Ten years have passed since Plasmodiophora brassicae, the clubroot pathogen, was profiled in Molecular Plant Pathology and identified as an emerging phytosanitary problem in Canada. Unfortunately, since then, the clubroot pathogen has made Canada its ‘forever home’ with hundreds of thousands of hectares currently affected by the clubroot pathogen, and more than 80 countries reporting its presence. This devastating pathogen affects mainly the roots of cruciferous plants like canola (rapeseed in Europe), cabbage and broccoli, causing millions of dollars in economic losses every year: the reason why several research groups are actively trying to understand the biology of the pathogen and looking for more efficient ways to manage the disease.
When people think about a plant pathogen, bacteria, viruses, or fungi come to their mind, but the clubroot pathogen is a protist, more related to the causal agent of malaria in humans than to a plant pathogen affecting our tomatoes. Today, we know more about the biology of the clubroot pathogen thanks to breakthroughs like the sequencing of P. brassicae genome in 2015, helping us to understand why this pathogen is unable to complete its life cycle outside the plant, and why it cannot be grown in axenic culture. Using advanced microscopy techniques and a lot of patience, scientists have been able to refine the different steps happening in the roots, from the penetration of resting spores to the release into the soil of new resting spores that will be viable for up to 20 years.
Something else we have learned this last ten years is to better manage the clubroot pathogen. Agronomic solutions have helped to contain the disease in some areas, but the main method that is changing the score in our favor is genetic resistance. Several clubroot resistance genes have been successfully introgressed into rapeseed from other cruciferous crops and those new elite cultivars are being used by growers. However, plants are never safe in the arms race against pathogens, and new virulent pathotypes have been able to breakdown the resistance and keep affecting cruciferous crops around the world. Why and how? We still don’t know, and those are precisely two of the main questions we should try to answer in the coming years. By revealing the mechanisms used by the clubroot pathogen to infect the susceptible host and induce the galls characteristic of this disease, we will better understand how this disease leads to death of the plant. Arming us with knowledge so that we will be prepared to fight an enemy we barely know.
In the pathogen profile entitled: “The clubroot pathogen Plasmodiophora brassicae – a profile update”, we summarized the new findings regarding this pathogen and the main areas that should be deepened in the coming years.
Blog written by Edel Pérez-López.
Muhammad Asim Javed, Arne Schwelm, Nazanin Zamani-Noor, Rasha Salih, Marina Silvestre Vañó, Jiaxu Wu, Melaine González García, Thies Marten Heick, Chaoyu Luo, Priyavashini Prakash and Edel Pérez-López published this pathogen profile in Molecular Plant Pathology: