Study On The Soil Organic Amendment Suppressing The Black Shank On Tobacco

Black shank of tobacco caused by Phytophthora nicotianae is one of the most serious soil-borne diseases in flue-cured tobacco cultivation,expecially in the humid tropical region such as Puer in Yunnan.It is an urgent for the sustainable development of tobacco industry to explore an safe control measure for tobacco diseases.Soil organic amendment is one of the effective measures to control soil-borne diseases,but there is little research and application in tobacco cultivation.In this paper,the following studies were carried out on the control of black shank by soil organic amendment:(1)Investigation of the occurrence of black shank in Puer tobacco-planting area;(2)Analysis on the correlation between soil physical-chemical properties and black shank,as well as the difference of microbial flora between rhizosphere soils with or without black shank.(3)Investigation of the mechanism of Trichoderma hamatum YMF1.00247 for its functions concerning growth-promoting and disease-suppressing on tobacco.(4)Evaluate the efficacies of four organic fertilizers applied alone or combined with two microbial agents to control black shank.(5)Analysis on the quantity change of soil beneficial microorganisms,fertilizer utilization rate and organic volatiles released from soil under the condition of organic amendment.The main results were obtained as the following.1.The incidence of black shank and climatic factors in 2018 and 2019 in Puer tobacco-planting area were investigated.In 2018,the incidence was 8390.8 mu,with an average incidence rate of 2.27% and an average disease index of 0.48.In 2019,the incidence was 11219 mu,with an average incidence of 3.03% and an average disease index of 1.26.In addition,the climatic factors such as average temperature,rainfall,sunshine hours during the occurrence period of black shank in Puer tobacco-planting region in 2018-2019 were investigated.2.The changes of physicochemical properties and rhizosphere microflora before and after tobacco infection with black shank were analyzed.The contents of organic matter and available potassium in rhizosphere soil of tobacco were significantly decreased after tobacco was infected by black shank.The disease index of black shankwas negatively correlated with soil organic matter content(y =-11.88x+36.26,r =-0.807)and negatively correlated with soil pH(y =-1.703 x + 6.473,r =-0.59).Before and after tobacco infected by black shank black shank,the microbial flora of rhizosphere soil changed in terms of species composition,however,no regularity was found in the four groups of tested samples.3.The mechanism of T.hamatum YMF1.00247 promoting the tobacco growth by producing GABA and inhibiting the occurrence of black shank by improving the defense enzymes of tobacco was revealed.The content of GABA in the fermentation broth of YMF1.00247 was 1.33 g/L.The efficiency of the fermentation broth to promote tobacco growth was equal to the GABA of 1.5 g/L,which reached 135%.Application of YMF1.00247 fermentation broth(100 mL/ plant)could significantly improve the enzyme activities of PAL,POD and PPO of tobacco plant,and the control effect against black shank reached 78.41%.4.The effects of four organic fertilizers(cow manure,eucalyptus waste,Yide organic fertilizer,BKWT organic fertilizer)and two microbial agents(T.hamatum,Brevibacillus brevis)as soil amentments against balck shank were evaluated.In the treatment of applying organic fertilizer alone,500 kg/mu cow manure had the best effect,and the control effect was up to 36.09%.In the treatment of organic fertilizer agent plus bacterial agents,500 kg/mu organic fertilizer(cow manure,eucalyptus organic fertilizer or Yide organic fertilizer)plus 5 kg/mu T.hamatum showed a medium level of control effects,and the control effects were 53.32%,54.32% and 60.38%respectively in the tobacco cluster stage.In the treatment of single application of microbial agents,5 kg/mu T.hamatum had the best effect with control effects of 74.75%and 62.78% respectively,in rosette stage in Ninger and Jinggu test sites.5.The quantity change,fertilizer utilization rate and organic volatiles released from soil were analyzed.It was found that the quantity of antifungal bacteria,nitrogen-fixing bacteria,phosphorous solubilizing bacteria and soil organic volatile increased after soil organic improvement.The N,P and K utilization rates of chemical fertilizer increased by 35.41-68.72%,4.36-11.83% and 17.68-34.71%,respectively.