| Tobacco black death disease(Colletotrichum capsici(Sdy)Bulter & Bisby f. nicotianae G.M.Zhang & G.Z.Jiang) is an important tobacco disease , which made yield decline abruptly. In 1995, Zhang Guangmin firstly certified that Colletotrichum capsici f. nicotianae could produce toxin-like substance causing tobacco wilt. So further studies on Colletotrichum capsici f. nicotianae toxin are of great significance to reveal the interaction between Colletotrichum capsici f. nicotianae and tobacco. This dissertation made studies on screening toxin-producing strains, basic properties of Colletotrichum capsici f. nicotianae toxin, preliminary TLC analysis about rough toxin, effects of the toxin on membrane permeability, MDA amount and some defensive enzymes respectively. The results were as follows: 1. Colletotrichum capsici f. nicotianae strains all can produce toxin that can make tobacco wilt, and the toxicity is not from osmotic potential. Strain C-Ⅲ-1, C-Ⅴ-1 and C-Ⅲ-5 had stronger capability of producing toxin than the others, and C-Ⅲ-1 is the strongest one. Results showed that the optimum condition of producing toxin was: under the condition of pH6, 25℃～30℃, and 13 days of continuous oscillation culture; PDB, tobacco leaf frying juice and maltose liquid cultural medium were the three suitable cultural media. With plant pickling in vivo method and excised leaf acupuncture inoculation method, we found that among 10 families and 25 species of plants Colletotrichum capsici f. nicotianae toxin could infect Solanaceae,Leguminosae,Chenopodiaceae,Cucurbitaceae,Cruciferae,6 families and12 species of plants,in which Nicotianae tabacum, and N. glutinosa were most susceptible.2. Studies on Colletotrichum capsici f. nicotianae toxin showed that: the toxin was thermostable after being treated for 20min in 70℃ and acid-basically stable in the range of pH4-pH9; ultraviolet radiation could tenuate its toxicity. After being treated by alcohol precipitation, dialysis membrane and papain,the bioassay results showed that Colletotrichum capsici f. nicotianae toxin belonged to small molecular weight and non-protein. Colletotrichum capsici f. nicotianae toxin could dissolve in organic solvent ethyl acetate, chloroform,n-butyl alcohol,and sodium bicarbonate saturated solution; and could not in benzene; the active constituent could dissolve in ethyl acetate more easily in acid condition.Ultraviolet spectral scanning analysis showed that the toxin had absorption peak at wavelength 248,252,264,272 and 284nm. 3 active constituents were obtained by TLC segragation:Ⅲ(Rf=0.41),Ⅳ(Rf=0.47) and Ⅶ(Rf=0.67).3. Colletotrichum capsici f. nicotianae toxin could increase the cell permeability of tobacco leaf and root, which caused electrolyte leakage,and this kind of action is more violent with the prolongation of time and the increasing of toxin concentration; Susceptible tobacco is more sensitive to the toxin. The toxin could decrease the content of tobacco leaf chlorophyll. There are great changes in tobacco leaf microstructure after being treated by the toxin; cell wall was broken into fragment and many cells swelled. That showed that Colletotrichum capsici f. nicotianae toxin action position might be on the cell membrane and chloroplast.4. Resistant tobacco Burley21 and susceptible tobacco NC82 were inoculated with rough toxin respectively,and the changes of the defensive enzyme activity were detected after inoculation. For SOD, the activity of resistant tobacco descended firstly in early time(2h-12h),but that of susceptible tobacco ascended and was lower than the control. SOD activity of resistant tobacco reached the peak at 36h and subsequently descended,but theactivity were higher than that of the susceptible at all the inoculation time. For POD, the activity of resistant tobacco and susceptible tobacco both ascended after inoculation and reached the peak at 48h. Subsequently POD activity of resistant tobacco could keep high level,but that of susceptible tobacco came down to the control lev...
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