CACAO RESISTANCE TO PHYTOPHTHORA - EFFECT OF PATHOGEN SPECIES, INOCULATION DEPTHS AND POD MATURITY

Two species of Phytophthora (P. palmivora and P. capsici) and inoculat ions at two depths (3 mm and 9 mm) were tested each on 10 clones of Th eobroma cacao to determine their effects on pod resistance. Ripe and u nripe pods were also assessed to determine the influence of physiologi cal status of the pod on the expression of resistance. The two pathoge ns tested (P. palmivora and Ti capsici) differed significantly in thei r reactions on pods, with P. palmivora being more aggressive than P. c apsici. However, the lack of interaction between clones and pathogen s pecies and the similarity in the ranking of clones based on lesion siz e suggested that selection for resistant clones can be based on one of the two pathogens, preferably the more aggressive one. Pod reactions differed between inoculation depths (3 mm and 9 mm), and between pod m aturity stages (ripe and unripe pods) with relatively larger lesions b eing recorded at 9 mm depth and on unripe pods as compared to those ob served at 3 mm depth and on unripe pods, respectively. The magnitude o f increase in lesion sizes, however, varied with genotypes, indicating that inoculation depth and pod maturity stage should be standardized in screening cacao germplasm for resistance to Phytophthora.