School of Agriculture, Food and Ecosystem Sciences - Theses

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Studies on brown rot of stone fruits, with particular reference to the causal fungi, dispersal and longevity of conidia

Jenkins, Peter Thomas ( 1970)

Brown rot of stone fruits was studied with particular reference to causal fungi, and dispersal and longevity of conidia. Surveys showed that brown rot was caused by Sclerotinia fructicola, throughout Victoria, and also by Sclerotinia laxa in Southern Victoria. In studies with S. fructicola, conidia, but not ascospores, were inoculum for new infections. Dispersal of conidia was studied in detail. In the field, large numbers were dispersed by rain falling on to sporulating blossoms, but only little aerial dispersal was detected. In laboratory experiments, both water splash and aerial dispersal was demonstrated, aerial dispersal being greatest at minimum humidities and maximum temperatures. Longevity of conidia was studied in an orchard environment. Viability and virulence was reduced by exposure within tree canopies, and on unsterilized soil; and was further reduced by prior wetting. A species of Bacillus antagonistic to S. fructicola in plate cultures and on surfaces of mature fruits was associated with exposed conidia. Cell free filtrates of Bacillus cultures prevented germination of conidia, or caused germ tube abberations. A technique was developed to isolate airborne bacteria antagonistic to S. fructicola. The mode of dispersal, longevity and virulence of conidia are discussed in relation to spore load and infection.