Measuring the Cost of Resistance to Puccinia coronata CDA in Avena fatua L.

Abstract

(1) Fifteen separate lines of Avena fatua L. resistant or susceptible to infection by the fungal pathogen Puccinia coronata Cda were compared in glasshouse and field plot experiments. These lines were selected from a natural population growing at Canberra in south-eastern Australia. (2) The germination behaviours of the resistant and susceptible genotypes of A. fatua were found to differ with respect to temperature. Susceptible genotypes showed no difference in the rate of germination at 15, 20 or 25.degree.C. Resistant lines, however, were similar in response to susceptible lines at 15.degree.C but were progressively slower to germinate at 20 and 25.degree.C. (3) The relative fecundity of resistant and susceptible genotyes of A. fatua, growing in mixtures in a disease-free environment, varied with temperature. When grown in mixtures at high temperatures in the glasshouse, susceptible genotypes performed consistently better than resistant genotypes. At low temperatures in the field the reverse was true. (4) Because of apparently chance correlations between resistance to P. coronata and late germination in these lines of A. fatua it was not possible to draw any conclusion about the cost of resistance. It was not possible to separate the effects, if any, of specific resistance alleles from the correlated structure of the entire genome of this highly inbreeding species.