Screening And Biocontrol Effect Of Antagonistic Actinomycetes Against Monilinia Fructicola

Postharvest diseases of peach fruit are serious,with the decay rate as high as 50%,causing huge economic losses.Brown rot caused by M.fructicola is an important infection disease of postharvest peach fruit.At present,the control of peach brown rot mainly depends on chemical control.However,long-term use of chemical fungicides not only causes drug resistance of pathogenic bacteria,but also causes environmental pollution and pesticide residues.Biological control has become an important direction in the research of disease control due to its high efficiency,safety,innocuity and no residue.Antagonistic strain is considered to be a promising alternative to chemical fungicides in biological control.At present,there are more and more reports on the screening and control of biocontrol strains of peach brown rot,and the main research focuses on Bacillus subtilis and B.amylolyticus.But the research reports of using actinomycetes to inhibit peach brown rot are relatively rare.Therefore,it is of great significance to study the biological control effect of antagonistic actinomycetes on peach brown rot.The purpose of this study is to screen antagonistic strains with strong inhibitory effect on M.fructicola through a series of experiments.The inhibition mechanism and control effect of actinomycetes were studied through aseptic fermentation filtrate and volatile metabolites,and the utilization of carbon and nitrogen sources of antagonistic actinomycetes against M.fructicola were analyzed.In order to provide new antagonistic strains resources for prevention and control of peach brown rot.It will also lay theoretical foundation for efficient screening of biocontrol strains of peach brown rot and practical application in the future.The main research results are listed as follows.(1)410 strains of actinomycetes were isolated from the soil of non-farm ecosystems such as lawns and bamboo forests by soil dilution method,and 79 strains with inhibition zone width of greater than or equal to 5mm were screened by plate confrontation method with M.fructicola as the target pathogen.(2)27 strains with inhibition zone width of greater than or equal to 7mm were selected for in vitro and in vivo experiments.The results showed that the sterile fermentation filtrate of strains XDS1-5 and HCD1-10 had the best inhibitory effect on the growth of M.fructicola.The inhibitory rates respectively of 80.29% and 70.64%.The pathogen cells were rapidly damaged,resulting in increased cell membrane permeability and cytoplasmic leakage.The treated pathogenic hyphae are deformed,spores are shriveled and shrunk,and cavities appear.In the in vitro fruit test,the control group was covered with gray mold layer,while the treatment group had only small spots with water stains.The control effect was obvious.(3)The volatile substances produced by strains JCP1-7 and ZBY1-20 have a weak inhibition on the growth of mycelia of brown rot of peach,but it can still destroy the mycelium structure and significantly reduce the spore production.It is determined the species and relative content of volatile substances produced of the strain through GC-MS detection and database comparison on 14-day-old.A total of 20 substances were detected in strain ZBY1-20,and 28 substances were detected in strain JCP1-7,including alcohols,organic esters,terpenes and so on.(4)The taxonomic status of strains XDS1-5,HCD1-10,JCP1-7 and ZBY1-20 was determined.Micromorphology,culture characteristics,physiological and biochemical characteristics and 16 S r DNA analysis indicated that the four strains respectively were S.virginiae,S.rapamycinicus,S.lincolnensis,and S.diastaticus.(5)The four strains were selected to use Biolog phenotypic analysis technique to determine the utilization about 190 kinds of carbon sources of PM1 and PM2 A and 95 nitrogen source of PM3 B.The results showed that the carbon sources utilization ratio of four strains ZBY1-20,JCP1-7,XDS1-5 and HCD1-10 were 46.84%,52.63%,34.21%and 35.79% respectively.And the nitrogen sources utilization ratio were 28.42%,33.68%,7.37% and 3.16% respectively.The antagonistic strain ZBY1-20 both JCP1-7of volatile substances to peach brown rot and the antagonistic strain XDS1-5 both HCD1-10 of metabolites of fermentation broth to peach brown rot were determined.The metabolic capacity of the two strains was roughly similar.There were obvious differences in the quantity and type of metabolic carbon and nitrogen sources between the two groups.