What are the common causes of plant disease?

Fungi and bacteria are two of the most prevalent agents responsible for plant diseases. Fungi can cause a variety of issues, including root rot, leaf spots, and blights, through their widespread nature and ability to thrive in various environments. They reproduce through spores that can be dispersed by wind, water, or insects, leading to infection in healthy plants. Bacteria, on the other hand, can cause diseases such as bacterial wilt or soft rot, often resulting in symptoms like wilting, discoloration, and tissue breakdown. Both fungi and bacteria can infect plants through wounds or natural openings, making them significant threats to plant health.

In contrast, the other options pertain to different aspects of plant health. Insects can damage plants but are not direct causes of disease in the same way that pathogens like fungi and bacteria are. Sunlight, while essential for photosynthesis, does not cause plant disease. Soil pH and temperature can affect plant health and susceptibility to disease but are not direct causes of disease themselves. Similarly, while water and nutrients are critical for plant growth, an imbalance can lead to stress but does not inherently cause disease. Therefore, fungi and bacteria stand out as the primary causes linked directly to the occurrence of plant diseases.