Antagonism ofAthelia bombacinaandChaetomium globosumto the Apple Scab Pathogen,Venturia inaequalis

Abstract

A. bombacina and C. globosum, applied to apple leaves, decreased production of ascospores by V. inaequalis and altered leaf decomposition. In autumn, inocula of the antagonistic fungi were sprayed on detached leaves or leaf disks naturally infected with V. inaequalis. Each antagonist was applied as a suspension of fungal propagules in buffer, as a suspension of propagules in CM cellulose:malt extract:yeast extract solution (36:46:18, wt/wt), or as a suspension of colonized bran particles in buffer. Leaf disks were incubated in the laboratory at 4.degree. C and intact leaves were overwintered on the orchard floor. The fungi colonized the leaf disks and the intact leaves. On leaf disks the antagonists reduced ascospore production by 40-100% on a logarithmic scale (.apprx. 80-100% on an arithmetic scale). For the outside incubations, no ascospores were produced on the leaves treated with A. bombacina and production was decreased about 30% on a logarithmic scale (.apprx. 90% on an arithmetic scale) on leaves treated with C. globosum. Those treated with A. bombacina were about 60% softer and weighed up to 50% less than control leaves. C. globosum affected leaf decomposition variably. The nutrient accompanying the antagonists altered the extent of leaf colonization, softening, and dry weight loss, but had no influence on the effect of either antagonist on ascospore production by V. inaequalis.