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Y.H. Huang, C.E. Johnson, G.A. Lang, and M.D. Sundberg

Ovule abortion occurred between 5 and 10 days after pollination (DAP) in self- and cross-pollinated `Sharpblue' blueberry (Vaccinium corymbosum L.) fruit. More ovule abortion occurred with self-pollination (35%) than with cross-pollination (22% for `Sharpblue' × `O'Neal' and 29% for `Sharpblue' × `Gulfcoast'), and there were more poorly developed ovules with self-pollination (88.1%) than with cross-pollination (× `O'Neal', 33.6%; × `Gulfcoast' 50.8%). The increase in ovule area correlated exponentially with fruit growth during early developmental stages, regardless of pollination treatment. However, cross-pollination resulted in significantly greater ovule area and fruit mass during early fruit development as well as at ripening. Ovule area was maximum at 25 to 30 DAP for both pollination treatments, followed by exponential fruit growth (stage III). Cross-pollination resulted in greater fruit growth and a shorter stage III. At 10 DAP, ovules from cross-pollination were larger than those from self-pollination, suggesting that cross-pollination initiated ovule growth immediately after fertilization. This research suggests that southern highbush blueberry fruit growth and development is intimately associated with ovule growth and development, which is affected by pollen sources.

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Donald J. Merhaut and Rebecca L. Darnell

Ammonium and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} uptake and partitioning were monitored in `Sharpblue' southern highbush blueberry plants (Vaccinium corymbosum L. interspecific hybrid) using 10% 15N-enriched N. Shoots and roots were harvested at 0, 6, 12, 24, and 48 hours after labeling. The rate of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\mathrm{-}\mathrm{N}\) \end{document} uptake was higher than that of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\mathrm{-}\mathrm{N}\) \end{document} uptake, averaging 17.1 vs. 8.6 g N/g plant dry weight per hour during the 48-hour period for \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\mathrm{-}\) \end{document} and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\mathrm{-treated}\) \end{document} plants, respectively. At the end of the 48 hours, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\mathrm{-}\mathrm{N}\) \end{document} accumulation averaged 79 mg N/plant compared to 40 mg accumulated by the \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\mathrm{-}\mathrm{N}\mathrm{-treated}\) \end{document} plants. Similarly, the translocation rate of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\mathrm{-}\mathrm{N}\) \end{document} to shoots was higher than translocation of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\mathrm{-}\mathrm{N}\) \end{document} to shoots (7.7 vs. 1.9 g N/g shoot dry weight per hour, respectively) during the 48 hours. Shoot accumulation of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\mathrm{-}\mathrm{N}\) \end{document} averaged 40 mg N/plant at the end of 48 hours, while accumulation in shoots of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\mathrm{-}\mathrm{N}\mathrm{-treated}\) \end{document} plants averaged 10 mg N/plant. Short-term \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} uptake and translocation to shoots appears to be limited relative to \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} uptake and translocation in southern highbush blueberry when plants are previously fertilized with NH4NO3.

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Jeffrey G. Williamson and E. Paul Miller

Bearing `Misty' and `Star' southern highbush blueberries were grown on pine bark beds and fertilized at three rates using granular and liquid fertilizers with a 3–1–2 (1N–0.83K–0.88P) ratio. Granular fertilizer was applied 8 times per year at 4-week intervals beginning in April and continuing through October. Liquid fertilizer was applied with low volume irrigation 16 times per year at 2-week intervals during the same period. During the growing season, irrigation was applied at 2- to 3-day intervals in the absence of rain. A 2 cultivar × 2 fertilizer type × 3 fertilizer rate factorial arrangement of treatments was replicated 8 times in a randomized complete-block design. All fruits were harvested from single-plant plots at 3- to 4-day intervals. Canopy volume was not affected by fertilizer type, but fruit yield was slightly greater for granular than for liquid fertilizer treatments. In 2003, fruit yield of 2.5-year-old `Misty' and `Star' plants increased with increasing fertilizer rates up to the highest rate tested (50 g N/plant/year). Similarly, in 2004, fruit yields increased with increasing fertilizer rates up to the highest rate (81 g N/plant/year). Root distribution was limited to the 12-cm-deep layer of pine bark with very few roots penetrating into the underlying soil. The positive growth responses of blueberry plants to high fertilizer rates in pine bark beds suggests that soluble fertilizer was leached through the pine bark layer into the soil below the root zone. More frequent, lighter applications of soluble fertilizers, use of slow-release or controlled-release fertilizers, and careful irrigation management may improve fertilizer use efficiency of blueberry plantings on pine bark beds.

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Gena R. Silva, Frank B. Matta, and James M. Spiers

Late spring frosts are a major concern to blueberry growers in the southeastern United States. Cold hardiness of flower buds (stages 4 to 6) was evaluated in three southern highbush blueberry cultivars (`Cooper', `O'Neal', and `Gulfcoast'). Differential thermal analysis (DTA) and tissue browning tests revealed that the critical temperature and ovary damage occurred at –11C in `Cooper', –12C in `O'Neal', and –13C in `Gulfcoast'.

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Jeffrey G. Williamson* and E. Paul Miller

Poor fruit set and sub-optimum berry size are potential yield- and profit-limiting factors for southern highbush (Vaccinium corymbosum) blueberry production in Florida. The cytokinin N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) has increased fruit size and fruit set of a number of fruit crops including rabbiteye blueberry. The purpose of this study was to determine the effects of CPPU applied at different rates and phenological stages of bloom and/or fruit development on fruit size, set, and yield of southern highbush blueberry. `Millennia' and `Star' southern highbush blueberry plants located on a commercial blueberry farm in Alachua County, Fla., were treated with 5 or 10 ppm CPPU at various stages of development ranging from full bloom to 20 days after full bloom. In contrast to findings with rabbiteye blueberry, fruit set in this study of southern highbush blueberry was not affected by any of the CPPU treatments when compared to the controls. Nor was total fruit yield affected by CPPU treatments. The most noticeable potential benefit found in this study was an increase in mean fruit fresh weight from CPPU treatments. However, cultivars responded differently to CPPU with respect to mean fruit fresh weight. For `Millennia', only one CPPU treatment increased mean fruit weight compared to controls. However, for `Star', all but one CPPU treatment increased mean fruit fresh weight. Several CPPU treatments resulted in delayed fruit ripening for `Star' but not for `Millennia'. For `Star', the treatments that most consistently delayed fruit ripening tended to have greater fruit fresh weights.

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James B. Magee

The southern highbush blueberry (Vaccinium, mostly corymbosum) cultivars Jubilee, Pearl River, and Magnolia and the rabbiteye cultivars Climax and Premier were stored for 4 weeks at 1-2 °C. Berries were held in pint “clam shell” plastic retail units and were evaluated weekly for physical and compositional quality. As groups, the rabbiteyes were higher in SSC, SSC/TA, glucose and fructose, anthocyanins, and malic, quinic, and succinic acids. `Jubilee' was the southern highbush and `Climax' the rabbiteye least affected by the storage. `Pearl River' and `Magnolia' were less firm and more shriveled than the other cultivars. `Magnolia' had the highest incidence of decay; decay was slight overall.

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Y.H. Huang, C.E. Johnson, and M.D. Sundberg

Floral morphology and differentiation of `Sharpblue' southern highbush blueberry (Vaccinium corymbosum L.) were studied under natural growing conditions. There was no rest period during floral development of `Sharpblue' blueberry in Louisiana. Basal florets were already present within a racemic inflorescence in early September. All floral and reproductive organs were clearly visible in early December. Microspores and pollen grains were observed in mid- and late-January, respectively. Megasporocytes, two-cell, four-cell, and seven-cell embryo sacs were found to be simultaneously present in developing ovules in late January, suggesting that megasporogenesis and megagametogenesis in `Sharpblue' blueberry are asynchronous.

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Ingrith D. Martinez and P.M. Lyrene

Fruit set, fruit size, and seed production after hand pollination in a greenhouse were compared for southern highbush blueberry managed in two ways: a) 69 clones were allowed to go dormant and lose their leaves in the field before being dug and subjected to 1000 hours at 5 °C and b) 26 clones were kept growing in a greenhouse through fall and winter without leaf loss and without chilling, to induce flowering on plants that had mature leaves. On each plant in both management systems, some flowers were self-pollinated, some were cross-pollinated, and others had the styles removed before anthesis to prevent pollination. For >1000 flowers per pollination treatment on the deciduous plants, fruit set averaged 1% for no pollination, 46% for self-pollination, and 76% for cross-pollination. The corresponding values for the evergreen plants were 23%, 59%, and 81%. Parthenocarpic berries averaged 0.37 g/berry for deciduous plants and 1.01 g for evergreen plants. Both crossed and selfed berry weights averaged slightly higher for the evergreen plants than for the deciduous plants, but seed number per berry was much lower for the evergreen plants (12 seeds in crossed berries and four seeds in selfed berries) compared to deciduous plants (37 and 8). Southern highbush blueberry plants that flower without going dormant appear to have much higher parthenocarpic capabilities than those that flower after a dormant period.

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Timothy M. Spann, Jeffrey G. Williamson, and Rebecca L. Darnell

Experiments were conducted with `Misty' southern highbush blueberry (Vaccinium corymbosum L. interspecific hybrid) to test the effects of high temperature on flower bud initiation and carbohydrate accumulation and partitioning. Plants were grown under inductive short days (SDs = 8 hour photoperiod) or noninductive SDs with night interrupt (SD-NI = 8 hour photoperiod + 1 hour night interrupt), at either 21 or 28 °C for either 4 or 8 weeks. Flower bud initiation occurred only in the inductive SD treatments and was significantly reduced at 28 °C compared with 21 °C. The number of flower buds initiated was not significantly different between 4- and 8-week durations within the inductive SD, 21 °C treatment. However, floral differentiation appeared to be incomplete in the 4-week duration buds and bloom was delayed and reduced. Although plant carbohydrate status was not associated with differences in flower bud initiation between SD and SD-NI treatments, within SD plants, decreased flower bud initiation at high temperature was correlated with decreased whole-plant carbohydrate concentration. These data indicate that flower bud initiation in southern highbush blueberry is a SD/long night phytochrome-mediated response, and plant carbohydrate status plays little, if any, role in regulating initiation under these experimental conditions.

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Robert G. Danka and Gregory A. Lang

`Gulfcoast' southern highbush blueberry (Vaccinium corymbosum × V. darrowi) plants were placed in 3 × 6 × 2.5 m net cages with one colony of honey bees per cage and one of three pollinizer treatments: “self (other `Gulfcoast' plants), “cross/highbush” (other southern highbush cultivars), or “cross/rabbiteye” (various rabbiteye blueberry cultivars). In addition to unlimited pollination, bee foraging was controlled on individual flowers by placing small bags over corollas after 0, 1, 5, or 10 visits. Fruit set, fruit weight, fruit development period, and seed number data were taken, as well as data to relate floral morphology to duration of bee foraging. All measures of fruiting increased significantly with increased bee visitation; the threshold for significant gains in production occurred between 1 and 5 visits. Ten visits generally provided a good approximation of unlimited pollination. Set, weight, and earliness of ripening was as good, or better, for fruit derived from rabbiteye pollen compared to fruit from self- or cross/highbush-pollination.