Which of the following is an example of a Nematode Disease?

Pine wilt is indeed an example of a nematode disease, specifically caused by the pinewood nematode, Bursaphelenchus xylophilus. This disease affects coniferous trees, primarily pines, leading to rapid decline and often death of the tree. The nematodes are transmitted by particular beetles that bore into the trees, allowing the nematodes to enter and disrupt the tree's vascular system, ultimately affecting its water and nutrient transport.

The other diseases listed are caused by different pathogens and are not classified as nematode diseases. Powdery mildew is primarily a fungal disease affecting a wide range of plants, while black spot is also a fungal disease, notably affecting roses. Root rot, on the other hand, is usually caused by various soil-borne fungi that attack the roots of plants. Understanding the specific characteristics and causative agents of these diseases is crucial for effective management and treatment in horticultural practices.