If the plant is infected with one diseae, it makes the plant resistant to other disease. This phenomenon is known as

If the plant is infected with one disease, it makes the plant resistant to other diseases. This phenomenon is known as Cross protection.
Cross-protection, also known as “pre-immunization" is a method of plant virus control, whereby a plant is deliberately infected with a mild strain of a virus to protect the plant against damage caused by a more severe strain of the same virus.