1. International Institute of Tropical Agriculture (IITA) , BP 2008 Messa, Yaounde , Cameroon
2. Center for Tropical Research, Institute of the Environment and Sustainability , UCLA , USA
3. University of Douala, Faculty of Science , BP 24157 Douala , Cameroon
4. University of Maroua, Faculty of Science , BP 814 Maroua , Cameroon
5. University of Basel, Faculty of Science , Basel , Switzerland