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  • Author or Editor: Mark Ehlenfeldt x
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Self- and cross-fertility were evaluated in the highbush blueberry (Vaccinium corymbosum L.) cultivars Bluegold, Duke, Legacy, Nelson, Sierra, Sunrise, and Toro, all of which have been released since 1985, by comparing them with `Bluecrop' and `Rubel', which were used as standards. Cross-pollination increased fruit set in all cultivars except `Bluecrop', in which set was reduced 13%. The average increase among recently released cultivars was 43%. Cross-pollination also increased fruit weight for all cultivars except `Rubel'. Average increase in fruit weight with cross-pollination of the recently released cultivars was 27%. Fruit set and fruit weight measurements suggest that `Duke', `Legacy', and `Nelson' would perform satisfactorily in solid stands, and that `Sierra' and `Toro' probably need cross-pollination for maximum yields.

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Self- and cross-fertility was evaluated in the highbush blueberry cultivars Bluegold, Duke, Legacy, Nelson, Sierra, Sunrise, and Toro, all released since 1987, by comparing them to standards of `Bluecrop' and `Rubel'. Percent fruit set increased with cross-pollination in all cultivars except `Bluecrop', which decreased by 13%. The average increase in the recently released cultivars was 43%. Fruit weight also increased in cross-pollinations for all cultivars except `Rubel', which showed a decrease of 2%. Average increase in fruit weight on cross-pollination in the recently released cultivars was 27%. Fruit set and fruit weight measurements suggest that `Duke', `Legacy', and `Nelson' could perform well in solid stands, but `Sierra' and `Toro' are more likely to need cross-pollination for best yields. Investigations were also made on a group of 10 cultivars, to evaluate whether ripening time of the pollen source cultivar had any effect on the ripening time of the fruiting parent. No single pollen source had consistent general effects on ripening, although specific combinations of females and males appeared to either hasten or delay ripening. The largest deviations were seen in delays of ripening, suggesting that poor pollination may have been the greatest factor contributing to the observed variation in ripening times.

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Blueberry cultivars were treated with either soil drenches or foliar applications of paclobutrazol. Soil drenches of 25 mg·L-1 inhibited shoot elongation and stimulated earlier and greater flower bud production on `Bluetta', `Bluecrop', and `Jersey'. The treatments increased bud numbers 359% to 797%, and stimulated compound bud formation, while reducing formation of vegetative buds. This resulted in overcropping and reduced fruit size. Foliar applications at concentrations of 5, 10, 50, and 100 mg·L-1 increased bud set. Treatments did not significantly alter time to 50% flowering in `Bluecrop' or `Duke', but hastened flowering up to 5 days in `Blueray' at 200 ppm. Fruit ripening was significantly delayed at 100 and 200 ppm in `Bluecrop' due to overcropping, but no delays were observed in `Blueray' or `Duke'. Plant size and vigor appeared to be a determining factor in plant response. Chemical name used: PP333 or (2RS,3RS)-l(4-chlorophenyl)-4,4-dimethyl-2-(l,2,4-triazol-1-yl)pentan-3-ol (paclobutrazol).

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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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Inbreeding coefficients were calculated for highbush blueberry (Vaccinium corymbosum L.) cultivars based on a tetrasomic inheritance model. This model yielded lower inbreeding coefficients than previous calculations based on a disomic tetraploid inheritance model. Recent trends in breeding have resulted in significant use of V. darrowi Camp as a source of low-chilling germplasm for use in the southern United States. There is also a trend toward increased inbreeding in several crosses from which recently released cultivars have been derived. Increased inbreeding coefficients do not represent a detrimental situation in blueberry per se.

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Antioxidant capacity as measured by ORAC, total phenolic, and total anthocyanin concentrations were evaluated in leaf tissue of the same 86 highbush blueberry cultivars, and ORAC and phenolic levels evaluated in leaf tissue of the same materials. Average values for ORAC, phenolics, and anthocyanins in fruit were 15.9 ORAC units (1 unit = 1 μmol Trolox Equivalent), 1.79 mg/g (gallic acid equivalents), and 0.95 mg/g (cyanidin-3-glucoside equivalents), respectively. `Rubel' had the highest ORAC values, at 31.1 units. Values for ORAC and phenolics in leaf tissue were significantly higher than fruit tissue, with mean values of 490.4 ORAC units and 44.8 mg/g in leaf tissue, respectively. No significant correlations were found between fruit ORAC and leaf ORAC, or between fruit ORAC and leaf phenolics. Investigation of ORAC values in a family of 44 `Rubel' × `Duke' seedlings showed negative epistatis for ORAC values. However, an analysis of ORAC values vs. pedigree in plants from the 86 cultivar groups suggested that, across cultivars, ORAC inheritance in generally additive.

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Antioxidant capacity as measured by ORAC, total phenolic, and total anthocyanin concentrations were evaluated in fruit tissue of 86 highbush blueberry cultivars, and ORAC and phenolic levels evaluated in leaf tissue of the same materials. Average values for ORAC, phenolics, and anthocyanins in fruit were 15.9 ORAC units (1 unit = 1 micromole Trolox Equivalent), 1.79 mg·g–1 (gallic acid equivalents), and 0.95 mg·g–1 (cyanidin-3-glucoside equivalents), respectively. ëRubel' had the highest ORAC values, at 31.1 units. Values for ORAC and phenolics in leaf tissue were significantly higher than fruit tissue, with mean values of 490.4 ORAC units and 44.8 mg·g–1 in leaf tissue, respectively. No significant correlations were found between fruit ORAC and leaf ORAC, or between fruit ORAC and leaf phenolics. Investigation of ORAC values in a family of 44 `Rubel' × `Duke' seedlings showed negative epistasis for ORAC values. However, an analysis of ORAC values vs. pedigree in plants from the 86 cultivar groups suggested that across cultivars, ORAC inheritance is generally additive.

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