Biological Characteristics Of Pear Tree Rot Bacteria,screening And Action Mechanism Of Biocontrol Bacteria

Korla Fragrant Pear is a special fruit in Xinjiang.It is well-known at home and abroad for its long cultivation history and high fruit quality.After considerable development,Korla fragrant pear industry has become the main pillar of the forest and fruit industry in the region.Its economic value and strategic value are extremely important.It not only has an important impact on agricultural efficiency and farmers’ income,but also its healthy development is of great significance to consolidate the achievements of poverty alleviation and realize rural revitalization.In recent years,pear tree rot caused by Valsa pyri,a fungus of Ascomycetes,has occurred seriously and caused huge losses to Korla pear industry.In this paper,the biological characteristics and pathogenicity of V.pyri were studied.Through the methods of in dish confrontation and in vitro branch inoculation,the pear endophytic bacterium Bacillus velezensis J3 with significant control effect on V.pyri was screened,and the effects of B.velezensis J3 on the defensive enzymes of pear trees in the process of V.pyri infecting pear trees were preliminarily studied.The main results are as follows:1.Biological characteristics and pathogenicity of phenotypic strains of pear rot pathogen.In order to clarify the intraspecific diversity and pathogenicity differentiation of fragrant pear rot pathogen V.pyri,the V.pyri strains with large differences in colony phenotypes were screened from 303 strains isolated and purified from Korla Fragrant Pear production area.According to the difference in colony color and sporulation ability on PDA medium,the strains were divided into four phenotypes,and their biological characteristics and pathogenicity differentiation of different phenotypes were studied.The results showed that the golden yellow phenotype was easy to produce spores,and about 174 spores were produced in 20 days.The light had a significant promoting effect on them,the suitable p H for growth was 6～7,the wettable starch and glutamic acid were used well,and the pathogenicity was medium.Those with milky yellow phenotype are not easy to produce spores.The p H suitable for growth was5.The temperature range suitable for growth was the narrowest.They made good use of wettable starch and peptone and had weak pathogenicity.Those with brown green phenotype were not easy to produce spores.The p H suitable for growth was 5.The temperature range suitable for growth was the widest.They made good use of glutamic acid,wettable starch and glucose and had strong pathogenicity.It was not easy to produce spores with gray black phenotype,which was significantly promoted by light,and had medium pathogenicity.This study showed that there were differences in biological characteristics between different phenotypes,and the pathogenicity was related to the culture phenotype.2.Isolation and identification of endophytic control bacteria of Korla fragrant pear tree rot.In order to screen the biocontrol bacteria with antagonistic effect on pear rot,the strains with high control effect on pear rot were isolated from pear bark by dilution separation in Petri dish,two kinds of confrontation tests in Petri dish and in vitro branch determination,and their physiological and biochemical tests and molecular identification were carried out.The results showed that a total of 34 endophytic strains were isolated from pear bark by dilution separation in Petri dish,and 8 strains with inhibition rate of more than 50% were screened by two methods of confrontation in Petri dish.A strain J3 with the best control effect was obtained by re screening on isolated branches.The inhibition rates of the two methods of confrontation in Petri dish were 78.90% and 59.28% respectively,and the inhibition rate of re screening was 82.30%,The results of physiological and biochemical tests showed that strain J3 was gram-positive,which could hydrolyze starch,and was positive by V-P test.Strain J3 was identified as B.velezensis by 16 S r DNA.3.Effect of B.velezensis strain J3 on defensive enzyme activity of pear branch.In order to understand the response mechanism of B.velezensis strain J3 against the infection stress of pear rot pathogen V.pyri,the changes of defensive enzyme activity in Pear branches within 7 days after inoculation of pathogen V.pyri,Biocontrol bacterium B.velezensis strain J3 fermentation broth and pathogen V.pyri + B.velezensis strain J3 fermentation broth on pear branches in vitro were measured by spectrophotometry,with healthy branches as the control.The results showed that the PPO activity of polyphenol oxidase had little difference compared with the control after inoculation with V.pyri pathogen.The activities of peroxidase pod,superoxide dismutase SOD and phenylalanine ammonia lyase pal increased in the early stage of the experiment and tended to be stable in the late stage of the experiment;The enzyme activities of the treatment group inoculated with the pathogen V.pyri and the fermentation broth of the pathogen V.pyri + Biocontrol bacterium B.velezensis J3 gradually increased with time.On the 7th day,the activities of PPO,SOD,pod and PAL were higher than those of the treatment group inoculated with the pathogen V.pyri alone and the control group.This experiment showed that the fermentation broth of B.velezensis strain J3 could induce plants to increase the activity of defensive enzymes.The results laid a foundation for further study on the biological control mechanism of biocontrol bacteria against pear rot.