Title Page

Contents

1. Introduction 6

2. Materials and Methods 11

2.1. Plant material preparation 11

2.2. Infected material collection 11

2.3. Isolation and maintaining of the sporangia 12

2.4. Phenotypic characterization 13

2.5. Pathogenicity test 14

2.6. Grapevine host resistance reaction to Downy mildew infection 15

2.7. Genomic DNA extraction 16

2.8. Molecular characterization and Phylogenetic analysis 17

2.9. Data collection and statistical analysis 18

3. Results 20

3.1. Zoospore Germination and Development of P. viticola infection 20

3.2. Surface sporulation on the leaf 22

3.3. Pathogenicity variability among field isolates 22

3.4. Screening for Host resistance reaction 30

3.5. Phylogenetic relationship among Korean P. viticola isolates 34

4. Discussion 41

5. References 48

ABSTRACT 56

Table1. Primer set used for phylogenetic analysis 19

Table2. Analysis of evolutionary relationship among P. viticola isolates 36

Figure1. In vitro development of Plasmopara viticola infection. A. Lemon shape sporangia B. zoospores released from mature sporangia 3 hours of... 21

Figure2. Evaluation of the pathogenicity among field isolate based on latent period. 24

Figure3. Phenotypic expression of most virulent isolates from four Korean grape growing regions. JN-9: Isolate nine from Jonju, CHKU-3: isolate three... 27

Figure4. Pathogenicity variability among field isolates based on sporulation potential of isolates. 28

Figure5. Sporulation diameter exhibited by field isolates as a measure for pathogenicity test 29

Figure6. Grape host resistance reaction; A. abundant sporulation no necrotic spot, B. limited sporulation no necrotic spot, C. scattered sporulation with... 32

Figure7. Tested grape varieties and the proportion of their host resistance reaction to D.M infection. 33

Figure8. Molecular Phylogenetic analysis by Maximum Likelihood of allele relationship by employing Actin(ACT) [A], Cytochrome C oxidase II (Cox2)... 38

Figure9. Molecular Phylogenetic species tree by Maximum likelihood obtained by linking Actin, Cytochrome oxidase II, Internal Transcribed... 40