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Mark K. Ehlenfeldt and Bryan T. Vinyard

A study was conducted to determine if early-fall pruning (vs. more typical winter pruning) of either northern highbush or southern highbush blueberries was detrimental to the development of optimum levels of mid-winter cold hardiness in floral buds under New Jersey conditions. Using a detached-shoot freeze-thaw assay, flower-bud LT50 values were determined in early January for both ‘Jersey’ (northern highbush) and ‘Legacy’ (southern highbush) blueberry bushes that had been subjected to early- or late-pruning protocols. Across 2 years, intrinsic differences due to genotype and genotype × year were present, but no significant differences due to pruning time were observed. The lack of pruning effects on flower-bud LT50 values suggests that cultivars with southern germplasm selected in areas such as North Carolina and further north may be treated similarly to northern highbush with respect to pruning time, including early-fall pruning.

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Kathleen G. Haynes, Beverly A. Clevidence, David Rao and Bryan T. Vinyard

Carotenoids have a wide range of human health benefits. Yellow-fleshed tetraploid potato (Solanum tuberosum) cultivars have more than twice the concentration of carotenoids as white-fleshed cultivars. However, carotenoid concentrations in some diploid potatoes have been reported to be up to 13 times higher than in ‘Yukon Gold’, the most popular yellow-fleshed potato cultivar grown in the United States, and up to 22 times higher than in white-fleshed potatoes. The purpose of this study was to determine the feasibility of using these high-carotenoid diploids to develop high-carotenoid tetraploid germplasm. Three diploid clones with high (dark yellow-flesh), moderate (moderate yellow-flesh), and low (white–cream-flesh) carotenoid levels that produced 2n pollen were crossed with a light yellow-fleshed tetraploid advanced breeding selection to determine the inheritance of carotenoid content. Twenty-six to 43 progeny from these three 4x-2x families were grown in a replicated field experiment in Presque Isle, ME, for 2 years. After harvest, carotenoids were extracted and quantified by high-performance liquid chromatography in 13 to 14 randomly selected clones from each family; however, flesh color was scored as white or yellow in all progeny. A continuous distribution of carotenoid concentration with high- and low-carotenoid segregants was observed in all three families. There were no significant differences among these three families for individual or total carotenoid concentrations; however, there were significant differences among clones within families. Broad-sense heritability estimates were high for total carotenoid (0.81), lutein (0.77), zeaxanthin (0.73), and the lycopene beta-cyclase pathway carotenoids (0.73); moderate for neoxanthin (0.42); and low for violaxanthin (0.21) and antheraxanthin (0.13). Based on flesh color segregation, the two yellow-fleshed diploid parents were heterozygous for the Chy2 allele governing yellow-flesh and produced 2n gametes by a second division restitution mechanism. It appears that selection for high-carotenoid tetraploid germplasm can be made from within any family with at least one yellow-fleshed parent. Selections will have to be made on an individual clonal basis rather than on a family basis.

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

Cold injury to plants can occur by early fall freezes before cold acclimation, by severe midwinter freezes that exceed the limits of the plant's tolerance, or by hard freezes in late winter or early spring after partial or complete deacclimation. Ideally, blueberry (Vaccinium L.) cultivars for temperate regions should acclimate to cold quickly in the fall, have a high midwinter-hardiness, and deacclimate late and/or slowly during spring or during unseasonably warm spells in winter, and do all of this without adversely delaying time of fruiting. Until recently, only limited evaluations have been done on the acclimation and deacclimation process in blueberry, although it is an integral part of flower bud survival and, thus, is directly related to potential yield. In this study, we have measured the timing and rate of acclimation and deacclimation in seven blueberry genotypes with different amounts of diverse species germplasm in their backgrounds. Primary differences observed among the seven genotypes were differences in maximum hardiness levels and the date at which they were reached, and differences in the date at which maximum acclimation levels were no longer sustained and deacclimation started. Highbush cultivars Bluecrop and Legacy (V. corymbosum L.), rabbiteye cultivar Tifblue [V. ashei Reade (= V. virgatum Aiton)], and two rabbiteye hybrid derivatives (US 1043 and US 1056) all reached maximum or near maximum cold-hardiness by late December with temperatures causing 50% lethality (LT50) in a range from –22 to –27 °C. The half-high, ‘Northsky’, and a hybrid of V. constablaei Gray × V. ashei ‘Little Giant’ both achieved cold acclimation of –28 °C or below (the lowest value we could measure) by the end of November. After reaching their maximum hardiness in late December, ‘Legacy’, ‘Tifblue’, and US 1043 began a sustained and relatively linear deacclimation, whereas US 1056, ‘Bluecrop’, ‘Northsky’, and ‘Little Giant’ sustained their acclimation for longer intervals. ‘Bluecrop’ and US 1056 did not begin to deacclimate until early March, and ‘Little Giant’ and ‘Northsky’ had no LT50 values higher (warmer) than –25 °C until late March. As concerns about climate change increase, knowledge of the ability of breeding germplasm to tolerate greater temperature extremes and fluctuations will prove increasingly valuable.

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Kathleen G. Haynes, Beverly A. Clevidence, David Rao, Bryan T. Vinyard and J. Marion White

Consumption of carotenoid-containing foods can promote human health. Although yellow-fleshed potatoes (Solanum tuberosum) have a higher carotenoid content than white-fleshed potatoes, little is known about how growing environments may affect individual and total carotenoid content in different potato clones. The purposes of this study were to estimate the amount of genetic variability in potato for five xanthophyll carotenoids, their concentration, and to determine the stability of these carotenoids across environments. Nine white- or yellow-fleshed tetraploid clones were grown in Maine and Florida for 2 years. Carotenoids were extracted in acetone and analyzed by high-performance liquid chromatography. There were significant differences among clones for zeaxanthin, antheraxanthin, lutein, and total carotenoid content. There were significant clone × environment interactions for zeaxanthin, antheraxanthin, violaxanthin, neoxanthin, lutein, and total carotenoid. Broad-sense heritabilities (and their 95% confidence intervals) were 0.89 (0.79–0.98) for zeaxanthin, 0.93 (0.87–0.99) for antheraxanthin, 0.68 (0.14–0.92) for violaxanthin, 0.51 (0.00–0.88) for neoxanthin, 0.85 (0.70–0.97) for lutein, and 0.96 (0.89–0.99) for total carotenoid. Clonal mean total carotenoid content ranged from 101 to 511 μg/100 g fresh weight. A higher proportion of carotenoids were produced by the lycopene epsilon cyclase branch of the carotenoid biosynthetic pathway in white-fleshed than yellow-fleshed clones. Total carotenoid content in B2333-5 was significantly greater than in ‘Yukon Gold’. With genetic variation for individual and total carotenoid content in potatoes, improving the levels of carotenoids has been and should continue to be feasible; however, concentrations are likely to vary in different environments.

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

Deacclimation response is an important part of reproductive success in woody perennials because late winter or early spring thaws followed by hard freezes can cause severe injury to dehardened flower buds. There is a need to develop more spring-frost tolerant cultivars for the blueberry (Vaccinium L.) industry. The identification of later or slower deacclimating genotypes could be useful in breeding for more spring-frost tolerant cultivars. This study was undertaken to investigate cold hardiness and deacclimation kinetics under field conditions for 12 Vaccinium (section Cyanococcus A. Gray) genotypes (the cultivars Bluecrop, Duke, Legacy, Little Giant, Magnolia, Northcountry, Northsky, Ozarkblue, Pearl River, Tifblue, and Weymouth; and a population of V. constablaei Gray) with different germplasm compositions and expected mid-winter bud hardiness levels. Examination of bud cold hardiness (BCH) vs. weeks of deacclimation over a 7-week period in 2 consecutive years (2002 and 2003) revealed clear genotypic differences in cold hardiness and timing and rate of deacclimation. Among cultivars, `Legacy' was the least cold hardy at initial evaluation, even less so than `Tifblue'. Regarding deacclimation kinetics, the weekly intervals with the largest losses (i.e., high rates of deacclimation) also varied among genotypes. For `Duke', the largest losses in BCH were detected at weeks 2 and 3, making it the earliest deacclimator. For `Bluecrop', `Ozarkblue', `Weymouth', `Tifblue', and `Legacy', the greatest losses in BCH were observed at weeks 3 and 4. For `Little Giant', `Magnolia', `Northcountry', `Northsky', and `Pearl River', losses in BCH were greatest at weeks 4 and 5, while for V. constablaei, losses were greatest at weeks 6 and 7, making it the latest deacclimator. Deacclimation kinetics were not correlated with mid-winter hardiness or chilling requirements in any fixed pattern. On the other hand, a strong positive correlation was found between BCH and stage of bud opening (r = 0.84). A comparison of timing of deacclimation with germplasm composition indicated that V. constablaei was particularly late to deacclimate. `Little Giant', a 50:50 hybrid of V. constablaei and V. ashei Reade, was nearly as late to deacclimate as the 100% V. constablaei selections. Thus, V. constablaei may be useful in breeding programs to contribute genes for late deacclimation, which should translate into greater spring frost tolerance, in addition to genes for mid-winter hardiness.

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Susan L.F. Meyer, Dilip K. Lakshman, Inga A. Zasada, Bryan T. Vinyard and David J. Chitwood

Clove oil derived from the clove plant [Syzygium aromaticum (=Eugenia caryophyllata)] is active against various soil-borne plant pathogens and therefore has potential for use as a bio-based pesticide. A clove oil formulation previously found to be toxic to the southern root-knot nematode (Meloidogyne incognita) in laboratory assays was investigated in greenhouse studies for nematode suppression and phytotoxicity on vegetable crops. Phytotoxicity studies were conducted with 0.1%, 0.2%, and 0.3% clove oil applied to soil 0, 2, 5, and 7 days before transplant of cucumber (Cucumis sativus), muskmelon (Cucumis melo), pepper (Capsicum annuum), and tomato (Solanum lycopersicum) seedlings. Tomato seedlings were the most sensitive to clove oil. The 0.2% and 0.3% clove oil concentrations applied as drenches at transplant (0 day) were the most phytotoxic to seedlings of all the tested vegetable species, with only 0% to 50% seedling survival. Most of the clove oil concentrations applied as drenches at transplant decreased shoot heights and fresh shoot weights of all seedlings. Some applications of clove oil at 0.2% and 0.3%, applied 2, 5, or 7 days before transplant also significantly reduced shoot growth, especially of pepper and tomato. Greenhouse experiments evaluating suppression of nematode populations on cucumber were conducted with 0.10%, 0.15%, and 0.20% clove oil applied 7 days before transplant. Overall, plants inoculated with nematodes tended to have smaller shoots and heavier roots than plants without nematodes. Effects of clove oil treatments on nematode population densities were inconsistent between the two trials. In Trial 1, 0.10% and 0.15% clove oil decreased population densities compared with the carrier control. In Trial 2, nematode population densities were lowest in the water and carrier control treatments. The results indicate that, with the tested clove oil formulation and application times, southern root-knot nematode populations would not be consistently reduced with clove oil concentrations that were not phytotoxic to one or more of the tested vegetable crops.

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

From 2004 to 2006, cold hardiness assays were performed to evaluate the relative winterhardiness of flower buds in selections of pure Vaccinium ashei Reade and V. constablaei Gray as well as in selections/families composed of various combinations of V. ashei and V. constablaei germplasm. Significant differences were observed among entries with LT50 values ranging from −17.2 to −28.4 °C. An analysis of LT50 versus percent V. constablaei yielded a regression of LT50 (°C) = (−0.08 × V. constablaei percentage) – 21.57. Families or selections with 50% (or greater) V. constablaei and some with 25% V. constablaei had LT50 values equivalent to or better than ‘Bluecrop’. Based on this information, a 25% V. constablaei constitution appears suitable to develop northern-adapted rabbiteye types if proper parents are selected and if sufficient selection pressure for winterhardiness is exercised.

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

The midwinter cold hardiness of 25 rabbiteye (V. ashei) blueberry cultivars was assayed across 2 years using a shoot freezing assay. LT50values (i.e. temperature at which 50% of buds are damaged) for the cultivars ranged from –24.9 °C for `Pearl River' (a 50% V. ashei derivative) to –13.7 °C for `Chaucer'. Under New Jersey conditions, numerous cultivars were observed to exhibit dimorphism for dormant floral bud size. Comparisons of bud dimorphism with LT50 values, found dimorphism more common in cultivars with lower floral bud hardiness. LT50 values generally supported empirical observations of winter hardiness, but exceptions suggest that additional factors contribute to observed winter hardiness under field conditions.

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Robert A. Saftner, Judith A. Abbott, William S. Conway, Cynthia L. Barden and Bryan T. Vinyard

Fruit quality, sensory characteristics, and volatiles produced by 'Gala' apples (Malus ×domestica Borkh.) were characterized following regular atmosphere (RA) storage without and with a prestorage heat treatment (38 °C for 4 days) or controlled atmosphere (CA) storage at 0 and 2 °C for 0 to 6 months plus 7-day shelf life at 20 °C. Static CA conditions were 0.7 kPa O2 plus 1.0 kPa CO2, 1.0 kPa O2 plus 1.0 kPa CO2, and 1.5 kPa O2 plus 2.5 kPa CO2. Most of the more abundant volatiles were esters; the rest were alcohols, an aldehyde, a ketone, and an aryl ether. Respiration and ethylene production rates, internal atmospheres of CO2 and ethylene, and volatile levels were reduced following CA storage compared with RA storage without and with a prestorage heat treatment. Magness-Taylor and compression firmness, titratable acidity, and sensory scores for firmness, sourness, apple-fruity flavor, and overall acceptability were higher for CA-than for RA-stored fruit. Soluble solids content and sensory scores for sweetness were similar among all treatments. Quality and sensory characteristics were generally similar in heated and nonheated RA-stored fruit, and between 0 and 2 °C in CA- and RA-stored fruit. While one CA regime had a higher CO2 concentration than the others tested, CA effects on quality and sensory characteristics were generally more pronounced at the lower O2 levels. Quality characteristics declined between 2 and 4 months storage. The results indicate that short-term CA storage can maintain instrumental and sensory quality of 'Gala' apples.

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Rajeev Arora, Lisa J. Rowland, Elizabeth L. Ogden, Anik L. Dhanaraj, Calin O. Marian, Mark K. Ehlenfeldt and Bryan Vinyard

Loss of freeze tolerance, or deacclimation, is an integral part of winter survival in woody perennials because untimely mid-winter or spring thaws followed by a hard freeze can cause severe injury to dehardened tissues. This study was undertaken to investigate deacclimation kinetics, particularly the timing and speed, of five blueberry (Vaccinium L.) cultivars (`Bluecrop', `Weymouth', `Ozarkblue', `Tifblue', and `Legacy'), with different germplasm compositions and mid-winter bud hardiness levels, in response to an environmentally controlled temperature regime. Based upon bud cold hardiness evaluations in 2000 and 2001, `Tifblue', a Vaccinium ashei Reade cultivar, was one of the least hardy and the fastest to deacclimate; `Bluecrop', a predominantly V. corymbosum L. cultivar, was the most hardy and the slowest to deacclimate; and `Ozarkblue', a predominantly V. corymbosum cultivar but including southern species V. darrowi Camp. and V. ashei, was intermediate in speed of deacclimation. `Weymouth' (predominantly V. corymbosum) and `Legacy' (73.4% V. corymbosum and 25% V. darrowi) were slow to intermediate deacclimators. Deacclimation rates did not correlate strictly with mid-winter bud hardiness. Data suggest that the southern germplasm component V. ashei may be responsible for the observed faster deacclimation whereas both southern species, V. darrowi and V. ashei, may contribute genes for cold sensitivity. Strong positive correlations between stage of bud opening and bud cold hardiness existed in both years (r = 0.90 and 0.82 in 2000 and 2001 study, respectively). Previously identified major blueberry dehydrins, 65-, 60-, and 14-kDa, progressively decreased in their abundance during incremental dehardening in `Bluecrop', `Weymouth', and `Tifblue'. However, down-regulation of the 14-kDa dehydrin most closely mirrored the loss in cold hardiness during deacclimation, and, therefore, may be involved in regulation of bud dehardening. Because differences in deacclimation rate were clearly evident among the genotypes studied, rate of deacclimation of the flower buds of blueberry should be an important consideration in breeding to improve winter survival.