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James M. Spiers

A greenhouse study was conducted to evaluate the influence of substrate temperatures (16, 27, and 38C) on root and shoot growth of six blueberry (Vaccinium spp.) clones (three clones each of two types). Between types, southern highbush (primarily V. corymbosum L.) produced more roots and total growth than rabbiteye (V. ashei Reade). Comparing clones, `Gulfcoast' (southern highbush) was the most vigorous and `Tifblue' (rabbiteye) the least vigorous. Each clone had a negative linear response to substrate temperatures in all growth characteristics. Root and shoot growth was best at 16C. This study indicates that both rabbiteye and southern highbush blueberries would respond favorably to cultural practices that lower soil temperatures during the summer growing season.

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Ann Marie Connor, James J. Luby, and Cindy B.S. Tong

Variation in antioxidant activity (AA), total phenolic content (TPH), and total anthocyanin content (ACY) was examined in 1998 and 1999 in fruit of 52 (49 blue-fruited and 3 pink-fruited) genotypes from a blueberry breeding population. The species ancestry included Vaccinium corymbosum L. (northern highbush blueberry), V. angustifolium Ait. (lowbush blueberry), V. constablaei Gray (mountain highbush blueberry), V. ashei Reade (rabbiteye blueberry), and V. myrtilloides Michx. (lowbush blueberry). Using a methyl linoleate oxidation assay (MeLO) on acidified methanolic extracts of the berries, a 5-fold variation was found in AA in 1998 and a 3-fold variation in 1999 among the blue-fruited genotypes. Analyses of variance (ANOVA) revealed variation among genotypes (P < 0.0001) in single and combined years, regardless of inclusion of pink-fruited selections and adjustment for berry size. While mean AA of all genotypes did not change between the 2 years, ranking of some genotypes for AA changed significantly between 1998 and 1999. Of the 10 genotypes that demonstrated the highest AA in 1998, four were among the 10 genotypes that demonstrated highest AA in 1999. Similarly, of the 15 genotypes with the highest AA, 10 were the same both years. As with AA, mean TPH of all genotypes did not change between years and ANOVA demonstrated genotypic variation regardless of adjustment for berry size/weight or exclusion of pink-fruited selections. Changes in genotype rank occurred between years. The difference in TPH between lowest- and highest-ranking blue-fruited genotypes was ≈2.6-fold in both 1998 and 1999. Seven of the 10 highest-ranking genotypes were the same both years and TPH correlated with AA (r = 0.92, P < 0.01) on a genotype mean basis for combined years. ACY correlated less well with AA (r = 0.73, P < 0.01 for combined years). When genotypes were categorized into six groups according to species ancestry, V. myrtilloides and V. constablaei × V. ashei crosses ranked highest and second highest, respectively, for AA in both years. The groups comprised of V. corymbosum genotypes, V. angustifolium genotypes, and those with both V. corymbosum and V. angustifolium in their lineage were indistinguishable from each other. Samples from some of the genotypes were analyzed for oxygen radical absorbance capacity and ferric-reducing antioxidant power, and these aqueous-based antioxidant assays correlated well with the lipid emulsion-based MeLO (all r ≥ 0.90, P < 0.01). The three antioxidant assays may be equally useful for screening in a blueberry breeding program and the choice of assay may depend on the goal of the program and the resources available.

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Peter Boches, Lisa J. Rowland, Kim Hummer, and Nahla V. Bassil

Microsatellite markers for blueberry (Vaccinium L.) were created from a preexisting blueberry expressed sequence tag (EST) library of 1305 sequences and a microsatellite-enriched genomic library of 136 clones.

Microsatellite primers for 65 EST-containing simple sequence repeats (SSRs) and 29 genomic SSR were initially tested for amplification and polymorphism on agarose gels. Potential usefulness of these SSRs for estimating species relationships in the genus was assessed through cross-species transference of 45 SSR loci and cluster analysis using genetic distance values from five highly polymorphic EST-SSR loci. Cross-species amplification for 45 SSR loci ranged from 17% to 100%, and was 83% on average in nine sections. Cluster analysis of 59 Vaccinium species based on genetic distance measures obtained from 5 EST-SSR loci supported the concept of V. elliotii Chapm. as a genetically distinct diploid highbush species and indicated that V. ashei Reade is of hybrid origin. Twenty EST-SSR and 10 genomic microsatellite loci were used to determine genetic diversity in 72 tetraploid V. corymbosum L. accessions consisting mostly of common cultivars. Unique fingerprints were obtained for all accessions analyzed. Genetic relationships, based on microsatellites, corresponded well with known pedigree information. Most modern cultivars clustered closely together, but southern highbush and northern highbush cultivars were sufficiently differentiated to form distinct clusters. Future use of microsatellites in Vaccinium will help resolve species relationships in the genus, estimate genetic diversity in the National Clonal Germplasm Repository (NCGR) collection, and confirm the identity of clonal germplasm accessions.

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James R. Ballington

Own-rooted `Premier' blueberry (V. ashei Reade) was compared to `Premier' grafted on V. arboreum Marsh. (sparkleberry) for yield and fruit characteristics in a five-rep RCB design with three plants/rep. With grafted plants, three reps were on rootstock #17 and two on rootstock #10, and results were combined for statistical analyses. Production of suckers by rootstocks was also recorded. Plants wereestablished on an upland doughty mineral Fuquay soil, modified with sawdust, at Jackson Springs, N.C. Supplemental irrigation was applied only in the establishment year and the following year, and landscape fabric was installed in the rows for weed control also in the year following establishment. `Premier' grafted on V. arboreum yielded significantly higher than own-rooted `Premier' in all three harvest seasons. Fruit size on grafted plants was also significantly larger than on own-rooted plants in harvest years 2 and 3. There were no differences in fruit color, picking scar, firmness, or flavor in years 2 and 3, and only small differences in harvest year 1. The data for years 2 and 3 indicated that there were differences among stocks in yield; however, both graft combinations were higher-yielding than own-rooted plants. There were also differences among stock clones for the number of suckers produced in harvest years 2 and 3. The highest-yielding graft combination also had the lowest number of rootstock suckers.

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R.L. Darnell, R. Cano-Medrano, and K.E. Koch

Variability in sucrose levels and metabolism in ripe fruit of several Vaccinium species were examined. The objective was to determine if sufficient variability for fruit sucrose accumulation was present in existing populations to warrant attempts to breed for high-sucrose fruit, which potentially would be less subject to bird predation. Three-fold differences in fruit sucrose concentration were found among species, ranging from 19 to 24 mg·(g fw)-1 in V. stamineum and V. arboreum to about 7 mg·(g fw)-1 in cultivated blueberry (V. ashei and V. corymbosum) and V. darrowi. Soluble acid invertase activity was negatively correlated with fruit sucrose concentration. There was no apparent correlation between fruit sugar concentration and either sucrose phosphate synthase or sucrose synthase activities, both of which were low for all species studied. The degree of variability in fruit sucrose accumulation among Vaccinium species supports the feasibility of developing high sucrose fruit, which would be a potentially valuable addition to current strategies of minimizing crop losses to birds.

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W.R. Miller, R.E. McDonald, and T.E. Cracker

Blueberry cultivars Sharpblue (mainly Vaccinium corymbosum L.) and Climax (V. ashei L.) were band-harvested on three occasions and manually packaged into 0.275 liter fiber-pulp cups or automatically packaged in vented polystyrene cups. Berries were evaluated after 1,2, or 3 weeks of storage at 1C and after 2 additional days of storage at 16C, a time frame that simulated a merchandising period. Weight loss of fruit packaged in polystyrene cups was <1% during 3 weeks of storage at 1C, whereas weight loss of berries packaged in fiber-pulp cups was ≈5.0% after similar storage. `Sharpblue' berries were softer at harvest and after each storage duration than `Climax' berries. Decay increased to ≈7% for `Climax' and 28% for `Sharpblue' after 3 weeks of storage at 1C. Package type did not affect decay incidence after 3 weeks of storage; but after 2 additional days at 16C, decay incidence was slightly higher for berries packaged in polystyrene compared with those packaged in fiber-pulp cups. `Sharpblue' should be packaged only in fiber-pulp cups and marketed quickly after harvest to avoid excessive decay.

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John R. Clark and Robert Robbins

Two replicated blueberry plantings, one containing one highbush, (Vaccinium corymbosum) two southern highbush and two rabbiteye (V.ashei) cultivars, and another containing one highbush and three rabbiteye cultivars were sampled in October, 1991 and plant parasitic nematodes extracted and counted. Additionally, 15 commercial rabbiteye plantings were sampled. Standard and southern highbush samples had total plant parasitic nematode levels of 228-451 nematodes/250 ml soil compared to 4-14 nematodes/250 ml soil for rabbiteye. No difference in nematode population was found among the standard highbush ('Bluecrop') and southern highbush ('Cooper', 'Gulfcoast') cultivars. Xiphinema americanum was the most common nematode species found, along with very small populations of Paratrichodorus minor. All commercial plantings had lower nematode levels in samples from the blueberry plants as compared to those from the sod middles between the rows. Nematode levels from commercial plantings ranged from 1477/250ml soil from blueberry plants and 11-1546/250 ml soil from the sod middles. Species found at high levels in the sod samples were usually distinctly different from those found associated with the blueberry plants.

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Paul M. Lyrene

Vigorous, upright shoots on mature V. ashei Reade cv. Aliceblue plants growing in a commercial field planting were used to study the effects of premature defoliation on flower bud formation. Three treatments (total shoot defoliation, alternate-node defoliation, and no defoliation) were applied on each of three dates (20 Aug., 17 Sept., and 15 Oct. 1987). For the August defoliation, the number of flower buds present per shoot on 6 Jan. of the following year averaged 1.3 for shoots that were totally defoliated, 3.7 for shoots on which alternate nodes had been defoliated, and 4.2 for control (nondefoliated) shoots. Shoots treated on 17 Sept. averaged 2.6 buds per shoot for total defoliation, 4.1 for alternate-node defoliation, and 4.8 for controls. Defoliation on 15 Oct. did not reduce flower bud formation. Reduction in flower bud formation due to defoliation was localized at the defoliated nodes. For shoots on which alternate nodes were defoliated on 20 Aug., 59.8% of the apical five nodes that were not defoliated produced flower buds compared with 1.4% of the defoliated nodes.

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Mark K. Ehlenfeldt, Filmore I. Meredith, and James R. Ballington

The fruit of six highbush (Vaccinium corymbosum L.) cultivars and eight rabbiteye (V. ashei Reade) cultivars and selections were evaluated by high-performance liquid chromatography for levels of the commonly found organic acids, citric, malic, succinic, and quinic. The two cultivar groups possessed distinctive patterns of relative organic acid proportions that could unambiguously separate pure rabbiteye and highbush clones in a principal component analysis. Highbush clones were characterized by high citric acid content, with percentages averaging 75% (range 38% to 90%). Succinic acid was the second most plentiful acid, averaging 17%. In contrast, rabbiteye cultivars and selections contained 10% citric acid, and no clone had >22%. Succinic acid and malic acid were found in greater quantities than in highbush, averaging 50% and 34%, respectively. Analysis of the fruit of seven albino-fruited highbush selections exhibited a profile similar to standard highbush cultivars, but with a citric acid average of <50%, and proportionally greater amounts of succinic and quinic acids. Given the differences in sensory quality of these four acids, it is likely that acid partitioning patterns can largely account for some of the perceived flavor differences between rabbiteye and highbush blueberries. Because several current breeding efforts involve hybridization between highbush and rabbiteye blueberries, a consideration of acid composition of breeding parents maybe worthwhile.

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John R. Clark and Robert Bourne

The southern highbush blueberry (Vaccinium spp.) `Blueridge', `Cape Fear', `Cooper', `Georgiagem', `Gulf Coast', and `O'Neal'; the rabbiteye (V. ashei Reade) `Climax'; and the highbush (V. corymbosum L.) `Bluecrop' were evaluated for ovary damage following exposure of flower buds to 0 to 30C in a programmable freezer in Dec. 1993 and Jan. and Feb. 1994. The plants sampled were growing at the Univ. of Arkansas Fruit Substation, Clarksville. Damage was based on oxidative browning of the ovaries following an incubation period after removal from the freezer. With the exception of `Climax', a minimum temperature of –15C was required before bud damage was sufficient enough to differentiate among cultivars. All southern highbush cultivars and `Bluecrop' had superior hardiness compared to `Climax' at –15C in December, –20C in January, and –15C in February. Maximum hardiness of all cultivars was found in January. The hardier southern highbush cultivars were `Cape Fear' and `Blue Ridge'. Less hardy cultivars were `Gulf Coast, `Cooper', `Georgiagem', and `O'Neal', although the date of sampling affected the ranking of these clones for hardiness, especially for the February sample date. `Bluecrop' was not consistently hardier than the hardier southern highbush cultivars, except at the February sample date.