THE ROLE OF COLLETOTRICHUM SPP. IN POSTHARVEST ANTHRACNOSE OF CITRUS AND SURVIVAL OF C-ACUTATUM ON FRUIT

Colletotrichum gloeosporioides causes postharvest anthracnose of citru s fruit and is a common saprobe in citrus groves, whereas C. acutatum infects flower petals and causes postbloom fruit drop (PFD). The purpo se of this study was to determine whether C. acutatum caused anthracno se, survived as quiescent infections on fruit, and represented a threa t for introduction of the PFD pathogen to disease-free areas. When Rob inson tangerine fruit were artificially inoculated with both species a nd exposed to high levels of ethylene, only fruit inoculated with C. g loeosporioides developed postharvest anthracnose. However, C. acutatum was readily reisolated from inoculation sites on asymptomatic fruit. Navel oranges harvested from groves with severe PFD the previous sprin g developed low levels of anthracnose, but only C. gloeosporioides was isolated from lesions. Valencia orange fruit harvested at bloom durin g a PFD outbreak had high surface populations of C. acutatum which dec lined rapidly during 2 to 3 weeks of storage. Quiescent infections for med on artificially inoculated and naturally exposed fruit were reduce d but not eliminated by washing, waxing, and fungicide treatment in th e packinghouse. Since C. acutatum does not produce postharvest anthrac nose, the risk of introduction of this pathogen to disease-free areas is minimal. However, if fruit were harvested during a PFD outbreak, C. acutatum might survive standard packinghouse treatment and shipment a s quiescent infections.