부산대학교 도서관

Novel strains of rhizobacteria, Pseudomonas fluorescens Pf 9A-14, Pseudomonas sp. Psp. 8D-45 and Bacillus subtilis Bs 8B-1, showed broad-spectrum antagonistic activity and provided suppression of Pythium damping-off and root rot of cucumber. Their biocontrol potential was further investigated for suppression of additional seedling diseases of cucumber ( Phytophthora capsici) and radish ( Rhizoctonia solani). Bacterial strains were also characterised for production of antibiotics, metabolites, volatiles, phytohormones and lytic enzymes. Seed and pre-plant applications of all three antagonistic bacteria as cell suspension and talc or irradiated peat formulations to the infested potting mix provided overall high level of suppression of Phytophthora damping-off and root rot of cucumber (66-85% healthy seedlings) and relatively low level of suppression of Rhizoctonia damping-off of radish (18-38% healthy seedlings). Bacterial treatments also resulted in higher plant fresh masses. Seed coating with irradiated peat formulation of a mixture of three bacteria resulted in superior control of Phytophthora damping-off and root rot of cucumber and much higher plant fresh masses. The presence of genes for biosynthesis of phenazine-1-carboxylic acid, 2,4-diacetylphloroglucinol, pyrrolnitrin and pyoluteorin was confirmed in Pseudomonas strains, and that of fengycin, bacillomycin, bacilysin, surfactin and iturin A in B. subtilis Bs 8B-1. All three strains produced HCN, salicylic acid, indole-3-acetic acid, protease and β-1,3-glucanase. Both Pseudomonas strains produced siderophores and only P. fluorescens Pf 9A-14 showed phosphate solubilisation and chitinase activity. All three strains inhibited pathogen growth by producing volatiles, and gas chromatography-mass spectrometry analysis revealed eight compounds in Pf 9A-14, 10 in Bs 8B-1 and 4 in Psp 8D-45, some with known antifungal activity. The antagonistic and plant-growth promotion activities of these strains might be due to production of antibiotics, metabolites, lytic enzymes or phytohormones. [ABSTRACT FROM AUTHOR]