Tree architecture of columnar apple tree genotypes

Growth habit of columnar apple genotypes leads to a unique form of plant architecture characterized by the tree axis with short fruit spurs instead of lateral branches. Columnar tree growth habit was discovered in the 1960s and described as 'McIntosh Wijcik'. The compact shape of columnar type apple trees is based on their very thick and upright stems with almost no difference in diameter between the top and the bottom. Apple cultivars carrying Columnar (Co) gene differ in tree vigor, density, and length of fruit spurs. Differences among genotypes in the total tree growth, the annual increase in primary axis length, the length of spurs, their density along the tree axis, and the tendency to biennial cropping all affect yield and economy of growing. We evaluated a total of 101 genotypes of B clones (F1 hybrids grafted on rootstocks). Out of this number, 80 genotypes carrying the Co gene were compared with 21 genotypes that exhibited an extremely weak growth but not carrying Co gene. The mean annual increase in the primary axis length of tested genotypes carrying Co gene responsible for columnar growth was 0.25 m, the mean number of fruit spurs on the length of 1 m of the tree axis was 33.2 pieces, and the mean length of fruit spurs was 68.6 mm. Optimal growth of the columnar apple cultivars is discussed. The evaluation of columnar apple genotypes in this work can be used in practical breeding programs for forming the optimal tree canopy.