Population Genetic Diversity Analysis Of Plasmopara Viticola Which Is Related To The Host Varieties

Plasmopara viticola is an obligate biotrophic pathogen causing downy mildew in grapes. Yield and quality of grapes is badly reduced by this pathogen because it can infect leaves, tender branches, young fruit and other green tissues as well. This disease is a worldwide issue to grapes industries, particularly in China.Downy mildew samples were collected from grape varieties in Changli, Hebei province and Ziyuan, Guangxi province. The two places are different in historically plantation, cultivars and ecological types. In order to obtain pure strains in this study, a laboratory Plasmopara viticola rapid purification and expanding propagation system was established. The population genetic diversity and host plant specialization were also studied through morphological variation, sporangium size measure, pathogenicity identification and SSR sequence polymorphism analysis. The present work provide a theoretical basis for identification of variety resistance, forecasting mechanism in grapes for efficient control of downy mildew. The results are as follows: 1. The field epidemic surveillance of grape downy mildewThe disease index was surveyed during the year 2014 and 2015 at Changli and Ziyuan. The results obtained regarding the disease index of different host varieties in the same area were quite different from each other. The disease index of ?Red Globe" was significantly higher than any other grape varieties at Ziyuan. Two years consistent results exhibited that there was a cooperative coevolution between pathogen and host species. The disease index of the same host varieties in different areas was not stable, during first year of study(2014) all varieties showed significant difference, however, during 2015 no significant difference observed in varieties except for the var. ?Gold Finger", ?Flame Seedless" and ?Red Globe". This may be related to the climate and the survey time. Specific reason need to be explored and validated in further tests. 2. Morphological diversity of Plasmopara viticola sporangiumOver all 34 grapes varieties of which 18 from Ziyuan and 16 from Changli were measured regarding morphological diversity of sporangium. The results showed that the sporangial size showed significant difference among the isolates from different varieties in the same area. The sporangial size of the same variety in different areas showed no visible difference in the length of isolates from ?Ruby Seedless", ?Gold Finger", ?Shine-Muscat" and even in the width of isolates from ?Shine-Muscat". The sporangial size was significantly different among other isolates besides those varieties. The above results validated that there is a certain degree of differentiation among different strains on the sporangium morphology. 3. The pathogenicity analysis of Plasmopara viticolaPlasmopara viticola strains samples were collected and isolated from ?Ruby seedless", ?Red Globe" and ?Kyohō". We use leaf disk inoculation methods to carry out these experiment. The results showed that the pathogenicity were significant differenct among strains and the differences of Ziyuan were more significant than those of Changli. Therefore, there were genetic differentiation among the pathogen groups from different areas and the isolates from different varieties. 4. Genetic diversity analysis of Plasmopara viticola at the molecular levelSimple Sequence Repeat polymorphism analysis by using 8 specific primers for 751 Plasmopara viticola strains from Ziyuan and Changli and the result showed that the Plasmopara viticola obviously divided into two groups A and B. But the pathogen in two regions are mainly falls in group A. The diversity within group is the main source of genetic variation. 30 alleles were detected, the range of He was 0.21-0.74, the Shannon"s information index was 0.38-1.36 and Fst=0.344(P<0.001). The population genetic diversity of detected pathogens is rich, and the division of group A and B has significant relationship with the grape cultivar group.