Abstract

Sweet potato (Ipomoea batatas) cultivars ‘Bosbok’ and ‘Mvuvhelo’ were previously shown to be resistant to Meloidogyne incognita race 2, without information on the mechanism of resistance. Among the two mechanisms of nematode resistance, the latter is the only one that is useful in plant breeding programmes. The objective of this study was to determine the existing nematode resistance mechanism in cultivars ‘Bosbok’ and ‘Mvuvhelo’ to M. incognita race 2. Uniform rooted cuttings in 250 ml polystyrene beakers containing fine sand were inoculated with 100 second stage (J2) with four plants harvested every other day for 30 days. Roots were severed, cleaned, stained and then distained, assessed under the stereomicroscope for the existence of (1) necrotic spots, (2) poorly developed giant cells, (3) formation of rootlet interferences, (4) absence of root galls and (5) non-detectable J2 in roots. All plant variables over time exhibited quadratic relations with coefficients of determination ranging from 65 to 85% and from 72 to 94% in cultivars ‘Bosbok’ and ‘Mvuvhelo’, respectively. In conclusion, the two cultivars were shown to contain post-infectional nematode resistant attributes and could, therefore, be candidates to serve in introgression intended for breeding nematode-resistant sweet potato cultivars.