Comparative Study On The Rootzone Soil Microecology Of Diseased And Healthy Plants Of Casuarina Spp.Bacterial Wilt

Casuarina spp.is an evergreen tree or shrub found in tropical and subtropical regions,native to Australia,the Pacific Islands and southeastern Asia.Casuarina spp.is highly adaptable and has the characteristics of drought resistance,barrenness resistance,and saltalkali resistance.It has a wide range of uses,can prevent wind and sand,resist natural disasters along the coast,and improve the ecological environment.It is the main tree species planted in the backbone forest belt of coastal protection forests in my country.In recent years,Casuarina spp.has frequently occurred in coastal areas of my country,especially in western Guangdong Province,and the ecological security of coastal areas has been seriously threatened.The bacterial wilt of Casuarina spp.,which caused by Ralstonia solanacearum,is a soil-borne disease.Because Ralstonia solanacearum has a wide range of hosts,unique pathogenic mechanism,strong mutation ability and strong survivability under the conditions of absence of host,which decide that its prevention is extremely difficult.The pathogenic mechanism of Ralstonia solanacearum is very complicated.It usually invades the plant from the root of the host,propagates in the intercellular space of the cortex invades the vessel and the adjacent tissues,and produces a lot of exopolysaccharides(EPSI)in the host,clogs and destroys the host’s vascular system,ultimately killing the host.At present,studies have shown that inoculation with Frankia and mycorrhizal fungi have a significant role in improving Casuarina spp.against bacterial wilt.However,in the practice of controlling bacterial wilt of Casuarina spp.,there are still problems such as unstable effects of biocontrol agents and low soil survival efficiency of biocontrol bacteria.Therefore,this study aims to address the problem of prevention and control of bacterial wilt of Casuarina spp.from the regulation of soil.This study selected the same cloned Casuarina spp.from Dacheng Town,Raoping County,Chaozhou City of Guangdong Province,Tangwei Town,Wuchuan City and Qianshan Town,Xuwen County of Zhanjiang City as the research objects.Investigating the disease index of bacterial wilt and collecting soil from the root-zone of diseased and healthy plants of Casuarina spp.in 3 plots.A total of 54 soil samples were collected.This study analyzed and compared the biological characteristics of the root-zone soil of healthy and diseased plants of Casuarina spp.,including the physicochemical properties of root-zone soil,extracellular enzyme activity and microbial(bacteria and fungi)community structure,and explored the relationship between the root-zone soil physicochemical properties,extracellular enzyme activity and microbial community structure of Casuarina spp.and the occurrence of bacterial wilt.In order to start from the regulation of root-zone soil microenvironment to address the prevention and control of bacterial wilt problem of Casuarina spp.,so as to provide reference and technical guidance for the effective prevention and control of the bacterial wilt.It was found that:(1)The organic matter,total nitrogen,alkaline nitrogen,total phosphorus,rapid available phosphorus,total potassium and rapid available potassium contents of the root-zone soil of healthy plants were higher than those of diseased plants,with significant differences in total nitrogen content and extremely significant differences in organic matter,rapid available phosphorus,total potassium,rapid available potassium and alkaline nitrogen.(2)There was an extremely significant positive correlation between disease degree and polyphenol oxidase activity,and a negative correlation with acid phosphatase,invertase,catalase and peroxidase.(3)The contents of available silicon,exchangeable calcium,exchangeable magnesium,available iron and available manganese in the root-zone soil of the diseased plants of Casuarina spp.are lower than those of healthy plants.There were significant differences in the root-zone soil of available silicon content between the diseased and healthy plants in all plots,the content of available silicon,exchangeable magnesium,and available manganese in the root-zone soil of Casuarina spp.showed a significant negative correlation with the disease degree of bacterial wilt.(4)Crossiella and Conexibacter are dominant microorganisms in the root-zone soil of the healthy plants,and Crossiella has an extremely significant positive correlation with the contents of total potassium and alkaline nitrogen in the soil.Conexibacter has a significant negative correlation with the contents of total phosphorus,rapid available phosphorus and organic matter in the soil,and extremely significantly negatively correlated with soil p H.Gloniaceae is the dominant microorganism in the root-zone soil of healthy plants and negatively correlated with the contents of rapid available potassium,rapid available phosphorus,alkaline nitrogen,total potassium,total phosphorus and electrical conductivity,and positively correlated with soil p H,the contents of total nitrogen and organic matter.Therefore Crossiella,Conexibacter and Gloniaceae have great application potential in the development of biological agents and should be given sufficient attention in future research.