CONSTRUCTION OF AN APPLE BAC LIBRARY AND ITS USE FOR GENE ISOLATION

¹ Dipartimento di Colture Arboree, University of Bologna, 40126 Bologna, Italy

² Plant Pathology, Inst. of Pant Sciences, Swiss Federal Inst. of Technology, 8092 Zurich, Switzerland

³ Soil and Crop Sciences Department, Texas A&M University, College Station, TX 77843-2123 USA

Apple (Malus x domestica Borkh.) is one of the most valuable fruit crops in the world. Its consumption and economic importance is one of the largest of all perennial fruit crops. Apple has a broad genetic base and is interfertile with wild small-fruited apple species. Breeders have therefore a considerable gene reservoir to exploit. To clone genes in this species we have constructed an apple BAC library from the variety `Florina' resistant to scab due to the Vf gene introgressed into `Florina' from the small-fruited Asian selection M. floribunda 821. The library contains approximately 5 x haploid genome equivalents and has an average insert size of 120 kb. Using this library we have constructed a contig of 550 kb covering the entire Vf region by chromosome walking. Construction and characterization of the library and the methods used to perform the chromosome walk will be elucidated. We will discuss the specific problems we have encountered when using the auto-incompatible and therefore highly heterozygous species apple for chromosome walking. Performing the chromosome walk we came also to some conclusions on the possibilities of using the library for gene cloning in apple varieties different from `Florina'. The feasibility of constructing an integrative map of the apple genome and its consequences for apple breeding and apple gene isolation will also be discussed.