Final answer:
Root rot and root parasitic nematodes, such as root knot nematodes, cause damage to plant roots, leading to stress symptoms including leaf discoloration and the formation of root galls or tumors. Option C is correct.
Step-by-step explanation:
Root rot and root parasitic nematodes cause damage to plant roots. This damage can manifest in several ways, such as impeding the normal uptake of water and nutrients, which is critical for the plant's growth and overall health. Root knot nematodes (RKNs), for instance, establish feeding sites within the roots of crops, leading to the formation of root galls or tumors, the main visible symptom of their presence. As a result of such damage, plants often exhibit stress symptoms, including leaf discoloration.
Other impacts from root parasitic nematodes include the triggering of an immune response in the plant. This includes the local production of reactive oxygen species (ROS) during the hypersensitive response (HR) and systemic acquired response (SAR), which involves reprogramming of the plant's defense genes. If a plant is resistant, it may activate its defense mechanisms more efficiently, preventing extensive damage caused by the nematodes.