A NOVEL METHOD FOR THE CONTROL OF POD DISEASES OF COCOA

Pod diseases of cocoa are widespread in cocoa-growing countries and are responsible for substantial losses in income. Black pod, Moniliophthora pod rot, Witches' broom and Watery pod rot are the major diseases of cocoa pods. The conventional methods of fungicide application by spraying an aqueous suspension using diverse equipment so far yielded only limited control. The drawback of these methods seem to be the inability of the system to release adequate quantities of the chemical during the prolonged rainy spells which are frequent in the tropics. The need for the development of an alternative method for the control of pod diseases was recognized. A new method is being developed at the Cocoa Research Unit, Trinidad. Copper fungicides were placed in a collar-like device and attached to the top of the main trunk or branches of cocoa trees. The water flow from rains passes through the collar permitting a slow release of the fungicide during rainy periods. This guarantees the availability of fungicide in sufficient concentration to prevent pod infection during the prolonged rainy spells. Preliminary studies on Black Pod disease have shown very significant reduction in pod losses when collars with log or 5g a.i. were used

Sustaining cocoa production through genetic resistance to back pod and leaf blight

The resistance of cocoa to Phytophthora palmivora and its mechanism(s) were investigated in leaves and pods of twelve clones. Anatomical and morphological characteristics including ; cuticle thickness, stomata! frequency and pore length were assessed on leaf and correlated with foliar resistance at penetration stage. Post-penetration resistance was also determined on leaf and pod, and their relationship assessed. Results show a significant difference in leaf susceptibility between surfaces. The adaxial surface appeared less susceptible possibly due to lack of stomata and/or the presence of a thick cuticle. Leaf susceptibility differed significantly at penetration and postpenetration stages suggesting different mechanisms. Correlation analysis shows a strong relationship between the joint effect of cuticle thickness, stomata! frequency, stomata! size and leaf resistance at penetration stage. A close relationship in the rate of spread of lesion in leaf and pod indicates that a reliable assessment of clonal reaction can be based on leaf observation. The results suggest that there are two mechanisms of resistance; one at th,e point of penetration and the other at post-penetration stage. The resistance mechanism(s) at postpenetration stage seems to be common for both leaf and pod, and possibly controlled by biochemical factor(s). This suggest that pod resistance to P.palmivora can be reliably assessed at the seedling stage using leaf resistance to spread as an indicator. Both pathological and genetic implications of these findings are discussed for the improvement of cocoa resistance to P.palmivora infections