Pathology and breeding for resistance to black pod in Côte d'Ivoire
Resistance to black pod is becoming an increasingly important selection criterion in Côte d'Ivoire. Early pathology research had shown presence of phytoalexins in #Theobroma# spp. but not in #T. cacao#. No interaction between #Phytophthora palmivora# isolates and clone resistance was identified. Seasonal variation in pod resistance was observed, which appeared to be related to variations in humidity and/or light intensity. Recent results have shown significant variation for field resistance in hybrid and clone trials. Heritibility at single tree level was relatively high after many years of observation under uniform growing conditions. Genetic markers (QTL's) for field resistance were identified in one progeny, explaining 20 to 38% of total variation. Field level of attack appeared also to be affected by pod load and period of pod production (escape). Early screening tests applied to 9 clones showed good correlation among leaf, twig and root inoculations and between these methods and general combining ability for field resistance. The use of leaf inoculations will be routinely introduced in the recurrent selection breeding programme initiated in the early 1990's.