Nodal vine cutting technique for assessing nematode resistance in yams

Identifying resistance to plant-parasitic nematodes in yams is a major challenge in yam breeding programmes due partly to insufficient planting material (tubers) for evaluation. Susceptible yam cultivar, TDr 93-31 was inoculated with 0 (control), 200, 500, 1000 and 2000 eggs/individuals each of Meloidogyne incognita, Scutellonema bradys and Pratylenchus brachyurus. Vine cuttings of two cultivars each of Dioscorea rotundata, D. alata and D. dumetorum were compared to conventional minisett method in a second experiment. Planted vines and minisetts were inoculated with 500 and 5000 eggs/individuals respectively. Data were collected on percentage vine survival, fresh root and tuber weight, number of tubers and nematode population and damage. Vine survival was not significantly different between control and inoculated vines. Maximum damage rating (>60%) was observed with initial inoculum of 1000 eggs of M. incognita and 200 individuals of S. bradys and P. brachyurus. The two cultivars of D. alata and D. rotundata developed visible symptoms and supported nematode reproduction while the D. dumetorum cultivars did not. The reaction of yam cultivars planted as vines was consistent with results from conventional minisett method. The lowest inoculum of 200 egg/juveniles was sufficient to elicit a reaction from vines in the vertical sack system.