VARIATION IN ADULT-PLANT RESISTANCE TO POWDERY MILDEW IN SPRING OATS UNDER FIELD AND LABORATORY CONDITIONS

Ten oat genotypes were assessed for adult plant resistance (APR) to powdery mildew (Erysiphe graminis f.sp. avenae) in small field plots and on detached leaf segments in the laboratory using glasshouse-grown plants. Significant genotype differences were observed in the held and on leaf segments for latent period, infection frequency and spare production, components used to assess APR. The genotype OM1711, which was selected because it expressed a higher level of mildew resistance than its most resistant parent, cv. Maldwyn, showed this transgressive resistance in both field and laboratory tests. By contrast, the genotype OM1387, also selected for high mildew resistance, only showed this enhancement in the held. It is concluded that quantitative assessment of mildew in detached leaves is not sufficiently precise to be used alone in selecting segregants for high levels of APR, and that field data are also needed.