Clubroot
Plasmodiophora brassicae
What is Clubroot (Plasmodiophora brassicae)?
Clubroot, caused by a soil-borne pathogen Plasmodiophora brassicae, poses a significant threat to Brassica crops worldwide, including vegetables like cabbage, radish, cauliflower, and broccoli. It is particularly common in cool and moist climates. The pathogen infects the roots of these plants, causing them to develop swollen, or "clubs." It impairs the plant's ability to take up water and nutrients, resulting in stunted growth, yellowing leaves, and eventual plant death. Clubroot can persist in the soil for several years, making it challenging to control. It is a known problem in several Canadian provinces.
How does Clubroot (Plasmodiophora brassicae) occur?
Clubroot is reproduced through resting spores in the soil. These spores germinate into motile zoospores, which infect susceptible plant roots, causing the formation of galls. As the galls mature, they release more resting spores into the soil. These resting spores can survive in the soil for several years, even in the absence of host plants. When a new susceptible plant is grown in the infested soil, the resting spores germinate, restarting its life. Spread occurs through soil movement and contaminated materials.
Symptoms
2 - Plant Effects
Clubroot causes root deformities, reduces nutrient uptake, stunts growth, and leads to plant death, resulting in significant yield losses.
3 - Soil Effects
The presence of clubroot alters soil structure and nutrient availability. The galls formed on infected roots can impede soil aeration and water infiltration. Moreover, the long-term survival of the pathogen can disrupt soil health.
Solutions
7 - Soil Solarization
• Clear the affected area of plant debris and weeds. • Moisten the soil to ensure good heat conduction. • Cover the soil with clear plastic sheets, securing the edges to create a seal. • Leave the plastic sheets in place for 4-6 weeks during the hottest period of the year. • The heat trapped under the plastic will help reduce the population of Plasmodiophora brassicae and other soil-borne pathogens.
9 - Biofumigation
• Plant biofumigant crops such as mustards (Brassica juncea) in the affected area. • Allow the plants to grow until they reach the flowering stage. • Incorporate the biofumigant crops into the soil while still green, chopping them finely. • Cover the soil with a plastic sheet or tarp to trap the released gases. • Leave the cover in place for 2-4 weeks, allowing the breakdown of plant tissues to release bioactive compounds that suppress the pathogen.
10 - Resistant Varieties and Soil Amendments
• Plant brassica crop varieties that have been specifically bred for resistance to Plasmodiophora brassicae. • Amend the soil with calcium to raise the pH level above 7.0, creating an unfavorable environment for the pathogen. • Incorporate organic matter such as compost or well-rotted manure into the soil to improve its structure and nutrient content. • Maintain proper soil moisture levels and drainage to discourage disease development.
