Powdery mildew disease symptoms and phylogenetic relation of E. necator with other grapevine fungal pathogens and other powdery mildew pathogens. E. necator infections are initiated when conidia come in contact with a susceptible host and germinate, forming hyphae with multilobed appressoria and penetration pegs. Haustoria are formed within the epidermal cell membrane to maintain the parasitic relationship with the host. Young colonies are macroscopically visible and appear white on the surface of (A) leaves, (B) fruit, and other green tissue. Multiseptate conidophores form along the hyphae perpendicularly to the epidermis, and (C) conidia begin to develop within a few days of the initial infection (white bar = 0.2 mm). (D) Phylogenetic relationship of E. necator with other powdery mildews (gray) and grape fungal pathogens (red). The Neighbor-Joining tree was constructed in MEGA5  using the complete rDNA ITS (ITS1, 5.8 rDNA, ITS2). Multiple publicly available ITS sequences per species were used independently to confirm clustering. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1,000 replicates) is shown next to the branches . Only bootstrap values greater than 60 are shown. The evolutionary distances were computed using the Maximum Composite Likelihood method  and are in the units of the number of base substitutions per site. The analysis involved 11 nucleotide sequences. All positions containing gaps and missing data were eliminated. There were a total of 372 positions in the final dataset.