Which of the following is an example of a non-pathogenic plant disease?

Non-pathogenic plant diseases are issues that affect plants but are not caused by pathogens such as bacteria, viruses, or fungi. Instead, they typically arise from environmental factors or physiological conditions. The correct answer indicates that none of the provided examples represent non-pathogenic plant diseases.

Stem rust, powdery mildew, and fungal blight are all caused by various types of fungi and fall into the category of pathogenic diseases. They involve specific pathogens attacking the plant, leading to symptoms of disease. This means that each of these conditions is pathogen-driven and therefore cannot be classified as non-pathogenic.

In horticulture, understanding the distinction between pathogenic and non-pathogenic concerns is crucial for effective disease management and treatment strategies. Non-pathogenic concerns might involve nutrient deficiencies, environmental stress, or improper cultural practices, rather than infections from disease-causing organisms.