1 West African Centre for Crop Improvement, College of Agriculture and Consumer Sciences, University of Ghana, P. M. B. LG 30, Legon, Ghana. 2 CSIR-Crops Research Institute, P. O. Box 3785, Kumasi, Ghana. 3 Deparment of Agricultural and Resource Economics, Faculty of the Professions, University of New England, Armidale, NSW, 2350, Australia. 4 CSIR-Savanna Agricultural Research Institute, P. O....