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The Role of Colletotrichum spp. in Postharvest Anthracnose of Citrus and Survival of C. acutatum on Fruit

Colletotrichum gloeosporioides causes postharvest anthracnose of citrus fruit and is a common saprobe in citrus groves, whereas C. acutatum infects flower petals and causes postbloom fruit drop (PFD). The purpose of this study was to determine whether C. acutatum caused anthracnose, survived as quiescent infections on fruit, and represented a threat for introduction of the PFD pathogen to disease-free areas. When Robinson tangerine fruit were artificially inoculated with both species and exposed to high levels of ethylene, only fruit inoculated with C. gloeosporioides 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 spring developed low levels of anthracnose, but only C. gloeosporioi-des was isolated from lesions. Valencia orange fruit harvested at bloom during a PFD outbreak had high surface populations of C. acutatum which declined rapidly during 2 to 3 weeks of storage. Quiescent infections formed on artificially inoculated and naturally exposed fruit were reduced but not eliminated by washing, waxing, and fungicide treatment in the packinghouse. Since C. acutatum does not produce postharvest anthracnose, 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 as quiescent infections.