The Screening Of Biocontrol Bacteria And The Field Control Effect Of The Antifungal Substance HSAF In Lysobacteria

Plant disease is one of the natural disaster affecting agricultural production all over the world.The most effective and convenient measure to solve plant diseases is still chemical control.Environmental problems caused by chemical control are becoming more and more concerned.To decrease the use of chemical fungicide,it is necessary to screen novel biocontrol bacteria and natural secondary metabolites for developing efficient biofungicide.In this study,we collected soil samples from orchards in different regions of the country and used a traditional screening method.157 strains of biocontrol strains with antimicrobial effects targeting 22 pathogenic bacteria were obtained.These pathogenic bacteria includes common pathogenic fungi,Fusarium graminearum,Rhizoctonia solani,Valsa pyri,Alternaria brassicicola,etc.,as well as pathogenic bacteria of common diseases,Xanthomonas campestris pv.campestris,Xanthomonas oryzae pv.oryzicola and so on.Thirty strains with potent antimicrobial activity were identified by 16S rDNA,and these biocontrol strains have the potential to be studied.Among them,GM-7 and GM-8 were identified as Lysobacter.Lysobacter belong to Xanthomonadaceae,which can produce a large number of extracellular enzymes and active secondary metabolites,and is environmentally friendly.It is a new type of biocontrol bacteria to be developed.These two strains and the other four typical Lysobacter strains,including Lysobacter enzymogenes OH11,Lysobacter antibioticus OH I3,Lysobacter gummosus OH17,Lysobacter bnmescens OH23 were compared in terms of extracellular enzymes,twitching motility,antagonistic activity and so on.The GM-7 and GM-8 showed extracellular protease,chitinase,cellulase and glucanase activities as the other four typical Lysobacter strains and exhibited the same motility phenotype with OH11.With mass spectrometry analysis,we found that GM-7 produced antifungal HSAF(heat-stable antifungal factor,dihydromaltophilin)and GM-8 produced a small amount of HSAF and its analogue ATB(Alteramide B).HSAF and ATB have been reported to be derived from L.enzymogenes OH11,which has strong antagonistic activity against a variety of phytopathogenic fungi and oomycetes.HSAF has a unique mechanism of action and has the potential to be developed as a biopesticide.To further study the development value of HSAF,we conducted a field control trial of HSAF on wheat Fusarium head blight(FHB).The results indicated that the application of 20 jag/mL HSAF showed similar field efficacy as 50%carbendazim.Moreover,40?g/mL HSAF yielded significantly higher control effects.Depending on the national pear industry system,the HSAF biocontrol agent field trials were conducted at various test stations to control pear disease.The results showed that the control efficacy of HSAF on the anthracnose of pear was more than 90%,and the effect was equivalent to that of mancozeb.The control effect of HSAF on the disease of pear black spot was similar to that of 40%of Fuxing 8000,both are above 80%.The cure rate of HSAF gel for pear rot disease is between 84.27%and 95.12%,both higher than 80%,and better than humic acid copper agent,stone sulphur mixture,methyl sulfide,which are commonly used agent.These results all indicate that HSAF can be used as a prospect fungicide for biocontrol of plant disease.