Which of the following is NOT a major group of plant pathogens?

The response identifies that "Microbes" is not categorized as a major group of plant pathogens, which is correct because the term "microbes" encompasses a wide range of organisms, including bacteria, fungi, and viruses. In the context of plant pathology, it is more precise to refer specifically to the major groups known to significantly affect plants.

Fungi play a significant role in plant diseases, responsible for issues like root rot, powdery mildew, and rust diseases. Viruses are also a critical group, causing a variety of plant ailments that can decrease yield and affect plant health. Nematodes, though small and often overlooked, are a major group of plant pathogens that can cause damage to roots and disrupt nutrient uptake.

By identifying "microbes" as not a specific major group of plant pathogens, the answer underscores the importance of specificity in the terminology used in plant pathology. Each of the other choices represents distinct and recognized categories of pathogens that have well-documented impacts on plant health and management practices.