Does carbohydrate availability play a role in sweet cherry fruitlet abscission?

Fruitlet abscission is an issue impacting the profitability of the cherry industry, with particular cultivars showing enhanced susceptibility. This study examined the role of carbohydrate availability in fruitlet abscission in two sweet cherry cultivars, 'Kordia' and 'Lapins'. Starch and soluble sugar concentrations in branch, trunk and root tissue were measured regularly throughout the growing season of 2012/2013. Normal transport of carbohydrates was disrupted 5 weeks after full-bloom by applying trunk girdling and limb defoliation treatments, and the rate of flower and fruitlet abscission was monitored. In 'Lapins', trunk girdling decreased the rate of abscission, but abscission was unaffected by girdling in 'Kordia'. When fruit was assessed at commercial harvest, the fruit from the defoliated treatment was immature in both cultivars. The highest sugar concentration was found in fruit from the girdled trees in both 'Kordia' and 'Lapins'. Trunk starch concentrations ranged from 22.6 mg g^-1 at the beginning of the season to 28.80 mg g^-1 just after harvest in 'Lapins', and were higher in 'Kordia' with 42.02 mg g^-1 at the beginning of the season to 39.13 mg g^-1 just after harvest. Shoot starch concentrations were very similar to trunk in both cultivars, whereas root carbohydrate concentrations did not recover after the trunk girdling treatment in either cultivar, which is expected to have an impact on the following season's return bloom.