Effects of planting methods and tuber weights on growth and yield of yam cultivars (Dioscorea rotundata Poir.) in Gabon

A study was conducted to investigate the influence of planting methods and tuber weight on growth and yield of local yam cultivars obtained by the minisett technique from white yam (D. rotundata) in Gabon. Trials were carried out in 2014 and 2015 at the experimental ground of the Higher National Institute of Agronomy and Biotechnology, under natural conditions of lightness, temperature and relative humidity. Twenty- four weeks old mini tubers obtained from local cultivar MVA of D. rotundata were harvested, weighed and categorized ( 40-80 g; 100-150 g; 200-300 g), and three planting methods (horizontal, oblique and vertical), arranged in ridges constituted the main factors. The experiment was laid out in Randomized Completely Block Design with eighteen treatments and two replications. Data pertaining to sprouting were recorded for 30, 60, 90 and 180 DAP, for tuber length (cm), tuber weight (Kg) and number of tubers per plant 270 DAP. Significant differences among tuber weight in all variables tested were observed. The larger tubers had better sprouting ability than the rest of the tuber weight. The methods of planting had no effects on yield and its components but they affect the depth and spread of tubers. Vertical planting produced deeper but more compactly arranged tubers while horizontal planting produced tubers which were shallower but more widespread. Slanting was intermediate for both depth and spread. The number and weight of tubers obtained from mini tubers planted out according to slanting method were significantly different (P< 0.05) from other planting methods. The production of seedlings from mini tuber is an improvement of traditional production of seed yam. Mini tubers must have at least 100-300 g and they should be planted slanting or vertically.