Scutellonema bradys, the yam nematode, newly reported affecting Irish potato (Solanum tuberosum) in Nigeria

Scutellonema bradys, the yam nematode, was recovered from potato tubers (Solanum tuberosum) originating from the potato growing area of Jos, Nigeria, representing the first record of this nematode damaging potato. Infested tubers showed cracking, similar to the symptoms S. bradys causes on yam (Dioscorea spp.) (Fig. 1). Although some Scutellonema spp. have been recovered from potato, such as S. brachyurum (Schuerger & McClure, 1983), S. paralabiatum(Coyne et al., 2003) and S. unum (Njuguna & Bridge, 1998), tuber damage has not been reported. Scutellonema bradys is recorded mostly from West Africa and responsible for significant yam tuber losses, especially during storage, but also from the Americas and Asia (Bridge et al., 2005).

To confirm the effects of S. bradys,potato tubers sourced locally in Ibadan, Nigeria were transplanted from sawdust sprouting beds into sterile soil-filled pots. Two weeks later half of the pots were inoculated with 2000 S. bradys nematodes (recovered from yam). Plants were harvested at onset of haulm senescence. Plants inoculated with S. bradys produced tubers with substantial cracking of the cortex (Fig. 2) and evident tuber rot, unlike plants that had not been inoculated. Symptoms included scaly appearance, surface cracking, deep tissue cracks and distortions, and sub-surface rot, which tend to differ from external symptoms caused by Ditylenchus destructor and D. dipsaci (and the knobbly and pimply appearance resulting from Meloidogyne spp. infestations). Scutellonema bradys was recovered only from soil, roots (8/gsoil) and tubers (14/gsoil) in inoculated pots. Morphological identification confirmed mature female and male nematodes as S. bradys. This report establishes that Irish potato is prone to damaging infestation by S. bradys. With increasing movement and exportation of yam tubers, there is increased likelihood of a spread of S. bradys. For example, S. bradys has been intercepted on yam imported to South Africa (Esther van den Berg, ARC, Pretoria, Republic of South Africa, personal communication). This note therefore reinforces the importance for both phytosanitary staff and farmers to ensure correct diagnosis of damage to tubers.