Biological Characteristics Of The Pathogen And Fungicides Screening In Laboratory For Tobacco Black Spot Stalk

Tobacco is one of the most important economic crops in Guizhou province.However,during the large-scale cultivation of tobacco,diseases have been taken place terriblySerious diseases leading to serious product loss and reduction in tabacco quality,which heavily affect the production activities and economic benefits of the tobacco industry.At present,the tobacco black spot stalk is not prevalent in large area.The studies about tobacco black spot stalk are still needed.Therefore,in this study,we investigated the occurrence of tobacco black spot stalk in several tobacco producing areas,such as Zunyi,Liupanshui,Dafang,Qingzhen,Pingba and the New Area between Guiyang and Anshun in Guizhou Province.Finally,we found it in The New Area between Guiyang and Anshun.In this paper,we conducted experiments on pathogen identification,biological characters study,the virulence examination of Phoma omnivirens.The results are as follows:1.In July 2016,tobacco black spot stalk was found in tobacco farmland of Guizhou University at Guian New District,Guizhou,China.To determine the causing agent,the infected stalks were collected from infected areas.Typical pycnidium,conidiospores and cultures of Phoma were observed and isolated from infected tissues.Pathogenicity test was conducted according to Koch,s Rule.The study showed that the pathogen could infect leaves and stalks of tobacco at the root-extended period and flourishing-growth period.Based on the study of morphology,culture feature and partial sequence of rDNA-ITS and LSU,the pathogenic strain was identified as P.omnivirens.Continuous dark conditions is helpful for fugal growths.2.The biological characteristics of P.omnivirens were studied.Our results showed that NA,OMA and PDA are the most suitable medium for the pathogen.Colony growth of the optimum temperature is 30?,however it can not grow when the temperature under 5?.The colony growth was suppressed when temperature over 35?.The most suitable p H value for mycelium growth is p H 8¹0 in solid medium,and pH 9 in liquid medium.For P.omnivirens,sucrose is the best carbon source and KNO₃ is the most suitable nitrogen source.The killing temperature for mycelium is 58?,nevertheless for conidiophore is 54?.3.Mycelial growth rate was determined upon seven kinds of chemical fungicides and five kinds of biological fungicides treatment against Phoma omnivirens.The results demonstrated that80%Mancozeb showed the best inhibitory effect on the mycelium growth,with 2.7917 mg/L EC₅₀and the correlation coefficient?r?was 0.9755.EC₅₀0 of 20%Difenoconazole and 40%Propiconazole were 16.8945 mg/L and 19.4453 mg/L respectively with the correlation coefficients?r?0.9902 and 0.9941.Among biological fungicides,3%Zhongshengmycin showed the best inhibitory effect on the mycelium of the pathogen.Its EC₅₀0 was 0.9419mg/L and the correlation coefficient?r?was 0.9915.Among all the fungicides,the EC₅₀0 of 3%Zhongshengmycin is the lowest.4.According to the results of indoor screening 80%Mancozeb,20%Difenoconazole,40%Propiconazole and 3%Zhongshengmycin were selected for indoor pot experiment with the recommended concentration on the package water was as the negative control.The results illustrated that the disease index dealt of the four treatments were declined obviously compared with water control.The disease index was investigated after sprayed fungicides treatment for three times during 21 days.It was showed that 80%Mancozeb 500 times diluent had the best control effect?58.54%?against tobacco black spot stalk.The second was 3%Zhongshengmycin?800times diluent?,showing 43.90%control effect.The control effect of 20%Difenoconazole?2000times diluent?is 14.36%.