Which symptom is most characteristic of clubroot in affected plants?

The most characteristic symptom of clubroot in affected plants is the presence of club-shaped roots. This root deformation is caused by the pathogen Plasmodiophora brassicae, which infects the roots of cruciferous plants, leading to an abnormal swelling and growth that resembles clubs. The distinctive swollen roots disrupt the plant's ability to absorb water and nutrients effectively, which can subsequently affect the overall health and vigor of the plant.

While yellowing leaves, wilting foliage, and browning stems can be symptoms of various plant stress factors, they are not unique to clubroot. Yellowing leaves often indicate nutrient deficiencies or other environmental stresses, wilting foliage can result from drought or root problems independent of clubroot, and browning stems can be associated with various diseases or stressors. Therefore, the club-shaped roots serve as a key diagnostic indicator specific to clubroot disease, distinguishing it from other conditions that may affect plant health.