The Epiphytes of Theobroma Cacao in Nigeria in Relation to the Incidence of Black-Pod Disease (Phytophthora Palmivora)

Abstract

The disease known as "black-pod" caused by the fungus Phytophthora palmivora affects the fruit of cacao (Theobroma). and is known to be favored by high humidity. Therefore, knowledge of local climates is important for study and control of this disease. In nigeria, (including the Cameroons)cacao is grown under rainfall conditions which range between a minimum annual mean of 45 inches and a max. annual mean of over 300 inches. Because there are relatively few rainfall recording stations, meteorological information is lacking for large areas. A study was made of the epiphytes on cacao trees with a view to equating occurrence of epiphytes with climatic conditions. Only the bryophytes and vascular plants were found suitable for use as climatic indicators. An "epiphyte rating" system is adopted whereby an individual cacao tree is given a numerical value (between 1 and 7) based on the observation that the liverworts occur under relatively dry conditions, vascular plants require relatively wet conditions, and the mosses are intermediate in degree of dryness they will tolerate. The mean rating is obtained for 100 or more trees in a cacao farm by averaging these individual ratings. Positive and significant correlations were found for the following pairs of variables: mean epiphyte rating and rainfall; mean epiphyte rating and mean number of black-pods per tree; mean number of black-pods per tree and mean number of total (healthy plus diseased) pods per tree. Mean epiphyte rating and mean number of total pods per tree were negatively and significantly correlated.