Chaetomium globosum antagonizes the apple scab pathogen, Venturia inaequalis, under field conditions

Abstract
During the 1981 and 1982 growing seasons, Aureobasidium pullulans (de Bary) Arnaud and Chaetomium globosum Kunze: Fr. spore suspensions were applied to apple saplings in an orchard at 1- to 2-week intervals to control the apple scab pathogen, Venturia inaequalis (Cke.) Wint. (anamorph, Spilocaea pomi Fr.). Population densities of applied antagonists were monitored during 1982 trials by dilution plating of leaf washings onto selective media. Aureobasidium pullulans and C. globosum populations averaged 54 and 314 colony-forming units (CFU) per milligram of leaf tissue 3 h after application and declined to means of 15.9 and 35.7 CFU mg−1, respectively, before the next application. Relative to buffer controls, spore suspensions of A. pullulans were only slightly antagonistic to V. inaequalis infection, but C. globosum ascospore suspensions reduced scab more than 20% in both years. Light and scanning electron microscope examination of leaf surfaces following inoculation of seedlings in growth chambers showed a 25% increase in C. globosum ascospore germination on scab-infected tissue relative to healthy tissue. The minimum concentration of C. globosum inocula effectively reducing apple scab in growth chamber experiments was approximately 1 × 106 ascospores mL−1.

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