| The soil borne diseases caused by Botrytis cinerea and Meloidogyne incognita have been endangering the development of vegetables in protected areas for a long time.With the specialization of vegetable,the simplification of cultivar,the long-term of continuous cropping and so on,the number of B.cinerea and M.incognita are becoming increasing in the field,these difficulties have greater impacts on the yield and quality of vegetable and become more and more serious.B.cinerea usually develop and spread in each growth period of pepper.Meanwhile,the occurrence of pepper grey mold also plays a significant position in pepper storage,transportation and sale.M.incognita has a wide range of hosts,which can infect Solanaceae,Leguminosae,Cucurbitaceae and other vegetables.At present,Chinese pepper and tomato production is still dominated by chemical agents,which used as the main means of controlling B.cinerea and M.incognita.Even though traditional chemical control methods have some advantages,it can bring many drawbacks.The unreasonable use of chemical agents can cause negative impacts on the ecological environment and the health of human and animal owing to high residuals.Therefore,with the rapid development of "pollution-free",green and organic agriculture,biocontrol method,as an effectively new means to control the occurrence of B.cinerea and M.incognita,have gradually becomes the hotspot of research.The antagonistic bacteria we used in this research were selected from our lab's biocontrol strains library.In accordance with their biocontrol efficiency to a variety of plant disease,the 100 strains with better biological efficacy were selected.B.cinerea that can cause pepper grey mold is our target pathogen.100 strains' plate antagonism test and their activity of producing protease,chitinase,cellulase and siderophore were detected.According to the results of antagonistic activity and hydrolytic enzyme activity,6 potential strains were screened out for the greenhouse disease prevention experiments.Refer to the results,We found they all had biocontrol efficacy(32.44%-58.44%)against B.cinerea.and 2 antagonistic bacteria have better biocontrol efficiency against pathogen.5YN8 showed the highest biocontrol efficiency which was 58.44%,while the biocontrol efficacy of DSN012 was 56.23%.The 2 biocontrol bacteria that have the significant biocontrol efficiency also can promote pepper growth to some extent,especially by increasing the content of chlorophyll in the leaves of plants,which showed their potential of biocontrol These results of plate antagonism test,hydrolytic enzyme test and greenhouse disease prevention experiment indicated that the main mechanism of 2 biocontrol bacteria inhibit B cinerea through competition for nutrients and space conditions as well as secretion of hydrolytic enzyme.Both of 2 biocontrol strains were identified as Bacillus velezensis by morphology and molecular biological methods.In addition,the secondary metabolites of the two kinds of biocontrol bacteria were collected and tested antagonistic activity again The results showed that the secondary metabolites that produced by these biocontrol bacteria had some antagonistic effects against B.cinerea.Moreover,the volatile organic compounds that produced by B.velezensis 5YN8 can inhibit the growth of B.cinerea and the production of its spores.To understand its mechanism and principle in the control and prevention of pepper grey mold,pepper leaves that pretreatment with biocontrol bacteria can be observed large amounts of brown regions after inoculating B.cinerea.It showed that biocontrol bacteria can increase the accumulation of hydrogen peroxide by activating the cellular defense responses of leaves.At the same time,the defense-related enzyme activities including superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)were significantly enhanced.In different treatment groups,pepper defense-related gene expressions also had striking differences.The expressions of NPR1 and PR1 that related to salicylic acid(SA)signal pathway were significantly enhanced in pepper treated with biocontrol bacteria and B.cinerea.In conclusion,B.velezensis 5YN8 and DSN012 exerted biocontrol efficiency against Botrytis cinerea via SA signal pathway.Bacillus cereus(Bacillus cereus)AR156 can be used as a biocontrol agent for the control of M.incognita,which was screened by our lab.This study screened mortality of M.incognita and biocontrol efficiency under greenhouse in the AR156 miniTnlO random insertion transposon library to find mutants associated with biocontrol ability in AR156.Gene involved in biocontrol in AR156 was identified.And we continued to compare producing-protease ability,colonization,biofilm formation and swarming motility Compared with the wild-type AR156,BC41 was reduced the ability of producing protease,the colonization of plant rhizosphere,the formation of biofilm and swarming motility.Its insertion site is the M60 family peptidase,which caused a decrease in the ability to biocontrol M.incognita. |
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