Genetic Diversity Analysis And Infection Process Of Bipolaris Sorghicola In Heilongjiang Province

Sorghum target spot disease is a fungal disease of sorghum leaves.At present,there are few reports about sorghum target spot disease at home and abroad.Sorghum is one of the main crops in the western region of Heilongjiang Province.During the investigation of sorghum diseases,it was found that a leaf disease was very common and seriously damaged,and it was suspected of sorghum target spot disease.In this study,diseased leaves of sorghum from different locations in Heilongjiang Province were collected for isolation and identification,and identified as the pathogen of sorghum target spot disease.On this basis,the biological characteristics,genetic diversity and infection process of the pathogen were studied in order to further study the epidemic,The pathogenic mechanism of pathogenic bacteria and disease prevention have laid an important theoretical foundation.The results of the study are as follows:1.Collecting diseased leaves of sorghum from different locations in Heilongjiang,obtain pure culture of pathogenic bacteria through tissue isolation,select 1 strain from each location to verify the Koch’s rule,and use morphology and molecular biology to identify the pathogen.The results showed that the morphological characteristics of different strains were the same,but the colony growth rate was different.The ITS sequence of the tested strain has 99～100%homology with Bipolaris sorghicola(accession number AF071332.1),and is on the same branch as Bipolari sorghicola.Combined with the identification of morphological characteristics,it was determined that the pathogen was Bipolaris sorghicola,which caused sorghum target spot disease.2.Studying the biological characteristics of different strains,the results show that the tested strains grow best in the OMA medium,and the mycelial growth rate of different strains is significantly different;the tested strains can grow in the range of 10～35℃.The optimum growth temperature of the strains is different;the light can promote the growth of the hyphae;the pH 8is the optimum growth of the pathogenic bacteria;for the utilization of suitable carbon and nitrogen sources,there are big differences between different strains.3.Use rDNA-ITS primers and the selected SRAP and URP primers to study the genetic diversity of the tested strains and determine the pathogenicity of the strains.The results showed that the cluster analysis of ITS sequencing results showed that all 48 strains were in the same branch as the Bipolaris sorghicola,and some strains continued to branch on the basis of the original branch.SRAP,URP primer amplified band cluster analysis results showed that when the similarity coefficient was 0.77,the isolates from Suihua city clustered into LⅠgroup,and the isolates from Harbin clustered into LⅥcluster.The gene mobility between the tested strains was relatively large,and the geographic populations The coefficient of genetic differentiation(Gst)and gene flow(Nm)were 0.3762 and 0.8290,respectively,indicating that there is a certain degree of genetic differentiation among the nine geographic populations.The pathogenicity of 48strains to sorghum was significantly different,with a disease index ranging from 2.02 to 26.10.The pathogens were divided into three types:strong,medium and weak.The pathogenicity of sorghum target spot pathogen in Heilongjiang Province is genetically differentiated,and the genetic relationship is complicated.The pathogenicity of the tested strains is differentiated,and the pathogenicity is not related to genetic diversity.4.Explore the inoculation conditions of sorghum target spot pathogen.The results showed that the best inoculation conditions for sorghum target spot pathogen were spore concentration of5.0×10~4 spores/mL and moisturizing at 30℃for more than 18 hours.5.Using optical microscope to study the infection process of sorghum target spot pathogen against and susceptible sorghum leaves.The results showed that among the susceptible varieties,the conidia of the pathogenic bacteria could germinate within 2 h;Appressorium began to form at 18 h,and most of the invasion points were the intercellular space and the base of leaf hair,and a few were on the cell surface,and no intrusion from the stomata was seen;24 h cells Infected hyphae can be seen inside;chlorotic spots appear on leaves at 72 h,and intracellular hyphae are clearly visible;96 h after inoculation,conidiophores protrude from the stomata,and typical lesions can be seen on the surface of the leaves;among disease-resistant varieties,24 h Appressorium is formed,the infection rate is low,and the pathogen invades from the intercellular space;the hyphae can be seen inside the cells at 72 h,and there is no intercellular expansion of the hyphae.The above results indicate that the target spot pathogen of sorghum directly invades the leaves,and the invasion process of the pathogen of resistant susceptible varieties is different.