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Most Vaccinium species, including V. corymbosum, have strict soil requirements for optimal growth, requiring low pH, high iron, and nitrogen, primarily in the ammonium form. V. arboreum is a wild species adapted to high pH, low iron, nitrate-containing soils. This broader soil adaptation in V. arboreum may be related to increased efficiency of iron or nitrate uptake/assimilation compared with cultivated Vaccinium species. To test this, nitrate and iron uptake, and nitrate reductase (NR) and ferric chelate reductase (FCR) activities were compared in two Vaccinium species, V. arboreum and the cultivated V. corymbosum. Plants were grown hydroponically for 15 weeks in either 1.0 or 5.0 mm NO₃ with 0.09 mm Fe. Root FCR activity was greater in V. arboreum compared with V. corymbosum, especially at the lower external nitrate concentration. However, this was not reflected in differences in iron uptake. Nitrate uptake and root NR activity were greater in V. arboreum compared with V. corymbosum. The lower nitrate uptake and assimilation in V. corymbosum was reflected in decreased plant dry weight compared with V. arboreum. V. arboreum appears to be more efficient in acquiring nitrate compared with V. corymbosum, possibly due to increased NR activity, and this may partially explain the wider soil adaptation of V. arboreum.

Containerized `Climax' and `Beckyblue' rabbiteye blueberry plants (Vaccinium ashei Reade) were exposed to 5 weeks of natural daylengths (i.e. gradually decreasing daylengths from 12 to 11 hr) or shortened daylengths (i.e. gradually decreasing daylengths from 10 to 8 hr) starting October 1. `Beckyblue' initiated twice as many flower buds under short days compared to longer days. The following spring, `Beckyblue' plants exposed to shortened photoperiods the previous fall had a greater percentage of floral budbreak (based on the number of flower buds formed within each treatment) and a shorter, more concentrated bloom period than did plants exposed to longer photoperiods the previous fall. Fresh weight per berry increased following the short fall photoperiod treatment, despite the fact that fruit number was higher. `Climax' did not respond to the photoperiod treatments in any way. Leaf carbon assimilation rates of both cultivars increased under short days, but there was no detectable effect of photoperiod on current carbon partitioning in either cultivar, suggesting that flower bud initiation is not limited by current source leaf assimilate supply under these conditions.

Containerized `Climax' and `Beckyblue' rabbiteye blueberry plants (Vaccinium ashei Reade) were exposed to 5 weeks of natural daylengths or shortened daylengths starting 30 Sept. `Beckyblue' plants exposed to short daylengths in the fall initiated more flower buds and had a shorter, more concentrated bloom period than did plants exposed to natural fall daylengths. Reproductive development of `Climax' was not influenced by photoperiod treatments. Leaf carbon assimilation of both cultivars increased under short days. Partitioning of translocated ¹⁴C-labeled assimilates to stem tissue increased under short photoperiods for `Beckyblue'; however, partitioning patterns in `Climax' were not affected. Increased carbon fixation and increased partitioning of carbon to stem tissue under short days may contribute to the observed effect of short days on enhancing reproductive development in `Beckyblue'.

Graduate student enrollment in the plant sciences has decreased over the past several years, and there is increasing interest in recruitment/retention strategies. Before successful strategies can be implemented, however, the status of current plant science graduate programs needs to be determined. Survey data on graduate student demographics, research area, support levels, current recruitment strategies, and career opportunities were collected from 23 plant science graduate programs. Overall, 55% of graduate students in plant sciences were male and 45% were female; about 60% were domestic and 40% were international. Cellular/molecular biology and breeding/genetics were the two disciplines that had the greatest number of graduate students and the greatest number of job opportunities. Most programs cited financial support as the biggest obstacle to recruitment. However, stipend number, the guarantee of multiple years of support, the funding of tuition waivers, and health insurance costs also impact student numbers. As more of these costs are shifted to faculty, there appears to be an increasing inability and/or reluctance to invest grant funds (which support 60% of the plant science graduate students) in graduate student education. These data suggest that the decline in plant science graduate student enrollment may be due to shifting of more of the total cost of graduate training to faculty, who may be unable/unwilling to bear the cost. There is also a clear shift in the research focus of plant science graduate students, as postdoctoral and career opportunities are weighted toward molecular biology/genetics, leaving the more applied plant science areas particularly vulnerable to low graduate enrollment.

Graduate student enrollment in the plant sciences has decreased over the past several years, and there is increasing interest in recruitment/retention strategies. Before successful strategies can be implemented, however, the status of current plant science graduate programs needs to be determined. Survey data on graduate student demographics, research area, support levels, current recruitment strategies, and career opportunities were collected from 23 plant science graduate programs. Overall, 55% of graduate students in plant sciences were male and 45% were female; approximately 60% were domestic and 40% were international. Cellular/molecular biology and breeding/genetics were the two disciplines that had the greatest number of graduate students and the greatest number of job opportunities. Although most programs cited financial support as the biggest obstacle to recruitment, there was not a strong correlation between graduate student number/program and stipend amount. However, other funding factors besides stipend amount; such as stipend number, the guarantee of multiple years of support, the funding of tuition waivers, and health insurance costs, likely impact student number. As more of these costs are shifted to faculty, there appears to be an increasing inability and/or reluctance to invest grant funds (which support 60% of the plant science graduate students) in graduate student education. These data suggest that the decline in plant science graduate student enrollment may not be directly due to low stipend amounts, but rather to shifting of more of the total cost of graduate training to faculty, who may be unable/unwilling to bear the cost. There is also a clear shift in the research focus of plant science graduate students, as postdoctoral and career opportunities are weighted towards molecular biology/genetics, leaving the more applied plant science areas particularly vulnerable to low graduate enrollment.

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.

Vaccinium corymbosum, one of the cultivated blueberry species, is not well-adapted to mineral soils, which are generally marked by high pH, the predominance of NO₃-N over NH₄-N, and limited iron availability. A wild species, V. arboreum, grows naturally on mineral soils, and thus may be better adapted than V. corymbosum. This adaptation may be related to the ability of V. arboreum to assimilate NO₃ and/or iron more efficiently than V. corymbosum. Both species were grown in a hydroponic solution containing 5.0 mM N as (NH₄)₂SO₄ or NaNO₃, and buffered to pH 5.5. Nitrate reductase (NR) and iron reductase (FeR) activities were measured. NR activity was higher in V. arboreum compared with V. corymbosum when grown with N0₃-N, while no difference between species was observed when grown under NH₄-N. Activity of FeR was higher in V. arboreum compared with V. corymbosum, and higher under NO₃-N compared with NH₄-N. After 5 months in hydroponics, Fe was removed from one-half of the solutions. The activity of NRA in both species was higher under Fe-sufficient compared with Fe-limited conditions, but in both cases, activity was higher in V. arboreum compared with V. corymbosum. FeR activity continued to be higher in V. arboreum compared with V. corymbosum, and under NO₃ compared with NH₄-N. Activity decreased in both species under limited Fe conditions, and there were no interactions between species and Fe. These data indicate that V. arboreum possesses higher NR and FeR activities than V. corymbosum, under both Fe-sufficient and Fe-limited conditions. This may play a role in the better adaptability of V arboreum to mineral soil conditions.

To determine if multiple applications of GA₃ would increase size of parthenocarpic fruit, and to assess the interaction between GA₃ applications and pollination, `Beckyblue' rabbiteye blueberry (Vaccinium ashei Reade) flowers were treated with single or multiple applications of GA₃ alone or in combination with full or partial pollination. Single or multiple applications of GA₃ resulted in similar or increased fruit set compared with pollination, and increased fruit set compared with no pollination. GA₃ applications decreased fruit mass and increased the fruit development period in comparison with pollination alone. Multiple, late applications of GA₃ were ineffective in overcoming these effects. Partial (nonsaturating) pollination resulted in an average fruit set of 60%, while set following GA₃ treatment in combination with full or partial pollination averaged 85%. Fruit mass was greater in the full pollination ±GA₃ treatments than in all other treatments. The number of large seeds and seed mass per fruit were greatest in the full pollination treatment, and were significantly decreased by all treatments in which GA₃ and/or partial pollination were used; however, there were no concomitant effects of GA₃ in delaying the fruit development period. Our results indicate that under optimal pollination conditions, no detrimental effects of GA₃ applications on fruit set, fruit size, or fruit development period in blueberry are to be expected, even though GA₃ reduces seed number and seed mass. Furthermore, GA₃ applications appear to be beneficial in increasing fruit set under suboptimal pollination conditions, although smaller fruit are to be expected under such conditions. Chemical name used: gibberellic acid (GA₃).

Cultivated Vaccinium species (e.g. highbush blueberry, Vaccinium corymbosum, or cranberry, V. macrocarpon) commonly require acidic soil (pH 4.5 to 5.5) for optimum growth. Under these conditions, ammonium (NH₄ ⁺) is the dominant form of inorganic N. In contrast, V. arboreum, the sparkleberry can tolerate higher-pH mineral soils, where nitrate (NO₃ ^-) is typically the predominant inorganic N form. This tolerance may be related to increased ability to acquire and utilize NO₃—N. Measurements of ¹⁵NO₃ ^- and ¹⁵NH₄ ⁺ influx kinetics in excised roots of V. arboreum, V. corymbosum, and V. macrocarpon did not support this hypothesis. NO₃ ^- influx kinetics measured from 10 micromolar to 200 micromolar NO₃ ^- were similar among all three species. NO₃ ^- influx was consistently lower than NH₄ ⁺ influx at all concentrations for all three species.

Commercial blueberry production is limited primarily to soils where ammonium, rather than nitrate, is the predominant N form. However, Vaccinium arboreum, a species native to northern Florida, often is found growing in soils where nitrate is the major N form. This species may serve as a breeding source or rootstock for commercial blueberries, expanding the potential soil types that may be used for blueberry cultivation. In our study, in vivo nitrate reductase activity (NRA) was measured in roots and leaves of 2-year-old seedlings of V. arboreum and a commercial cultivar, V. corymbosum `Sharpblue'. Plants were grown hydroponically in sand culture and fertilized with a modified Hoagland's solution containing N as either ammonium, ammonium nitrate, or nitrate. Vaccinium arboreum averaged nitrite at 200, 60, and 20 nmol/g fresh weight per h for nitrate, ammonium nitrate, and ammonium fertilized plants, respectively. `Sharpblue' root NRA was significantly lower, averaging nitrite 50, 38, and 8 nmol/g fresh weight per h for nitrate, ammonium nitrate, and ammonium fertilized plants, respectively. NRA was much lower in leaves than roots of V. arboreum, averaging nitrite at ≈15 nmol nmol/g fresh weight per h across N treatments. No NRA was detected in the leaves of `Sharpblue', regardless of N treatment. These data suggest that V. arboreum may be used as a rootstock or breeding source to expand blueberry production into soil types that are higher in nitrate than the soils typically used for blueberry production.