The Identification Of The Pathogen Of Tobacco Fusarium Root Rot Disease And Preliminary Study On The Screening Of Resistant Tobacco Varieties

The tobacco Fusarium root rot is a serious tobacco root disease in Fujian tobacco growing area.The selection and application of resistant varieties is a cost-effective method for controlling the disease.In order to establish a screening and identification system for the variety of tobacco resistant to Fusarium root rot disease,the pathogen of the disease was isolated and identified.The pathogens and their crude toxin was used as screening pressures to identify the disease resistance respectively and their correlation was analyzed,and field trials results verified the feasibility of the two methods for screening resistant varieties,the main results are as follows:1.First report of Fusarium commune as a pathogen causing the tobacco root rot disease:From 2015 to 2016,31 strains of Fusarium spp.were isolated from the tobacco root rot disease samples which collected from the main tobacco growing area of Sanming City,Fujian Province.The morphological observation,phylogenetic analysis,species-specific molecular identification and pathogenicity tests of the isolated strains were performed.The results showed that the microscopic morphological features of the isolated strains were similar to the species Fusarium oxysporum and F.commune.The phylogenetic analysis of the intergenic spacer(IGS)genes of the four isolates F-04,F-18,F-19 and F-28 was performed by using Bayesian analysis.The strains were clustered with F.commune and clearly distinguished from F.oxysporum;the species-specific molecular identification results showed that the isolates were all F.commune.The pathogenicity of isolated strain F.commune was verified by indoor inoculation test,and it was identified as the main pathogen of tobacco root rot disease.This is the first report of F.commune causing tobacco root rot disease in China.2.The resistance to the pathogens of five tobacco varieties was identified by indoor inoculation test:The resistance to the disease of the main cultivated tobacco varieties CB-1,K326,Yunyan 87 in Fujian Province and other two varieties TN90 and B08-4 was evaluated by using the pathogens inoculation to injured roots.The results showed that there were pathogenic differentiation among four strains F.commune F-04,F-18,F-19 and F-28 which caused tobacco root rot disease.There were also differences in the resistance of tobacco varieties to pathogen.The resistance ability to the disease among varieties was identified as B08-4>CB-1>TN90>K326>Yunyan87.3.Identified the positive correlation between the resistance of crude toxins and resistance to pathogens of tobacco varieties,and using the crude toxin screening method to classify 36 tested tobacco varieties:Using the method of controlling single factor variables,the crude toxin abstracted from the fermentation broth of pathogens was used as screening pressures for screening disease resistance of the varieties,and tobacco disease resistance was evaluated by observing the degree of toxicity of crude toxins against tobacco.The results showed that there was a certain difference in the ability to produce toxin between different strains,and the production of strain F-19 was highest and there was no correlation between the ability to produce toxins and the pathogenicity of pathogens.The crude toxin has pathogenicity to the tobacco seedlings,and the symptoms of the tobacco seedlings after toxin treatment are similar to the infection symptoms of the pathogens.The optimum processing time of crude toxin was 5 d,and the optimal treatment concentration was 60-80 mg/L.There was a significant difference in resistance to toxins among tobacco varieties,and there was a certain degree of differentiation of toxin resistance among the strains.There was a positive correlation between tobacco antitoxin ability and anti-pathogenic ability,and the correlation coefficient was 0.849.Under certain conditions,the crude toxin screening method can replace the pathogen direct inoculation method for the identification of tobacco resistance to root rot screening method,using this method,36 varieties of tobacco disease resistance were graded.4.There are some differences in the results of indoor resistance and field resistance identification,tobacco plant has the characteristics of stage disease resistance:Using diseased tobacco fields combined with artificial inoculation of pathogens as a disease garden to test the disease resistance of tobacco varieties,the results showed that resistance of tobacco varieties at different stages of growth differentiates,factors that affect the incidence of tobacco in the field are complex and changeable,many tobacco varieties has the characteristics of stage disease resistance.Field-resistance identification results showed that Yanyan 97>K326>Gexin-3>Cuibi-1>Yanyan 87>B08-4.This result was different from the result of indoor variety assessment.