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flower bud removal achieved by several methods on growth of young rabbiteye blueberry plants, and to determine the effect of rate and timing of hydrogen cyanamide sprays on flower bud removal and growth of young southern highbush blueberry plants

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Fruit splitting and cracking occurs in rabbiteye and southern highbush blueberries if they receive preharvest rainfall when fully ripe or approaching full ripeness. The splitting can be particularly severe if the rain follows a long period of dry

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has become a major disease of southern highbush blueberries in Georgia and Florida ( Brannen et al., 2007 ). Given these findings, it is critical that the blueberry industry begins regular screening for cultivars that are resistant or tolerant to X

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Three experiments were conducted in north-central Florida to determine the effects of fall defoliation on flower bud initiation and yield of southern highbush (SHB) blueberry (Vaccinium corymbosum hybrid). In 1998, randomly selected upright shoots of mature, field-grown `Misty' and `Sharpblue' plants were hand-defoliated at monthly intervals beginning 4 Sept. and ending 7 Dec. In 1999, a similar study was conducted using different plants of the same cultivars. Representative shoots were defoliated at monthly intervals beginning 14 Sept. and ending 15 Dec. Additional shoots were also partially defoliated by removing the distal two-thirds of each leaf at monthly intervals from 15 Oct. through 15 Dec. In a third experiment, 2-year-old container-grown `Star' SHB plants were completely defoliated at monthly intervals beginning 13 Sept. and ending 15 Dec. In each experiment, control shoots, or plants ('Star'), were not defoliated. Although there were differences among cultivars and years, all cultivars tested demonstrated negative effects on reproductive growth and development from September and October defoliations. For `Sharpblue', reduced fruit yield from early fall defoliation appeared to be due to fewer fruit set per flower bud. However, for `Misty', reduced fruit yield from early fall defoliation was the result of large reductions in flower bud numbers as well as fewer fruit set per flower bud. September and October defoliations of `Star' reduced yields or delayed fruit ripening. Collectively, these experiments demonstrate the importance of maintaining healthy foliage through October in the lower southeastern United States for adequate flower bud initiation and high yields of SHB blueberry the following spring.

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Blueberry fruit were harvested at commercial maturity from variety trials and shipped overnight to UC Davis. Fruit quality was evaluated upon receipt and after 6 and 20 days of cold storage at 0.5 °C in air shelf life. Firmness, external color, soluble solids, and titratable acidity were measured. Sensory evaluations were conducted by trained tasters to rate the blueberries for crispness, mealiness, sweetness, tartness, blueberry flavor, and off-flavors at harvest and again after 21 days of storage. Many of the blueberries increased in firmness during cold storage. Firmness at harvest tended to be softer in `Santa Fe' and `Jewel' and firmer in `Star'. Sensory data also found `Sharpblue' and `Southmoon' to be more firm; however the objective measurements did not agree. Overall, `Saphire' was low in sugars and acids, and `Jewell' and `Star' were high in acids. `Misty' and `Sharpblue' were consistently high in sugars and acids. Overall objective fruit quality ratings were highest for `Misty', `Sharpblue', and `Southmoon', and lowest for `Santa Fe'. Blueberry flavor was rated highest in `Jewell', `Star', and `Sharpblue', and lowest in `Santa Fe', `Saphire', `Misty', and `Emerald'. These data indicate that blueberry flavor may be closely tied to acid content, as most of the high-flavor varieties had high acid and many of the low-flavor varieties had low acid. Over 3 years, the varieties consistently rated highest for overall objective quality were `Misty' and `Southmoon'. `Star' was rated high for overall quality in 2 years and moderate in 1. `Jewell', `Star', and `Sharpblue' were rated highest in flavor. `Santa Fe' was ranked low in flavor quality in 2 out of 3 years. Selection of variety appears to have a strong influence on the sensory quality of the blueberries marketed.

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Southern highbush (“low chill tetraploid”) blueberries are an earlier-ripening, self pollen-compatible alternative to rabbiteye blueberries. `Sharpblue', the first southern highbush cultivar planted on a commercial scale, has been shown to require cross-pollination for optimal fruit size and earliness of ripening. `Gulfcoast', a recently released cultivar for Gulf states growers of about latitude 30 to 32 N, differs in heritage from `Sharpblue', incorporating about 50% more self-compatible northern highbush germplasm. `Gulfcoast' fruit development after honey bee-mediated self- or cross-pollination with `Sharpblue' was similar in terms of set (85.5 vs. 82.2%), weight (1.26 vs. 1.18g), and seed number (32.8 vs. 33.6), respectively. Cross-pollination did not result in significantly earlier ripening. Thus, `Gulfcoast' appears to be more self-fertile than `Sharpblue'. Other closely-related cultivars are being examined to determine the genetic influence on potential for self-fruitfulness.

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To determine the effects of pollen source on blueberry production, we made a partial diallel set of crosses involving seven rabbiteye (Vaccinium ashei Reade) and seven southern highbush (SH; V. corymbosum L.) parents. Pollination of rabbiteye blueberry flowers with SH pollen reduced fruit set, seeds per berry, and berry weight and increased fruit development period (FDP) compared to pollination with rabbiteye pollen. Pollination of SH flowers with rabbiteye pollen resulted in about the same fruit set and FDP but fewer seeds per berry and slightly lower berry weight compared to intraspecific pollination. Self-pollination significantly decreased the number of seeds per berry and berry weight and increased FDP in SH. Pollination of rabbiteye and SH flowers with mixed pollen produced the same results as intraspecific pollination. Using `Tifblue' and `Baldwin' (rabbiteye) as the pollen parent significantly increased FDP in rabbiteye blueberry. Using `Georgiagem' and `Cape Fear' as pollen parents produced the longest FDP, and using `O'Neal' and `Gulfcoast' produced the shortest FDP in SH blueberry. The heaviest berries were produced by using `Blue Ridge', `O'Neal', and `Gulfcoast' (SH) as pollen parents on SH females. These results suggest that xenia possibly could be used to increase yield and reduce FDP in blueberry.

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Calcium is commonly known to affect the developmental processes of many plants, and its role as a major nutrient has been interpreted in terms of its interaction with components of the cell wall and membrane. A 2-year study was conducted to assess the affects of calcium foliar feed fertilization applied at bloom and throughout floral development on the reduction of rain-related splitting in blueberries. Foliar-applied calcium at 0.2% or 0.9% concentration did not successfully decrease splitting in blueberries to a statistical and, more importantly, an economically significant level. Calcium sprays also had no adverse affects on the fruit firmness, quality, or calcium concentrations within the fruit.

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Experiments were conducted with V. darrowi and two cultivars of southern highbush blueberry, `Sharpblue' and `Misty,' to test whether V. darrowi and cultivars derived from it are photoperiodic with respect to flower bud initiation. Plants of each cultivar were grown under three different photoperiod treatments [long days (LD) = 16-hour photoperiod; short days (SD) = 8-hour photoperiod; and short days + night interrupt (SD-NI) = 8-hour photoperiod with 1-hour night interrupt] at constant 21 °C for 8 weeks. Vegetative growth was greatest in the LD plants of both cultivars. Flower bud initiation occurred only in the SD treatments, and the lack of flower bud initiation in the SD-NI treatment indicates that flower bud initiation is a phytochrome mediated response in Vaccinium. Previously initiated flower buds on the V. darrowi plants developed and bloomed during the LD treatment, but bloom did not occur in the SD and SD-NI treatment plants until after those plants were moved to LD. These data indicate that flower bud initiation in both V. darrowi and southern highbush blueberry is photoperiodically sensitive, and is promoted by short days, while flower bud development is enhanced under long days.

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of cracking of fruit by rain Science 105 334 335 Rooks, S.D. Ballington, J.R. Mainland, C.M. 1995 ‘Bladen’ southern highbush blueberry HortScience 30 150 151 SAS Institute 2001 SAS

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