PAENIBACILLUS POLYMYXA AS POTENTIAL BIOLOGICAL CONTROL AGENT ISOLATED FROM VEGETABLES GROWN HYDROPONICALLY IN THAILAND

Abstract

The survey was conducted to collect root samples from the hydroponic vegetable farms as sources of potential bacterial antagonists for controlling root rot disease caused by Pythium helicoides. The root samples (in the bottles containing sterile water which had been incubated in the water bath at 84◦C for 20 minutes) were plated onto potato dextrose agar (PDA) for the isolation of the potential bacterial antagonists. There were 441 isolates of bacteria isolated from 129 root samples, in which 20 isolates showed significant inhibitory effect to the mycelial growth of P. helicoides. Both the sterile (at 121◦C, 15 psi for 20 minutes) and the non-sterile culture supernatant of these 20 isolates were tested further for the inhibition of mycelial growth of P. helicoides on the PDA. The capacity of these 20 bacteria was also tested for their capacity to inhibit the mycelial growth in potato dextrose broth (PDB).  Paenibacillus polymyxa (isolated from Brassica chinensis), P. polymyxa (isolates from Ipomoea aquatic) and P. polymyxa (isolated from B. alboglabra) were selected as potential bacterial antagonists based on their capacity to produce heat stable toxic substance against the pathogen. P. polymyxa (isolated from B. chinensis), however, was also detected to produce IAA, a plant growth promoting hormone.