Local Effect of Fruiting on Different Anatomical and Physiological Traits in Apple

Flowering is a key stage of plant development. The deceivingly simple appearance of flowers is in reality a complex interaction of puzzling endogenous pathways and environmental conditions. It has been well-established that the crop load directly impacts the flowering cycle of biennial bearing fruit trees. This effect occurs on a molecular level; affecting the endogenous pathways that are responsible for flower formation. In this study, we investigated the local effect of fruiting on the physiological and anatomical traits of bourse leaves adjacent to the fruiting structures in six apple cultivars. We hypothesized that the physiological and anatomical traits of bourse leaves may be the source of different flowering habits between annual and biennial cultivars. In six different cultivars, three biennial cultivars (Honeycrisp, Fuji, and Golden Delicious) and three annual cultivars (Gala, Pink Lady, and Ruby John) we tagged fruited and de-fruited spurs at time of initial fruit set, we collected samples throughout the growing season to measure stomatal density and leaf area and measured stomatal conductance, photosynthesis, assimilation, and transpiration. At the end of the season we looked at flower formation in fruited versus de-fruited spurs. We observed differences in these anatomical and physiological traits among the six cultivars and occasionally within the fruited and de fruited spurs of the same cultivar. These findings should help us to create better understanding on the source of flowering regulations in biennial versus annual cultivars and the effect of these physiological and anatomical traits on endogenous flower formation of fruit trees.