In many fruit trees, the thinning of buds, flowers, or fruits is used to increase the leaf area-to-fruit ratio (LA:F) and reduce competition for carbohydrates. Meanwhile, calcium (Ca) sprays during fruit development are also used to increase fruit quality and postharvest storage. Such practices have been recommended to increase fruit firmness and reduce fruit cracking in sweet cherries. To understand the effects of foliar Ca sprays and crop load reductions in the combination ‘Lapins’/‘Colt’, trained as the Kym Green Bush, a factorial experiment to determine the interactions between both managements was established in the Central Valley of Chile during the 2018/2019 growing season. Two levels of crop load (CL) were established—thinned (50% crop load) and unthinned (100% crop load) during Stage I of fruit development (31 days after full bloom, DAFB). Three timings of foliar applications of CaCl₂ (TFA; 0.8%) were evaluated: early 26 DAFB, later 39 DAFB, or late 62 DAFB. Natural fruit contents and concentrations of Ca were determined on unsprayed control trees. Fruit from the thinned trees were significantly larger and heavier and had a higher titratable acidity than unthinned trees did. Significant interactions between TFA and CL were observed for SSC, without a clear trend. Thinned trees were less affected by pedicel detachment, browning, and fruit decay after 45 d of storage (0 °C). In unthinned trees, a foliar CaCl₂ spray at Stage I allowed a higher fruit firmness than CaCl₂ sprays at Stage II and III of fruit development. The CaCl₂ applications at 39 or 62 DAFB reduced the incidence of cracking in thinned trees. Natural Ca concentrations decreased during fruit development, indicating a cessation of Ca import and a dilution by subsequent growth. Our results suggest that the early reduction of crop load has positive effects on fruit quality and condition during storage, and early Ca sprays (Stage I) improve fruit textural properties, even under high crop loads.

Sweet cherry ( Prunus avium ) tree canopies comprise three types of leaf populations: fruiting spur (FS), nonfruiting spur (NFS), and extension shoot (ES) leaves. The contribution of each leaf population as sources of photoassimilate synthesis and distribution for sweet cherry fruit development has not been described previously. To determine how carbon fixed by different leaf populations is distributed to reproductive and vegetative sinks during fruit development, fruiting branches of 7-year-old ‘Ulster’ sweet cherry trees grown on ‘Gisela ^® 6’ (Gi6) ( Prunus cerasus × Prunus canescens ) rootstock at Michigan State University’s Clarksville Research Center (Clarksville, MI) were exposed to ¹³ CO ₂ labeling on five dates in 2003 [25, 40, 44, 56, and 75 days after full bloom (DAFB), which occurred on 30 Apr.], comprising the period from late Stage I (SI) to late Stage III (SIII) of fruit development. Forty-eight hours after labeling, whole branches were removed and separated into different organs for ¹³ C analysis by gas chromatography–mass spectrometry (GC-MS). The organs analyzed included: FS leaves, NFS leaves, ES leaves, fruit, and wood + bark from the segment of the branch corresponding to each leaf population. Relative distribution of C from each leaf population source to each sink varied during fruit development. Overall, the proportion of ¹³ C recovered in the fruit was highest for the FS leaf population (which included fruit exposure to ¹³ CO ₂ ), followed by the NFS leaves, then ES leaves. From SI to SIII, ≈60% of the ¹³ C recovered in the FS portion of the branch was found in the fruit, except during the exponential growth of fruit in mid-SIII (56 DAFB) when this proportion was nearly 80%. About 30% of the ¹³ C fixed by NFS leaves was found in the fruit during Stage II (SII) (40 DAFB) and early (44 DAFB) and late (75 DAFB) SIII, with higher proportions at SI (45% at 25 DAFB) and mid-SIII (70%). About 25% of the ¹³ C fixed by ES leaves was found in the fruit during SI, SII, and late SIII, with a lower proportion (17%) at early SIII when shoot growth was exponential, and a higher proportion (nearly 60%) at mid-SIII. The proportion of ¹³ C fixed and translocated to ES growth was minimal from FS and NFS leaves throughout the sampling dates, but that by the ES leaves was significant, peaking at early SIII. The results illustrate the dynamics of C contribution from each leaf population between vegetative and reproductive sinks during growth in sweet cherry orchards, which provides useful physiological information for canopy pruning and crop load regulation.

The use of protective covers, such as high tunnels, is recognized as an effective technology to reduce rain-induced fruit cracking in sweet cherries; however, there is a lack of information concerning the effects of this production system on the fruit’s mineral concentration, quality, and postharvest life. This study assesses the feasibility of using high tunnels on ‘Santina’ sweet cherries under the Mediterranean climate of the Central Valley of Chile to obtain earlier harvests of high-quality fruit with long storage life. The study included two plots: Plot 1 during the 2018/2019 growing season, and Plot 2 during the 2019/2020 growing season. High temperatures and relative humidity inside the high tunnels during bloom and fruit set decreased fruit yield, particularly in Plot 1. On average, trees inside the high tunnels were harvested 11 days earlier than those in the open. Fruit from covered trees were significantly larger (13%) and softer (10%) than those from the outside. Fruit quality characteristics, such as soluble solids concentration and titratable acidity, were not affected by high-tunnel-protected cultivation. Fruit from covered and uncovered trees maintained the firmness differences obtained at harvest between treatments, but showed similar postharvest quality after 45 days at 0 °C and a further 3 days at 20 °C on the other characteristics. The covered fruit had lower Ca concentrations (7.7 mg 100 g⁻¹) and higher K:Ca, Mg:Ca, and N:Ca ratios. Significant relationships were found between Ca or K:Ca and fruit firmness at harvest. Lower Ca concentrations in the fruit may explain the lower firmness of fruit grown under plastic covers. There were no differences between covered and uncovered cherries in either cracking susceptibility or induced pitting. ‘Santina’ cherries were very sensitive to pitting damage, but this is not associated with the fruit’s Ca concentration. The results obtained show that high tunnels influenced fruit yield, development, and quality, and emphasize that the fruit’s Ca concentration under this growing condition plays a significant role in the firmness of ‘Santina’ sweet cherries.

Annual pruning is one of the most efficient ways to regulate crop load and renew fruiting wood in highly productive sweet cherry (Prunus avium L.) combinations. Although Chilean growers did not previously prune cherry trees of more vigorous combinations, in recent years, the adoption of more dwarfing rootstocks and self-fertile cultivars has led to the inclusion of annual pruning as a practice in modern orchards. At first, this alteration in orchard management practices was not considered by growers, and thus, many of the initially established cherry orchards were not pruned as intensively as they should have been. As a consequence, many trees showed a reduction in fruit quality after 4 or 5 years of being planted, as they became overcropped and, consequently, registered reductions in their vegetative growth. There are only a few studies related to the effect of corrective pruning on dwarfing combinations that display an imbalance between reproductive and vegetative growth due to a reduction in the leaf area to fruit ratio of the tree. For this reason, the objective of this research was to study the effect of pruning in an orchard consisting of the dwarfing combinations ‘Bing’/‘Gisela®5’ (‘Bing’/‘GI®5’) and ‘Bing’/‘Gisela®6’ (‘Bing’/‘GI®6’), which shown a reduction in vigor, fruit quality and yield. Trees of both combinations were treated with a medium intensity pruning in late winter (early September). Several vegetative (shoot length, leaf area of spurs and shoots, trunk cross sectional area) and reproductive (total yield per tree, fruit growth and quality) parameters were evaluated after pruning. One of the most important effects of pruning for both combinations was an increase in the total current season shoot (CSS) growth, which was 112.5 and 125.6% for ‘Bing’/‘GI®5’ and ‘Bing’/‘GI®6’, respectively. Additionally, the average shoot length increased by 820.0 and 325.4% for ‘Bing’/‘GI®5’ and ‘Bing’/‘GI®6’, respectively. Furthermore, CSSs developed a higher leaf number in the pruned trees. There was no change in leaf number for reproductive spurs, but these had bigger leaves in the pruned trees, demonstrating increased total leaf area per spur. Additionally, pruning allowed crop load regulation and increased fruit size by 8.5 and 6.1% for ‘Bing’/‘GI®5’ and ‘Bing’/‘GI®6’, respectively. However, fruits from pruned trees showed a higher susceptibility to mechanical damage compared with unpruned trees of both combinations.