Which of the following is an example of a biotic plant disease?

A biotic plant disease is caused by living organisms such as fungi, bacteria, viruses, or parasites. Canker development on branches specifically refers to a localized area of dead tissue on a plant, often resulting from biotic pathogens such as fungi or bacteria that infect the plant, leading to disease symptoms.

In this context, canker is a direct manifestation of such an infection and demonstrates how a living organism can disrupt the normal functioning of the plant tissue. The disease is characterized by necrotic tissue and can significantly affect the overall health of the plant if not managed properly.

The other options describe conditions related to abiotic stress, which stem from environmental or non-living factors rather than from living pathogens. Yellowing leaves from lack of water pertains to drought stress, soil nutrient deficiency refers to a lack of essential nutrients in the soil, and excessive sun exposure relates to solar damage—none of which are caused by living organisms. Therefore, recognizing canker as a product of biotic influences emphasizes the importance of understanding plant disease mechanisms.