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Mark K. Ehlenfeldt, Lisa J. Rowland, Elizabeth L. Ogden, and Bryan T. Vinyard

), moderate vigor, and a nonsuckering growth habit. Its fruit are small, aromatic, not objectionably seedy, and can have very good quality. Vaccinium ashei is a hexaploid species traditionally grown commercially in southern areas with mild winters

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D. Scott NeSmith, Gerard Krewer, and Orville M. Lindstrom

Plants of `Brightwell' and `Tifblue' rabbiteye blueberry (Vaccinium ashei Reade) were subjected to 0, -1, -3, or -4.5 °C for 1 hour during flowering. After treatment, half of the plants were exposed to bees (Bombus sp.) only, and half were exposed to bees and received applications of GA3. Fruit set of both `Brightwell' and `Tifblue' pollinated by bees declined sharply after exposure to -1 °C for 1 hour, but there was no visible damage to corollas, styles, and ovaries. Fruit set of GA3-treated plants of both cultivars equaled that of control plants (plants having no cold exposure) at temperatures ≥+-3 °C. Both pollinated and GA3-treated plants had ≤2% fruit set after exposure of flowers to -4.5 °C. Both prefreeze and postfreeze applications of GA3 were beneficial for fruit set. Assessment of flower part damage at the different temperatures indicated corollas were most sensitive to freeze damage, followed by styles, and then ovaries. Results suggest fertilization and fruit set of pollinated rabbiteye blueberries can be greatly impaired by even mild freezes (-1 to -2 °C), whereas, appropriately timed applications of GA3 can result in little reduction in fruit set even after moderate freezes (-3 to -4 °C) of blueberries during bloom. Chemical name used: gibberellic acid (GA3).

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Myneni Aruna, Max E. Austin, and Peggy Ozias-Akins

Cultivars of the economically important rabbiteye blueberry (Vaccinium ashei Reade) were differentiated at the DNA level using the technique of randomly amplified polymorphic DNA. Single decanucleotide primers of arbitrary sequence were used to amplify genomic DNA by the polymerase chain reaction. All cultivars tested exhibited a unique set of collective amplified fragments of distinct molecular weight. A blind fingerprinting experiment resulted in identification of unknown samples without ambiguity. We also clarified the genetic identity of two wild selections of rabbiteye blueberry, `Ethel' and `Satilla', which have been maintained as two different selections, hut are considered by some blueberry breeders to be of the same genetic constitution. The technique also verified the probable identity of two cultivars in a commercial blueberry field by comparing their amplified DNA patterns with those of standard cultivars. No variation was observed between the amplification profiles of `Brightwell' and its presumed sport. A cultivar key based on 11 markers amplified by four primers is presented.

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D. Scott NeSmith

Experiments were conducted during 1999 and 2000 at Griffin, Ga., with rabbiteye blueberries (Vaccinium ashei Reade) to determine how the growth regulator CPPU affected fruit set, berry size, and yield. CPPU (applied at two different timings) was used alone, and in conjunction with GA3 on mature, field-grown `Tifblue' plants. A control treatment without either growth regulator was also included. The CPPU concentration used was 10 mg·L-1 (a single application per treatment), and the GA3 concentration used was 200 mg·L-1 (two applications per treatment). Results from both years showed a positive benefit of CPPU with respect to fruit set and berry size, especially in the absence of GA3. Depending on timing, berry number per plant was increased by more than 200% in 1999 using CPPU. Berry size increases of more than 30% occurred in 2000 when CPPU alone was applied at 17 d after flowering (DAF). CPPU did not increase berry size of GA3-treated plants in either year. Total yield per plant during 2000 was 5.0, 7.1, and 8.3 kg for control, CPPU applied 7 DAF, and CPPU applied 17 DAF treatments, respectively, without GA3. While CPPU did substantially increase fruit set, berry size, and yield of `Tifblue', there was a notable delay in fruit ripening. These results suggest that CPPU may be useful for increasing yield of rabbiteye blueberries under conditions of inadequate fruit set (such as occurs in much of the Southeast), but a delay in ripening will likely result. Chemical names used: N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU); gibberellic acid (GA3).

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Donna A. Marshall, James M. Spiers, and Kenneth J. Curry

Marshall, D.A. Spiers, J.M. Braswell, J.H. 2006 Splitting severity among rabbiteye ( Vaccinium ashei Reade) blueberry varieties in Mississippi and Louisiana Intl. J. Fruit Sci. 6 77 81 Marshall, D

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Jose R. Cartagena, Frank B. Matta, and James M. Spiers

The thinning potential of various chemicals sprayed on `Tifblue' rabbiteye blueberry was examined in the greenhouse in 1990 and under field conditions in 1991 and 1992. In the greenhouse, BA concentrations ranging from 25 to 500 mg·liter-1 and carbaryl concentrations ranging from 400 to 2100 mg·liter-1 reduced fruit set when treatments were applied 16 days after corolla drop (ACD). GA3 reduced fruit set only at 50 mg·liter-1 and NAA did not influence fruit set. In the field, BA at 75 mg·liter-1 and the combination of carbaryl at 400 mg·liter-1 and BA at 25 mg·liter-1 reduced fruit set in 1991 and 1992. Combinations of carbaryl and GA3 reduced fruit set, but the response depended on GA3 concentration and varied from year to year. GA3, NAA, and carbaryl also reduced fruit set, but the results were inconsistent. In 1991, greater thinning occurred when the treatments were sprayed 10 days ACD. BA at 25 mg·liter-1 increased fruit diameter at first harvest in 1991, and carbaryl at 400 mg·liter-1 increased fruit diameter in 1991 and 1992. Fruit diameter was increased in the presence and absence of thinning, depending on year and application time. Yield and return bloom were not influenced by any of the treatments. Chemical names used: 7 benzylamino purine (BA); gibberellic acid (GA3); 2-naphaleneacetic acid (NAA); 1-naphthyl N-methylcarbamate (carbaryl).

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James M. Spiers

The effects of varying rates of a complete fertilizer and irrigation on the growth and fruit yields of `Tifblue' rabbiteye blueberries (Vaccinium ashei Reade) established 3 years before treatment initiation were determined in a field study. Increased rates of irrigation resulted in increased plant growth and fruit yields. Five- and 6-year-old plants were more responsive to increasing irrigation rates than older plants. Irrigation water efficacy was greatest at lower rates and progressively less at higher rates of irrigation. Five- and 6-year-old plants fertilized with the lowest rate (14N–4P–7K; 150 g/plant) grew and yielded less than those fertilized with higher rates. Older plants did not respond to fertilization rates higher than 150 g/plant. Yearly rates of fertilization above 300 g/plant did not influence plant growth or fruit yields. Fertilization and irrigation responses were independent.

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D.S. NeSmith and D.C. Bridges

A Weibull distribution function was used to develop a model for estimating cumulative flowering and the distribution of flowering of `Titblue' rabbiteye blueberry (Vaccinium Ashei Reade) as a function of growing degree days (GDD) following exposure to chilling temperatures for 300 to 1200 hours. Controlled chilling and flowering conditions were imposed on blueberry plants to obtain data for model development. Once developed, the model was validated using independent data sets from the literature. Given information concerning chilling and historical GDD, the model can be used to predict the onset of flowering, cumulative flowering, total number of flowers, and flower frequency at discrete intervals. The techniques developed likely will be applicable to a range of fruit species in which chilling influences flowering habit.

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Mark Ehlenfeldt and Lisa Rowland

In recent years, the U.S. Department of Agriculture has generated V. ashei and V. constablaei derivatives to provide late-flowering, earlyripening rabbiteye germplasm for the southern U.S.; however, this germplasm has also performed well in New Jersey, and could potentially provide northern-adapted rabbiteye types. When combined, these germplasms complement each other in many respects. Crosses with varying percentages of V. constablaei germplasm ranging from 100% to 0%, in 25% increments, were evaluated for mid-winter cold-hardiness using a detached twig assay. Hybrids with 50% or more V. constablaei germplasm were hardy to –25° C or lower. Further backcrosses to V. ashei resulted in dramatic segregation for hardiness, but still yielded some progeny as hardy as typical northern highbush. Assays of rabbiteye cultivars have been recently completed to enhance the ability to generate cold-hardy hybrids. Recombination and selection have begun to yield hybrids improved for critical commercial characteristics, and further rapid progress is expected.

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D. Scott NeSmith, Gerard Krewer, and Jeffrey G. Williamson