| Grape downy mildew is one of the four major diseases of grapes, originated in North America, was discovered in1834. China had its record for the first time in1899. The disease is caused by Plasmopara viticola, would seriously affect the production and quality of grape after onset. This study through the investigation of grape downy mildew disease occurred in Hunan province and the weather factors on the impact of disease occurrence, to provide some basis for prevention and control of grape downy mildew; In addition,collecting the grape leaves which have typical symptoms of grape downy mildew from Hunan, Hubei, Jiangxi and Fujian provinces,then separate the Plasmopara viticola from these leaves. Testing the pathogenicity of Plasmopara viticola to different kinds of grapes and its fungicide resistance to four kinds of fungicide, and its genetic diversity research.(1) A field survey of grape downy mildew in nine areas of Hunan Province In July2012.The resultes showed that disease resistance of Europe and the United States hybrids grape is stronger than Eurasian species;Rain-shelter-cultivation could significantly reduce the incidence of downy mildew.In the nine areas,the occurrence of grape downy mildew is the most serious in Huaihua and Xiangxi, followed by Hengyang,Yongzhou and Chenzhou,then Yiyang, the lightest in Changde, Changsha and Zhuzhou.(2) A system investigation was proceed on epidemic regularity of grape downy mildew in Jingzhou,Huaihua, Hunan Province in2012and2013, On the basis of it analysis the influence of meteorological factors on the occurrence of the disease.The results showed that: the disease can occur at temperatures in the range of3～28℃, the optimum is20～25℃. Under20℃, the occurrence of diseases ease with temperature drop; Above25℃, with the temperature rising then reduce.The disease occurs when the relative humidity reached by65%, then with a positive correlation. High rainfall and rainfall frequency is very important to the popularity of downy mildew. Trrough multiple regression analysis of meteorological factors during the grape growing seasons in the area, establish the region grape downy mildew prediction model, forecasting grape downy mildew disease index in the region by this model, the prediction accuracy in2012and2013achievid77.18%and81.77%.(3) Twenty grape downy mildew pathogen strains were from Hunan, Jiangxi, Fujian and Hubei provinces,determined the pathogenicity of these pathogen strains to five different varieties of grapes by isolation leaf disks inoculations,the results show that there are some differences between the different sources of pathogenic strains. It was found that NP-2which was isolated from Nanping of Fujian had the highest pathogenicity, and the lowest one was CS-1which was isolated from Changsha of Hunan.(4) Through four kinds of fungicides virulence measurement of different strains, we found that the average EC50of Dimethomorph copper to20strains is3.23μ.g/ml(Max:3.82μg/ml, Min: 2.57μg/ml), azoxystrobin’s is8.25μg/ml(Max:9.22μg/ml, Min:6.14μg/ml).; kresoxim-methyl’s is12.24μg/ml(Max:14.08μg/ml, Min:9.62μg/ml); metalaxyl’s is25.96μg/ml(Max:30.57μg/ml, Min:19.88μg/ml). All of fungicides has a good inhibition to P. viticola.(5) PCR amplification was carried out on the20strains through ITS primers, β-tubulin primers and CytB primers,The amplified fragment length,in order,770bp,800bp,400bp.After the sequencing construct phylogenetic tree analysis its genetic diversity. Results showed that four places in hunan province the downy mildew strains of close relatives,the srains from Wuhan,Pingxiang and Nanping also has a certain relationship.But individual stains affinity is inconsistent.All could be able to distinguish close genetic relationship strains of different species,,But the discrimination degree of CytB gene sequence is the highest classification effect is the best, it played a important role in the distinction between the trains belongs to same species with more closely genetic relationship. |
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