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Marlene Ayala and Gregory Lang

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 13CO2 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 13C 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 13C recovered in the fruit was highest for the FS leaf population (which included fruit exposure to 13CO2), followed by the NFS leaves, then ES leaves. From SI to SIII, ≈60% of the 13C 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 13C 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 13C 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 13C 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.

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Marlene Ayala and Greg Lang*

In deciduous fruit trees, some storage reserves accumulate during fall and are used for early spring growth. In sweet cherry (Prunus avium L), stored reserves are critical for early growth and there is a transition phase during which current photoassimilates become the primary source for support of reproductive and vegetative sinks. As little is known about this transition, an experiment using 4-year-old `Regina' sweet cherry on the semidwarfing rootstock, Gisela 6, was established. Using whole canopy exposure chambers, five trees were pulsed with high levels of 13CO2 on three different dates during fall (Sept.-Oct). At leaf drop, leaves, buds, wood, bark and roots were sampled for GCMS analysis of pre-winter storage reserves. The major storage organs (those which had the highest change in isotopic ratios) were roots and wood in the trunk and branches. During spring, newly developing organs (flowers, fruits and young leaves) were sampled weekly from bloom to stage III of fruit development for additional GCMS analysis. The stored 13C was mobilized and partitioned to flowers, fruits and young leaves from early spring until one week after fruit set. The highest 13C levels in growing sinks were observed between bloom and fruit set. The isotopic composition of new organs did not differ initially (3 May). During the three next sampling dates (10-24 May) reproductive organs had higher 13C levels compared to vegetative growth. The role of storage reserves, as a source of assimilates for early spring growth and their implications for crop development, will be discussed.

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Marlene Ayala, Lorena Mora and Joaquín Torreblanca

In sweet cherry, highly advanced dwarf combinations using ‘Gisela’ rootstocks promote higher productivity than do more vigorous combinations but require maintaining the leaf area to fruit area (LA:F) ratio. An experiment using double isotopic enrichment with 13C and 15N was carried out in 5-year-old ‘Bing’/‘GI 6’ trees in a commercial orchard located in Santa Cruz, Chile (34°39′S; 71°19′W), and characterized by a Mediterranean climate. Forty whole sweet cherry trees (TR1) trained as central axes were pruned in winter [July 20, 60 days before full bloom (DBFB)] and another 40 trees were left without pruning (TR2). A single 13CO2 pulse and 15N-urea application to the mature leaves of individual 4-year-old branches on trees of both TRs was carried out during stage III (SIII). Winter pruning reduced yield by 44%, improved fruit quality [i.e., size, weight, and soluble solids content (SSC)] and induced the growth of extension shoots (ES) (i.e., number, length, and LA). For both TRs, fruits were stronger sinks for 13C-photoassimilates and 15N than were ES. ES of pruned trees had higher sink strength than ES of unpruned trees. Pruned trees developed more ES that were longer and that had higher LA compared with the ES of unpruned trees.