Some epidemiological investigations on Colletotrichum leaf disease on rubber tree

The inoculum of some species of the genus Colletotrichum, responsible for the secondary leaf fall of rubber tree (SLF), is present as conidia on all the organs of the tree. On young lesions, the fungus produces acervuli, but on old lesions kept in prolonged wetness, conidia are produced without acervuli. Acervuli occur frequently on senescent tissues, especially on the epidermis of the fruits, which are infected in the early stages of their development. The fungus can spread from diseased organs to healthy organs and sporulate on them. Conidial production and pathogenicity differ greatly according to the organ of the rubber tree from which the fungus is isolated. The higher the leaf wetness duration and the inoculum concentration are, the greater are fungal sporulation and damage. Although heavy rains and high winds favour conidial dispersal, it can also occur in drizzle. Heavy dew is sufficient to ensure downward dispersal of the conidia. The epidemiological pattern of the disease in a rubber tree plot during 1.5 years agrees with all these observations. The results of these investigations will enable the control of the disease to be improved in the rubber estate of Mitzic (Gabon).