Screening And The Disease-Supression Effects Of Mycorrhiza Helper Actinomycetes From Pepper Rhizosphere

Soil-borne diseases cause serious damages to agricultural healthy development.For example,pepper(Capsicum annuum L.)Phytophthora blight,the most common and harmful disease in pepper facility cultivation,is widely spreading in many regions in our country.Among biocontrol agents,arbuscular mycorrhizal(AM)fungi perform well,but it is difficult to realize large-scale production of AM fungal inocula for a long time.Therefore,how to exert the disease-supression function of soil indigenous AM fungi has become a realistic need.Mycorrhiza helper(MH)bacteria,especially some actinomycetes,can promote the formation and thereby the ecological function of such symbiotic structure.However,the application potential of MH bacteria in preventing and controlling soil-borne diseases is still unclear.In view of this,this study took pepper Phytophthora blight as the research object.Firstly,actinomycetes strains were isolated from pepper rhizosphere,then the strains with helper effects on the disease-suppression function of AM fungi were screened.Finally,both pot and field tests of MH actinomycetes strains on disease suppression by indigenous AM fungi were explored.The main results are as follows:1)Three rhizosphere soil samples,including both diseased and healthy plants in a diseased plot and a common plant in a healthy plot,were collected from a pepper facility planting base in the suburb of Nanjing City,Jiangsu Province,followed for actinomycetes isolation and purification.Five actinomycetes strains were successfully isolated.After preliminary identification by 16 S r RNA,astrain of Streptomyces pseudogriseolus was isolated from the rhizosphere of diseased plants in the diseased plot.Both strains of S.albogriseolus and S.griseoaurantiacus were isolated from the rhizosphere of healthy plants in healthy plots.In addition,both strains of S.tricolor and S.tendae were isolated from the rhizosphere of healthy plants in the diseased plot.2)A soil susceptible to soil-borne disease was collected,and the MH actinomycetesscreening pot experiment was carried out after soil sterilization and Phytophthora capsicum incoculation.Both strains of S.tricolor and S.tangde isolated from the rhizosphere of healthy plants in the diseased plot were identified as MH actinomycetes,which increased the mycorrhizal colonization rate from 26% to 36% and 40%,decreased the blight severity from35% to 20% and 23%,and increased the fruit yield per plant from 21 g to 35 g and 34 g,respectively.In addition,the S.tendae had a stronger performance in directly promoting the mycorrhizal function,while the S.tricolor was also a biocontrol strain that can antagonize P.capsicum.However,the biocontrol strain S.griseoaurantiacus which was isolated from the rhizosphere of diseased plants did not belong to MH actinomycetes.3)The soil susceptible to soil-borne disease was collected again,and another pot experiment was conducted ro evaluate the inoculating effects of MH actinomycetes in the P.capsicum-enriched soil.Inoculation of S.tricolor or S.tendae could change the community composition of soil indigenous AM fungi,and increased the population and colonization of AM fungi,but decreased the population of P.capsicum and the severity of Phytophthora blight,while increased the fruit yield of pepper.Furthermore,the combined inoculation of the two strains performed best,increased AM fungal abundance 2.5 times,and decreased and increased the relative abundances of Claroideoglomus and Paraglomus,respectively.The combined inoculation also increased the colonization from 14% to 40%,and decreased the blight severity from 61% to 20%,but increased the fruit yield per plant from 65 g to 143 g.4)A field which occurred Phytophthora blight frequently was selected to conduct a plot experiment inoculated with or without MH actinomycetes agents.The combined inoculation of S.tricolor or S.tendae could greatly increase the population of actinomycetes in the soil.The combined inoculation had no significant effects on the community composition and diversity of indigenous AM fungi,but significantly increased soil AM fungal abundance,increasing the colonization from 24% to 43%.The combined inoculation also significantly decreased the population of P.capsicum in the soil,decreasing pepper Phytophthora blight severity from 61% to 25%,and finally increasing fruit yield by 40%.As a result,the combined inoculation showed a great application potential in field control of pepper Phytophthora blight.In summary,both strains of S.tricolor and S.tendae isolated from the rhizosphere of healthy plants in the diseased plot could enhance the pepper Phytophthora blight-suppression function of soil indigenous AM fungi,and the combined application had the best effect.