Gliovirin, a new antibiotic from <i>Gliocladium virens</i>, and its role in the biological control of <i>Pythium ultimum</i>

A compound with antibiotic activity toward Pythium ultimum was isolated from potato dextrose broth shake cultures of Gliocladium virens, a common soil mycoparasite known to inhibit but not parasitize P. ultimum. The mass spectrum and an X-ray crystallograph of the purified antibiotic indicated that it was a new diketopiperazine, and we have given it the trivial name gliovirin. Gliovirin is highly toxic to P. ultimum but is inactive against other fungi associated with cotton seedling disease. The antibiotic does not persist in nonsterile soil where it is apparently inactivated by the soil microflora.An ultraviolet light induced mutant of G. virens deficient for gliovirin production was overgrown by P. ultimum in culture and did not protect cotton seedlings from damping-off in P. ultimum infested soil. A mutant with enhanced gliovirin production was more inhibitory to P. ultimum in culture than the parent isolate and showed similar efficacy as a seedling disease suppressant, even though its growth rate was reduced when compared to the parent isolate. These results indicate that gliovirin may be important to the antagonist–pathogen interaction.