May 2024 | Agriculture and Agri-Food Canada and Canadian Food Inspection Agency
Potato wart requires attention from plant health scientists around the world, including those at Agriculture and Agri-Food Canada (AAFC) and the Canadian Food Inspection Agency (CFIA). Potato wart is a disease of potatoes caused by the fungus Synchytrium endobioticum – a particularly hardy and persistent pest. While potato wart does not pose a risk to human or animal health, the disease can deform potato tubers, making them unmarketable, and reduce crop yields.
A worldwide pest
Potato wart is an issue for many countries, as the fungus has been detected on every continent except Antarctica – which also happens to be the only continent where potatoes do not grow! Globally, the pest is recognized as a serious potato pathogen that can cause devastating economic impacts. Potato wart is a significant threat to Canadian potato crops, the largest vegetable crop grown in Canada. In 2022-2023, Canada exported $3.4 billion dollars of potatoes and potato products.
The international scientific community, including Canada, can benefit from exchanging knowledge on potato wart to better understand this pest and inform future research and development priorities to help prevent its spread.
The biology of a challenging pest
Like many plant pests, the biology of S. endobioticum makes it very challenging to manage and control. This is mainly because the soil-borne fungus reproduces and spreads via microscopic spores that are not only tiny, but can remain stable and dormant in a field for over 40 years. The signs of potato wart infection are not always easy to see. The pest can spread when infected seed potatoes are planted in a new field, when contaminated soil or equipment moves between fields, or even through the manure of animals that eat infected tubers.
Once present in a field or garden, potato wart stays in the soil and produces spores that can then infect future potato crops. When environmental conditions such as temperature and soil moisture are right, the spores can germinate and each release around 300 tiny mobile zoospores that can infect other potato crops.
After infecting a potato plant, the fungus multiplies and forms new spores that can germinate and re-infect the same plant. This cycle of infection and re-infection may repeat for the entire growing season if conditions are suitable. The more often this cycle repeats itself, the larger the warts become – this is what causes the characteristic “cauliflower-like” wart tissue on infected potato tubers.
Unlocking the mysteries of potato wart spores
When conditions are drier, the fungus can adapt and start producing resting spores. These resting spores can remain in the soil for decades until the conditions for germination and further spread are just right. Exactly what triggers these resting spores to “wake up” and germinate is currently unknown, but increasing our understanding of potato wart spores may be an important piece of the puzzle to help control the spread of the pest.
So how can we determine spore viability – in other words, whether a potato wart spore is dead, alive or in that alive-but-dormant phase? While scientists have attempted to use microscopic examination and bioassay testing methods both in the lab and in the field, these tests have limited reliability to conclusively determine spore viability.
Given the role of spores in the pest’s biology and pathways for spread, AAFC, CFIA and other international plant health research organizations have identified a need to advance scientific research on spore viability.
Knowledge exchange with international potato wart experts
In March 2024, scientists with AAFC and CFIA met virtually with international experts from Canada, Australia, France, Germany, the Netherlands, the United Kingdom and the United States of America to discuss the science of potato wart spore viability and opportunities for collaborative research.
Participants shared information about research underway as well as:
- current methods to test for spore viability, and their limitations
- criteria to determine the viability of spores
- emerging technologies and the potential for research to develop and advance new technologies
- considerations for implementing spore viability testing methods in lab settings
The group agreed that viability testing is a complex challenge. There are unanswered questions about the biology of the pest itself and how infection is triggered. These areas were identified as opportunities for further research that could provide new insights and support the development of new viability testing methods.
The group will continue to meet regularly and share data, materials and results on potato wart research. This ongoing collaboration will help refine our collective knowledge about spore viability testing with the goal of supporting our efforts to help contain, control and prevent the spread of potato wart. Keep an eye on Cultivating Science for additional stories from the group to highlight progress.