Relationships between the severity of leaf blotch (Rhynchosporium secalis) and the water-soluble carbohydrate and nitrogen contents of barley plants

Water-soluble carbohydrate (WSC) and total nitrogen (N) contents of leaves of field-grown barley plants were measured in 1966 and 1967. Consistent differences were found between cultivars. The susceptibility of cultivars to leaf blotch was correlated negatively with WSC content and positively with N content at G.S. 10.4. Application of nitrogen fertiliser (which increased N and decreased WSC) also increased the severity of leaf blotch. The occurrence of primary lesions on seedlings does not seem to be affected by their WSC and N contents and the relation between WSC and N contents of leaves and severity of leaf blotch possibly depends on differences in growth and sporulation of the pathogen on substrates containing different amounts of carbohydrate and nitrogen.