Studies on Antagonistic Effects of Trichoderma Isolates Against Phytophthora cactorum

Abstract

AbstractBioassays were used to demonstrate the antibiotic effect of Trichoderma isolates on P. cactorum. When both fungi were grown on benomyl‐containing PDA medium, the mycelial growth of Trichoderma was suppressed. However, the production of antibiotics by this fungus remained active, leading to inhibition of the mycelial growth of P. cactorum. The antibiotic effect of Trichoderma on zoospores and cysts was tested on a PDA substrate precultured with Trichoderma on cellophane sheets. On the substrate of some Trichoderma isolates, lysis of zoospores, formation of extracellular vesicles, and hypertrophy of the water expulsion vesicle did occur, both resulting in the death of the zoospores. Conidial suspensions of Trichoderma isolates also induced zoospore lysis. It is presumed that membrane‐active peptide antibiotics (peptaibols) are involved in zoospore lysis. The peptaibol paracelsin caused lysins of zoospores at a concentration of 2.5 × 10−4 M. The effect on cysts depended on the Trichoderma isolate tested and the age of Trichoderma preculture. Old cultures (after beginning of sporulation) affected cysts more severely than young cultures (before sporulation) which usually were not lethal to the cysts but induced preferably microsporangium formation, inhibition of cyst germination, and retardation of germ tube growth.