The effect of sowing date on adult plant resistance to Erysiphe graminis f.sp. avenae in oats

SUMMARY A technique developed for detecting small differences in mildew infection under glasshouse/laboratory conditions is described. A satisfactory correlation was found between results obtained by this method and infections in the field. Detailed examination of the levels of infection in cultivars Maldwyn and Milford showed that the upper and more recently developed leaves of Maldwyn had a significantly smaller area infected than those of Milford, although seedling leaves of both genotypes were very susceptible. This was most marked when plants were in the 6‐ to 7‐leaf stage. Comparison of host plants sown on successive dates during the spring and early summer showed that with the acceleration of the rate of growth occurring in later‐sown plants, resistance was expressed progressively earlier in the life of the plant. Newly expanded leaves which show very low level of infection at the 6‐ to 7‐leaf stage become susceptible as they age, resistance being then expressed in the younger leaves.