Examining the influence of different leaf populations on sweet cherry fruit quality

Understanding sweet cherry (Prunus avium L.) carbohydrate (CH2O) partitioning and source-sink relationships might lead to better management strategies for sweet cherry fruit quality on high-yielding, vigor-reducing rootstocks. Six limb treatments were established on fruiting branches of 'Hedelfinger'/Gisela 5 and 'Ulster'/Gisela 6 to isolate or combine two of the main leaf populations that serve as CH2O sources for developing fruit: the leaves on the branch segment of newly-formed spurs (previous season growth having non-fruiting spurs and some new lateral shoots) and the leaves on the branch segment of previously-formed spurs (two-year-old growth having fruiting spurs, plus some previous season and new lateral shoots). At harvest, fruit weight, diameter, and soluble solids (SS) were evaluated for each treatment. For both scion/rootstock combinations, fruits from the branch treatment isolated from the rest of the tree by girdling and having a full complement of leaf populations were larger and had higher SS than the partial leaf population treatments or the branch having a full set of leaf populations but not isolated by girdling. Fruits supplied exclusively by the leaf populations on either the fruiting spur branch segment or the non-fruiting spur branch segment were significantly smaller and had decreased SS levels. It was evident that the leaf populations most closely associated with the fruiting spur branch segment were insufficient sources of CH2O for optimal fruit development. However, these populations were clearly important, as similar sub-optimal results were also found when only the leaf populations on the non-fruiting spur branch segment were present. Leaf populations on both fruiting and non-fruiting branch segments were required for full fruit development and there was not a sufficient compensatory effect when one of the main leaf populations was eliminated.