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How we’re getting to the root of a global pest threatening potatoes in East Africa

The Conversation

Demand for potatoes in eastern Africa has been growing steadily, achieving an annual growth of 3.1% between 1993 and 2020. This growth is driven in part by rising demand from the fast food industry and for processing into high value products such as crisps, chips and starch.

Despite an increase of 60% in the area of cultivated land, production has been declining from an average of 20 tonnes a hectare to around 9.1 in Rwanda, 8.6 in Kenya and 4.3 in Uganda. This is way below the potential production of 40 tonnes a hectare. Farmers are thus being denied much-needed income and food.

The factors contributing to the low and declining yields include losses due to attack by a range of pests and diseases. A second main reason is the repeated cropping of potato on the same land without rotation. Third is the use of poor quality or substandard seed, partly due to limited availability of certified high quality seed.

Potato cyst nematodes are the most recent pest threat to emerge in the region. These are parasitic worms that are microscopic, and therefore invisible to the farmer. They infect potato roots, suppressing crop growth and can cause huge yield losses of up to 80%, and even total crop failure.

Globodera rostochiensis and Globodera pallida, both found in East Africa, are among the most important pests of potatoes globally. They are particularly lethal because the hundreds of eggs produced by the female nematode can remain dormant in the soil for years, awaiting the next potato crop host. The eggs remain protected in a hardened, protective cyst long after the nematodes die.

Chemical signals from newly planted potato roots trigger the eggs to hatch and start the life cycle again. Some of our current research is focused on disrupting this life cycle. When the newly hatched juvenile nematode leaves its protective cyst it is guided to the potato root by different chemical signals emitted from the roots.

High levels of infection lead to thousands upon thousands of nematodes infecting each potato plant. They are therefore a difficult pest to control. Finding new ways to control them is a challenge, but a challenge we have strongly embraced, across collaborating institutes. We are working on a number of potential avenues, including the assessment of new resistant varieties, alternative trap crop hosts and interfering with the chemical signals between potato roots and the pests.

Identifying these chemicals and synthetically producing them may offer possibilities for manipulating nematode hatch and host location. This includes working out when they are most vulnerable.

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