Diversity Of The Microbial Communities In Cotton Field Soil And Roots Infected By Verticillium Dahliae In Xinjiang

Xinjiang is the main cotton-producing region of China.The cotton Verticillium wilt which is very difficult to prevent and causes serious damages.We did this reseach in which we will study the occurrence of cotton Verticillium wilt in the main cotton planting areas of Xinjiang,and also molecular identification of defoliating strains and genetic variation analysis of V.dahliae was researched.This study intends to analyze the diversity of microbial communities in soil and cotton root which infected by V.dahliae using high-throughput sequencing and other methods.The major results are summarized as follows:The proportion of cotton Verticillium wilt fileds in Xinjiang is above 50%in 2015,among them,the proportion of disease fields in traditional cotton-planting areas such as Aksu,Bole and Shihezi has exceeded 70%,and the proportion of severe disease field which has a disease index over 20 is 10.8%.The initial period of Verticillium wilt in Aksu is advanced,the occurrence of Verticillium wilt is obviously related to the monthly cumulative temperature,and there is one disease peak in the whole growth period of cotton.In terms of the culture characters,the V.dahliae in Xinjiang are mainly sclerotia types,accounting for 70.1%.From the defoliating types,the proportion of V.dahliae defoliating strains is above 50%,and these strains are widely distributed in Xinjiang.Genetic variation analysis shows that there is a stable genetic difference between the defoliating and nondefoliating pathotype strains of V.dahliae,however,the genetic variation of V.dahliae is not significantly correlated with its cultural characteristics and geographical origins.The fermentation liquor of V.dahliae significantly inhibits bacterial growth under pure culture conditions,and the highly pathogenic strain has even stronger inhibition ability.However,the invasion of V.dahliae has no significant effect on the bacteria number and the actinomycetes in the soil.Correlation analysis shows that the number of bacteria and actinomycetes in soil are determined by the soil fertility level.The abundance and the diversity of bacterial are negatively correlated with the total salinity in soil and positively correlaed with the total potassium,organic matter,the total nitrogen and the total phosphorus,but it has no significant correlation with the degree of Verticillium wilt.RDA analysis shows that the most of bacterial communities have no significant correlation with the degree of Verticillium wilt in cotton filed soil.However,it has significantly correlation with the content of soil organic matter,total salinity and total nitrogen.Cluster analysis shows that the diversity of bacterial communities has been changed significantly in different sampling periods,the bacterial communities firstly show obvious temporal tendency in Korla cotton soil,and secondly,show obvious spatial tendency.The temporal tendency and spatial tendency of bacterial communities in Shihezi and Aksu soil are opposite to Korla.The cultivated fungi amount of cotton field soil having serious disease in Aksu and Shihezi is larger than that in the controlled field,and in some months this difference is significant.There is no significant difference about the number of cultivated fungi in Kurla between cotton fields having serious disease and controlled cotton fields.The invasion of V.dahliae has no significant effect on the number of cultivated fungi in short term.The number of fungi in soil is positively correlated with the organic matter and the total nitrogen content,and it is negatively correlated with the total potassium content.The microsclerotium of V.dahliae is mainly distributed in the soil layer of 0-20cm and the content of microorganism is positively correlated with the degree of Verticillium wilt.The number of microsclerotium of the bulk soil in the diseased cotton is significantly higher than that in healthy cotton.The higher disease resistance cotton has the lower number of microsclerotium in the soil.The diversity index of fungi is positively correlated with microsclerotium,organic matter and total nitrogen content,but significantly negatively correlated with total potassium content in soil.RDA analysis shows that there is significant correlation between the fungal communities with organic matter,total nitrogen and total salt content in soil.Cluster analysis shows that the fungal communities in different regions are similar in a certain period.The fungal communities firstly show an obvious temporal tendency in Korla cotton soil,and secondly show an obvious spatial tendency,the temporal tendency and spatial tendency of fungal communities in Shihezi and Aksu soil are opposite to Korla.The abundance and diversity of the endophytic bacterial communities in the root of susceptible cotton cultivars are higher than that of resistant varieties.When the cotton was infected by V.dahliae the abundance of bacterial communities in the root decreases and the diversity increases,there was a difference in the abundance of bacterial communities in the root of resistant between tolerance cotton cultivar.The cluster analysis shows that in the root of healthy cotton there is a high similarity of endophytic bacterial communities between resistant and susceptible varieties,however the changes of endophytic bacterial communities in the root of susceptible cotton cultivars are larger than these in resistant cotton varieties when they are infected by V.dahliae.