virulence of oat crown rust, Puccinia coronata f. sp. avenae, and wheat leaf rust, Puccinia recondita

Abstract

This study was conducted to determine the nature and extent of variation in cereal leaf rusts. Two different races of oat crown rust, Puccinia coronata f. sp. avenae, were recovered from a mixture of single-spored cultures of races 228 and 393. A further subculturing yielded nine non-parental virulence combinations, which could have resulted from somatic recombination.Single-spore isolates of race 228, avirulent on the oat variety Saia were increased, and screened on Saia. Eighty-seven susceptible infections were obtained from a total of nearly 40 000 infections. This variation could result from a high mutation rate.A unique form of variation was observed when Saia-virulent isolates of race 229 were subcultured. Approximately half the subcultures were virulent and half were avirulent on Saia. Further isolations from the avirulent subcultures were all avirulent. Serial propagation of race 229 continued to give cultures virulent and avirulent on Saia. A stable culture of race 229 virulent on Saia was not obtained. Cytological examination of this race 229 culture showed that most of the spores were dikaryotic. Aneuploidy or cytoplasmic inheritance might account for this variability on Saia.Uredial isolates of wheat leaf rust, Puccinia recondita, differing in virulence and color were also studied for the possible occurrence of recombinants. No recombinants were found in six mixtures, each consisting of two different uredial isolates.