1. Present address: Center of Molecular Biosciences, University of the Ryukyus, Nishihara, Okinawa 903‐0213, Japan
2. Permanent address: University of Nairobi, Faculty of Agriculture, Department of Soil Science, P.O. Box 29053, Nairobi, Kenya
3. International Center of Research in Agroforestry, P. O. Box 30677, Nairobi, Kenya
4. University of Nairobi, Faculty of Agriculture, Department of Soil Science, P.O. Box 29053, Nairobi, Kenya
5. Center of Molecular Biosciences, University of the Ryukyus, Nishihara, Okinawa 903‐0213, Japan