Population Genetic Analysis Of Cucumber Mosaic Virus From Different Regions In Sichuan Province And The Study Of Co-Infection

There is a high variation frequency of Cucumber mosaic virus(CMV)in natural.In Sichuan Province,the population genetic analysis of CMV was deficient.In the field,the incidence of CMV is affected by aphids,weeds,field configuration and other factors.Under natural conditions,it is easy for plants co-infected with CMV and other pathogens.It is a representative viral disease of crop in Sichuan.Based on the rules of genetic and evolution of population of CMV,the complexity of epidemic factors and infection in Sichuan,this study has been carried out.More than 300 samples of CMV were collected from different regions of Sichuan.After the gene sequence of coat protein(CP)was amplified by RT-PCR,the genetic analysis of CMV population was carried out using various genetic analysis methods.In different field configuration,the incidence of aphids and CMV was investigated.The related biological factors of the occurrence of aphids were also analyzed.The correlation degree of the incidence of CMV and poisonous weeds were investigated and analyzed as well.The incidence of diseases,pathogen accumulations,peroxidation of membrane lipid,photosynthetic efficiency and activation of defense signal were detected in Nicotiana tabacum co-infected with CMV and Alternaria alternata(A.alternata).The conclusions were drawn as follow:1.In this study,33 isolates of CMV were obtained.They mostly belong to subgroup I.The genetic analysis results showed that in single nucleotide polymorphism,transitions were 1.69 times of that of transversions.CMV in Sichuan Province has been stable for a long time and it is dynamic balance now.The negative selection pressure was strong and the polymorphism of population was low.But there was significant genetic diversity in the population.The communication of CP gene of CMV among different regions was frequently.There was no obvious recombination of the CP gene.2.When the ratio of maize and soybean was 2:3 or 2:4,the control of major insect pests of soybean was the most effective.The population of aphids was affected by field configuration.When the ratio of maize and soybean was 2:3,the number of aphids was the least.There should be a positive correlation between the disease index and the occurrence of aphids.The disease index was the lowest in 2:3 ratios.When the ratio of intercropped maize and soybean was 2︰3 or 2︰4,the growth-related indicators and yield of soybean were close to that in sole cropping system of soybean.In addition,the occurrence of CMV disease on crops was significantly affected by poisonous weeds.3.In Nicotiana tabacum co-infected by CMV and A.alternata,the symptom induced by these two pathogens was aggravated.The synthesis of chlorophyll was suppressed by invasion of pathogen.Co-infection causes more damage of oxidative stress.Correspondingly,the activities of antioxidant enzyme and contents of malondialdehyde in co-infected plants were higher than that in single infected plants.The accumulation of reactive oxygen species led to the oxidative damage of photosystem and reduction of photosynthetic efficiency.However,the activation and intensity of defense responses was related to the order of the inoculation of the two pathogens.There were synergistic effect between salicylic acid and jasmonic acid signaling pathway,in which the salicylic acid signaling pathway plays a major role.