The Distribution Of Antagonistic Bacteria Against Fusraium Oxysporum F.sp.melonis In The Different Cultivated Soils And Their Functions In Biocontrol

Fourteen batches (42 samples) of different soils were collected from vegetable garden and muskmelon field in Hangzhou and Jiaxin of Zhejiang province and the proportion of antagonistic bacteria to the total in the soils was measured. The result showed that the ratio of total number of bacteria and Fusarium oxysporum improved in the soils of crop rotation, the number of Fusarium oxysporum greatly decreased and the antagonistic bacteria increased. Especially in the soil of muskmelon and garlic rotation the number of the antagonistic bacteria was the highest. Eight hundreds and forty bacterial isolates were isolated from the soil samples and screened in vitro for antagonists against Fusarium oxysporum f.sp.melonis. It showed that 43 strains, 5.11% of total, were antagonistic to the pathogen. Among them 17 strains from the rhizosphere of muskmelon soil, 5.67% of total, were antagonists; 10 strains from the non-rhizosphere soil of muskmelon, 3.33% antagonists and 16 strains from rhizosphere soil of the vegetable garden, 6.67% of total antagonists. Fifteen strains were further tested for the antagonistic index, of which 9 strains were above 2.0 and 4 strains were between 1.0 to 2.0. The distribution of antagonistic bacteria was correlated to the total number of bacteria in the soils. In general the more the number of bacteria were in the soil, the higher the proportion of antagonistic bacterium. The proportion of the antagonistic bacteria to total number in the vegetable garden soil was higher than those of the melon soil; the proportion in the soil of rhizosphere was also higher than those of in non-rhizosphere soil. It was noted that the antagonistic bacteria from the rhizosphere soil were stronger against the pathogen than those from non-rhizosphere in vitro.Nine stronger antagonistic strains were further tested for their antagonistic stability and anti-fungal spectra and 7 of them selected. Their culture filtrates were tested for their effect on inhibiting mycelial growth and conidial germination. It showed that strains Hc2 and Hc3 were strongest among the 7 strains. At the concentration of 50% they completely suppressed mycelial growth. Even if at the concentration of 5% they still inhibited 50% of conidia germination. The treatments of the melon seed dressing in pots showed that 4 strains, Hcl, Hc2, Hc3 and Jt6, were not only antagonistic to the pathogens but also had effect ongrowth-promoting of the melon seedlings. They performed better control effect 10 days after treatment and the highest relatively control effect reached 65.4%. However, the control effect decreased obviously 20 days after the treatment. Identification of the antagonistic bacterial strains by bacteriological, Biolog and molecular biological test (RAPD-PCR) showed that among 16 Gram negative strains most of them belong to Pseudomonas spp. and they were predominant in the isolation. The species with over 0.50 of Biolog similarity were P.aeruginosa; P.putida; P.resinovorans; P.fluorescens C; P.viridilivida A Burkholderia cepacia.