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

The glycolipid antibiotic rhamnolipid B isolated from Pseudomonas aeruginos a strain B5 was evaluated for in vitro antifungal activity and in vivo cont rol against phytophthora blight and anthracnose under glasshouse conditions . Rhanmolipid B showed antifungal activity against Cercospora kikuchii, Cla dosporium cucumerinum, Colletotrichum orbiculare, Cylindrocarpon destructan s, Magnaporthe grisea and Phytophthora capsici. Microscopic observation rev ealed that the high level of antifungal activity (10 mug ml(-1)) against P capsici was mainly due to a lytic effect on zoospores. Zoospore lysis began in the presence of 10 mug ml(-1) of rhamnolipid B and most of the zoospore s were collapsed at 25 mug ml(-1) Rhamnolipid H showed inhibitory activity against the germination of zoospores and hyphal growth of P capsici ab conc entrations of 50 mug ml(-1). Spore germination of the anthracnose plant pat hogen C orbiculare was also inhibited in the presence of 50 mug ml(-1) of r hamnolipid B, although hyphal growth was not affected at this concentration . In the glasshouse, the efficacy of rhamnolipid B against phytophthora bli ght was similar to that of metalaxyl on pepper plants when treated just bef ore inoculation with P capsici. Treatment with either at 500 mug ml(-1) com pletely protected pepper plants fi om phytophthora blight. Rhamnolipid B al so suppressed the development of C orbiculare infection on leaves of cucumb er plants. (C) 2000 Society of Chemical Industry.