The southern highbush blueberry (Vaccinium, mostly corymbosum) cultivars Jubilee, Pearl River, and Magnolia and the rabbiteye cultivars Climax and Premier were stored for 4 weeks at 1-2 °C. Berries were held in pint “clam shell” plastic retail units and were evaluated weekly for physical and compositional quality. As groups, the rabbiteyes were higher in SSC, SSC/TA, glucose and fructose, anthocyanins, and malic, quinic, and succinic acids. `Jubilee' was the southern highbush and `Climax' the rabbiteye least affected by the storage. `Pearl River' and `Magnolia' were less firm and more shriveled than the other cultivars. `Magnolia' had the highest incidence of decay; decay was slight overall.
Shoot growth of six blight-resistant highbush blueberry (Vaccinium corymbosum L.) cultivars and of one susceptible cultivar was manipulated during the primary infection period of mummy berry disease to determine if some portion of the observed resistance was based on disease avoidance. In experiments across 2 years, resistant cultivars either increased continually in susceptibility or exhibited a peak and then decreased in susceptibility as shoots elongated. In a larger experiment that included both susceptible and resistant cultivars, peaks of susceptibility were identified for `Bluejay', `Darrow', and `Jersey'. In contrast, general decreases in susceptibility were identified for `Duke', `Blueray', and `Croatan' as shoots elongated. Shoot lengths associated with peak susceptibility varied among and within cultivars across experiments. The increases in susceptibility observed at longer shoot lengths were generally small. This finding suggests that cultivars identified as resistant have intrinsic levels of resistance, but maturity and general condition of the plant tissue can also affect disease levels.
Abstract
The highbush blueberry cultivars, ߢRancocasߣ and ߢEarliblueߣ, failed to acclimate in time to avoid low temp injury to stems exposed above the snow level during the 1st year seasonal change in hardiness was studied. In the 2nd year, however, they hardened to temp as low as -40°C and survived the winter. Acclimation occurred earlier in a native selection of Vaccinium angustifolium Aiton and in ߢRancocasߣ. Selections of V. angustifolium and natural hybrids of V. angustifolium and V. cormybosum L. were found to be hardier than any of the highbush cultivars. A selection of V. constablaei Gray and V. membranaceum Douglas, respectively, were also hardier than the highbush types. A low temp exotherm was found to be present in blueberry stems, but it was associated only with xylem injury which was not as critical for survival as the bark tissues. The bark was injured at temp higher than the xylem and was not associated with any exotherm.
Many growers in the Pacific Northwest are planting blueberry fields at higher densities to improve yields and increase the number of berries harvested per acre in the first few years after planting. The objective of this study was to determine the effect of high-density planting on blueberry water requirements. Although close spacing reduces individual plant size, we expected that plants spaced closer together would require more irrigation per unit land area than those spaced further apart due to increased canopy coverage within rows. The study utilized a 5-year-old planting of highbush blueberry, consisting of three cultivars, `Duke', `Bluecrop', and `Elliott', planted at 0.5- and 1.2-m in-row spacings. Plant water use was calculated from changes in soil water content measured using TDR probes for shallow depths and a neutron probe and access tubes for deeper depths. Stem water potentials were also measured periodically using a pressure chamber to determine how well irrigation was meeting crop water demands throughout the season. Surprisingly, plants spaced 0.5 m apart required only slightly more water than those spaced 1.2 m apart. They did, however, require more frequent irrigations due to their smaller root systems, especially during fruit filling. Water use by each cultivar increased during fruit filling and then rapidly decreased after harvest. `Duke' required the most water among cultivars, using 5–10 mm/day from mid-May to mid-August, while `Elliott' required the least, using 3–5 mm/day.
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.
Dietary antioxidants may have a role in preventing some of the chronic diseases in humans resulting from free radical oxidation of lipids and other cellular components. Blueberries (Vaccinium L. sp.) are considered one of the best fresh fruit sources of antioxidants, and there is the potential to increase the antioxidant activity further through breeding. Thus, the variability of fruit antioxidant activity (AA) was examined among a set of 16 highbush and interspecific hybrid cultivars grown at locations in Minnesota (MN), Michigan (MI), and Oregon (OR) over 2 years (1998 and 1999) to determine effects of genotype, year, and location. Nine cultivars were common to all three locations in both years. Antioxidant activity, total phenolic content (TPH), and total anthocyanin content (ACY), were determined in triplicate samples from each genotype. Cultivars differed significantly (P ≤ 0.05) in AA, TPH, and ACY both within and over locations. The single location mean AA for all cultivars changed significantly between the 2 years in OR and in MI, while the single location mean for TPH differed between the 2 years in MN and MI. Changes in cultivar rank were significant for AA, TPH, and ACY between years within each location. Significant changes in rank for TPH and ACY were also noted between pairs of locations as well. Pearson's correlation for AA (based on cultivar means) appeared highest between MN and OR (r = 0.90) and MN and MI (r = 0.69) in 1998; correlations between locations for the combined years were 0.74 for MN and OR, 0.55 for MN and MI and 0.45 for MI and OR. For the group of nine cultivars, AA correlated well with TPH within each location, with r ranging from 0.67 to 0.95 for data from individual and combined years. Correlation of AA with ACY at each location was lower than that for AA with TPH, in both individual and combined years. This study demonstrates significant genotype× environment interaction for AA in blueberry.
Yield data from a highbush blueberry planting established in 1993 at the Univ. of Kentucky Research and Education Center, Princeton, Ky., was collected over a 5-year period for eight cultivars. The economic impact of yield of each cultivar was calculated for each cultivar using a net present value model based on prevailing market prices and costs of production. These returns were compared across cultivars and an assessment of the economic potential for Kentucky growing conditions was considered. `Duke' and `Sierra' produced the most fruit over the 5-year period of this study. `Duke' was also the earliest ripening cultivar in the planting, with 14.3% of `Duke's fruit ripening during the first week of June. Sunrise also ripened early, with 7.7% of its fruit ripening during the first week of June. Picking for the other cultivars (`Sierra', `Bluecrop', `Blue Gold', `Toro', `Nelson', and `Patriot'), began during the second week of June and was finished for all cultivars by the end of the fourth week of June. An exception was `Nelson', which was picked through the first week of July. Despite relatively low yields observed in the first year of production, `Duke' had the highest net present values for the assumed 12-year life of the planting. The ranking of the other seven cultivars from highest to lowest in terms of their respective net present values was: `Sierra', `Blue Gold', `Bluecrop', `Toro', `Nelson', `Sunrise', and `Patriot'.
Sixty-eight highbush blueberry (Vaccinium corymbosum L.) cultivars and selections were evaluated over 3 years for their resistance to the fruit infection phase of mummy berry disease [Monilinia vaccinii-corymbosi (Reade) Honey]. Average incidence of fruit infection under test conditions was 34.3% in 1995, 14.4% in 1996, and 27.9% in 1997, with significant differences occurring among clones in all 3 test years. Several cultivars exhibited consistent resistance to mummy berry fruit infection across all years of testing. `Northsky', `Reka', `Northblue', `Cape Fear', `Bluegold', `Puru', and `Bluejay' were among the most resistant, and `Atlantic', `Berkeley', `Herbert', and `E-176' were among the most susceptible. The consistent resistant reaction of certain cultivars indicates that they may be suitable as parents for introducing resistance into a breeding program. No significant correlation was observed between blighting resistance and fruit infection resistance.
Abstract
Symptom development in resistant and susceptible blueberry cultivars was studied following inoculation with zoospores of Phytophthora cinnamomi Rands. Three rabbiteye (Vaccinium ashei Reade ‘Tifblue’, ‘Woodard’, and ‘Bluegem’), two highbush (V. corymbosum L. ‘Bluetta’ and ‘Patriot’), and one interspecific tetraploid hybrid (US 109) genotypes were grown hydroponically and permitted to develop healthy root systems prior to immersing the roots in a zoospore suspension for 10 hr. P. cinnamomi infected the roots of all cultivars tested. During a 6-week test, root symptom development progressed steadily in ‘Bluetta’ and ‘Patriot’, but leveled off in the other cultivars. ‘Bluetta’ was rated the most susceptible, ‘Patriot’ was intermediate in susceptibility, and US 109, ‘Tifblue’, ‘Woodard’, and ‘Bluegem’ showed increased resistance. The greatest tolerance was exhibited by US 109.
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.