ISOLATION AND IDENTIFICATION OF ANTIFUNGAL METABOLITES PRODUCED BY RICE-ASSOCIATED ANTAGONISTIC PSEUDOMONAS SPP

Antifungal secondary metabolites produced by six strains of rice-assoc iated Pseudomonas spp. were determined. Five different media, pigment production medium (PPM), 1/5M523, potato-dextrose agar (PDA), yeast ma lt (YM), and King's medium B (KMB), were used to determine the best me dium for plate assays of these strains against Rhizoctonia solani AGl, the rice sheath blight pathogen. Large inhibition zones were obtained on PPM, KMB, and YM using two strains of P. cepacia, In-b-6854 and In -b-6858, originating from the rice seed. The other four strains showed varying degrees of inhibition zones in the media tested. Their antifu ngal metabolites were isolated and compared with metabolites from refe rence strains and known compounds by regular and reversed-phase thin-l ayer chromatography. Pyrrolnitrin was present in the cell extracts fro m the two P. cepacia strains. Phenazine-1-carboxylic acid and pyocyani ne were produced by two strains of P. aeruginosa, In-b-109 and In-b-78 4. A strain of P. putida, In-b-1821, produced 2,4-diacetylphloroglucin ol. Several unidentified compounds were produced by a strain of P. flu orescens, In-b-7-14. Ten microliters of eluted spots from In-b-6854 an d In-b-6858 inhibited the mycelial growth of R. solani 20 to 24 mm awa y.