What occurs to plant leaves affected by mildew?

When plant leaves are affected by mildew, specifically powdery mildew, they often exhibit distressing symptoms that include darkening and wrinkling. The presence of mildew typically indicates a fungal infection, which can hinder the plant's ability to photosynthesize effectively, causing the leaves to show signs of stress. As the mildew spreads, the affected leaves may turn black as they decay, and the tissue can become wrinkled due to cellular damage and dehydration. This condition is detrimental to the overall health of the plant, often leading to reduced vigor and possibly plant death if not managed promptly.

In this context, the other choices do not accurately represent the effects of mildew on plant leaves. Brightening of leaf color and increased flower production are signs of healthy plant conditions and growth, while larger leaf size is also indicative of good health and not a symptom of mildew infection.