Distribution of polygalacturonase, total phenolic substances, polyphenol oxidase and peroxidase in rot zones in sweet potato

Botryodiplodia theobromae causes a spreading rot of sweet potato, while Botrytis cinerea, Phoma exigua var. foveata and Fusarium solani var. coeruleum cause rots of limited extent. Cladosporium cucumerinum does not rot sweet potato tuber tissue. Whichever of these fungi is inoculated into tubers, a zone at the margin of the lesion can be clearly distinguished, from slightly affected but uninfected tissue on one side and infected rotted tissue on the other, by its high content of phenolic substances and polyphenol oxidase and peroxidase activities. Polygalacturonase is present in this zone for spreading B. theobromae lesions but not for the limited lesions caused by the other fungi. Total content of phenolic substances is generally greater in and around limited lesions.