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Gregory A. Lang

Sweet cherries (Prunus avium L.) can be one of the most profitable tree fruits cultivated in temperate climates. While cherry trees grow naturally to relatively tall heights (≈35 ft [≥10 m]), new size-controlling cherry rootstocks similar to those used in high-density apple (Malus domestica Borkh.) orchards are now a reality. The Gisela (GI.) and Weiroot (W.) series from Germany, the Gran Manier (GM.) series from Belgium, the P-HL series from Czech Republic, `Tabel Edabriz' from France, and others of international origin are at various stages of scientific and field testing in North America, with some now being used for commercial fruit production. These stocks confer several advantageous traits besides vigor control, including precocious fruiting and high productivity. While these beneficial traits are exciting, serious problems also have been documented on occasion, such as small fruit size and tree decline. As many of these rootstocks are interspecific Prunus L. hybrids, might there be significant limitations for fruit quality and orchard longevity? What is known about their tolerance to various soil types and/or climatological stresses? What is known about their susceptibilities to pathogens and pests? Further, with the U.S. and worldwide orchard area planted to fresh-market sweet cherries already expanding to record levels throughout the 1990s and a time-honored agricultural tendency toward overproduction until grower profits are minimized (e.g., recent international apple markets), what might be the future impact of such precocious, productive rootstocks on sweet cherry profitability and sustainable production? This overview addresses these topics, providing some answers and some areas for future scientific investigation and industry discussion.

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Gregory A. Lang

Sweet cherries (Prunus avium) can be one of the most profitable tree fruit cultivated in temperate climates. While cherry trees grow naturally to relatively tall heights, new size-controlling cherry rootstocks similar to those used in high-density apple orchards are now a reality. The Gisela series from Germany, the Gran Manier series from Belgium, the Weiroot series, the P-HL series, Tabel Edabriz, and others of international origin are at various stages of scientific and field testing in North America, with some now moving into commercial fruit production. These stocks confer several highly advantageous traits besides vigor control, including precocious fruiting and high productivity. While these obvious traits are exciting, serious problems have also been documented, on occassion, with such phenomena as small fruit size and tree decline. As many of these rootstocks are interspecific Prunus hybrids, might there be significant limitations for fruit quality and orchard longevity? What is known about their susceptibilities to pathogens and pests? What is known about their tolerance to various soil types and/or climatological stresses? Further, with the U.S. and worldwide orchard area planted to fresh-market sweet cherries already expanding to record levels throughout the 1990s and a time-honored agricultural trend toward overproduction until grower profits are minimized (see recent international apple markets), what might be the future impact of such precocious, productive rootstocks on sweet cherry profitability and sustainable production? This overview will address these topics, providing some answers and some areas for future scientific investigation and discussion.

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Gregory A. Lang

High tunnel production systems typically use horticultural crops that are annually or biennially herbaceous, high in value, short in stature, and quick to produce. At best, tree fruits may fit only one of these criteria–high value. Sweet cherry (Prunus avium) may command high enough values in premium market niches to make high tunnel production strategies worth attempting. Furthermore, sweet cherry production can be a risky endeavor, even in optimal climates, due to the potentially devastating effects of preharvest rain that cause fruit cracking. Consequently, environmental modification by tunnels in regions like the Great Lakes provides a significant risk reduction. Additional potential benefits, such as protection from frosts, diseases, insects, wind scarring, etc., add further production value. Multi-bay high tunnels were constructed in 2005 at two Michigan State University experiment stations, over established and newly planted sweet cherry trees on dwarfing rootstocks, to study and optimize the effects of production environment modification on vegetative and reproductive growth, marketing season extension, and protection of cherries from diseases, insect pests, and/or physiological disorders. Results with tunnels thus far include premium fruit quality and high crop value; increased leaf size and terminal shoot growth; decreased radial trunk growth; decreased chemical pesticide inputs; decreased incidence of cherry leaf spot (Blumeriella jaapii) and bacterial canker (Pseudomonas syringae); increased incidence of powdery mildew (Podosphaera clandestina); inconclusive effects on brown rot (Monolinia fructicola); no or reduced infestation by plum curculio (Conotrachelus nenuphar) or cherry fruit fly (Rhagoletis cingulata); dramatically reduced japanese beetle (Popillia japonica) damage; and increased black cherry aphid (Myzus cerasi) and two-spotted spider mite (Tetranychus urticae) populations.

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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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Theoharis Ouzounis and Gregory A. Lang

Seasonal uptake, storage, and remobilization of nitrogen (N) are of critical importance for plant growth. The use of N reserves for new growth in the spring is especially important for sweet cherry (Prunus avium L.), for which new shoot and fruit growth is concomitant and fruit development occurs during a relatively short bloom-to-ripening period. Sweet cherries grafted on precocious, dwarfing rootstocks such as the interspecific (P. cerasus × P. canescens) hybrids Gisela® 5 and 6 tend to produce large crops but smaller fruit when crop load is not balanced with adequate leaf area. Study objectives were to: 1) characterize natural N remobilization during fall and winter to canopy reproductive and vegetative meristems; 2) determine the effect of fall foliar urea applications on storage N levels in flowering spurs; 3) determine whether differential storage N levels influence spur leaf formation in spring; and 4) determine whether fall foliar urea applications affect the development of cold-hardiness. During fall, total N in leaves decreased by up to 51% [dry weight (DW)] and increased in canopy organs such as flower spurs by up to 27% (DW). The N concentration in flower spurs increased further in spring by up to 150% (DW). Fall foliar applications of urea increased storage N levels in flowering spurs (up to 40%), shoot tips (up to 20%), and bark (up to 29%). Premature defoliation decreased storage N in these tissues by up to 30%. Spur leaf size in the spring was associated with storage N levels; fall foliar urea treatments increased spur leaf area by up to 24%. Foliar urea applications increased flower spur N levels most when applied in late summer to early fall. Such applications also affected the development of cold acclimation in cherry shoots positively during fall; those treated with urea were up to 4.25 °C more cold-hardy than those on untreated trees.

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Yuehe Huang and Gregory A. Lang

Five-year-old `Sharpblue' southern highbush (Vaccinium corymbosum) plants were self- and cross-pollinated (`O'Neal') to study peroxidase activities and isozyme patterns during fruit development. Both soluble and bound peroxidase activities were present throughout development. Activities were very high during early fruit development, with peaks at 10 and 20 days after self- and cross-pollination, respectively. Activity was much higher for cross-pollinations. During rapid fruit development, peroxidase activities were low. During ripening, the activity of soluble peroxidases increased, then declined in both treatments. Bound peroxidase activity increased during the color transition from blue to dark blue, with the increase being much greater in self-pollinated fruits. Banding patterns of both soluble and bound isoperoxidases varied by pollination treatment as well as fruit developmental stage. Pollen sources alter peroxidase isozymes and activities in developing fruits. During fruit ripening, soluble peroxidase activity appears to be associate with the color transition from light blue to blue, while bound peroxidase activity appears to be associated with the color transition from blue to dark blue.

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Gregory A. Lang and Jiaxun Tao

The postharvest performance of early ripening southern highbush blueberries `Sharpblue' and `Gulfcoast' was evaluated under storage and simulated retail conditions. In general, `Gulfcoast' fruit were 28% heavier than those of `Sharpblue', which had a higher percent soluble solids concentration (SSC) and lower titratable acidity (TA). Quality loss, as indexed by fresh weight, percent decayed fruit, or changes in SSC, pH, or TA, was insignificant in first-harvest fruit of either cultivar when kept in storage (2C) for up to 7 days. Transfer of fruit stored at 2C for 3 days to simulated retail conditions at 21C for 4 days significantly increased fresh weight loss and decay, but not beyond levels deemed unmarketable. Second-harvest fruit were smaller than first-harvest fruit, and those of `Sharpblue' fruit were more prone to decay. However, storage quality of both cultivars was acceptable through 11 days at 2C. Retail quality, as influenced by decay incidence, was acceptable after 3 days at 2C plus 4 days at 21C, but not after 3 days at 2C plus 8 days at 21C. Overall, fruits of these early ripening southern highbush blueberry cultivars performed well under postharvest conditions and are suitable for expanding production of premium fresh blueberries by growers in the Gulf coastal plains.

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Gregory A. Lang and Jiaxun Tao

We have previously demonstrated that a protein of ∼62 kD decreases in response to temperature during the final stages of chilling unit accumulation in dormant peach flower buds (Lang and Tao, 1991, HortSci. 26:733). To further examine proteins that potentially may be associated with endodormancy, floral buds, spurs, and/or shoots were collected during winter from `Anna' apple, various blueberry cultivars, `MidSouth' grape, `20th Century' pear, `Hawthorne' peach, and `Santa Rosa' plum. Soluble proteins were extracted and analyzed by one-dimensional SDS-PAGE. A major protein of ∼62 kD was present in plum, and lesser amounts of one or two similar proteins were found in blueberry, but not in apple or grape. The 62 kD peach protein originally found in buds was also present, in lesser proportions, in peach shoot xylem and phloem tissues, but not in petioles or seeds. Apple exhibited a major protein band at ca. 31 kD that may be a storage protein. The similarities and disparities in protein profiles between fruit crops, as well as changes that occur during winter, will be discussed with respect to dormancy, cold hardiness, and storage compounds.

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Gregory A. Lang and Joshua Tao

Plant dormancy research has long been stifled by the lack of appropriate biochemical markers to characterize the changing physiological status of dormant vegetative or reproductive buds. Two sets of experiments were conducted in an attempt to identify changes in soluble protein profiles during endodormancy of peach and blueberry reproductive apices. Bud samples from the peach cultivars `La Festival' (low chilling requirement) and `La White' (moderate chilling requirement) were taken every 15 days in the orchard during December and January, extracted for soluble proteins, and analyzed by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Outshoots were forced at 25C in a growth chamber to determine the intensity of endodormancy. A further experiment utilized potted `Bluechip' and `Meader' (troth high chilling requirement) blueberry plants given varying periods of cold (4.5C) chamber treatment, followed by forcing at 25C in a growth chamber. Bud samples were taken following cold treatment for extraction and SDS-PAGE. The relationship of the resulting protein profiles to chilling unit accumulation and intensity of endodormancy will be discussed.