Isolation and in vivo and in vitro antifungal activity of phenylacetic acid and sodium phenylacetate from Streptomyces humidus

The antifungal substances SH-1 and SH-2 were isolated from Streptomyces hum idus strain S5-55 cultures by various purification procedures and identifie d as phenylacetic acid and sodium phenylacetate, respectively, based on the nuclear magnetic resonance, electron ionization mass spectral, and inducti vely coupled plasma mass spectral data. SH-I and SH-2 completely inhibited the growth of Pythium ultimum, Phytophthora capsici, Rhizoctonia solani, Sa ccharomyces cerevisiae, and Pseudomonas syringae pv. syringae at concentrat ions from 10 to 50 mug/ml. The two compounds were as effective as the comme rcial fungicide metalaxyl in inhibiting spore germination and hyphal growth of P. capsici. However, the in vivo control efficacies of the two antifung al compounds against P. capsici infection on pepper plants were similar to those of H3PO3 and fosetyl-AI but less than that of metalaxyl.