Antibacterial Activity Of Three Actinomycetes And Their Control Effect On Fusarium Wilt In Cucumber

Fusarium wilt,one of the most serious diseases on cucumber.leads to a sharp decrease in cucumber yield and serious economic losses.Now.the most common method for controlling cucumber Fusarium wilt is using chemical agents.However,the improper application methods or excessive use of chemical agents will lead to serious environmental pollution and are harmful to human health.At the same time,long-term use of chemicals will lead to "3R" problems such as fungicide resistance of pathogen,pesticide residue and pests resurgence.Therefore,researchers all over the world begin to focus on finding new and efficient biological agents to replace chemical pesticides.Actinomycetes are widely distributed in nature,and the active metabolites from them are the main source of antibiotics which are widely used in various fields such as agriculture,medicine and industry,and have great application potential in controlling plant diseases.In this paper,three antagonistic actinomycetes strains isolated from the field of Jiangsu province were used to study their species,antibacterial spectrum,antagonistic activity stability.soil colonization capacity and control effect in cucumber Fusarium wilt.The results are as follows:1.The three actinomycete strains showed strong inhibiting abilities on the growth of Botrytis cinerea,Fusarium oxysporum f.sp.cucumerinum,Fusarium oxysporum f.sp.lycopersici,Gibperella zeae and Curvularia lunata,and had obvious inhibitory effect on spore germination of F.oxysporum f.sp.cucumerinum.Among them,the inhibition rate of 2F-1 culture filtrate on spore germination of F.oxysporum was 100.00%.and the inhibition effect of 30%2F culture filtrate on hypha growth was 99.7%.The mixture of 2F and 2F-1 culture filtrates had the best antagonistic effect against F.oxysporum f.sp.cucumerinum and the inhibiting bandwidth were up to 8.9 mm.The results of antagonistic stability test showed that the inhibiting activity of the three strain culture filtrates decreased rapidly when it was stored at room temperature.The filtrate of 2F8 decreased obviously and completely lost inhibiting activity after 7 days storing at room temperature.In addition,the culture filtrates of three strains were sensitive to high temperature,strong acid and alkali,but insensitive to ultraviolet ray.All of the three strains could produce protease and β-glucanase,but no siderophore and cellulase,while 2F and 2F8 also could produce chitinase.2.The spore suspension and fermented inoculants of three actinomycete strains had no significant effect on cucumber seed germination and radicle elongation while 2F and 2F-1 fermented inoculants could promote cucumber germ elongation and 2F8 inhibited it.When the actinomycete 2F and 2F8 strains fermented inoculants were poured into the rhizosphere of cucumber at 4-leave stage,it significantly enhanced the growth index,material accumulation and photosynthetic pigment content of the plants.The three actinomycete strains can also induce defense enzyme activity in cucumber,among which the defense enzyme activity of cucumber is most obviously improved after treatment with 2F-1 fermentation broth.After actinomycetes treatment,the content of callose,total phenol,soluble sugar and lignin in cucumber also increased to some extent3.The actinomycete 2F and 2F-1 strains had strong colonization ability in cucumber root zone,rhizosphere and root surface.When the actinomycete fermented inoculants were added into the soil with a final concentration of 107 cfu/g,105 cfu could be detected in 1 g soil after 28 days.However,2F and 2F-1 actinomycete strains all had relatively weak colonization ability on cucumber leaf surfaces.The mixture of actinomycete 2F and 2F-1 strains fermented inoculants had preventive and control effect on cucumber Fusarium wilt to a certain extent and the effect was 48.98%and 34.01%,respectively.