The Population Structure Of Pathogens Causing Red Kidney Bean Root Rot In Shanxi And Analysis Of Microbial Diversity In Rhizosphere Soil

Shanxi Province is one of the main production areas of red kidney bean(Phaseolus vulgaris)in China.The exports of red kidney beans produced in Shanxi account for more than 50% of the country.Root Rot disease is becoming more and more serious because of continuous cropping all year round,which seriously restricts the development of red kidney beans industry in Shanxi province.Clarifying the species and infection rule of pathogen causing red kidney beans root rot disease was the basis of effective control measures.This paper studied the population structure of pathogens and the effect of root rot disease on rhizosphere microbial diversity of red kidney beans in Shanxi Province,including the following aspects:1.In 2018 and 2019,a survey was conducted on red kidney beans root rot disease in Shanxi Province.The results showed that the disease was distributed in Kelan County,Jingle County,Yangqu County,Lan County,Ningwu County,Dai County,Shenchi County,Yuanping City,Wuzhai County.The disease field rate is generally between 10% and 50%,and the disease field rate in some serious plots can reach 80%.Multi-point sampling method were used to collect 168 samples.2.A total of 302 strains pathogen were separated by tissue isolation and single spore isolation,it was identified by the analysis of morphology and the r DNA-ITS gene sequence.Including Fusarium oxysporum,F.equiseti,Alternaria sp.,F.solani,Clonostachys rosea,Rhizoctonia solani,F.tricinctum,F.proliferatum,F.redolens,Colletotrichum sp.,Bipolaris sp.,Curvularia lunata,Phoma sp.,F.chlamydosporum,F.incarnatum.The pathogenicity test of representative strain isolated from 15 species was determined by wheat sand-soil mixing inoculative method.The results showed that all 15 species were pathogenic and the incidence rate was between 8.33%-100%.R.solani had the highest pathogenicity,the incidence rate was100% after inoculation.To our knowledge,this is the first report of F.redolens,Phoma sp.and Bipolaris sp.affecting Phaseolus vulgaris in China.The dominant pathogen was F.oxysporum,171 strains were obtained and the isolation frequency was56.62%.Among a variety of isolates,F.incarnatum,F.chlamydosporum,Bipolaris sp.and Phoma sp.were isolated only in Kelan County,while C.lunata was isolated only in Jingle county.Three or more pathogen species,two pathogen species and one pathogen species isolated from the same infected plant accounted for43.86%,29.82% and 26.32% respectively.3.The pathogens were selected for biological characteristic study.The results showed that the tested strain could grow in the range of 10~30 ?.The optimum temperature for the growth of F.oxysporum,F.redolens and Phoma sp.mycelial was 25?,that for R.solani mycelial was 20 ?,that for Bipolaris sp.mycelial were 25~30?,and that for F.equiseti mycelial was 30?.Light and alkaline conditions were more suitable for pathogen mycelial growth.Glucose and maltose was the most suitable carbon source for the mycelial growth of F.oxysporum.Except maltose,other carbon sources had significant effect on the mycelial growth of F.redolens;the carbon sources inhibited the mycelial growth of F.equiseti and Bipolaris sp.;maltose was the most suitable carbon source for the mycelial growth of Phoma sp.and R.solani.The results showed that the growth of F.oxysporum,Phoma sp.and R.solani was inhibited by the tested nitrogen source;the growth of Bipolaris sp.was less affected by the tested nitrogen source;glycine was the most suitable nitrogen source for the growth of F.equiseti,and sodium nitrate was the most suitable nitrogen source for the growth of F.redolens.4.The high-throughput sequencing method was used to analyze the relationship between microbial richness,diversity,community composition and soil physical and chemical factors in the block soil,the soil where root rot occurred and in the soil where root rot did not occur.The results of microbial diversity analysis showed that the diversity and richness of soil bacterial community decreased first and then recovered in the three stages of pre planting,early flowering and maturation stage.There was no significant difference in the diversity and richness of fungi in the three stages of pre planting,flowering and maturity,and there was no significant difference between the the soil root rot disease occurred and the soil root rot disease did not occur.The number of biocontrol strains such as Streptomyces,Bacillus,Allorhizobium-NeorhizobiumPararhizobium-Rhizobium and Chitinophaga increased significantly at the early flowing stage.Among the fungi,Metarhizium,Humicola,Mortierella and Chaetomium were significantly accumulated in the soil root rot disease did not occur.the content of Fusarium and Phoma in the soil with root rot disease was significantly higher than that in the soil root rot disease did not occur.The TP content in soil was positively correlated with Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium and Streptomyces,but negatively correlated with Fusarium.The content of AN was positively correlated with that of Humicola and Chaetomium,but negatively correlated with Fusarium.