• Nutrition Mode of Powdery Mildew (Erysiphe spp.):
• Ectoparasitic Biotrophic Nature: Erysiphe species (order Erysiphales) are obligate biotrophic plant pathogens that exhibit an ectoparasitic mode of life.
• Infection Pattern: Their vegetative mycelium, conidiophores, and conidia develop entirely externally on the outer cuticular surface of the host leaves and stems, forming a conspicuous white, powdery coating. They absorb nutrients strictly by sending specialized absorbing organs (haustoria) through the cuticle into host epidermal cells without killing them.
• Conclusion: The mode of nutrition of Erysiphe is ectoparasitic (Option 3).

Correct option: (3) Ectoparasitic