Final answer:
A few bacteria cause disease in plants due to specific bacteria's virulence factors, the presence of a susceptible host, and environmental conditions that enable the pathogen to thrive. A plant's genetic makeup and immune system, including its chemical defenses, play crucial roles in resistance to disease. The correct option is A.
Step-by-step explanation:
The question asks why a few number of bacteria cause disease in plants, presenting potential reasons such as a lack of suitable host plants, plant immune responses, limited bacterial virulence, and environmental factors.
The pathogenicity of bacteria, or their ability to cause disease, depends on several factors including the presence of virulence factors of the bacteria, the plant's immune defenses, and other environmental conditions that may facilitate the bacteria's growth or affect the plant's resistance.
To better understand why only some bacteria cause disease in plants, we must consider the disease triangle, which consists of a pathogen's virulence, a susceptible host (in this case, a plant), and environmental conditions that are conducive to disease.
For instance, certain bacterial infections might cause serious harm to a plant if the plant lacks the genetic defenses against that particular strain, whereas other plants may be unaffected. Moreover, plants also have chemical defenses to maintain dynamic homeostasis and protect themselves against infections, acting as part of their immunity.