1. Istituto Sperimentale per la Cerealicoltura, Via Mulino 3, 26866 S.Angelo Lodigiano (LO), Italy.
2. Corresponding author. E-mail: isc.sal@andromeda.it Fax: 0039 0371210372.
3. Present address: Istituto Agrario di San Michele all'Adige Via Mach 1, 38010 San Michele all'Adige (TN) Italy.
4. Agricultural University of Norway, Department of Biotechnological Sciences, N-1432 Ås, Norway.
5. Max Planck Institut, Carl-von-Linné-Weg 10, D-50829 Köln, Germany.