Affiliation: | 1. Department of Plant Science, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa;2. Department of Soil, Crop and Climate Sciences, University of the Free State, Bloemfontein, 9300, South Africa;3. Plant Research International, Wageningen University and Research Center, P.O. Box 16, 6700 AA, Wageningen, The Netherlands |