From the Soil to the Club in the Roots: Clubroot

Among the millions of microorganisms inhabiting the soils, some can be plant pathogens, meaning they can become a disease to plants. Some diseases are more well-known than others. This is the case of clubroot, a very atypical microorganism that infects cruciferous plants, such as cabbage, kale, canola, and the common research plant thale cress. In this article, I will tell you more about clubroot and clubroot disease because there is still a lot to discover about the pathogen and the disease. Maybe you will be part of our lab in the future and investigate a fascinating soil-borne pathogen.

well-known soil-borne pathogens for plants, but they are not

SOIL-BORNE PATHOGEN
Microorganisms that survive and move about in the soil and can make plants ill. the only ones. Some protists are also devastating soil-borne PROTISTS Tiny, one-celled organisms that are not animals, plants, or fungi. plant pathogens, although they are less studied and known. Protists are one-celled organisms that are not animals, plants, or fungi. The clubroot pathogen, or Plasmodiophora brassicae like scientist call it, is a protist that a ects the roots of cruciferous vegetables, such

CRUCIFEROUS VEGETABLES
Vegetables of the family Brassicaceae, including many green leafy vegetables like cauliflower, cabbage, kale, garden cress, bok choy, broccoli, and Brussels sprouts. as broccoli, cabbage, cauliflower, the oilseed plant known as canola, and thale cress that is commonly used in plant research [ ]. Thale cress and canola are one important host for clubroot, but for di erent reasons ( Figure ). Thale cress is a very useful plant for scientists that study various aspects of plants, such as their genomes, ecology, and relationships with beneficial microorganisms or pathogens [ ]. Thale cress plants infected by clubroot are the perfect model to study how the pathogen a ects the plant. Another plant that is extremely important from an economic point of view is canola (Figure ). Canola is the source of canola oil, a product used in many kitchens around the world. In Canada alone, canola represents around $ billion dollars (CAD) for the Canadian economy, so a pathogen that puts canola production at risk could be devastating for the economy [ ].

THE LIFE CYCLE OF CLUBROOT
The clubroot pathogen can live in the soil for up to years as an inactive spore. Spores are structures created by some plant pathogens SPORE Structure created by clubroot that has a thick cell wall to help it survive for many years in the soil when it is not able to infect a plant.
that are released to the environment and have a thick cell wall to help it survive for many years in the soil when are not able to infect a plant. If a susceptible plant grows in soil containing clubroot spores, then the resting spores "wake up" turning now in zoospores and attach to the roots of the plant and start an infection. The infection process is divided into two phases: primary infection and secondary infection ( Figure A). During primary infection, the clubroot pathogen encounter the roots and penetrate, starting the infection. Although primary infection is important, it is during secondary infection that clubroot induces galls, also called clubs, in the roots of susceptible

CLUBROOT OR A CLUB IN THE ROOTS?
The clubs are the reason why this disease is known as clubroot. When I heard of clubroot for the first time, I thought it meant "a club in the roots." However, as fun as it sounds, that expectation is quite di erent from reality ( Figure B). If anyone is having fun in the infected root, it is definitely not the plant! The reality is that the clubs induced by clubroot are devastating. In the laboratory, we found that days after adding clubroot to the soil, susceptible plants start to die. The xylem and phloem, which are the channels used by plants to transport water and nutrients, are totally blocked. It is also interesting to note that the galls caused by clubroot are quite similar in di erent plant hosts (Figure ).

HOW CAN WE MANAGE CLUBROOT AND FIGHT CLUBROOT DISEASE?
Although clubroot and the disease it causes were discovered back in the s, there are a lot of things that scientists do not know [ ]. To manage clubroot, farmers have been using chemicals, such as fungicides, with little success. Growing plants that are resistant to clubroot disease is the best strategy. However, after only a few years, clubroot develops new strategies to infect those resistant plants, making them susceptible to clubroot disease.
We are trying to fight an enemy that we do not understand very well, so the first step in the war against clubroot disease is to uncover all the tricks that this pathogen is hiding up its sleeves. In the University Laval (Quebec City, Canada), scientists are taking important steps toward understanding clubroot and the disease it causes. They want to know how clubroot escapes the plant immune system and how it can make the cells grow to form the galls. Their ultimate goal is to develop plants that are resistant to clubroot disease that can survive in a field with or without clubroot spores in it. Maybe in a few years you, the young curious mind reading this, will be part of the team tackling this intriguing pathogen.