PYRROLNITRIN AND PHENAZINE PRODUCTION BY PSEUDOMONAS-CEPACIA, STRAIN 5.5B, A BIOCONTROL AGENT OF RHIZOCTONIA-SOLANI

Rhizoctonia stem rot of poinsettia caused by Rhizoctonia solani is con trolled by strain 5.5B of Pseudomonas cepacia when poinsettia cuttings are rooted in polyfoam rooting cubes. Experiments were conducted to i solate and characterize secondary metabolites from strain 5.5B that we re inhibitory towards R. solani. Inhibitory compounds were detected in fractions processed from liquid cultures of strain 5.5B. The most inh ibitory compound isolated was pyrrolnitrin. A purple pigment consisten tly produced in culture by strain 5.5B was isolated and identified as 4,9-dihydroxyphenazine-1,6-dicarboxylic acid dimethyl ester, a phenazi ne. In vitro inhibition of R. solani occurred with the phenazine.