The Occurrence Regularity Of Tabacco Damping-off Caused By Rhizoctonia Solani And The Infection Characteristics Of The Pathogen

According to the pest survey of tobacco from 2010 to 2013 in Guangxi,tabacco damping-off caused by Rhizoctonia solani Kuhn is a common disease at field growth stages of tobacco.In this dissertation,the field systematic investigate on tobacco damping-off was made,and the regression model was developed by analyzing the disease index and its impact factors,The infection characteristical of the pathogens(strain LC11-6,AG4 HG-I)and its pathogenicity to tobacco cultivars were also investigated.Meanwhile,the control efficacies of 4 fungicides on the disease were tested.The main results are as follows.According to the field systematic investigate of tabacco damping-off in Jingxi county,the disease began to appear at the resettling stage and the high incidence at the harvest stage,with incidence rate 12.87%.By using SAS software,the regression model of disease index and impact factors was established,which was y=0.02018 x4+ 0.03945 x 7—1.0054,R2=0.994.x4 is weekly average relative humidity and x7 is weekly average amount of soil pathogens.Wound was beneficial for the infection of R.solani LC11-6.The tobacco leaf,leaf vein,stem and root could be infected by the pathogen.Pathogen-infecting favorable stage of tobacco was at seedling stage,and the disease rate under non-wound inoculation condition reduced significantly with the growth of tobacco plant.The range of 25 ? to 30 ? was the optimum temperature for the pathogen infection,and the pathogen could not infect tobacco under 15 ?.With the decrease of soil moisture in the range of 47.83%- 76.41%,the disease index would be increased.The results of modified selective medium testing showed that the higher the amount of soil pathogens had,the severer the disease occurred.Interactive pathogenicity test indicated that R.solani isolated from tabacco could infect rice and corn,and R.solani isolated from rice and corn also could cause the tobacco damping-off.The 14 tobacco cultivars had different resistance to R.solani LC11-6.Yunyan97,Honghuadajingyuan and Yunyan 87 belonged to resistant cultivars,but Yunyan 203 and Anyan No.2 belonged to susceptible ones.The control efficacies of azoxystrobin,difenoconazole,validamycin and mancozeb on tabacco damping-off in pot trials were 79.36%,46.66%,69.04%,68.34%respectively.When the disease rank was at 1 to 3,azoxystrobin could significantly control the disease,but not effectively if the disease developed to the rank of 5 and above.