Studies On The Bacterial Community Diversity Among Soil Depths And The Relationship With Tobacco Bacterial Wilt In The Topsoil

Tobacco bacterial wilt is a typical soil~borne bacterial and vascular bundle disease caused by Ralstonia solanacearum.R.solanacearum is famous for their wide range of hosts,complex geographical distribution,pathogenicity and diverse physiological characteristics,which results in the refractory treatment of bacterial wilt disease.In recent years,the global extreme climate,short~time heavy rainfall and long-term high-temperature dry weather give rise to the occurrence of bacterial wilt,resulting in the decline in the quality of agricultural products,which becomes more a prominent and seriously threatening to the agricultural production and sustainable development of human society.It's urgent to achieve the effective prevention and control of bacterial wilt!At present,the research on the bacterial wilt focuses on the mechanism of the interaction between pathogens and hosts,the process of interaction between soil microbes or some functional microbes and plants and pathogens,and the effects of plant root active substances on interaction between plants and pathogens.The exploration of control technology by soil microbial regulating to control bacterial wilt is only at the macroscopic overall level.This study works on achieving the effective control of tobacco bacterial wilt and exploring the key microbial factors related to the disease.We forced on soil layers,and evaluated the occurring of bacterial wilt among soil depths firstly,and then,we analysis the distribution of Ralstonia solanacearum and the characteristic of microbial structure diversity among soil depths systematically.This study makes up the blank of soil stereoscopic microbial structure in the research field of bacterial wilt,and provides theoretical support for figuring out the microbial mechanism of bacterial wilt,and realizing the accurate control of it.1.The content of Ralstonia solanacearum among soil depthsThe content of Ralstonia solanacearum in disease soil,ranged from 1.25×10~8 copies/g to 5.72×10~8 copies/g,was higher non~disease soil,which ranged from 0.907×10~8 copies/g to 2.30×10~8copies/g in all three soil depths,and it was found that the content of 10~30 cm was significantly higher than soil layer of 0~10 cm,while the content of Ralstonia solanacearum in the soil layer of10~20 was the highest.2.The relationship between bacterial wilt and soil depthsThe pathogenicity in soil layer of 20~30 cm is the strongest,and 0~10 cm is the second,10~20cm is the weakest.The suppressive ability of the soil layer in 10~20 cm is the strongest,and 20~30cm is the second,while 0~10 cm is the weakest.The results showed that the soil layer of 10~20 cm had obvious inhibitory effect on bacterial wilt,with the weakest pathogenicity and the strongest suppressive ability,which could be used as an important research object to find the key factors of suppressive disease in the next stage.At the same time,the soil layer of 20~30 cm has the strongest pathogenicity and weak suppressive ability,which can be used as the main research object to find the key factors of bacterial wilt,and be focued on its control effection on tobacco bacterial wilt.3.The microbial community structure among soil depths(1)The most top 4 abundant phylum were proteobacteria,Actinobacteria,chloroflexi,and Acidobacteria in disease soil and non-disease soil.By Principal Co-ordinates Analysis,we analyzed the microbial community structure among soil depths in disease and non-disease soil,and the results showed that there was no significant difference of bacterial community structure among soil depths.(2)Holophaga and Acidibacter were found that which were enrich in deeper soil layer,which could be related to bacterial wilt.A total of 22 genera closely related to the genus were screened in the disease soil.Among them,2 genera were positively correlated with the abundance of the genus Ralstonia,and 20 genera were negatively correlated.A total of 8 genera closely related to the genus Ralstonia were screened in the non-pathogenic soil.Among them,there were 5 genera negatively correlated with the abundance of the genus Pseudomonas,and 3 genera were positively correlated,and the results showed that the 28 of the selected species were negatively correlated with the abundance of the genus Ralstonia,and the two soil environments showed a negative correlation with the genus Nocardioides.Mucilaginibacter,on the other hand,was positively correlated with the genus.(3)Mucilaginibacter,whose abundance was positively correlated with the genus Ralstonia,was higher in the non-disease soil than in thedisease soil,and there was little difference in the distribution of different soil layers,while the genus Norcardia,whose abundance was significantly negatively correlated with the genus Ralstonia,abundance in 0~10 cm and 20~30 cm soil layer,the pathogenesis was higher than that of the non-disease soil,and in the 10~20 cm soil layer,the abundance of the genus Norcardia was higher than that of the disease soil.In the non-disease soil,the abundance of the genus Terrabacter,whose abundance is negatively correlated with the genus Ralstonia,was significantly higher in the surface soil(0~10 cm)than in the deep soil(10~20 and20~30 cm),while the genus Sorangium was a positive correlation with the soil layer,and the abundance increased through soil depths significantly.So,we should focue more on the bacterial communities Holophaga,Acidibacter,Norcardia,Mucilaginibacter,Terrabacter and Sorangium,trying to figure out what kind of function they executed and the relationship with tobacoo bacterial wilt.4.Regulating the soil microbial environment among soil depths to control tobacco bacterial wilt(1)Surface soil(0~10 cm)possessed the characteristics of with fast water loss,the most direct influence of rainfall and high fluctuation of soil temperature affected by illumination.While,temperature and humidity of the deeper soil(10~30 cm)are more stable,and less affected by light and rainfall.By wiping off the mulch,the soil temperature can be significantly reduced by 1.7?~3.7?,and soil humility were reduced by 50%,resulting in improving the soil environment with mulch.At the same time,the content of Ralstonia solanacearum in the soil layer of 20~30 cm were significantly reduced,and tobacco bacterial wilt reduced by 44.19%.The increase of soil on the ridge can further promote control effect on tobacco bacterial wilt.(2)After treatment of bioachar on different soil layers(0~10 cm,10~20 cm and 20~30 cm),the soil pH were significantly increased by 0.46~0.65(p<0.05),but there were no significant effect on the amount of Ralstonia solanacearum,and could not control tobacco bacterial wilt.The treatment of Fluorescent Pseudomonas and streptomycin sulfate can reduce the amount of R.solanacearum in a certain range and thus possessed a significant control effect on bacterial wilt.The difference was that Fluorescent Pseudomonas only inhibits R.solanacearum in the treatment soil layer,and the control effect of tobacco bacterial wilt was the best in deep soil layers(10~30 cm).while,the effect of streptomycin sulfate on the soil layer below the treatment layer is more obvious,and the control effect on tobacco bacterial wilt was the best when the surface soil(0~10 cm)is treated.After what this study had done and what we had figured out preliminarily,we strongly suggested to focus on the deeper soil when trying to control bacterial wilt in the future,in view of reducing the content of Ralstonia solanacearum in disease soil.