IDENTIFICATION OF GROWTH STAGE DEPENDENT EXPRESSION OF PARTIAL RESISTANCE OF BARLEY TO POWDERY MILDEW

Genotypic differences for growth stage dependent expression of partial resistance to barley powdery mildew have been identified on the basis of two components of resistance in the glasshouse and the pattern of epidemic development in the field. Differences for infection frequency and proportion of sporulating colonies were highly significant between the 16 genotypes investigated at four stages of plant development in the glasshouse. Both resistance components were significantly correlated mutually (r = 0.73 to 0.86) and with the infection level on leaves developed at comparable growth stages in the field (r = 0.52 to 0.73). The infection level of seedlings in the glasshouse was significantly correlated with the infection level of the leaves of the first until the third node in the field (r = 0.70 to 0.73). Adult plant resistance was predominantly expressed at the uppermost leaf. A clear genotype X growth stage interaction was apparent for infection level; some genotypes showed partial resistance predominantly at the seedling stage and others predominantly at the adult plant stage.