INFECTION OF FLOWER AND VEGETATIVE TISSUES OF CITRUS BY COLLETOTRICHUM-ACUTATUM AND C-GLOEOSPORIOIDES

Colletotrichum acutatum causes postbloom fruit drop of citrus, whereas C. gloeosporioides causes postharvest anthracnose on fruit but does n ot affect healthy leaf or flower tissues. Conidia of C. acutatum germi nated and hyphae grew profusely on the surface of petals and penetrate d without forming appressoria. This species developed abundant interce llular hyphae in 48 h and produced acervuli on the petal surface in 5 days. Conidia of C. gloeosporioides germinated and grew to a limited e xtent on the surface of petals but did not penetrate tissues until pet als had become senescent. On the leaf surface, conidia of both species germinated to produce appressoria. The appressoria of C. acutatum, bu t not of C. gloeosporioides, germinated to form hyphae and conidia und er moist conditions in response to applications of flower extracts but did not form acervuli. C. acutatum produced infection pegs and quiesc ent 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-ster ilized leaves. Under laboratory conditions, C. acutatum colonized sene scent leaves and produced abundant acervuli on the surface as did C. g loeosporioides. C. acutatum appears to overwinter primarily as appress oria on living leaves rather than in colonized dead tissues like C. gl oeosporioides.