Screening Of Disease Inhibiting And Growth Promoting Fungi And Their Growth Promoting Mechanisms

China is a large agricultural production country.Because of the problems of continuous cropping or excessive use of fertilizer,soil hardness,fertility decline and accumulation of sick and disabled bodies are often caused.Therefore,it is urgent to find a method which can prevent and control soil borne diseases and ensure sustainable development of agriculture.Studies have shown that beneficial fungi can inhibit disease and promote growth by secreting compounds,inhibiting the growth of pathogenic fungi,inducing resistance and other mechanisms,and improve soil texture and structure.Under different environments,endophytic fungi and rhizosphere soil fungi of different host plants will form specific fungal community structure in the long-term evolution process,some of these fungal species will play a certain role in maintaining plant health and ecological stability,while beneficial fungal species in plant tissues and rhizosphere soil may have high application potential.Therefore,this study combined traditional isolation and culture methods with high-throughput sequencing technology to comprehensively analyze the community composition of endophytic fungi and rhizosphere soil fungi of Cucurbitaceae plants cucumber,melon,watermelon and Solanaceae plants pepper in different environments,which is helpful to understand the influence and relationship between endophytic fungi of different plants and rhizosphere soil fungi,At the same time,some strains with the effect of disease inhibition and growth promotion were screened out.The main results are as follows:(1)A total of 1648 strains of fungi were isolated,cultured and identified from plant tissues and rhizosphere soil samples of cucumber,watermelon,melon and pepper in different environments.Endophytic fungi included 44 genera and 78 species,while rhizosphere soil fungi included 75 genera and 153 species.According to the distribution of endophytic fungi and rhizosphere soil fungi in all samples,the dominant genera in Shunyi greenhouse were Alternaria,Cladosporium,Fusarium and Penicillium,and the dominant genera in plantation of Chinese Academy of Agricultural Sciences(CAAS)were Alternaria,Aspergillus,Cladosporium,Fusarium and Plectosphaerella.In the similar cultivation environment,the number and species of endophytic fungi and rhizosphere soil fungi of different crops are different,and each has its own unique endophytic fungi.In the cucumber,melon and pepper plantations of CAAS,the number of endophytic fungi and rhizosphere soil fungi of the same species accounts for 31%,25% and 16% of all rhizosphere soil fungi,respectively.In the cucumber,melon and pepper in Shunyi greenhouse,the number of endophytic fungi and rhizosphere soil fungi of the same species accounts for 11%,17% and 10% of all rhizosphere soil fungi,respectively.The above results showed that the similarity between cucumber endophytic fungi and rhizosphere soil fungi was lower than that of pepper plant samples,and the similarity between melon endophytic fungi and rhizosphere soil fungi was higher.In different cultivation environments,the number and species of endophytic fungi of the same host plant varied greatly,but there were some common species,and the same was true of the rhizosphere soil fungi,indicating that the endophytic fungi of the plant were affected by the rhizosphere soil fungi.In the samples of healthy and diseased plants of watermelon and melon,the community composition of endophytic fungi and rhizosphere soil fungi were quite different.Although there was no significant difference in the number of fungal species and the total number of strains in rhizosphere soil between healthy and diseased plants,it was obvious that the total number of endophytic fungi in healthy plants was higher than that in diseased plants,and the species of endophytic fungi were also different.It was speculated that the health status of host plants was closely related to the number and community structure of endophytic fungi.(2)Illumina Mi Seq sequencing technology was used to evaluate the amplification efficiency of ITS3,ITS4;ITS5-1737 F,ITS2-2043R;FITS7,ITS4 primers for some samples.The results showed that primers ITS3,ITS4 had the highest amplification efficiency for common fungi in plant tissues and rhizosphere soil,and were used for subsequent sequencing analysis of all samples.The results of high-throughput sequencing showed that the diversity of endophytic fungi in different plants under similar cultivation environment was significantly different,and the order from high to low was pepper,cucumber and melon;The dominant genera and their relative abundances of cucumber and melon rhizosphere soil samples were similar in similar cultivation environments,while the dominant genera and their relative abundances of pepper rhizosphere soil samples were more different than those of cucumber and melon;The diversity of endophytic fungi and rhizosphere soil fungi in healthy plants of watermelon and melon was higher than that in diseased plants,but there was no significant difference.(3)Through pot experiment,eight strains with growth promoting effect on cucumber seedlings were obtained,which belong to Penicillium,Aspergillus,Trichoderma,Talaromyces.In the dual culture test,fifteen strains of Trichoderma had strong inhibitory effect on the colony growth of Fusarium oxysporum f.sp.cucumerinum,and four strains were found to have a control effect of more than 40% on cucumber Fusarium wilt,which provided fungi resource for the development of agriculture to prevent disease and promote growth.(4)In order to explore the correlation between the growth promoting traits of different fungi and their ability to promote plant growth,the siderophores production,indole-3-acetic acid(IAA)production and phosphorus dissolving capacity of eight fungi were measured.Five of them with different growth promoting traits were tested in pot experiment to verify their ability to promote plant growth.The results showed that the ability of strain M13026-2 to produce siderophores and dissolve phosphorus was 59% and 216% higher than other fungi,respectively.Although its ability to produce IAA was not significant,it was the only strain that significantly promoted the growth of cucumber seedlings.After r DNA ITS,TUB,Ca M genes sequencing,strain M13026-2was identified as Talaromyces purpureogenus.It was preliminarily judged that the ability of fungi to promote plant growth was most related to the trait of phosphorus dissolving,followed by siderophores production.The potted experiments showed that T.purpureogenus can colonize cucumber tissues and rhizosphere soil stably,which revealed the application potential of T.purpureogenus in agriculture.