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Olivia M. Lenahan, Matthew D. Whiting, and Donald C. Elfving

This paper reports on the potential of gibberellic acid (GA3 and GA4+7) to reduce sweet cherry (Prunus avium L.) floral bud induction and balance fruit number and improve fruit quality in the season following application. In 2003, GA3 was applied to `Bing'/`Gisela 1' trees at 50 and 100 mg·L-1 at the end of stage I of fruit development, end of stage II, and on both dates. These treatments were compared to the industry standard application of 30 mg·L–1 applied at the end of stage II and an untreated control. Fruit quality was evaluated in the year of application (i.e., nontarget crop) and return bloom, fruit yield and quality were assessed in the subsequent season (2004). In 2003, GA3 delayed fruit maturity proportional to rate. In 2004, bloom density and fruit yield were related negatively and linearly to GA3 concentration. GA3 reduced the number of reproductive buds per spur and did not affect the number of flowers per reproductive bud. Nonspur flowering at the base of 1-year-old shoots was more inhibited by GA3 than flowering on spurs. Double applications significantly reduced bloom density and yield versus single applications. Trees treated with two applications of 50 and 100 mg·L–1 yielded fruit with 7% and 12% higher soluble solids, 15% and 20% higher firmness, and 7% and 14% greater weight, respectively. However, no treatment improved crop value per tree. In a separate isomer trial, GA3 and GA4+7 were applied to `Bing'/`Gisela 1' trees at 100 and 200 mg·L–1 at both the end of stage I and II in 2004. GA3 and GA4+7 applied at 100 mg·L–1 reduced bloom density similarly by 65%. GA3was more inhibiting than GA4+7at 200 mg·L–1, reducing bloom density by 92% versus 68%. We observed a 4- to 5-day delay in flowering from both GA formulations at 200 mg·L–1. At both concentrations, GA3 reduced yield by 71% and 95% versus 34% and 37% reduction by GA4+7. Fruit weight and soluble solids were unaffected but fruit firmness was increased by all treatments (6% to 17%). However, crop value per tree was highest from untreated control because improvements in fruit quality were insufficient to offset reductions in yield. GA3 shows potential as a novel crop load management tool in productive `Bing' sweet cherry orchard systems.

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James W. Olmstead, Amy F. Iezzoni, and Matthew D. Whiting

Understanding the genetic control of fruit size in sweet cherry (Prunus avium L.) is critical for maximizing fruit size and profitable fresh market production. In cherry, coordinated cycles of cell division and expansion of the carpel result in a fleshy mesocarp that adheres to a stony endocarp. How these structural changes are influenced by differing genetics and environments to result in differing fruit sizes is not known. Thus, the authors measured mesocarp cell length and cell number as components of fruit size. To determine the relative genotypic contribution, five sweet cherry cultivars ranging from ≈1 to 13 g fresh weight were evaluated. To determine the relative environmental contribution to fruit size, different-size fruit within the same genotype and from the same genotype grown in different environments were evaluated. Mesocarp cell number was the major contributor to the differences in fruit equatorial diameter among the five sweet cherry cultivars. The cultivars fell into three significantly different cell number classes: ≈28 cells, ≈45 cells, and ≈78 cells per radial mesocarp section. Furthermore, mesocarp cell number was remarkably stable and virtually unaffected by the environment as neither growing location nor physiological factors that reduced final fruit size significantly altered the cell numbers. Cell length was also significantly different among the cultivars, but failed to contribute to the overall difference in fruit size. Cell length was significantly influenced by the environment, indicating that cultural practices that maximize mesocarp cell size should be used to achieve a cultivar's fruit size potential.

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Nnadozie C. Oraguzie, D. Ophardt, Matthew D. Whiting, Gregory A. Lang, and Lynn E. Long

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James W. Olmstead, Matthew D. Whiting, David Ophardt, Nnadozie C. Oraguzie, and Gregory A. Lang

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James W. Olmstead, Matthew D. Whiting, David Ophardt, Nnadozie C. Oraguzie, and Gregory A. Lang

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Tory Schmidt, Don C. Elfving, James R. McFerson, and Matthew D. Whiting

Potential strategies against biennial bearing in apple [Malus × sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] include promotion of return bloom with an “on”-year application of ethephon or inhibition of return bloom with an “off”-year application of gibberellic acid (GA), but the influence of initial crop load on the efficacy of these bioregulators is poorly understood. In 2004 and 2005, six total trials were initiated in which whole trees were manually adjusted shortly before anthesis to one of three levels of crop load (100%, 50%, 0%) in ‘Cameo’, ‘Honeycrisp’, and ‘Fuji’; GA4 + 7 was overlaid on trees of each crop level in four trials and ethephon in two. In all trials, initial crop load was the primary determinant of return bloom; proportional influence on flower density, fruit density, and yield was generally most pronounced at the 50% crop level. GA4 + 7 consistently reduced floral initiation, whereas ethephon promoted it. Flowering responses from a historically alternating ‘Cameo’ trial site showed greater sensitivity to ethephon and less sensitivity to GA4 + 7 than did responses from parallel trials established in an annually bearing ‘Cameo’ block, suggesting a predilection of nascent buds to a specific fate before the influence of exogenous bioregulators or gibberellins from seeds produced in developing fruit. Light crop loads and GA4 + 7 applications generally promoted shoot extension, whereas heavy crops and ethephon had the opposite effect.

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Nnadozie C. Oraguzie, David Ophardt, Matthew D. Whiting, Gregory A. Lang, and Lynn E. Long

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Torrance R. Schmidt, Don C. Elfving, James R. McFerson, and Matthew D. Whiting

Gibberellins inhibit flowering in apple (Malus domestica) and show promise as tools to promote annual bearing. The authors validated the efficacy of gibberellic acid (GA) to reduce return bloom dramatically in two biennial cultivars. ‘Honeycrisp’ fruit treated in 2004 with GA4+7 at 0, 200, 400, or 600 mg·L−1 demonstrated advanced maturity in terms of starch levels, flesh firmness, and titratable acidity, whereas ‘Cameo’ fruit showed variable treatment effects. In 2005, 0, 300, 600, 900, or 1200 mg·L−1 GA4+7 was applied to ‘Cameo’, and fruit maturity was once again unaffected. Two commercial GA products (GA4, GA4+7) were applied in 2005 to ‘Honeycrisp’ at 400 mg·L−1. Both formulations caused fruit to have less flesh firmness and acidity, and increased levels of starch conversion compared with the untreated control at harvest and after 140 d of common storage. All GA treatments in all four trials profoundly diminished flowering in the season after treatment. Results demonstrate differences in sensitivity to GA between the two cultivars.