Biology of Colletotrichum gloeosporioides Isolates From Tropical Pasture Legumes.

Abstract

The relationships between isolates of Colletotrichum gloeosporioides from Stylosanthes guianensis (an anamorphic and a teleomorphic isolate), Aeschynomene falcata and Centrosema pubescens were investi- gated by comparing their morphology, temperature relations, symptomatology and pathogenicity. The Stylosanthes and Aeschynomene isolates caused more severe symptoms on the host from which they were isolated than on the other hosts. The Centrosema isolate caused moderate infection on Stylosanthes and mild infection on Centrosema. The anamorphic isolate from Stylosanthes produced leaf blight while the other isolates produced localised necrotic lesions. Conidia of the Centrosema isolate and the teleomorphic isolate from Stylosanthes were relatively uniform in size and shape and rounded at both ends. Both isolates produced fertile perithecia. Conidia of the Aeschynomene isolate and the anamorphic Stylosanthes isolate were more variable in shape and usually tapered at one end. The optimum temperature for mycelial growth of the anamorphic Stylosanthes isolate and the Aeschynomene isolate was 25°C, and for growth of the teleomorphic Stylosanthes isolate and the Centrosema isolate 27-29°C.

Infection by the anamorphic and the teleomorphic Stylosanthes isolates proceeded in a similar fashion. Germinated spores and unmelanised appressoria were first observed at 6 h, melanised appressoria at 12 h and multiple appressoria and penetration at 24 h after inoculation. The anamorphic isolate produced significantly more successful penetrations than the teleomorphic isolate.