1. Scottish Crop Research Institute, Invergowrie, Dundee, DD2 5DA, Scotland.
2. Corresponding author, Fax: +44 (0)1382 562426, E-mail: jswans@scri.sari.ac.uk
3. Institut de Reserca i Technologia Agroalimentaries (IRTA), Reus, Spain.
4. Universidad de Lleida /IRTA, Lleida, Spain.