This study examined extracellular enzyme production by Phytophthora palmivora, a fungal pathogen causing rot in tropical and subtropical plants, particularly cacao blackpod disease. The researcher tested nine different P. palmivora isolates across thirteen defined media and five natural plant extract media, assaying for thirteen enzymes implicated in plant pathogenesis. All media supported adequate fungal growth, but enzyme production was more nutritionally demanding than growth itself. The major enzymes detected were endopolygalacturonase, maceration factor, α-L-arabinofuranosidase, and phenolase, primarily in defined media rather than natural extracts. In natural plant extracts, enzyme activity was largely absent except for α-L-arabinofuranosidase and phenolase, likely due to inhibition by oxidized phenolic compounds that accumulated during culture. The optimal medium for both growth and enzyme production consisted of pectin, glucose, asparagine, magnesium sulfate, yeast extract, and thiamine. This work demonstrates that different nutritional factors distinctly influence fungal growth versus enzyme secretion, suggesting previous failures to detect pathogenic enzymes resulted from unsuitable culture media rather than enzyme absence.

Key findings

• Phytophthora palmivora requires more specific nutritional conditions for extracellular enzyme production than for growth alone.
• The major detectable enzymes were endopolygalacturonase, maceration factor, α-L-arabinofuranosidase, and phenolase, detected primarily in defined media but absent from most natural plant extracts.
• Oxidized phenolic compounds in natural plant extracts inhibit pectic enzyme activity, explaining their absence from diseased tissues.
• The optimal medium for enzyme production contained pectin, glucose, asparagine, magnesium sulfate, yeast extract, and thiamine.
• Enzyme production was independent of both fungal growth yield and culture medium pH value.