How does downy mildew affect the vine?

How does downy mildew affect the vine?

• A. It causes grapes to rot on the vine.
• B. It damages only the roots.
• C. It improves the vine's photosynthesis.
• D. It attacks the green portions of the vine, causing leaves to drop and reducing photosynthesis.

Answer: (D)

Downy mildew is a foliar disease that attacks the green parts of the vine—mainly the leaves and young shoots. The pathogen colonizes the undersides of leaves, causing yellowing, a white cottony growth in wet conditions, and eventual leaf curl and drop. This directly reduces the leaf surface available for photosynthesis, so the vine produces less energy for growth and fruit development. It doesn’t primarily rot the fruit or damage the roots, and it certainly doesn’t improve photosynthesis. The damage to leaves and green tissue, leading to less photosynthetic capacity, is why this option best describes the effect.

Downy mildew is a foliar disease that attacks the green parts of the vine—mainly the leaves and young shoots. The pathogen colonizes the undersides of leaves, causing yellowing, a white cottony growth in wet conditions, and eventual leaf curl and drop. This directly reduces the leaf surface available for photosynthesis, so the vine produces less energy for growth and fruit development. It doesn’t primarily rot the fruit or damage the roots, and it certainly doesn’t improve photosynthesis. The damage to leaves and green tissue, leading to less photosynthetic capacity, is why this option best describes the effect.