MORPHOLOGICAL AND PATHOLOGICAL CHARACTERISTICS OF STRAINS OF COLLETOTRICHUM-GLOEOSPORIOIDES FROM CITRUS

Three strains of Colletotrichum gloeosporioides from citrus in Florida are described and characterized as fast-growing gray isolates from necrotic and senescent tissue (FGG), slow-growing orange isolates (SGO) associated with citrus postbloom fruit drop disease, and slow-growing isolates with deep orange pigmentation from Key limes affected by lime anthracnose (KLA) (formerly classified as Gloeosporium limetticola). All FGG isolates had large conidia most with both apices rounded, produced abundant setae, and had large lobulate appressoria. SGO and KLA isolates had smaller conidia, most with one fusiform apex, and rarely produced setae. The SGO isolates produced clavate, deeply pigmented appressoria, whereas the KLA isolates produced round, smaller, less pigmented appressoria. All strains had optimum temperatures for growth of 23-27 C, but FGG isolates grew better at 31 C than SGO or KLA isolates. The FGG isolates grew two to three timcs as rapidly as SGO isolates, and SGO isolates grew slightly faster than KLA isolates at most temperatures. The SGO strain, previously associated with postbloom fruit drop, reproduced all symptoms of the disease on sweet orange and Persian lime and was re-isolated from blighted blossoms. The KLA strain, previously associated exclusively with lime anthracnose, also reproduced all symptoms of postbloom fruit drop. The KLA strain produced typical lime anthracnose symptoms on Key lime, but SGO isolates produced only a mild mottle of Key lime leaves. The FGG isolates were not pathogenic to flowers of sweet orange or Persian lime or to foliage of Key lime. The postbloom times in Florida in 1983 may have originated from Key lime affected by lime anthracnose rather than from a foreign introduction.