Which of the following is NOT one of the three sides of the disease development triangle?

The disease development triangle is a fundamental concept in plant pathology used to describe the factors necessary for disease to occur in plants. This triangle comprises three critical components: the host, the pathogen, and the environment. Each of these elements must interact for a disease to develop.

The host refers to the plant or organism that can be affected by a disease. A suitable host is needed for the pathogen to thrive and cause infection. The pathogen is the organism that causes the disease, such as a fungus, bacterium, virus, or nematode. The environment includes factors such as moisture, temperature, and soil conditions that can influence the interaction between the host and the pathogen.

Antigens, on the other hand, are molecules that stimulate an immune response, and while they play a role in the broader context of disease and plant defense, they do not fit into the structure of the disease development triangle. Therefore, this concept clarifies that antigens are not one of the three sides of the triangle, making this the correct answer.