Study On The Mechanism Of Controlling Muskmelon Fusarium Wilt By Targeted Application Of Bacillus Velezensis ZF2

Fusarium wilt is one of the most destructive soil-borne diseases,which causes serious losses in the yield and quality and restricts the healthy development of muskmelon industry.Controlling Fusarium wilt is difficult due to the ability of Fusarium oxysporum to survive for decades in soil and spread in multiple ways.Using effective biocontrol microorganism to control Fusarium wilt to be one of the sustainable and safety control method,but the control efficiency of biocontrol agents is uncertain in field due to its colonization ability is influenced by the complicated soil environmental conditions.The application of biodegradable non-woven nursery bag can delay the infection of plant pathogen in soil and reduce the risk of root damage during planting.In this study,we established a simple method combing B.velezensis ZF2 with biodegradable non-woven nursery bag to control muskmelon Fusarium wilt.We further explored the correlations between the diversity of rhizosphere microbial community and function and the occurrence of Fusarium wilt,and revealed the mechanism of ZF2 combing biodegradable non-woven nursery bag to control muskmelon Fusarium wilt.(1)B.velezensis ZF2 combing biodegradable non-woven nursery bag had an excellent control effect on controlling muskmelon Fusarium wilt,with the control efficiencies of 62.96%in pot experiment and81.35%in field experiment.The control efficiency of ZF2 biodegradable non-woven nursery bag against Fusarium wilt was higher than that of ZF2 liquid culture and biodegradable non-woven nursery bag,and was close to the control efficiency of carbendazim.(2)Whole genome analysis showed that ZF2 genome contained a 3,931,418-bp circular chromosome,with an average G+C content of 46.50%.ZF2 was classified to B.velezensis based on the multiplegene phylogenetic analysis.ZF2 genome contained 14 gene clusters related to the biosynthesis of secondary metabolites,and a series of genes associated with motility,biofilm formation,flagella biosynthesis and capsular biosynthesis.A specific primer pair targeting the sequence of the D3N19＿RS13500 gene of B.velezensis ZF2 was screened and could distinguish B.velezensis from B.amyloliquefaciens.A rapid specific real-time quantitative PCR detection system for B.velezensis was established with the standard curve y=-3.8785x+30.713 and the R~2 value was 0.9972.(3)B.velezensis ZF2 had a strong colonization ability in desert soil,commercialized seeding substrate,and cow manure organic fertilizer,the optimal colonization soil temperature of ZF2 was28-35℃,and the optimal colonization soil p H was 7-8.Moreover,the colonization ability of strain ZF2was significantly enhanced when adding corn flour,yeast extract,peanut meal and peptone nitrogen sources to the soil.(4)B.velezensis ZF2 colonized stably in rhizosphere soil and significantly controlled muskmelon Fusarium wilt by regulating the rhizosphere microbial community and function.The colonization of ZF2 in rhizosphere soil reduced the abundance of F.oxysporum,increased the abundance of Lysobacter,Rhizobium,Streptomyces and Rhodovulum,and reduced the abundance of potential pathogenic fungi such as Fusarium,Trichophyton and Coniochaetes.ZF2 combing biodegradable non-woven nursery bag enhanced the connectivity of bacterial network,and weaken the correlation in fungal network.In addition,ZF2 combing biodegradable non-woven nursery bag increased the abundance of functional gene related to biofilm formation,polyketide,lipopeptide biosynthesis,autotoxin degradation,and down regulated the functional genes associated with environmental adaption,lipopolysaccharide biosynthesis,small-molecule sugars and amino acids metabolism.The study described an efficient method combing B.velezensis ZF2 with biodegradable non-woven nursery bag to control muskmelon Fusarium wilt,and revealed the potential biocontrol factors and mechanism for disease prevention,which provide scientific basis and technical support for the effective application of biocontrol agents and the safety sustainable control of soil-borne diseases by mediating microbial community.