Screening Of Salt-and Acid-tolerant Bacteria And Their Multi-resistance Against Som E Fungal Diseases On Plants

Soilborne fungal diseases are a type of plant diseases that are widely distributed and as such cause great harm in agricultural production.Misuse of fertilizer and longterm continuous cropping leads to unbalanced soil physicochemical properties,resulting in a series of problems such as soil acidification,salinization,accumulation of pathogenic bacteria and reduction of beneficial microorganisms,which contributes to soilborne diseases aiming at the current status on soil acidification and salinization,with fungal biocontrol agent in focus,this paper provides a study on the screening of salt and acid tolerant functional bacteria strains and their antagonistic activity on various pathogenic fungi and explores their functional properties on plant growth and development.The resistance and functional effects,of these strains and their cultivation and optimization of fermentation conditions lays the foundation for potential biological control agent.Firstly,acid and salt tolerant functional strains with high antagonistic activity were screened.These strains were obtained from acidic soil,saline soil and acid-salt-tolerant plants.Acid-tolerant high-salt medium was used to culture these strains.At the end of the screening,90 bacteria strains were obtained.These strains were tested on 6 plant pathogenic fungi(Athelia rolfsii,Fusarium oxysporum,I.mors-panacis,Colletotrichum fragariae Brooks,Glomerella cingulata and Botrytis cinerea Pers)for their antagonistic activity using the plate confrontation method.17 strains from 6 genus were selected for their high antagonistic activity: 10 strains of Bacillus,2 strains of Pseudomonas,2 strains of Lysinibacillusand,1 strain each for Rhizobium,Agrobacteriums and Burkholderia.The results of acid and salt tolerance tests showed that all 17 strains were resistant to 5% Na Cl,of which Pseudomonas starins LG-1 and SH8-4 were resistant to 7% Na Cl,and Bacillus strains HZMJW1-10,HZMJW1-11,ZJTZ2,SH8-2,SH8-5,SH8-6 and Burkholderia SH8-3 can withstand 11% Na Cl;Lysinibacillus HZLJC2-2 and HZLJC2-9 can be grown in acid-resistant medium with a p H of 2.Five strains(Bacillus HZMJW1-10,Bacillus HZMJW1-11,Pseudomonas LG-1,Bacillus ZJTZ2,and Burkholderia SH8-3)had more than 50% inhibition on all 6 pathogenic fungi.These same strains have a strong inhibitory effect on 9 other plant pathogenic fungi,thus obtaining 5 strains of acid-and salt-resistant and multi-resistant bacteria.Secondly,4 different kinds of antagonistic bacteria from the 5 strains of multiresistant bacteria were selected for disease resistance and other functional tests.In vitro tests showed that the inhibition effect of 4 strains of antibacterial mould and anthrax on grape,root rot of panax notoginseng,root rot on tomato,southern blight on tomato and blight on watermelon recorded more than 75%;The results of the pot experiment showed that HZMJW1-10,LG-1 and SH8-3 were effective against southern blight on tomato and blight on watermelon in normal soil(neutral,non-salinized)or facility soil(acidic,salinized)The biological control effect of the fungal diseases reached 100%,and the antagonistic activity of ZJTZ2 was 66.67%.Next,specific antibiotics were used to amplify the antibiotics synthase genes of the four strains.As a result,it was found that all four strains had the potential to synthesize iturin A.The iron-producing carrier,IAA and ACC deaminase production were detected,and it was found that all four strains can produce IAA;LG-1 and SH8-3 can produce iron carrier,of which SH8-3 has the highest yield,21.97 ?g/m L,LG-1 has ACC deaminase activity,which shows that these four strains do not only have the function of acid resistance,and high antagonistic activity,but also have the ability to promote plant growth and development.Finally,the single-factor test,orthogonal test and response surface method were used to optimize the medium composition,ratio and fermentation conditions of the four functional strains.Single factor and orthogonal test results showed that the best carbon source of strains HZMJW1-10,LG-1,ZJTZ2 and SH8-3 is glucose(2%),inorganic salt is potassium chloride(0.4%),strain HZMJW1-10 nitrogen source for ZJTZ2 is peptone(1%),and nitrogen source for strains LG-1 and SH8-3 is potassium nitrate(1%);The optimal culture conditions for the four strains were 28?,220 r/min,initial p H of 7 and 3% inoculation volume.The results of the optimal fermentation of functional bacteria through the response surface test showed that the inhibition rate of the optimized strain LG-1 against the pathogen of Glomerella cingulata was 1.38 times before optimization,and the inhibition rate of other strains after optimization were obviously improved.In summary,this study obtained 5 acid and salt resistance strains that can antagonize 15 common plant pathogenic fungi and have multi-functional abilty to promote plant growth and development.By optimizing the fermentation conditions,it can effectively improve the inhibition of pathogenic fungi,which induces soil acidification and salinization.This thesis therefore serves as a reference for biological control of fungal soilborne diseases.