| The occurrence of tobacco diseases has caused the decline of tobacco leaf quality and yield,and severely affected the economic benefits.In 2016,C.tabacum leaf spot was first reported in Chongqing,and the disease epidemic only occurred in some districts and counties.At present,there are relatively few reports and researches on this disease,so this article adjusts to the occurrence of tobacco leaf spot disease in Fuling district.Observe the symptoms,description of the disease,and pathogen identification of the collected tobacco leaf spot disease,and start from the external conditions related to the occurrence of the pathogen,determine the biological characteristics of the pathogen,screen the indoor drug screening and field control of tobacco leaf spot disease Research on the trial.The main test results are as follows:1.In late June 2018,plants suspected of Corynespora tobacco leaf spot disease were found in a tobacco test site in Chituba Village,Fuling District,Chongqing City,and continued observation entered the peak period of disease in July.In order to determine the pathogen,the diseased tobacco leaves were collected from the diseased field,and microscopic examination and isolation culture revealed that Corynesporacassiicola was present in the diseased tissues.The pathogenicity was determined according to Koch’s rule,and the results showed that the strain could cause Yunyan 87 and K326 to develop disease in the root extension stage and peak stage.The morphology,culture conditions and partial sequence of r DNA-ITS gene were studied by colony culture to construct a phylogenetic tree,and the pathogen causing the leaf spot disease of Corynebacterium nicotianae was initially identified as Deuteromycotina Hyderomyces phomycetes Hyphomycetales Hyphamycetales Demati-aceae Polycoccus Corynespora cassiicola.2.To study the related biological characteristics of Corynebacterium nicotianae.The test results show that the medium that is most conducive to the growth of pathogenic growth of hyphae is 30℃,and the growth of hyphae at low temperatures or more than 46°C stops growing;The p H value is 8;changes in light conditions have no significant effect on the growth rate of mycelium.When cultured under continuous dark,continuous light,12hours dark and 12 hours light conditions,there is no significant difference in colony morphology;sucrose is the optimal carbon for Corynespora Potassium nitrate is the most suitable nitrogen source;under aeration conditions,it is more conducive to the growth of pathogenic mycelia.3.In this paper,ten kinds of chemical fungicides were selected to determine the inhibitory effect of each fungicide on Corynebacterium nicotianae.Laboratory virulence was measured using the mycelial growth rate method.The test results showed that 98%of carbendazim had the best inhibitory effect on the pathogenic mycelia in the dish,but due to pesticide residues,it is not recommended to use it in large areas in the field.Secondly,the EC50 of 20%anisole and 98%Pyraclostrobin is 0.014 mg/L and 0.871mg/L,and the correlation coefficients R are 0.741 and 0.9832,respectively.5.According to the results of field surveys,the incidence and disease index of tobacco leaf spot disease of tobacco for three consecutive years were calculated.Combining with meteorological data of Fuling District,Index)value as the prediction object.Correlation analysis showed that DI（illness index）was significantly correlated with AP（average precipitation）（0.553*）,MRD（average precipitation day）（0.69**）,and MHVW（average hourly wind speed）（0.697**）.Using AP,MRD and MHVW as predictors to build the following predictive models:DI=6.052+0.09AP+1.608MRD+0.464MHVW... |
