| Tea brown blight(Guignardia camelliae)is one of several main leaf diseases of tea plant, having been more serious in some areas in recent years. The relevant research to the disease have been carried. Biological characteristics of the pathogen and the resistance of 13 cultivars of tea plant to tea brown blight were studied by means of natural infection in the field and artificial inoculation in vitro. Resistant cultivars and susceptible cultivars of tea plant were divided. And the resistance mechanism was researched tentatively. The findings are as follows: 1 Some biological characteristics of the pathogenic fungus The experiment result showed: the optimum temperature for the growth of fungus mycelium was from 24 to 27℃, the optimum temperature for sporulation ranged 22 to 30℃. Treated at 54℃ in 10 minutes, the spores didn't germinate. The optimum pH for the growth of the mycelium was 5.1～5.9, the optimum pH for sporulation ranged 5.0～6.0. Light had no much effect on the growth of fungus mycelium, but had much effect on the reproduction of the spore. 2 The identification of tea plant resistance to tea brown blight The resistance of 13 tea plant cultivars to tea brown blight had the difference or remarkable difference. In general, the resistance of big leaf cultivars was relatively weaker, the resistance of middle leaf cultivars was relatively stronger. In the experiment, the tea plant shoots were cultured in vitro, and inoculated artificially. The result showed the disease condition in vitro was basically consistent with that of the tea plantation in nature. Therefore, we thought this identification method of tea plant resistance to tea brown blight was feasible, especially a large number of cultivars. 3 The physiological and biochemical resistant mechanism of tea cultivars to tea brown blight caused by Guignardia camelliae. Making use of the mensuration of spectrophotometric analysis to study the enzyme activity of Peroxidas(ePOD), Polyphenol Oxidas(ePPO), Catalas(eCAT), Phenylalamine Ammenia-lyase(PAL). The result showed that there was definite difference to the metabolic rule of defence enzymes activity in the annual leaf tissue of the resistant and susceptible cultivars after infecting. Inoculating resistant and susceptible cultivars with Guignardia camelliae, the POD, PPO, CAT, PAL activities in the annual leaf cell increase rapidly. And the increment of POD, PPO, PAL activities in resistant cultivars were higher than susceptible cultivars. The polyacylamide gel electrophoresis(PAGE)and isoenzyme analytic technique were applied to study the variations of isoenzyme spectra of POD, PPO in tea plant. The result showed that there were some differences in the character of the two isoenzymes spectra of susceptible and resistant cultivars after inoculating. Before inoculating in vitro, the isoenzyme spectra of POD and PPO had 4～5 and 3～4 bands respectively in the annual leaf of both resistant and susceptible cultivars, But the isoenzyme bands of susceptible cultivars were darker in color and wider in width. After inoculating in vitro, the isoenzyme bands of both POD and PPO increased to 5～6 and 4～5 respectively. And isoenzyme bands produced newly in resistant cultivars appeared earlier, wider in width and stronger in activity, although new isoenzyme bands produced in susceptible cultivars, they appeared later, and weaker in activity. All above showed that protective enzymes system in cell of tea plant was actively concerned with the metabolizability of resistance disease.
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