| Cucumber downy mildew, tomato early blight and tomato leaf mold are three kinds of the most primary disease in vegetable cultivation in China. The three kinds of vegetable diseases have developed seriously with the development of vegetable cultivation. So strengthen control for the thtee kinds of diseases are very important. Some elicitors stimulate plants and then cause the defense system of plant, which can result in resistance to subsequent infection, this is induced resistance. For its advantage, such as safety, broad spectrum disease control, it has been paid attention for a long time. In the research, we study the resistance of tomato plants against tomato early blight and tomato leaf mold induced by BTH and we study the resistance mechanism too. We found BTH can induce obvious resistance in cucumber plant against downy mildew and tomato plant against early blight and leaf mold. After treatment by spraying BTH at 30μg/mL, 50μg/mL, 70μg/mL, 90μg/mL, the cucumber seedlings with one expanded leaves were inoculated with sporangium of Pseudoperonospora cubensis and incubated in greenhouse. Resistance of cucumber seedlings to downy mildew were evaluated by disease index and percent of diseased leaves. The results showed that the disease index were markedly lower in BTH treatments than that in untreated control. The relative efficiencies of control at 30μg/mL, 50μg/mL, 70μg/mL, 90μg/mL were 51.80%,55.52%,56.66%,47.38%,respectively. The field trials were conducted at onset of flowering stages in which some of the cucumber plants were infested naturally and showed symptoms of downy mildew. The development of disease could be controlled effectively by spraying 50μg/mL BTH. The relative efficiencies of control to disease was 62.63%in 13 d, 56.93%in 20d, 67.78% in 27 d, 61.55% in 34d and 53.80% in 41 d after BTH treatment. The disease index was significantly lower in BTH treatments than that in untreated control. Resistance to early blight of tomato plants was induced by spraying BTH at 30μg/mL, 50μg/mL, 70μg/mL, three days later, the tomato seedlings with four or five leaves were inoculated with sporangium of Alternaria solani and incubated in greenhouse. Resistance of tomato seedlings to early blight were evaluated by disease spots. The results showed that the disease spots were markedly lower in BTH treatments than that in untreated control. The efficiencies of control at 30μg/mL, 50μg/mL, 70μg/mL were over 50%.But 50μg/mL is the most effective induce density, the efficiencies of control to disease was 76.53% in 14d, 69.49% in 21d after BTH treatment. The field trials were conducted when some of the tomato plants were infested naturally and showed symptoms of early blight. The development of disease could be controlled effectively by spraying 50μg/mL BTH. The efficiencies of control to disease were 65.73% in 9d, 50.54% in 26d after BTH treatment. The field trials were conducted at seedlings stages when some of the tomato plants were infested naturally and showed seven disease spots of leaf mold. The development of disease could be controlled effectively by spraying 50μg/mL BTH. The efficiencies of control to disease were over 70% during the whole period of BTH treatment. The efficiencies of control to disease were 74.29 % in 56d after BTH treatment. The field trials were conducted at onset of flowering stages in which some of the tomato plants were infested naturally and showed five to eight disease spots of leaf mold. The development of disease could be controlled effectively by spraying 50μg/mL BTH. The efficiencies of 30μg/mL to disease were 59.39% in 13d after BTH treatment. The efficiencies of 50μg/mL to disease were 88.97% in 13d, 66.98% in 42d after BTH treatment. The efficiencies of 50μg/mL to disease was better than 30μg/mL . The field trials were conducted at onset of fruiting stages in which some of the tomato plants were infested naturally and showed twenty-five disease spots of leaf mold. The development of disease could be controlled effectively by spraying 50μg/mL BTH. The efficiencies were 79.13% in 10d, 58.55% in 21d, 46.58% in 31d after BTH treatment. The activities of defense-related enzymes were examined in tomato leaves treated with BTH, inoculated with sporangium of Alternaria solani after spraying BTH, inoculated with sporangium of Alternaria solani or treated with water. The increases of activities of PAL, POD, PPO and ?-1,3-glucanase were found in BTH treatments compared to untreated tomato leaves. The activities of the four kinds of defense-related enzymes were higher in tomato leaves inoculated with sporangium of Alternaria solani after spraying BTH than in the leaves only treated with BTH.When some of the tomato plants were infested naturally and showed symptoms of early blight ,the activities of PAL, POD, PPO and ?-1,3-glucanase were examined in tomato leaves treated with or without BTH. The increases of activities of the four kinds of defense-related enzymes were found in healthy leaves treated with BTH compared to untreated tomato leaves. The activities of PAL in treated leaves were not higher than untreated leaves in 32 days, but the activities of other three kinds of defense-related enzymes in treated leaves were still higher than untreated leaves in 32 days. The increases of activities of the four kinds of defense-related enzymes were also found in new leaves of tomato plants treated with BTH compared to untreated tomato plants. The activities of POD and?-1,3-glucanase in treated plants were still higher than untreated plants in 32 days, but the activities of PAL and PPO in treated plants were not higher than untreated plants in 32 days. When some of the tomato plants were infested naturally and showed symptoms of leaf mold, the activities of PAL, POD, PPO and ?-1,3-glucanase were examined in tomato leaves treated with or without BTH. The increases of activities of the four kinds of defense-related enzymes were found in healthy leaves treated with BTH compared to untreated tomato leaves. The activities of PAL, POD and PPO in treated leaves were still higher than untreated leaves in 42 days, but the activities of ?-1,3-glucanase were not higher than untreated plants in 29 days.
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