[1
] Departmento de Ciencias Morfologicas y Biologia Celular y Animal, University of Extremadura,
Badajoz, Spain
[2
] School of Biosciences, University of Nottingham, Nottingham NG7 2RD, United Kingdom
[3
] Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural
Sciences, S-901 83 Umea, Sweden
[4
] Department of Genetics, Universiteit Gent, B-9000 Gent, Belgium