| Tobacco(Nicotiana tobacum L.) is an important economic crop and has become one of the most important economic sources of China’s western development and farmers. The occurrence of tobacco powdery mildew seriously affects the yield and quality of tobacco, mildew Powdery even cause the death of the whole plant. Currently, there were no systematic researches on tobacco powdery mildew, especially on pathogenic differentiation of tobacco powdery mildew. Tobacco powdery mildew is a fungal disease caused by the obligate parasite. Carrying out the differentiation of pathogenic bacteria of tobacco powdery mildew can not only improve the quality of tobacco for cigarette industry, but also can improve competitiveness of our cigarettes in the international cigarette market.This paper carried out a systematic research on Erysiphe cichoracearum DC. The main contents included the following aspects:Firstly, we explored the suitable RH condition of conidia germination about E. cichoracearum DC in order to guarantee the success rate of vaccination. This experiment made by the method of germination on slides. Made the collected conidia to suspensions first, placed the suspension on slides with a layer agar. Then coverslips were added on the slides. Finally, put those slides under different RH conditions, such as RH44%, RH55%, RH65%, RH75%, RH81%, RH85%, RH92%, RH98%, RH100%at room temperature. Observed and recorded the germination of conidia with a microscope after a period of time. The results showed that the suitable relative humidity for germination of conidia was81%-92%.Secondly, this study was carried out in order to explore the resistance level of different tobacco (N. tabacum L.) varieties to powdery mildew and identify the resistant tobacco varieties for future breeding research program. The experiment was carried out in two separate phases during2011and2012with separate set of fungal inoculums from two different locations. In the first phase during2011,21tobacco varieties were selected as the experimental material and were subjected to fungal inoculums kept in greenhouse of Tobacco Research Institute of Chinese Academy of Agricultural Sciences. In the next phase during2012,15tobacco varieties were selected and inoculated with fungal inoculums collected from Daxingxiang Sichuan in isolated chamber. The results demonstrated that sun-cured tobacco varieties Tangpeng was immunity to both fungal inoculums tested. NC89showed high resistance. Three varieties Beihart1000-1, K346and Jiyan9were found with medium resistant level to powdery mildew. Two varieties "Zhongyan90" and "CF203" were found highly susceptible. The rest tested varieties were moderate or high susceptible to powdery mildew. In addition, the resistant levels of a few tobacco varieties were different to two different inoculums.E. cichoracearum DC as an obligate parasite fungus was generally accepted that its conidia could only be multiplied and stored on living plants. So purification, culture and store might be difficult issues. In order to improve this situation and overcome existing tech-shortcomings, this study has invented a simple and convenient in vitro store method. With the help of tobacco seed coating technology, the conidia adhered to the surface of tobacco seeds. Then made tobacco seeds into particles with the powders and stored at4℃and-20℃respectively. Did germination tests on a regular basis and recorded the germination rate of conidia. The results showed that the activity of conidia gradually reduced as storing time extending. But46.2%conidia still was live and could infect tobacco plants in120days.In order to figure out the physiological races and their genetic diversity of E. cichoracearum DC,12varieties of tobacco were inoculated with the33isolated of E. cichoracearum DC collected from main tobacco growing areas in China. Different tobacco varieties is divided into different disease types for different tobacco powdery mildew pathogens according to the inoculated tobacco’s resistance index which calculated by the disease index. A set of differential hosts for identifying the physiologic races was established by5varieties of tobacco with a better ability to identify selected from the12which including CF203、K346、Tangpeng、G140、Jingyehuang, and the33isolates were divided into4physiologic races.33isolates of powdery mildew were evaluated by using random amplified polymorphic DNA (RAPD) with14primers selected from50random primers. A total of130bands were amplified including95polymorphic bands. After analysis by software NTSYS-PC, The UPGMA dendrogram divided the33isolates into4groups at the similarity coefficient of0.84. It is indicated that obvious association was found between DNA polymorphism and pathogen races in biological tests on tobacco by comparing the two sets of data, the rates of similarity reached84.85%. Finally, the33isolates were divided into1-6physiologic races according to the results by two methods.This study was not only invented a simple and convenient in vitro store method, identified the resistant tobacco varieties for future breeding research program, more importantly, it was the first time to establish a set of host system to differentiate physiological races of E. cichoracearum DC on the world. Different varieties of tobacco were inoculated with the33isolated of E. cichoracearum DC collected from main tobacco growing areas in China, and the33isolates were divided into4physiologic races by the host system. On the other hand,33isolates of powdery mildew were evaluated by using random amplified polymorphic DNA (RAPD). Analyzed the correlation between pathogenicity differentiation and genetic polymorphisms, it is very important to control of tobacco powdery mildew because that is the first time to carry out such study of tobacco powdery mildew. |
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