Rootstock Effects On King Dominance In ‘Pink Lady' Apple

Rootstocks have a great impact on the productivity and precocity of scion cultivars through influencing their physiological processes. Thus, it can be assumed that rootstocks affect intraspur flower/fruit competition i.e. king dominance and fruitlet abscission as well. In this study, ‘Pink Lady’ apple characterized with strong king dominance was evaluated on three different growth inducing rootstocks; M.9 (dwarf), MM.106 (moderate) and seedling (strong vegetative vigor). Increasing flower number per cluster was observed with decreasing vegetative vigor of the stocks, differences, however, were not significant. Significant differences in flowering time between king flower and side flowers were found on all rootstocks, differences among side flowers were not expressed. Average fruit set was the greatest for MM.106 followed by M.9 and seedling. Fruit set of king flowers was the highest for seedling and the set of side fruits was the lowest for this stock. The greatest ratio of the occurrence of single fruit in a cluster, i.e. the intra-spur side-fruitlet abscission was for seedling, and thus the king dominance was the strongest from this point of view. Fruit number per cluster at harvest was the greatest for M.9 and MM.106, that is, significantly greater than seedling. Seed number per fruit was the greatest for M.9 followed by MM.106 and seedling. Significant differences in seed number between king fruit and lateral fruits were found for MM.106 and seedling stocks only; king fruit had lower seed number than side ones. Fruit weight and diameter was affected by king dominance; significantly greatest values were measured for king fruit, especially with higher fruit number per cluster. L:D ratio was usually greater for side fruits; these fruits were flattened compared to the king one. However, skin color, firmness and soluble solids of king fruit and side fruits were not significantly differed from each other. Generally, better fruit qualities were measured for M.9 and MM.106. Gibberellic acid (GA₃, GA₄ and GA₇ content of the seeds was significantly greater for M.9 and MM.106 compared to seedling, however the difference between king fruit and side fruits in GAs content was the greatest for seedling. Decreasing GAs content was measured with the opening order of the individual flowers in a cluster.