The differential influence of temperature on Phytophthora megakarya and Phytophthora palmivora pod lesion expansion, mycelia growth, gene expression, and metabolite profiles

Phytophthora megakarya and Phytophthora palmivora cause black pod rot of cacao. P. megakarya occurs in Africa while P. palmivora is distributed world-wide. P. palmivora has a higher temperature maximum (34 degrees C) than P. megakarya (30 degrees C). Factors contributing to temperature maxima in Phytophthora species have not been studied in detail. In culture, P. megakarya lost viability after 3 days at 32 degrees C while P. palmivora viability began decreasing after 3 days at 36 degrees C. When exposed to heat, genes encoding heat shock proteins and chaperones were most commonly induced in both species. Heat responsive genes in P. palmivora also tended to be induced at low temperatures (9 degrees C and 11 degrees C). In general, P. palmivora maintained higher metabolite pools than P. megakarya, although some temperature induced differences were recorded. When recovering from heat stress, P. megakarya produced a coralloid form of mycelia not previously observed in any Phytophthora species. P. megakarya's temperature range mimics the cacao production conditions in Africa and elevated seasonal field temperatures there are unlikely to persist long enough to eliminate P. megakarya although Phytophthora induced disease epidemiology may be influenced. Published by Elsevier Ltd.