Effects Of Bacillus Velezensis Strain YQ1 On Antagonism Of Fusarium Wilt

Fusarium wilt is a soil-borne fungal disease caused by Fusarium oxysporum f.sp.cubense(Foc),which increasingly jeopardizes global banana production.Few resistance genes to this disease have been used in the dessert or cooking banana cultivars breeding.Moreover,chemical or cultural measures are largely restricted to reduce propagation,transmission and spreading of this pathogen.Better biological management to this disease is needed.In our previous study,an endophytic bacterial strain,which was isolated from the root tissue of Canna indica,was identified and named as Bacillus velezensis YQ1.For understandings the biocontrol effect and the antagonistic mechanism of B.velezensis YQ1 on Fusarium wilt,we analyzed the antifungal activity of strain YQ1 against Foc in vitro and in vivo.Antagonism of the strain against Foc was tested via dual-culture and inhibition test on mycelial growth and conidia germination.Biocontrol activity against Fusarium wilt was evaluated under greenhouse conditions.The plant growth-promoting ability was analyzed by evaluating the activities of phosphorus-solubilization,potassium-dissolvability and nitrogen fixation.The antagonistic secondary metabolite biosynthesis genes were predicted by genomic and expression level analysis.The results are as follows:(1)The inhibition rates of strain YQ1 against Foc1 and Foc4 were 45.00% and48.33%(inhibition of hypha growth),95.67% and 86.33%(inhibition of colony growth growth),and 61.67% and 85.67%(inhibition of conidia germination),respectively.The results showed that YQ1 had a significant antagonistic effect on Foc by inhibiting the conidia germination and the infection structure formation.(2)Biocontrol activity of YQ1 against Fusarium wilt disease under greenhouse conditions was observed.The protective effects of YQ1 against Foc1 and Foc4 were71.00% and 84.67%,respectively.The curative effects cof YQ1 against Foc1 and Foc4 were 39.66% and 63.33%,respectively.And stain YQ1 promoted the growth of banana plants by significantly increasing the plant height,pseudostem diameter,and biomass.But YQ1 strain was negative for the solubilization of phosphate andpotassium and the fixation of nitrogen.(3)The supernatant of YQ1 strain had antifungal activity against Foc4.In the genome of YQ1 strain,508 secondary metabolite biosynthesis genes sort sorted into12 clusters were annotated using anti SMASH.The secondary metabolites are predicted as lipopeptides and polyketides,including Surfacin,Bacillaene,Fengycin,Difficidin and Bacilysin which would be the main antifungal secondary metabolites produced by strain YQ1.The expression level of the key antagonistic secondary metabolite biosynthetic genes had been detected,showing that F9286＿09325,F9286＿09335,F9286＿09420 and F9286＿09435 which synthesized Fengycin were significantly up-regulated at 24 h and 36 h during the antagonistic interaction between YQ1 and Foc4.Therefore,Fengycin may be the key antifungal substance produced by B.velezensis YQ1 against Fusarium wilt.