1. a Horticulture Research International , East Malling, West Malling, Kent , ME19 6BJ , UK
2. b Research Institute of Pomology and Floriculture , Pomologiczna 18, Skierniewice , 96-100 , Poland
3. c Federal Biological Research Centre for Agriculture and Forestry , Schwabenheimer Str. 101, Dossenheim , D-69221 , Germany