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Ecology and Epidemiology

Role of Mycosphaerella Ascospores in Stem-End Rot of Papaya Fruit. K. F. Chau, Student, Department of Plant Pathology, University of Hawaii, Honolulu, HI 96822; A. M. Alvarez, assistant plant pathologist, Department of Plant Pathology, University of Hawaii, Honolulu, HI 96822. Phytopathology 69:500-503. Accepted for publication 20 November 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-500.

A stem-end disease of papaya was caused by Mycosphaerella sp., the perfect stage of Ascochyta caricae-papayae. Perithecia were abundant on necrotic papaya leaves and petioles in the orchard. Ascospores germinated and grew on latex that exuded from stems when fruit was harvested and thereby entered the exposed vascular tissue. The pathogen also invaded the fruit through natural wounds at the stem end. Ascospore release followed a diurnal cycle during rainless periods. Numbers of ascospores in the air rose abruptly within 1 hr after 100% RH was reached, peaked in 24 hr (0300-0500 hours) and dropped abruptly. Ascospore numbers were consistently higher during periods of frequent, intermittent showers than during dry periods. Fruits showed initial symptoms in 34 days and extensive blackening by 7 days after inoculation. If hot water treatment (48 C for 20 min) was applied within 40 hr of inoculation, no symptoms developed.

Additional keywords: Ascochyta caricae, epidemiology.