Isolation,Identification And Antagonistic Mechanism Of New Biocontrol Streptomyces Sp. JRGG-11 Against Banana Fusarium Wilt

Banana is one of the four major agricultural products in global trade as well as the food crop for 400 million people.Fusarium Wilt of banana caused by Fusarium oxyspoum f.sp.cubense（Foc）is one of the most serious soil-borne fungal disease.So far,four races of Foc were reported.Foc 1 mainly injected Gros Michel（AAA）was first one to be identified,Cavendish（AAA）had immunity to it.Foc 4 almost injected all of the cultivars,became the most severely damaged race.Until now,there still have no safe and effective measures and disease-resistant cultivars to protect banana from the Foc infection.Therefore,this fungal disease severely restricts the sustainable development of banana industry.Biological control is considered as a promising method to control the fungal disease.Here,an actinomycete with high antagonistic activity on Foc 4 marked with JRGG-11 was isolated and screened from the rhizosphere soil of the medicinal plant Machilus pingii in Jianfengling Nature Reserve.We further identified strain JRGG-11 and assess the bio-control efficiency and its antifungal mechanism against Foc 4.Our results will lay a foundation for enriching banana wilt biocontrol resources and promote the development and application of actinomycetes JRGG-11.The detailed results are shown as follows:（1）Separation and identification.Using the rhizosphere soil of Machilus as the separation material,a total of 61 actinomycetes were isolated,and 17 of them exhibited antagonistic activities against Foc 4.Based on the re-screening using fermentation broth,strain JRGG-11 with the best antagonistic activitiey was selected.According to 16S r RNA sequence analysis,physiological and biochemical characteristics,strain JRGG-11 was identified as Streptomyces sp..Moreover,strain JRGG-11 has inhibitory effect on eighteen phytopathogenic fungi,which shows that JRGG-11 has broad-spectrum antifungal activity.（2）Pot experiment.According to the observation of banana root slices combine coating of rhizosphere soil,we found that the fermentation broth of actinomycete JRGG-11effectively reduced the colonization of Foc 4 in the banana root and rhizosphere soil.Besides,JRGG-11 fermentation broth significantly improved activities of banana defense system related enzymes,such as SOD,CAT,POD,and PPO.In addition,the fermentation broth of actinomycete JRGG-11 has effectively increased banana biomass and promoted growth of banana seedlings.Counted injected banana seedings and calculated disease index,we found that the prevention and control index of JRGG-11 fermentation broth on banana wilt reached83.10%.（3）Inhibiting mechanism.The actinomycete JRGG-11 extracts were obtained by a column chromatography.The EC₅₀and E_C95 values of the strain JRGG-11 extracts against Foc 4 were 18.70μg/m L and 274.43μg/m L,respectively.The morphology and cell integrity of mycelia were seriously destroyed and the conidia germination was completely inhibited under 4×EC₅₀ of extract treatment.Stability experiments showed that the JRGG-11 extracts exhibited a good tolerance to ultraviolet radiation and high temperature.The antagonistic activity was reduced under acidic conditions.In addition,Streptomyces sp.JRGG-11 extracts obviously reduced the soluble protein contents.Meanwhile,sugar contents of Foc 4 broth and activities of chitinase andβ-1,3-glucanase in the Foc 4 hyphae were significantly increased.It indicated that Streptomyces sp.JRGG-11 extracts can degrade cell walls and cell membranes of Foc 4.（4）Metabolite prediction.The total genome sequence of Streptomyces sp.JRGG-11 is10,590,458 bp,and the G+C content was 71.779%.COG functional annotations showed that 273 genes are involved in the biosynthesis,transportation and catabolism of secondary metabolites.158 genes are involved in defense mechanisms.GO annotations showed that most of genes related to molecular functions.KEGG analysis showed that 99 genes of Streptomyces sp.JRGG-11 related to terpenoid and polyketide metabolism.A total of 43secondary metabolite synthesis gene clusters were predicted by anti SMASH software analysis,four gene clusters were 100%similar to the known genes related to the biosynthesis of Toyocamycin,Naringenin,compound SAL-2242 and indole.Based on the above results,Streptomyces sp.JRGG-11 has a potential agent for biological control and plant growth-promoting.