The Growth And Decline Of Sweet Potato Stem And Root Rot Pathogens In Soil And The Effect Of Rotation On The Amount Of Pathogens

Sweet potato stem and root rot is a newly discovered and very harmful bacterial disease in China in recent years.It has become one of the most serious diseases in the main production areas of sweet potato in South China,which has a great impact on the agricultural economy.In this paper,a rapid,efficient and quantitative method for the detection of sweet potato stem and root rot pathogens in soil was established,and a corresponding standard curve for the concentration of Dickeya dadandii was established.The relationship between the population of pathogen groups in soil and the severity of sweet potato stem and root rot was studied to determine the concentration threshold of pathogenic bacteria causing the disease.Initially explored the law of the growth and decline of pathogenic bacteria in the soil under the stable environment,and carried out rotation experiments of sweet potato and a variety of non-host crops.This study aims to provide a scientific reference for the development of comprehensive prevention and control technical measures for sweet potato stem and root rot.The main findings are as follows:1.A corresponding standard curve was established for the concentration of sweet potato stem and root rot pathogen in soil.Add 1×10~7 CFU/mL、1×10~6 CFU/mL、1×10~5 CFU/mL、1×10~4 CFU/mL、1×10~3 CFU/mL、1×10~2 CFU/mL、1×10~1 CFU/mL bacterial suspension to the sterilized soil,extract the total DNA of microorganisms in soil,use fluorescence quantitative PCR technology and DNA as reference.In the reaction system,specific primers Ddad3/Ddad4 and probe ADdad2 designed by the predecessors of this laboratory were added to the reaction system to amplify the standard template.After the reaction,use the absolute quantitative method,take the pair value of the standard concentration of sweet potato stem and root rot pathogen in the soil as the x-axis,the Ct value determined by qPCR as the y-axis,establish the standard curve.The linear regression equation is y=-3.1886x+40.215,and the correlation coefficient is R~2=0.9978.Compared with the traditional plate separation method,the real-time fluorescent quantitative PCR method relies on the Ct of the samples by qPCR and comparing with the standard curve,the concentration of the sweet potato stem and root rot pathogens in the soil can be calculated,and the purpose of quantifying the pathogens can be achieved without the process of pathogen and soil were isolated and cultured.It shortens the detection time by 6 times and improves the accuracy by 20%.The standard curve of the concentration of sweet potato stem and root rot pathogens in the soil provides technical support for the efficient and quantitative detection of Dickeya dadantii.2.Study on the relationship between the population of pathogen groups in soil and the severity of sweet potato stem and root rot.In the seedling pot,mix the suspension of Dickeya dadantii of 1×10~7、1×10~6、1×10~5、1×10~4、1×10~3、1×10~2 CFU/mL,insert sweet potato seedlings with uniform growth,observe and record the incidence of sweet potato stem and root rot,and compare the impact of the number of different bacterial groups on the incidence of sweet potato plants.Studies have shown that the incidence rate of sweet potato stem and root rot is positively correlated with the initial soil bacterial load and the threshold value of pathogen concentration is 10~4 CFU/g.When≧10~4 CFU/g,the average plant incidence is85.0%,and almost all sweet potatoes die within a month;when<10~4 CFU/g,the average plant morbidity is 16.7%,and the sweet potato grew well.When the Ct value detected by qPCR in the field soil is lower than 28,it is known from the standard curve of Dickeya dadantii that the concentration of pathogen in the soil reaches the threshold of disease incidence,and there is a risk an outbreaks of sweet potato stem and root rot.It is suggested to carry out comprehensive control measures.This experiment provides a reference for forecasting the occurrence of sweet potato stem and root rot in the field.3.A preliminary study on the growth and decline of sweet potato stem and root rot pathogens in soil.Based on the study of sweet potato stem and root rot pathogen population and disease severity in the soil,use fluorescence quantitative PCR technology to detect regularly the amount of pathogens in the soil,and the dynamic changes and laws of Dickeya dadantii in the soil under a stable environment were initially explored.The results show that under stable environment,pathogenic bacteria population≧1×10~4 CFU/g will not be able to survive in the soil for a long period of time,the population will continue to decrease and the reduction rate is positively correlated with the amount of bacteria,eventually the population structure reached equilibrium and stable in the order of 10~2~10~3 CFU/g.4.Study on the effect of rotation on the pathogen population of sweet potato stem rot in soil.The rotation mode of sweet potato and non host crop was corn→potato→sweet potato,peanut→potato→sweet potato,soybean→potato→sweet potato,barley→rape→sweet potato,rice→rice→sweet potato,sweet potato chain were used as CK,three crops were sown for two years,and the concentration of D.dadantii in soil was detected by fluorescence quantitative PCR regularly.The test results show that corn,potato,peanut,soybean,barley,rape,rice and sweet potato rotation can accelerate the extinction of sweet potato stem and root rot pathogens in the soil and the rotation effect of corn and rape is more prominent;In the seriously ill field,after the rotation of non-sweet potato stem rot host crops,the soil bacterial base decreased by an order of magnitude,and the sweet potatoes are no longer susceptible to disease,and the growth state is better than that of continuous stubble.