1. Department of Plant Breeding Research, The Swedish University of Agricultural Sciences, S-268 31 Svalöv, Sweden.
2. Corresponding author. E-mail: eva.johansson@vv.slu.se Phone: +46 40 415562. Fax: +46 40 415519.
3. Department of Crop Science, The Swedish University of Agricultural Sciences, S-230 53 Alnarp, Sweden.
4. Svalöf Weibull AB, S-268 81 Svalöv, Sweden.