Study On The Relationship Between The Occurrence Of Typical Soil-Borne Diseases Of Tobacco And The Characteristics Of Root Micro-Environmental Factors

In order to further clarify the relationship between the occurrence of typical soil-borne diseases of tobacco and the number of pathogenic bacteria,microbial community and environmental factors in root microenvironment,the key factors leading to the occurrence of diseases were preliminarily revealed,so as to provide the necessary theoretical support for the screening and application of biocontrol bacteria in the future.The typical soil-borne diseases of tobacco,bacterial wilt or black shank,were selected.The roots and related soil samples of healthy and diseased tobacco plants in different ecological tobacco areas were collected by surface investigation.The differences in the number of pathogens,microbial communities and environmental factors in the root microdomains of healthy and diseased tobacco plants were compared.The relationship between the occurrence of soil-borne diseases and the number of pathogens,microbial communities and environmental factors in the root microdomains was analyzed.The main results are as follows :(1)Ralstonia solanacearum and Phytophthora nicotianae were simultaneously detected in all samples regardless of the individual or mixed disease symptoms of tobacco plants.The results further verified that the actual incidence of tobacco plants was not only related to the number of pathogens,but also significantly affected by other microecological environment factors.Even so,the number of pathogenic bacteria detected in each part of the root microdomain of the diseased tobacco plants was significantly higher than that of the healthy tobacco plants.The number of Ralstonia solanacearum gradually increased from the non-rhizosphere rhizosphere soil,and the number of Phytophthora nicotianae was the highest in the rhizosphere soil.(2)The microbial community structure of the root microdomains of the diseased tobacco plants was significantly different.The Alpha diversity of the rhizosphere and root bacterial communities was higher than that of the healthy tobacco plants,and the beta diversity tended to be consistent.Tax4 Fun function prediction showed that the metabolic function of bacterial community in rhizosphere and root of diseased tobacco plants was significantly different from that of healthy controls.The function of bacterial community in rhizosphere soil was mainly to promote the growth of bacteria and pathogens,while the function of endophytic bacterial community in roots was mainly to promote growth and resist stress.(3)The microbial composition of the root microdomain of the diseased tobacco plants changed significantly.The abundance of Actinobacteria was significantly lower than that of healthy tobacco plants,while the Firmicutes in the roots were the opposite..LEf Se analysis showed that the number of different species in rhizosphere soil was less than that in healthy control,while the number of different species in roots was significantly more than that in healthy control.The co-occurrence network analysis showed that the interaction between microbial species in each part of the root microdomain of the diseased tobacco plants changed,and there were significant differences in core species.(4)The soil physical and chemical properties of each component in the root microdomain of the diseased tobacco plants also changed greatly.The available potassium content in the rhizosphere soil increased significantly by 54.7 %,the soil invertase activity increased significantly by 11.6 %,and the soil urease activity decreased significantly by27.3 %.(5)Correlation analysis showed that root bacterial communities were more susceptible to pathogens than complex soil bacterial communities.Rhizosphere soil differential genera such as Acidobacteria RB41,Nitrospira and Anaerolinea were significantly correlated with multiple soil chemical indicators,while root endophytic differential genera were less significantly correlated with soil environmental factors.There was no significant correlation between the differential genera in the rhizosphere soil and the pathogenic bacteria in the rhizosphere soil.However,the root endophytic differential genera such as Comamonas,Chryseobacterium and Delftia were significantly positively correlated with Ralstonia solanacearum in the rhizosphere soil,and Flavobacterium was significantly positively correlated with Phytophthora nicotianae.In summary,the occurrence of soil-borne diseases in tobacco plants is closely related to environmental factors such as the number of pathogen colonization,bacterial community composition and diversity,and soil physical and chemical properties.While controlling the absolute number of pathogens,adjusting the soil micro-ecological environment is an important strategy to alleviate the occurrence of soil-borne diseases.