1. Institute of Agricultural Research for Development (IRAD) , P.O. 2067, Yaoundé , Cameroon
2. International Institute of Tropical Agriculture (IITA) , BP 2008, Yaoundé-Messa , Cameroon
3. CIRAD, UMR PHIM , F-34398 Montpellier , France
4. PHIM, Univ Montpellier, CIRAD, INRAE, Institut Agro, IRD , 7 Montpellier , France
5. Faculty of Science, University of Yaoundé I , P.O. 812, Yaoundé , Cameroon
6. Natural Resources Institute, University of Greenwich at Medway , Kent , UK
7. Center for Tropical Research, Institute of the Environment and Sustainability, University of California, Los Angeles (UCLA) , Los Angeles, CA 90095 , USA