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

Authors: Puig, Alina; ALI, SHAHIN - Non ARS Employee; Strem, Mary; Sicher Jr, Richard; Gutierrez, Osman; Bailey, Bryan

Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2017
Publication Date: 4/1/2018
Citation: Puig, A.S., Ali, S., Strem, M.D., Sicher Jr, R.C., Gutierrez, O.A., Bailey, B.A. 2018. The differential influence of temperature on Phytophthora megakarya and Phytophthora palmivora pod lesion expansion, mycelia growth, gene expression, and metabolite profiles. Physiological and Molecular Plant Pathology. 102:95-112.

Interpretive Summary: The oomycetes Phytophthora megakarya and Phytophthora palmivora cause black pod rot on cacao and severely reduce yields. P. megakarya is the most aggressive species causing black pod rot and occurs in the major cacao growing countries of Africa. It is unclear why P. megakarya is so aggressive on cacao since it does not tolerate the high temperatures which sometimes occur in cacao production areas. Studies were carried out dissecting the responses of P. megakarya and P. palmivora to temperature stress. Although both species suffer cold stress at similar temperatures, P. megakarya cannot survive long at 32ºC while P. palmivora survives extended periods of time at 34°C. This difference in temperature tolerance is sufficient to distinguish P. megakarya from any other species causing black pod rot on cacao. The 2 species use similar molecular mechanisms in responding to heat stress but employ them at different temperatures (P. megakarya at lower temperatures then P. palmivora). P. palmivora also appears to carry high concentrations of some amino acids and sugars which may contribute to its high temperature tolerance. Phytophthora species cause severe diseases on many crops in addition to cacao and scientists working with any Phytophthora species can use these results to form a basis for designing experiments concerning temperature stress in their species. In addition, the simple low tech means of identifying P. megakarya we discuss could be of benefit to those seeking to manage black pod rot in Africa.

Technical Abstract: Phytophthora megakarya and Phytophthora palmivora cause cacao 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°C) than P. megakarya (30°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°C while P. palmivora survived 3 days at 34°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°C and 11°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 eliminate P. megakarya although Phytophthora induced disease epidemiology may be influenced.