Selection of cocoa clones for resistance to Phytophthora palmivora by artificial inoculation and natural infection in the field

The objective of this study was to compare the resistance of 73 cacao clones against Phytophthora palmivora by inoculating leaf disks with a zoospore suspension (3 × 105 zoospores/mL) mixture from seven isolates or by placing paper filter disks immersed in the zoospore suspension mixture, at two points on detached pods. Existing data from CEPEC/CEPLAC Germplasm Bank on clone natural infection under field conditions was correlated to artificial inoculation results. The in vitro assays were duplicated (A1 and A2) for leaf disks (8 replicates of 5 disks each/block/clone), and for pods with a variable number of replicates per clone. Data were transformed to disease severity index (ID) and lesion area (A). Results showed that all the evaluated clones were effectively infected by the pathogen in all tests, and mean ID and A values varied significantly. Although significant correlations were observed between A1 and detached pod infection, and between A2 and field natural infection, the latter showed the highest correlation coefficient.