HPIPM:Club Root

Author: Howard F. Schwartz and David H. Gent

Taxonomy

Domain	Eukarya
Kingdom	Protozoa
Phylum	Plasmodiophoromycota
Class	Plasmodiophoromycetes
Order	Plasmodiophorales
Family	Plasmodiophoraceae
Genus	Plasmodiophora

Scientific Name

Plasmodiophora brassicae

Common Name

club root of crucifers

Identification and Life Cycle

Club root is caused by the fungus Plasmodiophora brassicae; and can be a destructive disease of cabbage, cauliflower, broccoli, brussel sprouts, kohlrabi, Chinese cabbage, radish, turnip, and rutabaga. It may also infect many wild mustards and cultivated ornamentals such as column stock and wallflower. Infection is most severe in acid soils, and does not occur above pH 7.0. Disease develops when soilborne spores germinate and infect young roots. The fungus spreads from cell to cell in roots, and causes a rapid growth of large cells. The pathogen is disseminated among fields in infected transplants, contaminated soil on equipment, and irrigation water. Resting spores of the pathogen survive for years in soil.

Plant Response and Damage

Disease symptoms first appear as slight wilting or flagging of leaves during the warmest part of the day. The wilting becomes progressively worse, until permanent wilting occurs. Roots of infected plants are enlarged and misshaped. If infection occurs at a single site, roots are spindle-shaped, but multiple infections result in extreme swelling and distortion.

Biological Control

No biological control strategies have been developed for club root.

Cultural Control

Plant transplants free from club root. Prevent the introduction of the pathogen into new fields by pressure-washing equipment after working in fields with the disease. Practice a three-year or longer crop rotation to non-hosts such as small grains. Avoid reuse of irrigation tail water. Club root is not a problem in alkaline soils, and liming acid soils can provide an effective control strategy. Tolerant varieties should be planted where available, but many strains of the pathogen exist that may overcome resistance in some varieties.

Chemical Control

PCNB (pentachloronitrobenzene) incorporation into soil at planting can delay root decay from secondary pathogens, but is most effective when used in combination with cultural practices such as liming.

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