Development of a Marker-assisted Selection System for Columnar Growth Habit in Apple Breeding

Abstract

To make progress in columnar apple breeding, we constructed genetic linkage maps of the Co genomic region and identified useful DNA markers that enable correct and efficient selection of columnar-type seedlings in a practical columnar apple breeding program. Linkage maps of three mapping populations were constructed on the apple linkage group 10, and the Co gene was mapped on two populations, ‘Fuji’ × 8H-9-45 and ‘Fuji’ × 5-12786. Closely linked marker genotypes of SCAR682, SCAR216, CH03d11, and Hi01a03 were determined on 33 columnar-type cultivars and/or selections, and non-columnar-type cultivars contained 7 ancestral cultivars of apple breeding in Japan. A 174 bp fragment for primer Hi01a03 was amplified in all columnar-type cultivars, selections, and ‘McIntosh’, but was not detected in other ancestral apples. Amplified products of 682 bp for SCAR682 and 177 bp for CH03d11 were detected in almost all columnar genotypes except for one selection, and ‘McIntosh’, but the products were not found in other ancestral apples. A 177 bp allele of CH03d11, characteristic of a columnar phenotype, was detected in all 170 columnar-type plants obtained from 18 crosses, suggesting that it is one of the most tightly linked DNA markers to the Co. These results indicated that CH03d11 was the most reliable marker to distinguish columnar and non-columnar phenotypes for the MAS system. In our two most advanced breeding selections, the Co gene-associated alleles of the original columnar mutant (‘Wijcik’) on CH03d11 (177 bp) and Hi01a03 (174 bp) remained, indicating that using these two breeding selections as Co donors in the breeding program, CH03d11 and Hi01a03 enable the selection of seedlings with columnar phenotype.