| Wildfire disease of tobacco is one of the most important diseases on tobacco. Starting from the separation and purification of Pseudomonas syringae pv. tabaci, author carried out the studies of the searching of way how to identify the disease resistance of tobacco to P. s. pv. tabaci, the identification of disease resistance of tobacco cultivars, the effect of tabtoxin extract on seed germination and action of pathogenicity on seedling growth, and the changes of defensive enzymes in tobacco cells inoculated with P. s. pv. tabaci respectively. Four aspcts of conclusive results were acquired as follow:1. 39 strains were screened out through plat streaking method, of which 18 strains have fluorescent phenomena. Electron microscopy and pathogenicity determination were used to screen out the virulent strains YS-3, ZJ-8, YP-3 and YY-1. PY4-1,which were storaged in Glycerine solution in our laboratory, was the virulentest one among all tested strains through rejuvenation.2. Decafoliate tobacco leaves were inoculated by spraying method, showing that inoculation concentration of 5><108CFU/ml was optimal. Duration of dew time of preinoculation had no effect on the development of wildfire disease and the duration of dew time of 48h was the most perfect after inoculation. Disease resistance of 45 tobacco cultivars on P. s. pv. tabaci were identified, the result indicated that each cultivar was different form others. Burley 21 and G80, whose disease index were 12.5, were the two most resistant of all cultivars; Resistant cultivars including Burley 37 and Xiaohuangjin 1025 et al took 31.1% of total tested cultivars; Susceptible cultivars, such as K326, Honghuadajinyuan and so on, took 35.6%; Highly suscepible cultivars including Yunyan 85, G28 et al, whose disease index were more than 70%, and they took 28.9% of all tested cultivars.3. Culture filtrate of P. s. pv. tabaci could inhabit germination of tobacco seed evidently; Extract of high concentration could inhabit elongation of tobacco roots and buds, but low one had growth-promoting effects. Seedling roots of 45 tobacco cultivars were immersed in extract, and the results showed that different cultivars had different reactions. Immersing seedling method, compared with spraying, was a simpler and more effective way to screen resistant cultivars. Goodness of fit of these two mithods was5785.5%.4. Tobacco plants (Var. Honghuadajinyuan) were inoculated with Pseudomonas syringae pv. tabaci, and the changes of the defensive enzyme activities were detected after inoculation. For SOD, the activity ascended firstly caused by the bacteria, but descended on the 8* day and became lower than that of the control after that day. For POD, the enzyme activity was lower than that of the control on the first day following a quick ascent, and reached the summit on the 10th day. The activity of PPO was lower than that of the control on the first day after inoculation, but then ascended to the peak on the 16th day. The changes of CAT were similar to those of POD, and the changes of PAL were similar to those of CAT and POD.By the determination on some enzymes activites of tabacco leaves inoculated by P. s. pv. tabaci, the resulsts showed that every enzyme changed differently.The activity of SOD increased slightly after challenge inoculation in four tabacco varieties.There were only two bands in zymogram before and after inoculating. The activities of PAL and CAT were irrigular before inoculation.,while decreased in resistant varities and increased in susceptible ones after inocuIation.There was a negative correlation of the activity of POD with the level of P. s. pv. tabaci infection.On the contrary, there was a positive correlation bewteen the level of P. s. pv. tabaci infection and the activity of PPO.Tabacco leaves inoculated with P. s. pv. tabaci, showed higher isoenzymatic activities and exposed one or two more bands in POD zymogram as compared with control leaves,while showed lower isoenzymatic activities and exposed one or two less bands in PPO zymogram. |
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