Plasmodiophora brassicae



Plasmodiophora brassicae is a soilborne organism that is best known for its high economic impact on Brassica oil and vegetable crops. It infects 30 different cruciferous plants, which consists of up to 16 crop species, 9 ornamentals, and 5 weeds. The fungus on those plants causes a disease referred to as clubroot.

Taxonomy
Plasmodiophora brassicae was once referred to as a slime mold but was then transferred to the Phytomyxea group.

Description
Plasmodiophora brassicae exhibits two main forms within its life cycle. It is either a spore that is ready to infect roots or it becomes a persistent spore in the soil. That, or the fungus can become a somewhat mobile zoospore, which is a spindle shaped biflagellate cell.

Life cycle
Plasmodiophora brassicae life cycle consists of two main phases. Phase one is a sporangial stage which will lead to a short-lived zoospore. Stage two leads to a sporogenic phase which creates persistent resting spores. Within the two phases P. brassicae has three distinct stages within its lifecycle. Starting with survival within the soil, from there it will find a host and infect the root hairs of the plant, and finally it will start the cortical infection.

Habitat and distribution
It was first discovered in Europe in the 13th century and has since traveled across the globe. It has been reported in over sixty different countries. including countries such as China, United States, and most other major countries. It survives in the soil around its target host while also being found in particular waterways, which most likely came from runoff of fields and soil that has already been infected with club root.

Affected crops
As P. brassicae can infect more than just crops such as ornamental flowers and other ornamentals and even some weeds, the focus will be on crops as that has the most detrimental effect to humans and other species. It has been found to infect many crops that we use as a main food source. Crops like cabbage, brussels sprouts, turnips, broccoli, mustard, and radishes.

Symptoms
Symptoms of P. brassicae are the swelling of the roots which cause “clubs”. These clubs can be found on primary roots, secondary roots, tap roots, and even the area of the stalk just under ground level. Larger clubs are formed on larger roots especially just under the surface of the soil.

Control
Controlling P. brassicae can be quite difficult. There are two main ways to help control this organism. The first way would be cultural control and the other is chemical control. Within cultural control the objective is to keep the fungi under control so that it does not affect the farmers’ bottom dollar. Do this by removing the fungus’ favorable conditions which are excessive moisture in the soil, temperatures ranging from 18 to 25 degrees Celsius, and low pH in the soil. Good draining soil while also raising the pH of the soil by adding lime powder are good non-chemical ways to control P. brassicae. Within chemicals there are soil sterilants and Fungicides that can be sprayed into the fields of effected soils.