In vivo control and in vitro antifungal activity of rhamnolipid B, a glycolipid antibiotic, against Phytophthora apsici and Colletotrichum orbiculare

摘要

The glycolipid antibiotic rhamnolipid B isolated from Pseudomonas aeruginosa strain BS was evaluated for in vitro antifungal activity and in vivo control against phytophthora blight and anthracnose under glasshouse conditions. Rhamnolipid B showed antifungal activity against Cercospora kikuchii, Cladosporium cucu merinum, Colletotrichum orbiculare, Cylindrocarpon destructans, Magnaporthe grisea and Phytophthora capsici. Microscopic observation revealed that the high level of antifungal activity (10 jig ml ‘) against P capsici was mainly due to a lytic effect on zoospores. Zoospore lysis began in the presence of 10 jig ml’ of rhamnolipid B and most of the zoospores were collapsed at 25 jig ml ?. Rhamnolipid B showed inhibitory activity against the germination of zoospores and hyphal growth of P capsici at concentrations of 50 jig ml ~. Spore germination of the anthracnose plant pathogen C orbiculare was also inhibited in the presence of 50 jig ml’ of rhamnolipid B, although hyphal growth was not affected at this concentration. In the glasshouse, the efficacy of rhamnolipid B against phytophthora blight was similar to that of metalaxyl on pepper plants when treated just before inoculation with P capsici. Treatment with either at 500 jig ml1 completely protected pepper plants from phytophthora blight. Rhamnolipid B also suppressed the development of C orbiculare infection on leaves of cucumber plants.