The impact of potato cyst nematode (PCN) on potato production in Kenya

The potato cyst nematode (PCN), Globodera rostochiensis, is a highly destructive pest of potatoes worldwide. The PCN attacks the crop’s roots, reducing plants’ growth and severely declining the size and number of marketable tubers per plant. Despite considerable global efforts to control PCN, it continues to cause substantial yield losses, partly due to its ability to survive in a dormant state inside protective cysts for more than twenty years, leading to strict quarantine regulations worldwide. PCN is endemic of the Andean region of South America, and it was introduced in Europe in the 1850s during the Irish potato famine with the transport of PCN-contaminated soil of potato seed consignments; since then, PCN has spread to other parts of the world.

In East Africa (EA), potatoes rank among the top-most valued crops, with more than 2.5 million people reliant upon the potato value chain for food, income and livelihoods. However, potato production in the region and most sub-Saharan African (SSA) countries is far below its potential, with smallholders only producing ¼ of the attainable yields of this crop. In 2014, G. rostochiensis was detected in Kenya, and later in Rwanda (2019) and Uganda (2020). A nationwide survey in Kenya in 2016 determined that G. rostochiensis is highly prevalent, often at remarkably high densities. Estimates extrapolated from fields with different densities of PCN shows that PCN is a significant cause of poor yields, causing annual losses to the value of US$ 127 million. Due to the informal cross-border trade of potatoes, researchers suspect that the potatoes’ yield gap observed in other countries could also be caused by the spread of PCN across the EA region.

Addressing Kenyan farmers’ needs and preferences for potato cultivation

According to a recent study, smallholders in SSA could increase potato production by 140% annually using good quality seed and adequate agronomic management, including control of pests and diseases. Of the various management options available, natural host resistance offers the most cost-efficient and effective strategy for farmers to build durable IPM strategies. 

Therefore, the potato industry has been actively looking for solutions to address Kenya’s new invasive pest. Since 2017, the National Potato Council of Kenya and the private industry have imported and released European PCN-resistant varieties. However, the popularity of these varieties among farmers and consumers is still limited for various reasons. Therefore, the PCN-susceptible cv. Shangi remains the most popular variety, planted by over 85% of farmers. The characteristics of cv. Shangi that farmers and consumers mostly value are: its low seed dormancy, short cooking time and versatility, and sweet taste. Varieties with these traits and which resemble cv. Shangi will be more attractive to end-users and hence, more prone to adoption in Kenya. 

In 2019, the nematologists from the James Hutton Institute (JHI) in the UK and the International Institute of Tropical Agriculture (IITA) in Kenya identified eight PCN-resistant genotypes from the UK, with characteristics resembling those of cv. Shangi, based on their low dormancy, nutritional, and fast-cooking properties. In 2020, the researchers established field trials with these new potato varieties in Kenya to assess their agronomic performance; scientists with researchers from Kenyatta University also used the demonstration plots to assess farmers’ perception of these new varieties’ for cultivation and taste. These activities further allowed understanding farmers’ awareness about the impact of PCN on their crops. 

After three planting seasons, the field trials have provided very encouraging results. Three of the UK varieties repeatedly retained robust agronomic performance in the field, yielding consistently more than cv. Shangi, due to its PCN-resistant nature. However, most importantly, these three lines have ranked significantly above cv. Shangi among consumers in the blind test regarding look, taste and smell when boiled, mashed and fried. Noteworthy, the PCN resistant control cv. Manitou, currently commercialised in Kenya, ranked last among the ten potato lines studied. Scientists also understood that more than 85% of the interviewed farmers were unaware of PCN, which is a significant obstacle to adopting new potato varieties and managing this pest.