Partial resistance of barley to leaf rust,Puccinia hordei. V. Analysis of the components of partial resistance in eight barley cultivars

Summary Eight spring barley cultivars, respresenting the known range in partial or slow rusting resistance to leaf rust, Puccinia hordei, were investigated for their effects on the components of partial resistance; infection frequency, latent period, infectious period and spore production per uredosorus per day. Considerable variation was observed among the cultivars for each of the components. The cultivar effects on the components tend to be associated. Cultivar L94 for instance, shows the highest infection frequency, the shortest latent period and a long infectious period. Julia and Vada both have a low infection frequency, a long latent period and a low spore production per sorus per day. This association, though, is only a partial one.The total spore production per unit leaf area (the combined result of the four components) appeared highly correlated with the partial resistance in the field (r=0.85). Only a relatively small portion of the variation in partial resistance cannot be explained by the four components studied. Several other aspects, which might affect the rate of epidemic development, are discussed.Latent period, measuring the onset of the new spore production, estimated partial resistance as well as total spore production did (r=–0.85). In order to evaluate the partial resistance of barley genotypes in the greenhouse the latent period is preferred above total spore production as it is measured more easily, more accurately and sooner after inoculation.