Screening And Evaluation Of Trichoderma Stains On The Growth Promotion,Stress Resistance And Its Biocontrol Efficacy Against Banana Fusarium Wilt

Trichoderma sp.are important fungal resource and widely exist in soil.Due to their characteristics of promoting plant growth,diverse biocontrol mechanisms,high efficiency and broad-spectrum in biocontrol,being safe to non-target organisms,and environmental friendliness,they are large numbers of commercialized functional Trichoderma spp.The serious problem of soil desertifi-cation in karst region,represented by Guizhou,is accompanied by the problem of saline-alkali and drought,which directly affects the healthy growth of plants and the development of local agricultural economy directly.At the same time,banana Fusarium wilt caused by FocTR4 has always been a difficult fungal disease to control worldwidely,and there is still no effective control method,causing huge economic losses to the banana industry.The research aims to screen Trichoderma strains with growth promoting,the functions that can improve the survival ability of Orychophragmus violaceus under drought and saline-alkali stress;Screening biocontrol strains of Trichoderma strains with efficient antagonistic FocTR4,and isolating,purifying,and identifying their fermentation metabolites,for providing important biocontrol strains and active compound resources for efficient biocontrol of banana wilt disease.We collected a total of 28 rhizosphere soil samples from 6 provinces,including Jiangsu,Anhui,Sichuan,Guizhou,Guangxi,and Guangdong.141 Trichoderma strains were isolated and screened using plate dilution method.The phosphate solubilizing ability of target Trichoderma strains was determined through MJN and PKO culture media,and the growth promoting ability of target Trichoderma strains was determined by using spore to germinate cucumber seeds and promoting growth of cucumber seedlings in vitro.The growth promoting Trichoderma strain that can improve the growth of O.violaceus under drought and saline-alkali stress were selected.Finnally,this research screened three excellent growth promoting strains,name GZZY-JM-825,GZZY-QS-842,and GZZY-QS-856 respectively;Through plate culture and fermentation broth inhibition tested on pathogen spore germination and mycelial growth,highly effective biocontrol strains on FocTR4 of Trichoderma strains were screened,and three of them with antagonistic effects were ultimately obtained,namely GZZY-QS-856,JSHA-CD-1003,and JSHA-XC-1005.A molecular phylogenetic tree was constructed to identify the taxonomic status of functional Trichoderma strains obtained from the 5 strains respectively.GZZY-JM-825 and GZZY-QS-842 were identified as T.hamatum,GZZY-QS-856 as T.caerulescens,JSHA-CD-1003 as T.brevicompatum,and JSHA-XC-1005 as T.asprellum.Through pot experiments on O.violaceus with greenhouse simulation of drought and salt-alkali reagents condition,the drought and salt-alkali stress resistance effect on the interaction between Trichoderma strains and O.violaceus system were tested.The experiment showed that strain GZZY-QS-856 could promote the growth and increase the survival ability under alt-alkalis and drought stress,and dry weight of O.violaceus increase by 27.4%,60.6% and 11.5% respectively.The enzyme activities of S-UE,S-SC and S-ACP significantly increased in the rhizosphere soil of O.violaceus under salt-alkali stress(43.0%,169.8%,and 41.7%),and under drought stress,S-UE activity increased 44.9%.Strain GZZY-QS-856 is a Trichoderma strain with excellent growth promoting functions.Through biocontrol experiments,the strain JSHA-CD-1003 showed a 60.6% inhibition rate against FocTR4 on plate culture confrontation.The fermentation broth could completely inhibit FocTR4 spore germination within 24 h,and the inhibition rate against FocTR4 mycelium growth within 7 d was 52.6%.The active compound was purified by column chromatography and identified by NMR as trichodermin,with a minimum inhibitory concentration(MIC)of 25 μg/m L.The biocontrol experiment of banana seedlings in pots showed that the fermentation broth of strain JSHA-CD-1003 had a leaf yellowing control rate of 47.4% and a bulbous browning control rate of 52.0% against banana wilt disease.The strain JSHA-CD-1003 has good biological control effects on banana wilt caused by FocTR4,and is a strain with excellent biological control potential.In this study,the Trichoderma strains with growth promoting and functional roles were isolated,which provided important strain resources and potential active compounds for the subsequent research and development of new biological fertilizers and biological agents,and also in the practice of green agriculture,ecological environment restoration of karst rocky desertification,and biocontrol of banana Fusarium wilt,too.