Early screening of cassava for resistance to root-knot nematodes

A method was developed for early screening of cassava for resistance to root-knot nematodes. One-node cassava cuttings were planted in plastic disposable beverage cups filled with sterile 1:1 (by volume) sand-soil mixture. Two weeks after planting, the plantlets were infested with a 10 ml suspension containing approximately 1 000 Meloidogyne spp. eggs. One month after inoculation, the cassava root systems were evaluated for damage and rated for gall index. Densities of Meloidogyne females in the roots were established by differential staining, followed by counting of the female root-knot nematodes under a stereomicroscope. Significant differences in gall index and number of established females, but not in reduction in fresh root weight, were observed among varieties. While some confirmatory field surveys are still required, findings from preliminary surveys carried out in two areas of Uganda suggest that the relative susceptibility of a variety in the field can adequately be predicted by using one-node cuttings.