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C.E. Finn, J.F. Hancock, T. Mackey and S. Serçe

Twenty blueberry (Vaccinium sp. L.) families were planted in Michigan and Oregon to determine variability among families, locations and the importance of family×location interaction. The families were generated at Michigan State University from crosses among parents with a diverse genetic background. Seedlings were planted in field locations in Corvallis, Ore., and East Lansing, Mich., in 1995 and managed following standard commercial blueberry production practices with no insecticide or fungicide applications. In 1998-2000 the plants were evaluated for survival, bloom date, ripening date, plant growth and the fruit were scored for crop load, color, picking scar, firmness and size. All traits, except fruit color, varied significantly between locations. Plants in Oregon had a 36% greater survival rate and grew to be much larger, 80% taller and 104% wider, than those in Michigan. Families in Oregon flowered earlier in the year than those in Michigan but ripened at a similar time. Between locations, family differences were only evident for survival and fruit color. In Oregon, there were differences among families for all traits whereas in Michigan only survival, ripening date, plant height and width, and picking scar differed significantly. The family × environment interaction was not significant for crop load, fruit color and fruit firmness, so individuals selected on the basis of crop load, fruit color and fruit firmness should perform similarly in either location. There was a significant family × environment interaction for the other traits including survival, bloom date, ripening date, ripening interval, plant height and width, and for picking scar. Therefore, there is a need for individual selection programs at each location. Genotypes well adapted to Michigan may also do well in Oregon, but numerous promising genotypes could be missed for Oregon, if families are first selected in Michigan. The loss of numerous individuals due to winter cold may have reduced levels of variability in Michigan.

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John C. Beaulieu, Rebecca E. Stein-Chisholm and Deborah L. Boykin

There are very few studies detailing the aroma, astringency, and flavor of rabbiteye blueberry [RAB (Vaccinium ashei)] fruit typically grown in the southeastern United States. The objectives were to investigate the rapid and qualitative solid-phase microextraction gas chromatographic–mass spectrometry volatile composition of several local RAB cultivars with an overall goal to build a database of possible flavor and aroma compounds. Volatile profiles were obtained in five Louisiana-grown RAB cultivars (Brightwell, Climax, Premier, Powder Blue, and Tifblue) assayed at four maturities. The method routinely captured 53 volatiles, including 12 aldehydes, six alcohols, 11 esters, four ketones, 17 terpenoids, one furan, and two aromatics. Of the 33 compounds considered important in blueberries, 17 were recovered in the RAB cultivars assessed. Herein, 10 compounds were recovered for the first time in blueberry (Vaccinium sp.) and five of those compounds were confirmed with standards [2-ethylfuran, (E)-2-pentenal, (Z)-dehydroxylinalool oxide, (E)-dehydroxylinalool oxide and 1,4-cineole]. In general, terpenoids and their subclass linalools were the most significant volatiles followed closely by esters, aldehydes, and then alcohols. Terpenoids and linalools displayed the greatest significant differences in ‘Powder Blue’ and ‘Premier’. Esters and aldehydes were the most significant compound classes based on cultivar effect per maturity in firm-ripe fruit. From the suite of 17 of the 33 important compounds in upright blueberry, 10 were recovered across the five cultivars at four maturities that displayed a high level of significance. These were linalool, methyl 3-methylbutanoate, 1,8-cineole, (E)-2-hexanal, (Z)-3-hexenal, (Z)-3-hexenyl acetate, limonene, hexyl acetate, hexanal, and α-terpineol. These data will be useful to evaluate aroma volatiles in RAB and changes in processed and value-added byproducts.

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Tripti Vashisth and Anish Malladi

A better understanding of fruit detachment and the processes mediating it is essential to improve the efficiency of mechanical harvesting in blueberry (Vaccinium sp.). In blueberry, fruit detachment may occur either at the point of attachment of the pedicel to the peduncle [peduncle–pedicel junction (PPJ)] or at the point of attachment of the pedicel to the fruit [fruit–pedicel junction (FPJ)]. The fruit detachment responses of the PPJ and the FPJ to different conditions are not entirely clear. Additionally, whether fruit detachment at these junctions is mediated by the physiological process of abscission or through physical separation of the organ from the parent plant is not well understood. In this study, a series of experiments were performed to determine the abscission zone (AZ) corresponding to the point of mature fruit detachment and to determine whether fruit detachment occurs as a result of abscission or physical separation in rabbiteye blueberry (Vaccinium ashei). Anatomical studies indicated the presence of an AZ at the PPJ. Greater than 92% of the natural detachment of mature fruit occurred at the PPJ. The morphology of the fracture plane at the PPJ in naturally detached fruit was even and uniform, consistent with fruit detachment through abscission at this location. Abscission agents such as methyl jasmonate (20 mm) and ethephon (1000 mg·L−1) enhanced the extent of fruit detachment at the PPJ, further indicating that mature fruit detachment through abscission occurred primarily at this location. Additionally, the fracture plane at the PPJ during fruit detachment in response to abscission agent applications was flattened and even, further supporting the conclusion that fruit detachment at this location occurred through abscission. In contrast, the majority of the fruit detachment in response to mechanical shaking occurred at the FPJ. Analysis of the morphology of the fracture plane at the FPJ during detachment in response to mechanical shaking indicated that fruit detachment at this location was associated with extensive tearing and mechanical disruption of cells, consistent with physical separation. Together, data from this study indicate that mature fruit detachment resulting from abscission occurs primarily at the PPJ, whereas fruit detachment during mechanical shaking occurs primarily at the FPJ as a result of physical breakage at this weak junction.

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

Narrow-sense heritability and among-family and within-family variance components were estimated for antioxidant activity (AA), total phenolic content (TPH), and anthocyanin content (ACY) in blueberry (Vaccinium L. sp.) fruit. AA, TPH, and ACY were determined in the parents and in 10 offspring from each of 20 random crosses for each of 2 years at Becker, Minn. Offspring-midparent regression analysis provided combined-year heritability estimates of 0.43 ± 0.09 (P ≤ 0.0001) for AA, 0.46 ± 0.11 (P ≤ 0.0001) for TPH, and 0.56 ± 0.10 (P ≤ 0.0001) for ACY. Analyses of variance delineated variation among and within families for AA, TPH, and ACY (P ≤ 0.001). Year-to-year variation in the means for all offspring genotypes was not significant for AA or TPH, but there were changes in rank between years for families and for offspring within families for these traits. Year-to-year variation in the mean for all offspring genotypes was significant for ACY, but rank changes were observed only among offspring within families, not among families. In total, 18 of 200 offspring from 7 of the 20 crosses were transgressive segregants for AA, exceeding the higher parent of the cross by at least two sds. Estimates of variance components showed that variation among families accounted for 24% to 27% of total variance for the three traits. However, variation within families was greater than that among families, accounting for 38% to 56% of total variance for the three traits. These results suggest that increasing antioxidant activity in blueberry through breeding is feasible, and that the breeding strategies utilized should exploit the large within-family variation that exists.

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Laurie Hodges and Ronald E. Talbert

Samples of soil, mulch, and the soil/mulch interface zone were collected from commercial highbush blueberry (Vaccinium corymbosum L.) fields typical in their use of mulch under Arkansas conditions. Mulches included 1-year-old hardwood sawdust, 5-year-old hardwood sawdust, and 1-year-old pine needle mulch. Herbicide adsorption (Kd values) of the samples was determined for diuron, terbacil, and simazine. The soils, mulches, and interfaces adsorbed nearly 10 times as much diuron and more than twice as much simazine as terbacil. Adsorption of the herbicides was three to five times greater to the mulches than to the soils. Adsorption was significantly correlated with the organic matter content of the mulch. Adsorption was not related to herbicide solubility. Although no statistical differences were found among the three mulch materials, adsorption coefficients (Kd values) were numerically lower for each chemical on the 5-year-old hardwood mulch than on the 1-year-old hardwood or pine mulch. Chemical names used: 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron); 3- tert -butyl-5-chloro-6-methyluracil (terbacil); 2-chloro-4,6-bis(ethylamine)- s -triazine (simazine).

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D. Scott NeSmith, Arlen D. Draper and James M. Spiers

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Ann Marie Connor, James J. Luby, Cindy B.S. Tong, Chad E. Finn and James F. Hancock

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.

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M.K. Ehlenfeldt and A.W. Stretch

Resistance to blighting by Monilinia vaccinii-corymbosi (Reade) Honey was evaluated under greenhouse conditions in multiple populations of the diploid species Vaccinium boreale Hall & Aalders, V. corymbosum L., V. darrowi Camp, V. elliottii Chapm., V. myrtilloides Michx., V. myrtillus L., V. pallidum Ait., and V. tenellum Ait., as well as in accessions of the polyploid species 4x V. hirsutum Buckley and 6x V. corymbosum f. amoenum Aiton. Significant species differences were found in mean blighting levels averaged over 2 years, with values ranging from 3.5% for V. boreale to 49.2% for 2x V. corymbosum, compared with 27.5% for the resistant 4x V. corymbosum check, `Bluejay', and 64.3% for the susceptible 4x V. corymbosum check, `Blueray'. Wild Vaccinium species may serve as new sources of resistance to blighting, if resistance can be transferred easily and horticultural type recovered.

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Max E. Austin and K. Bondari

Three field experiments were conducted to determine short- and long-term effects of hydrogel mixed with peatmoss, milled pine bark, or soil on growth and yield of blueberry. Rabbiteye blueberry cultivars (Vaccinium ashei Reade) Delite, Tifblue, and Climax, and southern highbush cultivar (V. corymbosum L.) Georgiagem were used as test plants. Hydrogel mixed with soil was detrimental to plant survival. Hydrogel with or without peatmoss or pine bark did not influence yield or berry weight of 3- to 4-year-old `Delite' and 2- to 3-year-old `Tifblue' plants. The southern highbush, `Georgiagem', grown in peatmoss + hydrogel, produced plants of larger volume than those grown in peatmoss alone. Yield or berry weight was not affected significantly by soil amendments. Genetic differences between cultivars affected growth, yield, and berry weight, but the cultivar x soil treatment interaction was not significant.

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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.