1. Agricultural Research Council-Small Grain Institute (ARC-SGI), Private Bag X1251, Potchefstroom, 2520, South Africa.
2. Corresponding author. Phone: (018) 299 6100 (Int: +27 18). Fax: (018) 294 7146 (Int: +27 18). E-mail: cravenm@arc.agric.za
3. Agricultural Research Council-Small Grain Institute, Private Bag X29, Bethlehem, 9700, South Africa.
4. University of the Free State, Department of Plant Sciences. Bloemfontein, 9300, South Africa.