Screening, Identification And Antagonism Of Antagonistic Organisms Against Phytopathogene

In production agriculture, Fungal and bacterial plant pathogens infect plants and crops easily and often seriously, causing millions of dollars worth of economic damage each year. So, how to control these diseases and maintain the normal growth of plants is always the highlight. Application of chemical pesticides is the effective measure to control the fungal and bacterial infection and plays an important role in preventive defence. With the further knowledge to chemical pesticides, however, many concerns, such as the pollution of soil, water and atmosphere, the increase of the leftover of germicides in agricultural produce which imperils human health and life directly, the unbalance of ecological environment resulting from the pesticides, and resistance of phytopathogenic fungi and bacteria to germicides, have caused the withdrawal of many of them. So, new and safe alternative control measures are much sought after. Biological control by natural antagonistic organisms is a potential nonchemical tool for crop protection against phytopathogenic fungi and bacteria and offers a promising alternative to synthetic pesticides, in part because it is perceived as safe to the environment and human health and can avoid the appearance of drug-resistance.In our study, 13 soil samples were gathered from fields in Chengdu,Jianyang and Yaan, from which 119 actinomyces strains and 67 bacterial strains were isolated by tube dilution assay. With Curuvularia Lunata (Walk) Boed as the tested stain, 21 antibiotic actinomyces stains were screened out by modified hyphal extension inhibition assay and 14 antibiotic actinomyces stains by traditional hyphal extension inhibition assay from 80 actinomyces stains, which indicated that the modified method was suitable to screen the antibiotic actinomyces. From these isolates, 39 antibiotic actinomyces strains and 5 bacterial strains (BS04, ST1 ST8, C3 and C4) against phytopathogenic fungi were screened by modified hyphal extension inhibition assay and traditional hyphal extension inhibition assay, respectively. Among 39 antibiotic actinomyces strains, there were 36, 29, 27, 28, 28, 25, 27, 27 and 25 strains against Phoma wasabiae Yokogi Curuvularia Lunata (Walk) Boed Thantephorus cucumris , Cochlibolus Heterostrophus , Exserohilum Turcicum Fusarium graminearum Cochliobolus carbonum Pestalotiopsis foedans and Altalaria altanata, respectively. With modified agar diffusion assay, 1 actinomyces strain, named P11, was screened out to be antibiotic against to phytopathogenic bacteria, and it was antibiotic against to Pseudomonas solanacearum only. Bacteria BS04, ST1 and ST8 were antibiotic against Xanthomonas axonopodis pv. Citri (Hasse) Dye and Pseudomonas solanacearum, while bacterium P18 was antibiotic only against to Xanthomonas axonopodis pv. Citri (Hasse) Dye.Because of good antibiosis against phytopathogenic fungi and bacteria, bacterium BS04 had the potential as biocontrol agent, and so further study on it was carried out. In order to determine the taxonomic placement, the identification of BS04 was performed with traditional bacterial systemic identification method. The result showed that the physiological and biochemical character of BS04 is similar to that of Bacillus polymyxa and that of Paenibacillus polymyxa so that it wasdifficult to ascertain its systematic position. Therefore, the molecular identification of BS04 was performed. Through the comparative 16s rDNA sequences analysis, the 16s rDNA sequence of BS04 had high homology with typical Paenibacillus bacteria from the RDP library (from 92% to 99%). And the constructed phylogenetic tree by using maximum-likelihood method with Bootstrap Trial 1000 proved that BS04 was subjected to Paenibacillus polymyxa.Through orthogonal test, the optimal fermentation conditions of producing antibiotic products of Paenibacillus polymyxa BS04 were given out. The fermentation cultures contained (g/liter): dextrose 10g, dextrin7.5g, sodium chloride5g, corn syrupl5g, soy meal30g, calcium carbonate 3g and pH5. 5-6.5. 3% seed media(V/V) with 108cfu/mL...