Evidence for antibiosis and induced host defense reactions in the interaction between Verticillium lecanii and Penicillium digitatum, the causal agent of green mold

Chronological events of the intercellular interaction between Verticillium lecanii and the postharvest pathogen Penicillium digitatum were investigate d by transmission electron microscopy and gold cytochemistry. Growth inhibi tion of P. oligandrum as a response to V. lecanii attack correlated with st riking host changes including retraction of the plasma membrane and cytopla sm disorganization. Such changes were associated with the deposition on the inner host cell surface of a chitin- and cellulose-enriched material which appeared to be laid down as a structural defense reaction. The accumulatio n of chitin in the newly formed material correlated with a decrease in the amount of wallbound chitin. However, the deposition of cellulase appeared t o correspond to a de novo synthesis, as evidenced by the occurrence of cell ulose-containing vesicles which released their content in the space between the invaginated plasma membrane and the host cell wall. Results of the pre sent study provide the first ultrastructural and cytochemical evidence that antagonism, triggered by V. lecanii, is a multifaceted process in which an tibiosis, with alteration of the host hyphae prior to contact with the anta gonist, appears to be the key process in the antagonism against P. digitatu m.