Development of a bioassay to test the effect of phosphorous acid on black pod of cocoa

A bioassay is described to test the extent and persistence of systemic protection of cocoa against black pod rot, caused by Phytophthora palmivora , by trunk injection and foliar spray of phosphorous acid. Lesions on inoculated pods from treated trees were between 62 and 93% smaller than those on pods from untreated trees. Lesion size and sporulation was reduced by both trunk injection and foliar spray treatments. The results show that the bioassay is a suitable technique, and suggest that, particularly when used as a trunk injection, phosphorous acid, could provide effective, persistent, low-cost control of the disease.