| Muskmelon（Cucumis Melo L.）is an important cash crop in China and has high value in food,medicine and industry.In recent years,continuous planting of muskmelon has increased the accumulation of pathogens,leading to increasingly serious diseases.The occurrence of disease not only reduces the quality and yield of muskmelon,but also seriously affects the economic income of farmers.Alternaria tenuissima and Stagonosporopsis cucurbitacearum are the common causal agents of muskmelon leaf spot.It is one of the effective ways to control muskmelon leaf spot by studying and utilizing actinomycetes with disease resistance in the relevant environment.In this study,actinomycetes were isolated and purified from the rhizosphere soil of muskmelon base in Malianzhuang,Shandong Province.A.tenuissima and S.cucurbitacearum served as the target pathogens,the control effect of active strains was evaluated by in detached leaf and pot experiments,and the active products of the antagonistic strains with strong antagonistic activity were isolated and identified.It provides active natural products and biocontrol actinomycetes for the control of muskmelon leaf spot.The main experimental results were as follows:（1）A total of 105 actinomycetes were isolated from muskmelon rhizosphere soil using six screening media.Three strains with superior activity and broad-spectrum antifungal activity were screened and named Lentzea sp.NEAU-D7,Streptomyces sp.NEAU-H20 and Streptomyces sp.NEAU-S6.The inhibitory rates of three actinomycetes against A.tenuissima were 71.90%,54.44%and 50.34%,respectively.The antifungal rates of three actinomycetes against S.cucurbitacearum were 58.65%,60.89%and 57.36%,respectively.（2）The results of detached leaf experiment showed that the control effect of strain NEAU-S6,NEAU-H20 and NEAU-D7 were the best when the spore concentration was 108CFU/m L,and the control effect on leaf spot caused by S.cucurbitacearum was 77.78%,77.67%and 80.85%,respectively.When the spore concentration of strain NEAU-S6,NEAU-H20 and NEAU-D7 were 107CFU/m L,the control effect on leaf spot caused by A.tenuissima were90.21%,88.89%and 89.95%,respectively.（3）Pot experiment results showed that when the spore concentration of strain NEAU-S6was 1.0×108CFU/m L,the control effect on leaf spot caused by S.cucurbitacearum was the best,reaching 76.21%,and when the spore concentration was 1.0×107CFU/m L,the control effect on leaf spot caused by A.tenuissima was the best,reaching 87.07%.When the spore concentration of strain NEAU-H20 was 1.0×108CFU/m L,the control effect on leaf spot caused by S.cucurbitacearum was the best,reaching 79.79%,and when the spore concentration was 1.0×107CFU/m L,the control effect on leaf spot caused by A.tenuissima was the best,reaching 87.61%.When the spore concentration of strain NEAU-D7 was 1.0×107CFU/m L,the control effect was the best,with 78.63%and 87.35%against leaf spot caused by S.cucurbitacearum and A.tenuissima respectively.（4）The optimal fermentation medium for strains NEAU-S6 and NEAU-H20 was GYM medium.The results showed that the active substances were stable under high temperature,strong acid and strong alkali,and not affected by ultraviolet light.The compounds isolated form the strain NEAU-S6 were identified as scopafungin and hygrocins A.The compounds from strain NEAU-H20 are autolysin and dihydroatramycin A.The fermentation broth of strain NEAU-D7 was inactive after fermentation,and no compound was separated.The whole genome of the strain was predicted,and it was found that the similarity with the gene cluster of2-methylisoborneol,staurosporine,indigoidine,GE2270,coelichelin,pyrazomycin,butyrolactol A,Ery-9/Ery-6/Ery-8/Ery-7/Ery-5/Ery-4/Ery-3 and isorenieratene were over 50%.It is speculated that these may be the active substances of strain NEAU-D7,which needs further study.（5）Solid fermentation and response surface optimization experiments showed that the ratio of wheat bran to earthworm manure was 1:3,which was the best substrate ratio of NEAU-D7.After analysis,water content,inoculation amount and temperature have great influence on spore yield.Based on the design principle of Box-Behnken center,response surface optimization was carried out after analyzing the three factors.The optimum conditions for solid-state fermentation of strain NEAU-D7 were as follows:temperature 30℃,water content 60%and inoculation amount 18%.After 7 days of fermentation,the maximum sporulation was 1.72×1012CFU/g.When the obtained product was mixed with soil as bacterial fertilizer,the control effect on leaf spot caused by S.cucurbitacearum was 82.79%,and the control effect on leaf spot caused by A.tenuissima was 91.61%. |
