Plasmodiophora

Plasmodiophora is a genus of obligate intracellular plant parasites belonging to the group Phytomyxea within the Cercozoa and historically treated as fungi. The most economically important species is Plasmodiophora brassicae, the causative agent of clubroot disease in cruciferous crops such as cabbage, broccoli, and oilseed rape. The genus includes other species that infect different hosts, but P. brassicae is the best studied.

The life cycle is soil-borne and involves resting spores that can persist in soil for extended periods. In moist conditions, resting spores germinate and release motile zoospores that swim to plant roots and infect root hairs. Inside the host, Plasmodiophora forms multinucleate plasmodia that proliferate within root cells and then invade cortical tissues, causing hypertrophy and gall formation (clubroot). The plasmodia develop into resting spores within the galls, and when plant tissue decays, these spores return to the soil to perpetuate the inoculum.

Disease symptoms include enlarged, distorted roots with club-shaped galls, impaired water and nutrient uptake, stunting, wilting, and yellowing of foliage, often resulting in reduced yields. Disease development is favored by cool, moist soils and certain crop rotations.

Management focuses on reducing inoculum and preventing infection. Approaches include long crop rotations away from Brassica hosts, raising soil pH (liming) to suppress infection, using resistant cultivars where available, sanitation to prevent spread of soil-borne inoculum, and soil management practices such as solarization or drainage improvements. Because resting spores can persist for many years, control remains challenging.