1. Department of Crop and Soil Sciences, Faculty of Agriculture, Kwame Nkrumah University of Science and Technology , PMB, Kumasi , Ghana
2. Faculty of Biological and Environmental Sciences, University of Helsinki , FIN-00014 Helsinki , Finland
3. Council for Scientific and Industrial Research, Savanna Agricultural Research Institute , PO Box 52, Tamale , Ghana
4. Department of Agricultural Sciences, University of Helsinki , FIN-00014 Helsinki , Finland
5. Department of Theoretical and Applied Biology, Kwame Nkrumah University of Science and Technology , PMB, Kumasi , Ghana
6. International Institute of Tropical Agriculture , PMB 5320, Ibadan , Nigeria