Effects of growth medium, incubation temperature, and mycelium age on production of five major fatty acids by six species of Phytophthora

Abstract

The effects of growth medium, incubation temperature, and mycelium age on the production of five major fatty acids by five isolates each of P. cactorum, P. citricola, P. citrophthora, P. cinnamomi, P. cryptogea, and P. nicotianae were investigated. Fatty acids were extracted from mycelia, and fatty acid methyl ester (FAME) profiles were analyzed by gas chromatography. Fifteen fatty acids were common in all species, but five of them comprised more than 75% of FAME profiles. These five fatty acids – myristic (14:0), palmitic (16:0), linoleic (18:2ω6c), oleic (18:1 ω9c), and eicosapentaenoic (20:5ω3c) acids – were used to investigate the effects of five liquid growth media (20% carrot broth, CB; 10% lima bean broth, LBB; 5% clarified V8 juice broth, V8B; ¼-strength potato dextrose broth, PDB; and ¼-strength Sabourand dextrose broth; SDB), six incubation temperatures (10, 15, 20, 25, 30, and 35°C), and four mycelium ages (4, 8, 12, and 16 days) on fatty acid production. The effect of medium on the relative percentages of five major fatty acids produced by the six species of Phytophthora was highly significant (P < 0.001). The effect of temperature on production of myristic acid was inconsistent and species-dependent. The production of palmitic and linoleic acids were promoted by higher temperature ( ≧ 25°C), whereas the production of oleic acid and eicosapentaenoic acid was promoted by lower temperatures (≦ 20°C). Palmitic acid production was greater in younger mycelia (four and eight days old), and oleic acid was greater in older mycelia (12 and 16 days). Effects of age on the production of linoleic and eicosapentaenoic acids were inconsistent among species.