Abstract
Phytophthora capsici caused a soft rot of cucumber fruits and produced a number of pectic enzymes in the macerated tissues. Both cell-free extracts of macerated tissues and fungus culture fluids effectively macerated potato tuber and cucumber fruit sections at pH optima of 6.2 and 7.0, respectively.
P. capsici produced two enzymes in culture which preferentially degraded pectic acid (pH optima of 5.0 and 6.2) and four which attacked pectin (pH optima of 3.5, 5.5, 6.5, and above 7.0). The activity for pectin above pH7 appeared due endo-pectin methyl-trans-eliminase (endo-PMTE) bassed on the thio-barbituric acid test. The culture filtrates also contained one exo-type activity for pectic acid with a pH optimum at 5.5, but almost no pectin methylesterase and cellulase (Cx) activities. The extracts from infected cucumber fruit, however, showed only one endo-pectolytic activity for pectic acid with a pH optimum at 6.2 and two endo-type activities for pectin with pH optima at 6.5 and above 7.0. The latter activity appeared due to endo-PMTE activity. The data show that P. capsici produces an endo-polygalacturonase and an endo-PMTE which could be responsible for soft rot development in rot development in cucumber fruit.
