POSSIBLE ROLE OF FUNGI IN NEGATIVELY AFFECTING FRUIT-SET IN AVOCADOS

Poor fruit set continues to be a major problem in the avocado industry in South Africa. In the past this was estimated to have caused a loss of income of millions of rands. In this investigation the role of fungi on the pistils of avocado cultivars after pollination was examined. Pollinated pistils of avocado cultivars 'Pinkerton', 'Ryan', 'Hass', 'Fuerte' and 'Nabal' were removed twenty-four hours after the first anthesis (female stage), for detection and isolation of fungi. Germinating conidia were seen on the surface of stigma adjacent to the germinated pollen grains. A number of dematiaceous fungi were isolated from the pistils and the most important species were identified. When a drop of the spore suspension of the most frequently isolated fungi was inoculated on the stigmas of emasculated flowers after hand pollination, a high rate of abscission was observed. Thus some of these fungi appear to have played a significant role which resulted in greater abscission of flowers.