PRANGOLARIN IS A CHEMICAL FACILITATOR FOR THE ENHANCED DEVELOPMENT OF THE INFECTION PROCESS IN THE EPICARP OF CITRUS-LIMON BY PENICILLIUM-DIGITATUM

The application of a water suspension of conidia of Penicillium digitatum caused complete ''green mold'' symptoms to develop on 65% of wounded lemon (Citrus limon) epicarps after 4 days. However, wounded lemon epicarps, exhaustively washed with water, exhibited only 2% green mold symptoms when inoculated with spores of P. digitatum. However, when a comparable amount of isolated lemon epicarp oil was topically applied to the washed wounds, 92% of the inoculated wound sites developed green mold symptoms. These observations indicated that some component of the lemon epicarp oil is essential for the development of P. digitatum in epicarp tissues and suggest that the fungal facilitating factor(s) could be present in the lemon epicarp oil. One of promoting factors from the oil was isolated by bioassay-guided fractionation and was identified as prangolarin (1) by spectrometric analyses. Prangolarin, by itself, enhanced disease development by P. digitatum on the wounded epicarp of lemon.