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Antagonism of Athelia bombacina and Chaetomium globosum to the Apple Scab Pathogen, Venturia inaequalis. Christian C. Heye, Department of Plant Pathology, University of Wisconsin, Madison 53706, Present address of senior author: Ciba-Geigy, Ltd., Basel, Switzerland; John H. Andrews, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 73:650-654. Accepted for publication 1 November 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-650.

Athelia bombacina and Chaetomium globosum, applied to apple leaves, decreased production of ascospores by Venturia 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 carboxymethylcellulose:malt extract:yeast extract solution (36:46:18, w/w), or as a suspension of colonized bran particles in buffer. Leaf disks were incubated in the laboratory at 4 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 (~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 (~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.

Additional keywords: biological control, eradication, Malus pumila, Spilocaea pomi.