Isolation and functional analysis of the Co-gene for a columnar architecture of apple trees

The ‘Wijcik’ mutant of the apple cultivar ‘McIntosh’ shows a columnar-type growth, characterized by altered branching and a thick stem. Instead of normal branches, spur-like short branches are produced, leading to apples produced close to the stem. Columnar-type growth is a desirable trait, as columnar apple trees need considerably less pruning compared to standard trees. Furthermore, apple picking and the application of chemicals is much easier on columnar trees. We limited the genomic window for the Co gene to ~800 kbp. Our project aims at detection of the causal mutation that leads to columnar growth, and functional analysis of the underlying Co. We are using two BAC libraries to screen for clones covering the Co region in both standard ‘McIntosh’ and its mutant. By sequencing these clones and comparing the sequences, we will identify the Co mutation. In addition, we will look at expression of Co gene candidates and potential downstream targets. This work will result into the development of a perfect marker for columnar growth for application in breeding, better understanding of the physiological background of columnar growth, and the availability of the Co gene for the development of cisgenic columnar apple trees.