What symptom might indicate a disease on individual plants?

The presence of small, circular, tan-colored lesions surrounded by brown or purple borders is a strong indicator of disease on individual plants. This symptom typically suggests that the plant is suffering from some form of pathogen infection, such as a fungal, bacterial, or viral disease. These lesions can disrupt the plant's ability to photosynthesize effectively, leading to further complications in growth and overall health.

In contrast, thick, lush growth usually indicates a healthy plant that is growing well, while stunted growth with yellow blotches can be associated with nutritional deficiencies or environmental stress, rather than a specific disease. Healthy green leaves with no discoloration signify that the plant is disease-free and thriving, so these options do not point to a disease condition. The specific symptoms described in the correct choice are more aligned with the visible signs of plant pathogens, making it clear that this is the most accurate indicator of disease.