| Tobacco root black rot is a kind of fungal disease.Tobacco seedlings and larger smoke strains can be infected,the destruction of tobacco seedlings,causing disease plant leaves yellowing,thinning,seriously affecting the tobacco yield and quality.At present,Chinese scholars have carried out research on the root black rot mainly in molecular identification,pathogenicity differentiation and biological characteristics.But in anhui province,the root black rot there has been no relevant report,smoke zone in anhui tobacco root black rot also has a gradually increase trend in recent years,mainly in the field tree phase,distribution of expanded year by year.Therefore,this paper studying the pathogen isolation and identification of tobacco root black rot in Anhui Province,Researching the biological characteristics of Thielaviopsis basicola,the condition and the evaluation of the resistance of tobacco varieties,and then screened out the effective medicament and the bacterium for controlling tobacco root black rot disease.to make a preliminary study on the occurrence and harm of tobacco root black rot and its regularity,which providing a theoretical basis for the research of sustainable control technology of tobacco root black rot in Anhui Province,and the main results were as follows:1.Isolation and identification of tobacco root black rot pathogen:Tobacco plants with typical black root rot were sampled to isolate pathogen by carrot disc culture,The species of pathogens were identified by morphology characteristics and analyzing sequences of rDNA-ITS,their pathogengicities were detected by irrigating the roots of tobacco seedings.The results showed the pathogen of tobacco black root rot was identified as Thielaviopsis basicola(Berk.et Br.)Ferraris and had the pathogenicity,which Separated by the carrot slice method,determined by morphological observation and rDNA-ITS molecular identification,Pathogenic assay and Kohlmann's law verification.2.Biological characteristics of tobacco root black rotThis test determined the optimum growth medium,optimum mycelial growth and spore germination temperature,pH value,spore lethal temperature of tobacco root black rot pathogen and the utilization degree of pathogen to different carbon sources and nitrogen sources.The results showed that the optimal culture mediums for Thielaviopsis basicola was V8 and PDA,in which V8 medium was the most suitable and the expansion trend was better,The mycelium of pathogen grew well between 15?~30?and the optimum temperature was 25?,The spores can germinate between the 5?~35?,when the temperature reaches 25?,the spore germination rate is the highest,the lethal temperature of the spore germination is 53?by the water bath 10min,the optimum pH is 6,pH10~12 the strain grows well,the pathogen could make use of carbon sources such as Starch,maltose,glucose,and nitrogen sources such as carbamide and zinc nitrate.3.The epidemic condition and resistance of cultivars of Tobacco root black rotThrough the development of the indoor pot experiment,studying the influence of pH value,soil moisture content,inoculum concentration on Thielaviopsis basicola infection situation.At the same time,the differences of disease resistance between different cultivars were determined by the subjects of cloud smoke 87,cloud fume 97,cloud smoke 85,K326,and the middle smoke 100.By investigating the disease strain rate and the index of disease,the pathogenesis of black rot of tobacco root was preliminarily determined,so as to provide theoretical basis for the safe production of tobacco.The results showed that When soil pH is weakly acidic and alkaline,it is beneficial to the occurrence of root black rot,and low pH value(pH<4)can inhibit the occurrence of disease.The higher the soil moisture content,the more serious the occurrence of the black rot of tobacco root,the highest in the soil moisture content and the disease index,88.9%and 60.2 respectively.The higher the concentration of inoculation,the higher the incidence and the more serious the disease.The application of nitrogenous fertilizer can aggravate the occurrence of tobacco root black rot,which is not conducive to controlling the occurrence of black rot of tobacco root.Yuanyan 87 and Yuanyan97 belong to high susceptible;Yuanyan85 and K326 belong to susceptible;Zhongyan 100 belong to disease-resistant varieties,without high resistance varieties.4.Screening of effective agents for the control of tobacco root black rot diseaseThe toxicity of seven fungicides to Thielaviopsis basicola(Berk.and Br.)Ferraris were tested by the mycelium growth rate and spore germination method,and compose difference fungicide to select fungicide and mixture with high efficiency,low toxicity and low residue.Results show that among 7 kinds of single dose,Carbendazim and prochloraz have better inhibitory effect on pathogen mycelial growth.Followed by pyrazole azoxystrobin and difenoconazole;pyrazole azoxystrobin and carbendazim have better inhibitory effect on spores germination.The optimal compounding combination was the combination of Carbendazim and difenoconazole:A:A and A:D,the combination of Pyrazole and azoxystrobin:A:B and C:B.5.Optimization of fermentation conditions of Bacillus subtilis KC80-6 and its inhibitory effect on black rot of tobacco rootStudying the inhibitory effect of three treatments of Bacillus subtilis on the mycelium growth and spore germination of Thielaviopsis basicola,and optimize the fermentation medium and fermentation conditions,to provide a scientific basis for the biological control of tobacco root black rot.The results showed that the inhibition rate of living bacteria liquid on mycelium growth and spore germination was best,the effect of 1×10~7cfu/ml living bacteria on mycelial growth and spore germination were 93.2%,95.3%,The inhibitory rate of 1x10~7cfu/ml filtration solution on mycelial growth and spore germination was 74.9%and 93.4%,The high temperature sterilization solution had no inhibitory effect on mycelial growth,but had lower inhibition on spore germination.Through single factor and orthogonal test,the optimum medium formula of Bacillus subtilis was determined as follows:sucrose 1.5%,yeast extract 0.5%,magnesium sulfate 0.06%,and the fermentation conditionswere the filling volume 40m L in 250m L shaking flask,inoculum5%,28?,shaking at 180r/min,and initial pH at 6.5,For the latter part of large-scale industrial production laid the foundation.6.Field Control effect of Chemical agents and Biocontrol Fungi on Tobacco Root Black RotOn the basis of laboratory experiment,the field control effect of effective insecticides and biocontrol bacteria were studied on Yunyan 87 in order to provide scientific basis for field popularization.The results showed that 6 kinds of single agent and 2 compound agents had certain control effect on black rot of tobacco root.Among them,80%carbendazim wettable powder and 70%methyl tobuzin wettable powder and 2(carbendazim:phenyletrazolium 800 times solution)are relatively good,with an average control effect of 92.48%,90.9%and 84.15%.The effect of biocontrol liquid on black rot of tobacco root was 87.34%,and it could promote the growth of tobacco plant,which provided the scientific basis for the field production and application in the later stage. |
PDF Full Text Request