Study On The Effects And Mechanisms Of Controlling Tobacco Black Shank With Endophytic Bacteria Of Tobacco

Tobacco Black Shank is one of the important ruinous diseases of tobacco. Chemical control is mainly adopted in production ,but tobacco is susceptible to Phytophthora parasitica var. nicotianae in the all growing time. Pesticide is difficult to control it continuously, and it also contaminates environment and harms men. Biocontrol is sustained effective and protects environment. Biocontrols of Tobacco Black Shankthat have been reported mainly isolated and utilized fungi , bacteria fromsurroundings of tobacco roots, their control effects are not steady for their poor abilities of colonization . Endophytic bacteria can exit in plant well, and control diseases stably. Endophytic bacteria are good biocontrol bacteria. In the thesis, I screened the Endophytic bacteria that can control Tobacco Black Shank and research on the mechanisms'of strain 118.1. Some ways of culturing hypha and producing zoosporangia were studied in this thesis. Through experiment, sesame agar, rye agar and oat ag&r can be used to culture Phytophthora parasitica var. nicotianae which grew well on them, their growth speeds were 1. 10cm, 0. 78cm, 0. 86cm per day. Sesame agar, rye agar can be used to culture Phytophthora parasitica var. nicotianae to produce zoosporangia, their outputs of zoosporangia were2.52×104 zoosporangia/cm2, 2.07×104 zoosporangia /cm2, their discharging rates were 40. 0% and 32. 1%.2. Through isolating endophytic bacteria and screening on plate, 238 endophytic bacteria strains were gained altogether. There were 13 strains that can restrain Phytophthora parasitica var. nicotianae growing on plates among them. They were isolated from roots and stems of tobacco. In greenhouse trail, endophytic bacteria 118,57,93 can control Tobacco Black Shank well, their control effects were high to 69. 23%, 61. 53%, 65. 38% , they can be used in production in advance.3. Through researching on the mechanisms of strain 118, its mechanisms include direct inhibition and induced disease resistance. Although the ferment liquid of strain 118 can not restrain zoosporangia discharging , but it can inhibit the hypha growing , zoospores moving about and germinating which are important links of Tobacco Black Shank developing , If any link is cut off , the disease could not develop. The strain 118 can induce activities of POD, PPO, PAL of tobacco increase, which are the plant defense enzymes. The research on the mechanisms of strain 118 can provide scientific basis for developing and utilizing endophytic bacteria on other plants.