MORPHOLOGY AND CULTURAL VARIATION AMONG <em>COLLETOTRICHUM</em> ISOLATES OBTAINED FROM TROPICAL FOREST NURSERIES
Keywords:Colletotrichum gloeosporioides, cultural variation, morphology, taxonomy, forest tree, tropical forest
Surveys of forest nurseries in Malaysia have shown that Colletotrichum is one of the major fungi associated with seedling diseases. Morphological and cultural characteristics of 12 Colletotrichum isolates from several forest nurseries in Peninsular Malaysia and an isolate from Guatemala were compared. Results from the preliminary morphological studies suggest that most of the isolates produced ovoid/straight conidia with rounded apices typical of C. gloeosporioides. The exception was isolate 689 (ex Gliricidia sepium, from Guatemala) which produced ovoid conidia with pointed apices. Morphological
analysis of the other isolates illustrated that most of them showed variation in their conidial size, appressorial shape and size, suggesting the existence of different forms of C. gloeosporioides. The results also revealed distinct appressorial shapes. Some produced globose appressoria, whilst in others appressoria were lobed. These features were reliable and reproducible characteristics. All isolates became septate on germination, suggesting that none of them are members of the C. orbiculare group. Other criteria such as culture characteristics, the presence and dimensions of setae, colour of conidial mass, growth rate and number of conidia nuclei were either too variable or too similar to make them useful taxonomic criteria. In addition to culture characteristic studies, lectin cytochemistry study, which was also conducted but not reported in this paper, was found to be not significant in distinguishing the forest tree isolates. From this study it was found that morphological study alone has many limitations in trying to distinguish species of Colletotrichum.