A Study On Effects Of Changes And Control Of Temperature And Humidity On The Occurring Of Tobacco Bacterial Wilt And The Control Techniques

Tobacco bacterial wilt is a typical soil-borne bacterial disease which caused by Ralstonia solanacearum (Smith1896) Yabuuchi et al.. Under suitable conditions of temperature and humidity, the disease occurs and spreads extremely rapidly. Tobacco bacterial wilt is one of the most important diseases on tobacco for its suddenly eruption and great destructive power. The disease seriously occurred in tobacco growing areas of Chongqing, Sichuan, Jiangxi, Hunan, Fujian, Taiwan, Guangdong, eastern part of Guangxi, southern of Anhui and part of Guizhou. The disease erupts in individual years in these places and often causes devastating loss. In recent years, the disease has had the trend of spreading to North tobacco growing area. The disease has occurred in Liaoning, Shandong, Henan and Shaanxi provinces and it is very serious in some areas of these places. At present, tobacco bacterial wilt disease prevention and control system is not perfect in our country, mainly reflected in the following aspects:In the forecast, the study of the key factors influencing the occurrence and epidemic of tobacco bacterial wilt is few, and more single; In disease prevention before the disease occurs, the lack of systematic and efficient technical measures can not effectively suppress the occurrence of tobacco bacterial wilt fundamentally; In the prevention and treatment after the disease occurred, we mainly use its resistant ability and application of chemicals in inhibiting the spread of the disease. So far, we have not yet found the ideal prevention ideas. With the long-term use of routine chemicals, the pathogens have developed resistance to conventional doses and it is very difficult to obtain good control effect. Based on the status of prevention and control of tobacco bacterial wilt, following the plant protection policy of "Prevention first combining integrated control" and the new plant concepts of "Health-warning-system control", under the guidance of the theory of modern plant medicine,"laboratory tests draw inferences, field monitoring verified" as main idea,"monitoring, investigation, analysis, summarize" of temperature, humidity and disease data as means, we have carried out systematic research of the influence on temperature and humidity changes and regulation in tobacco and Ralstonia solanacearum (Smith1896) Yabuuchi et al. interaction: Determination of growth interval of Ralstonia solanacearum and effect of temperature on the growth of the colony under indoor conditions; The measurement of optimal incubation temperature of Ralstonia solanacearum under laboratory conditions and the amount of bacteria of unit volume in culture medium with the change of temperature; The influence of the development of tobacco bacterial wilt under the regulating of temperature and humidity in laboratory conditions; The influence of the strains virulence under different regulation of temperature and humidity on the plant of tobacco bacterial wilt in laboratory conditions; The determination of temperature and humidity conditions on the occurrence of tobacco bacterial wilt in the field; The relationship between the development of tobacco bacterial wilt disease and the changes of the temperature and humidity in the field; Studies on the inhibitory effect of different straw mulching mode on tobacco bacterial wilt; Studies on the inhibitory effect of different plastics and ridging mode on tobacco bacterial wilt. Finally, We initially formed the research papers on the relationship between temperature and humidity and the development of tobacco bacterial wilt.1. Influence of the occurrence of tobacco bacterial under the control of temperature and humidity in indoor conditions(1) Determination of temperature on the growth of Ralstonia solanacearum under indoor conditionsThrough the research, we found:Colony diameter of Ralstonia solanacearum shows a trend of first increasing and then decreasing as temperature increased from16℃, under the indoor conditions, in2℃temperature gradient.In45℃, the bacteria can not grow to a visible colony. By these, we can be push out that:The grow interval of Ralstonia solanacearum is [16℃,43℃]; There is a strong correlation between the change of temperature and the size of colony diameter. When T=28.52℃, the colony diameter up to maximum. It means that28.52℃is the optimum growth temperature of colonies (The effective interval curve was16℃≤T≤43℃). There is a significant influence between incubation temperature and the growth and proliferation of Ralstonia solanacearum. At15℃, Ralstonia solanacearum have a certain amount of bacteria proliferation. Combined with the above test conclusions, we conclude that the growth range of Ralstonia solanacearum is [15℃,43℃]; Among10℃to45℃, the amount of bacteria is manifested as a first increased and then decreased irregular parabola with the increase of temperature, the maximum amount of bacteria is3.918×1010cfu/mL while temperature is28℃(2) The influence of the development of tobacco bacterial wilt and the strains virulence on the plant of tobacco bacterial wilt under the regulating of temperature and humidity in laboratory conditionsThrough the research, we found:Temperature15℃and below of soil temperature do not satisfy the necessary occurrence conditions of tobacco bacterial wilt; Temperature45℃and above is not suitable for the growth of tobacco seedlings; Tobacco bacterial wilt is more likely to occur at higher temperatures (30℃≤T≤45℃); However, tobacco bacterial wilt is most likely to develop around temperature30℃; The incidence of each treatment is very close with same temperature and different humidity, It shows that when the soil moisture satisfy the occurrence conditions of tobacco bacterial wilt, higher soil moisture favors the occurrence of the disease, but its effects is relatively small.Overall, the pathogenicity of Ralstonia solanacearum has been strengthened to a certain extent after inoculating; Low soil moisture treatment is more conducive to strengthening the virulence of Ralstonia solanacearum at the same temperature in certain range of soil moisture for Ralstonia solanacearum. Although the pathogenicity of Ralstonia solanacearum is the same, the incidence of each treatment still has very large difference under different temperature and humidity conditions; The virulence of Ralstonia solanacearum in the tobacco plant decreases with humidity increasing though the disease become more serious with humidity increasing under the cultivation of high humidity environment in same temperature and a certain range of humidity; The pathogenicity of Ralstonia solanacearum is not the only condition affecting the severity of tobacco disease; Temperature and humidity conditions can influence the pathogenicity of Ralstonia solanacearum, and they can aiso influence the physiological and biochemical status of tobacco and the interaction between tobacco and Ralstonia solanacearum.2. Effects of temperature and humidity change on occurrence and development of tobacco bacterial wilt(1) Through the research, we found: Tobacco bacterial wilt occurs when the air temperature is higher than22℃, the humidity of root dense regions and absorption region (the soil of15～20cm under the topsoil) stability reached51.4%(m3/m3) over16d in the field; Tobacco bacterial wilt occurs when average daily temperature of root dense regions and absorption region(the soil of15～20cm under the topsoil) is higher than21.1℃, the humidity of it stability reached58.5%(m3/m3) over16d in the field.(2) Through the research, we found: Each soil temperature are closely related to the development of the disease, and the20cm soil temperature curve fit the highest among them. Only when22℃≤T≤26℃(the20cm soil monitoring highest average temperature of the unit time), the fitting curve makes sense, and in this case, the curve is an incremented curve, and with temperature increasing, the amplitude of△disease index increase greater and greater. When T=22℃,f(T) has a minimum value;The5cm soil humidity curve fit the highest among the relation of each soil humidity and△disease index, its fitting degree are low and its correlation are poor. It shows that air humidity and soil moisture all play a role in the development of the bacterial wilt when the soil humidity satisfy the occurrence condition of tobacco bacterial wilt, but its effect is small compared with the temperature.3. The effects of several control technology of temperature and humidity regulation on tobacco bacterial wiltThrough the research, we found:(1) There is a certain inhibitory effect for the occurrence of tobacco bacterial wilt by using straw mulch of different models, and among them, rice straw coverage and corn straw half coverage are the best, and the average inhibitory effects were achieved respectively32.13%and30.04%by August10th; Straw mulch had a strong ability to adjust the soil temperature and humidity, and straw coverage can effectively reduce the temperature of the Soil Rhizosphere; The lower the temperature, the slower exacerbations, the higher the temperature, the faster exacerbations, under appropriate circumstances humidity within a certain range; Humidity is a key climate factors in the occurrence of tobacco bacterial wilt. There is a positive correlation between humidity level and disease index, however, once the humidity reaches the limit of occurrence condition of tobacco bacterial wilt, its effect is small compared with the temperature.(2) There is a certain inhibitory effect for the occurrence of tobacco bacterial wilt by using different plastics and ridging mode, and among them, three times plastics and ridging is the best, and the average inhibitory effects were achieved16.85%by August7th; There is a greater impact on soil temperature and humidity whether removing film or not, and the soil temperature of removing film is slightly lower than the treatment of not removing film; The progression rate of removing film is slower than the treatment of not removing film. With the changes of temperature and humidity of the period, we know that:In a certain range, the lower the soil temperature, the lighter the incidence; There is a positive correlation between humidity level and disease index, however, once the humidity reaches the limit of occurrence condition of tobacco bacterial wilt, its effect is small compared with the temperature.