Effects of Rootstock on Bud Development and Flower Formation of ‘Starkspur Supreme Delicious’ Apple

Abstract

Studies were conducted on mature ‘Starkspur Supreme Delicious’ trees growing on 17 rootstocks in Wooster, OH to examine differences in flowering and possible mechanisms for such differences. More dwarfing rootstocks had higher spur densities, but the relationship was weak. Spur density had no effect on flower density, but the proportion of spurs which formed flowers was closely related to flower density. Doming of the bud apical meristem, indicating a change to a floral state, only occurred after 20 appendages were present within the bud, and this critical number of appendages was constant across rootstocks and years. The timing of flower development was also unaffected by either rootstock or year. No differ ences in phosphorus concentration in spur leaves or in bud apical meristems were found among rootstocks, indicating no direct effect of P on flowering.