Resons For High Yield And Disease Resistance Of Intercropped Konjac In Locust Forest And Screening Of Antagonistic Strains Of Soft Rot Pathogen

Amorphophallus is the only plant capable of synthesizing glucomannan in large quantities.Konjac have great economic value and is widely planted in southeast mountainous area,Yunnan-Guizhou Plateau,Sichuan Basin and southern mountainous area of Qinling Mountains.However,the occurrence of konjac soft rot often leads to production reduction or even extinction,which affects the entire konjac industry chain from the source and restricts the high-quality development of our konjac industry.In the production,the characteristics of intercropped konjac under Robinia pseudoacacia with low obstacle,mild disease and high yield were particularly significant.In order to investigate the causes of high yield and disease resistance in intercropped,this paper analyzed the culturable microbial community structure and diversity in rhizosphere soil of healthy and diseased konjac under R.pseudoacacia and Paulownia fortunei pure forest.In addition,antagonistic strains of konjac soft rot were screened.The main research results were listed as follows:1.The pathogenic bacterium of konjac soft rot D36 is Pectobacterium aroidearum,which was isolated from the konjac disease plants under the black locust and paulowia forests in Taohe Town,Langao County,Ankang City.It had strong pathogenicity to dicotyledon plants such as carrot,cabbage and potato,without host specificity.2.In the case of three years of continuous cropping,the incidence of konjac soft rot in black locust forest was lower(18.83%),while that in paulownia forest was higher(30.33%).3.A total of 227 strains and 178 species of microorganisms were isolated from the rhizosphere soil of konjac intercropped under pure forest of black locust and paulowia.Among them,there were 32 same microorganisms species,81 and 65 unique microorganisms species,respectively.In the rhizosphere soil of konjac intercropped in black locust forest,Streptomyces,Bacillus and Fusarium were dominant genus,and Bacillus thuringiensis,Bacillus wiedmannii and Mortierella alpina were dominant species.In the rhizosphere soil of konjac intercropped in paulownia forest,Fusarium and Bacillus were dominant species,and Bacillus subtilis and Bacillus thuringiensis were dominant genus.In addition,the relative abundance of Streptomyces in the rhizosphere soil of intercropped konjac under black locust was significantly higher than that in paulownia forest(p<0.05).4.The dominant genera in the rhizosphere soil of healthy konjac were Bacillus,Fusarium and Penicillium,while the dominant species were Bacillus wiedmannii,Mortierella alpinum and Linnemannia elongata.The dominant species of Bacillus cereus,Bacillus thuringiensis and Lysinibacillus fusiformis in the rhizosphere soil of diseased konjac were Fusarium,Bacillus and Streptomyces.The relative abundances of Bacillus and Streptomyces were higher in diseased than that of healthy konjac rhizosphere soil.5.Five bacteria strains antagonistic effects against P.aroidearum were identified,namely Bacillus amyloliquefaciens,Bacillus velezensis,B.subtilis,Bacillus sp.and Paenibacillus sp..The antagonistic effects of the first three strains were significant,and their inhibition rates were between 60.95% and 70.00%.In conclusion,the pathogen of konjac soft rot in Taohe Town was P.aroidearum.Under three years of continuous cropping,the incidence of konjac soft rot in black locust forest was lower than that in paulownia forest.May be related to the relatively high abundance of unique rhizosphere soil microorganisms,especially Streptomyces,that are unique to black locust intercropped konjac.Bacillus is not only the dominant population in the rhizosphere soil of konjac,but also the main antagonist group of against soft rot pathogen.From the aspect of culturable microbial community structure and function in konjac rhizosphere soil,this paper preliminarily explored the reasons for lower incidence of konjac soft rot in black locust forest,and screened out several bacteria strains antagonistic konjac soft rot pathogen.This paper will provide theoretical basis and several bacteria strains for the prevention and control of konjac soft rot.