What must occur for disease to effectively manifest according to the disease triangle?

In the context of plant pathology, the disease triangle is a model used to illustrate the essential factors required for a plant disease to occur. The triangle consists of three components: the pathogen, the host, and the environment. For a disease to effectively manifest, all three components must interact harmoniously.

The presence of the pathogen alone does not guarantee disease; the host must be susceptible, and the environmental conditions must be conducive to the disease. This means that if any one of these components is absent or not interacting effectively with the others, the disease cannot occur. For example, a virulent pathogen can exist, but if the host plant is resistant or if environmental conditions are unfavorable (such as too dry or too cool), disease symptoms may not manifest.

The correct choice highlights the necessity of a combination of these three factors working together for a disease to develop. Understanding this interaction is crucial for effective disease management strategies in agriculture and horticulture.