Infection of flower and vegetative tissues of citrus by Colletotrichum acutatum and C. gloeosporioides

Abstract

Colletotrichum acutatum causes postbloom fruit drop of citrus, whereas C. gloeosporioides causes postharvest anthracnose on fruit but does not affect healthy leaf or flower tissues. Conidia of C. acutatum germinated and hyphae grew profusely on the surface of petals and penetrated without forming appressoria. This species developed abundant intercellular hyphae in 48 h and produced acervuli on the petal surface in 5 days. Conidia of C. gloeosporioides germinated and grew to a limited extent on the surface of petals but did not penetrate tissues until petals had become senescent. On the leaf surface, conidia of both species germinated to produce appressoria. The appressoria of C. acutatum, but not of C. gloeosporioides, germinated to form hyphae and conidia under moist conditions in response to applications of flower extracts but did not form acervuli. C. acutatum produced infection pegs and quiescent infections on leaves as did C. gloeosporioides as indicated by the presence of openings at the point of contact of the appressoria with the leaf surface, and by reisolation of both strains from surface-sterilized leaves. Under laboratory conditions, C. acutatum colonized senescent leaves and produced abundant acervuli on the surface as did C. gloeosporioides. C. acutatum appears to overwinter primarily as appressoria on living leaves rather than in colonized dead tissues like C. gloeosporioides.

Key Words:

• appressoria
• Key lime anthracnose
• postbloom fruit drop
• postharvest anthracnose
• quiescent infections