Screening Of Biocontrol Actinomycetes And Repair Mechanism Of Watermelon Continuous Cropping Obstacle

Actinomycetes are a kind of important biocontrol bacteria,which can resist plant diseases and promote plant growth by producing plant hormones,secondary metabolites,inducing plant systemic resistance,adjusting rhizosphere microbial community structure and so on,and have great application potential in controlling continuous cropping obstacles in soil.Screening of actinomycetes with good biocontrol potential and facilitating the development of actinomycetes products are still an important part of biocontrol research and development in China.Our previous study found that actinomycetes and their active substances had good control effect on watermelon fusarium wilt.In this study,the actinomycetes resources accumulated in the early stage of the research group were used as the test materials,and the excellent actinomycetes strains were selected to promote growth by antagonism and re-screening,and the watermelon continuous cropping obstacle soil was used as the test soil to study the repair effect and mechanism of the continuous cropping obstacle of watermelon through pot experiment,which laid a foundation for the development of actinomycetes products.The main research results of this study are as follows:(1)The results of antagonistic activity screening showed that there were 4actinomycetes with antagonistic activity against all 6 strains of pathogenic bacteria,accounting for 9.8% of the tested strains.Among them,18 strains had higher antibacterial activity against Fusarium oxysporum,and 20 strains had higher antibacterial activity against Fusarium oxysporum f.Sp.The test of growth-promoting results show that actinomycetes cell-free fermentation filtrate concentrate has inhibitory effect on plant growth,diluted 10 times or more actinomycetes fermented liquid can promote the growth of wheat seedlings,filter to obtain 14 strains of wheat seedling’s height,root length,fresh weight actinomycetes strains were has a significant role in promoting.The results showed that Streptomyces flavorariabilis had the best control effect on watermelon fusarium wilt.Compared with the control,the incidence of blight disease decreased by 80%,the crown area increased by 310%,and the root activity increased by 47%.(2)The application of Streptomyces aureus could significantly reduce the incidence of watermelon wilt and promote the growth of watermelon seedlings.Compared with the control,the plant height,root activity,SPAD and crown area of watermelon seedlings increased by 25.5%,49.4%,24.7% and 234.1% in the first crop soil,grafted continuous cropping soil and self-root continuous cropping soil,respectively.11.8%,22.2%,27.4%,170.6%,8.2%,33.6%,10.7%,175.7%;The activities of PAL,PPO and POD were increased by 95%,45%,10%,66%,6%,25%,77%,49%,23%,respectively.The contents of urease,sucrase and phosphatase in soil increased by 307%,47%,4%,45%,41%,10%,88%,61%,4%,respectively.(3)The application of yellow microgreen Streptomyces microbial agent significantly changed the rhizosphere soil microbial community structure of watermelon seedlings.After inoculation,the complexity of the microbial interaction network in the rhizosphere soil of the watermelon seedlings in the first crop of watermelon plants was reduced,and the key species changed from Phenylobacterium and Xanthomonadaceae to Nitrospira,Burkholderiaceae,Devosia,Pelagibius;the complexity of the soil microbial interaction network of grafted watermelon continuous cropping has increased,and the key species are Sphingomonas,Sphingopyxis,Novosphingobium,Ascomycota changed to Longimicrobiaceae,Lactobacillus,Unspecified＿Ascomycota,unspecified Fungi;self-rooting watermelon continuous cropping soil microbial interaction network complexity is reduced,the key species are Pseudomonas,Rhizobium,Geobacter Pedobacter,Micrococcaceae,Longimicrobiaceae changed to Xanthomonadaceae,MND1,Streptomyces,Nitrospira.The above results indicate that due to the influence of the soil background microbial community structure,Streptomyces aureus The role of soil microbial community structure in the rhizosphere of different types of soils is different.(4)The LEfSe enrichment analysis found that the application of the yellow and microgreen Streptomyces fungus to different types of watermelon continuous cropping soils will induce the enrichment of beneficial bacteria belonging to the genus Streptomyces,Pseudolabrys,and Acidothermus,Nocardioides,Kribbella and Amycolatopsis,and the relative abundance growth rate of beneficial bacteria on self-rooted soil is significantly higher than that of the other two types of soil.It indicated that Streptomyces aureus may improve the rhizosphere microbial community structure and improve the disease resistance of watermelon seedlings by recruiting these beneficial bacteria.(5)LEfSe enrichment analysis found that the relative abundance of beneficial bacteria in the soil of the first watermelon planting without the application of fungicides was significantly higher than that of the other two types,while the relative abundance of harmful bacteria in the soil of continuous cropping of self-rooted watermelon Significantly higher than the other two types,indicating that continuous planting of self-rooted watermelon will increase the species and number of harmful bacteria in the rhizosphere soil,resulting in an increase in the incidence of watermelon wilt.