Breeding Of Soil-Borne Muskmelon Leaf Spot Antagonistic Bacteria And Evaluation Of Its Biocontrol Potential

In recent years, the severity of the muskmelon leaf spot disease in china becomes heavier than ever due to wide replanting problems from intensive farming. The control methods commonly used such as agricultural control, chemical control usually caused problems including environment problems, high cost and labor-consuming. Therefore biological control has gathered much attention due to its environment-friendly characteristic. However, less research about the biocontrol of muskmelon leaf spot disease was reported.In the present study, a bacterial stain with high antagonistic efficient of muskmelon leaf spot disease was isolated. The influence of conditions on the growth of the strain was studied. The growth curve and inhibitory spectrum were measured; the production conditions of antagonistic substances and antagonistic mechanism were studied; the strain was breed by using UV and EMS mutation methods; the potential biocontrol of strain was evaluated through colonization experiment, pot-promoting test and pot control effect experiments.The main results obtained were listed as follows:1. The antagonistic strain BS-17 obtained was identified as Bacillus amyloliquefaciens, and had resistant to many antibiotics. The results showed that when the temperature was 30℃, liquid volume was 25 mL, initial was pH 7.0, carbon source was sucrose, nitrogen source was yeast extract, the growth of the strain reached maximum. The inhibition rates of BS-17 stain to nine plant soil-borne disease were above 80%.2. Experimental results showed that when the culture time was 72 h, temperature was 30℃, initial pH was 7.0, speed was 170 r/min, inoculum was 1%, the activity of antagonistic substance reached maximum. Antagonistic substances produced by BS-17 strain could lead hyphae distorted, the inner end enlarged and dissolved. And it also could reduce the amount of extracellular polysaccharides produced by pathogenic bacteria. Antagonistic substances were stable to temperature, pH, UV and protease. The strain BS-17 had a high ability to produce cellulase and protease.3. When the UV intensity was 15 w, mutagenesis time was 5 min, distance was 25 cm, strain age was 18 h, the strain BS-175 with inhibition rate 93.8% was obtained. Then the strain BS-175 was breed by EMS. The mutagenesis conditions respectively were EMS volume 20 μL, mutagenesis time 35 min, mutant strain concentration 108 mL-1. The mutagenesis strain BS-1754 was obtained and the inhibition rate reached 97.6%.4. Through colonization experiment, pot-promoting effect and pot control effect experiments, the results showed that strain BS-1754 had good colonization ability and the organic fertilizer adding biological BS-1754 could promote growth of muskmelon plants with the disease incidence rate 7.9%. It was found that bio-organic fertilizer could increase the activity of soil enzymes, and resistance plant disease related enzymes including POD enzyme, SOD enzyme and CAT enzyme. It was also found that bio-organic fertilizer could reduce the content of MDA related resistant plant disease in plant. In conclusion, the strain BS-1754 has good biocontrol potential.