What type of organism causes root-knot, lesion, and stunt diseases?

Root-knot, lesion, and stunt diseases are primarily caused by nematodes. Nematodes are microscopic, worm-like organisms that dwell in the soil and can infect the roots of plants. They establish feeding sites in the plant roots, leading to the symptoms associated with these diseases.

In the case of root-knot nematodes, the infestation results in the formation of galls or 'knots' on the roots, which disrupt normal root function and nutrient uptake. Lesion nematodes cause spots or lesions on the roots, hindering water and nutrient absorption, and stunt nematodes typically cause stunted growth due to their impact on the plant's root system. These conditions create significant stress on plants, resulting in reduced yields and overall vigor.

Understanding the role of nematodes is crucial in managing these diseases effectively, as different control strategies are required compared to other pathogens like bacteria, viruses, or fungi, which attack plants in different ways.