Clubroot

Clubroot is a common disease of cabbages, canola, broccoli, cauliflower, Brussels sprouts, radishes, turnips, stocks, wallflowers and other plants of the family Brassicaceae (Cruciferae). It is caused by Plasmodiophora brassicae, which was once considered a slime mold but is now a protist in the class Phytomyxea. It is the first phytomyxean for which the genome has been sequenced. The pathogen can evolve rapidly, and in Canada alone, 55 distinct pathotypes (sometimes called races) have been identified as of 2023, an increase from 43 pathotypes in 2020. It can cause club- or spindle-like galls to form on latent roots, interfering with head development, and followed often by decline in vigor or by death. It is an important disease, affecting an estimated 10% of the total cultured area worldwide. There are records of clubroot from the 13th century in Europe. Plasmodiophora brassicae was discovered and named in 1875 by Russian scientist Mikhail Woronin after an epidemic in cabbage crops in St. Petersburg. Other English names for clubroot include finger-and-toe or anbury, the latter also meaning a soft tumor on a horse. The potential of cultural practices to reduce crop losses due to clubroot is limited, and potential chemical treatments to control the disease are either not effective in field conditions, banned due to environmental regulations, or are not cost effective. Breeding of clubroot-resistant cultivars is the most common and effective method of control in canola, but the pathogen can evolve to affect these resistant plants in as little as four years. These stronger pathogens are called resistance-breaking pathotypes, and they have become a major challenge in clubroot management.