1. IRD, Laboratoire des Symbioses Tropicales et M�diterran�ennes (LSTM), UMR IRD/ SupAgro/INRA/UM2/CIRAD, Montpellier, France
2. BioTechnology Institute and Department of Soil, Water, and Climate, University of Minnesota, St. Paul, Minnesota, USA
3. CIRAD, UMR BGPI INRA/CIRAD/SUP AGRO, Campus International de Baillarguet, Montpellier, France