Increased international exchange: what happens when the yam nematode is introduced to potato?

There is an increasing interest for potato production in Africa, where the crop offers an alternative to traditional food crops and provides extra income as a fresh-market commodity. Yam is a tuber crop that can be stored for several weeks and a traditional source of starch in many tropical parts of the world. A major problem in yam is the yam nematode, Scutellonema bradys, which keeps developing during storage of yam and can result in considerable production loss. With increasing exchange of both yam and potato between continents, we wanted to investigate the possible threats of S. bradys on potato production in the EU, and confirm reports of potato infection by S. bradys in Africa [1]. The host suitability and damage symptoms of the nematode were evaluated in a pot test on five potato varieties commonly grown in Europe and Africa: Désirée, Nicola, Spunta, Diamant and Draga. The yam nematode was able to reproduce and caused brown root lesions, a scaly surface appearance of the tubers, as well as tuber rot. Reproduction and damage symptoms varied with potato variety, but larger scale experiments are needed to establish more realistic field-related numbers. We also investigated the probability of nematode entry, spread and establishment in Europe by performing a pest risk analysis (PRA). This PRA showed that the likelihood of entry of S. bradys from third countries into the European Union is high due to importation of contaminated yam tubers from infested regions of Africa, although reaching a susceptible host (potato, tomato) is less probable. However, establishment of the nematode is considered possible in the most southern parts of the EU where temperatures are high and tomato is present. The study highlights the need to reduce the risk of nematode entry and spread in the EU region. It also showed that expansion of potato production in Africa should take notice of the presence of S. bradys.

[1]. Coyne D. L., Akpheokhai L. I., Adeniran A. F. 2011. The yam nematode (Scutellonema bradys), a potential threat to potato (Solanum tuberosum) production in West Africa. Plant Pathology, 60, 992-997.