Leaf scorch (Kabatiella caulivora (Kirch.) Kirk.) of subterranean clover (Trifolium subterraneum L.): Influence of host cultivar,growth stage and pathogen isolates on the disease severity

Summary Interaction of six isolates of Kabatiella caulivora (545, 547, 2212, BNL, BDG and KLN) collected from different geographical regions of Western Australia and Victoria with six cultivars (Clare, Daliak, Enfield, Guildford D, Karridale and Woogenellup) of subterranean clover was studied at seedling (2-week old) and adult-plant (12-week old) stages. Seedling response measured as percentage of diseased plants showed cultivar Daliak to be immune to all isolates, while the remaining cultivar x isolate combinations showed differing degrees of susceptibility.The adult-plant response, measured as percentage of petioles affected per plant, showed that all the cultivars were susceptible to varying degrees to all the isolates, with Daliak being the most resistant cultivar.Analysis of variance of both seedling and adult-plant resistance showed significant (P<0.05) effects due to cultivars, isolates and their interaction. The magnitude of variance due to the isolates was substantially reduced when measured as adult-plant response. Leaf scorch severity was clearly influenced by cultivar and its developmental stage, and by isolate of the pathogen.