1. Landcare Research, Private Bag 92170, Auckland 1003, New Zealand
2. Plant Sciences Institute, Beltsville Agricultural Research Center, USDA-ARS, 10300 Baltimore Ave., Beltsville, MD 20705, USA
3. Centro de Investigación sobre Fijación de Nitrógeno, UNAM. AP 565 - A, Cuernavaca, Morelos, Mexico
4. 419 Carrington Street, Adelaide, South Australia 5000, Australia
5. National Institute of Agro-Environmental Sciences, 3-1-1 Kannondai, Tsukuba, Ibaraki 305-8604, Japan