Genetic variation was surveyed within and among 5 Vaccinium species and several hybrid taxa for 6 aspects of flower size and shape. Sufficient variation was found to allow radical changes in flower architecture through breeding. The goal is a flower that pours pollen directly from the anthers onto the stigma without the assistance of pollinating insects. The flowers of V. elliottii had very short styles (mean in mm 5.3 compared to 10.2 for rabbiteye cultivars and 8.5 for highbush cultivars), and certain short-style recombinants from highbush cultivar × V. elliottii crosses came close to the desired positioning of stigmas relative to anthers. The distance (in mm) from the anther pore to the stigma averaged: V. ashei 2.7; V. corymbosum 2.4; V. darrowi 2.3; and V. elliottii 1.0. Compared to highbush cultivars, rabbiteye cultivars tended to have long corollas and narrow corolla apertures, two features believed to be related to poor honeybee pollination. These features were much more favorable in V. ashei × V. constablaei hybrids, with values averaging close to those for highbush cultivars.
Diploid blueberry (Vaccinium section Cyanococcus) was pollinated in a greenhouse in 1981 with pollen from sparkleberry (V. arboreum, Section Batodendron). Cyanococcus parents included V. darrowi, diploid V. corymbosum, and various intra-sectional diploid hybrids. Forty one vigorous seedlings showing characteristics of both sections were selected from a field nursery when 2 ½ years old. Some of these plants flowered heavily in subsequent years, and several were more than 3 m tall by 1990. Although the F1 hybrids had very low fertility, some open-pollinated progeny were obtained. Some of these were vigorous, fruitful when open-pollinated in the field, and intermediate between V. arboreum and Cyanococcus in many features. Six of the best progeny from open-pollination of the F1's were used in greenhouse crosses. Some branches were self-pollinated and some were pollinated with pollen from tetraploid V. corymbosum -based cultivars. Two of the 3 selfed plants had a high percent fruit set (277 fruit from 441 flowers). Four of the six plants pollinated with pollen from tetraploid V. corymbosum cultivars had high percent fruit set (452 fruit from 793 flowers). Flowers of the open-pollinated progeny of the F1 hybrids were much larger than those of the F1 `s. This, along with the fruitfulness after 4× pollination, suggests that at least some of the open-pollinated progeny are tetraploid. These hybrids give hope that sparkleberry genes can be used to improve highbush cultivars.
To determine if the net CO2 assimilation and water use efficiency (WUE) of highbush blueberry under high temperature can be improved genetically, gas exchange determinations were made for a selection of Vaccinium darrowi Camp (Florida 4B), a highbush cultivar (Bluecrop) (V. corymbosum L.), their F1 hybrid (US75), and two crosses of the F1 hybrid to another improved genotype (US239 and US245). All genotypes responded parabolically to increasing temperature at vapor pressure deficits <1 kPa. Maximum CO2 assimilation of US75 (15 µmol·s–1·m–2) was 30% to 40% higher than either parent. Carbon dioxide assimilation of US75 and Florida 4B was optimum at 30°C and that of ‘Bluecrop’ at 20°. The optimum for US239 was similar to ‘Bluecrop’, and that of US245 to Florida 4B. Florida 4B had higher WUEs than ‘Bluecrop’ at both 20° (5.64 µmol CO2/mmol H2O to 4.01) and 30° (3.73 to 2.53). US239 and US245 had significantly (P < 0.05) higher WUEs at 30° than did ‘Bluecrop’. Residual conductance to CO2 (gr) decreased in ‘Bluecrop’ when temperature was raised from 20° to 30°, but increased in all other genotypes. Due to the favorable gas exchange properties of US75 and US245 at 30°, we suggest that the high temperature tolerance of V. darrowi may be heritable and that US245 may be used to improve the heat tolerance of highbush blueberry.
Bulk A horizon samples of 4 soils, with or without the addition of peatmoss, and 5 blueberry crosses were used in a study of the adaptability of blueberries to upland soil conditions under 3 fertilization regimes and trickle irrigation in outdoor pots. Blueberry progenies ranged from essentially pure highbush (Vaccinium corymbosum L.) to interspecific hybrids containing varying amounts of evergreen (V. darrowi Camp), lowbush (V. augustifolium Aiton), black highbush (V. atrococcum Heller), and rabbiteye (V. ashei Reade) blueberry germplasm. Blueberry growth, as measured by plant volume, initially was greatest on Manor clay loam, a Piedmont soil high in clay (30%), but by the 2nd growing season, growth was superior on Berryland soil. Various fertilizer sources affected small differences in growth. Generally those progenies that contained less highbush (V. corymbosum) parentage produced more vigorous growth. Depth of rooting and estimated root distribution were affected significantly by soil, but the addition of peatmoss had no consistent effect. Berryland sand and Manor loam soils, which represent extremes in clay content, both produced the deepest root systems. Fruiting and fruit characteristic data from the 2nd growing season indicated a significant effect of peatmoss on the Pope and Galestown soils, which resulted in lowered total fruit acidity. The Berryland soil produced fruit with the lowest total acidity. Blueberry plant growth over the first 2 seasons indicates that soil type can have pronounced effects on plant growth and rooting. These growth differences were due to soil characteristics other than particle size distribution, with fertilizer source having minimal effects on growth.
A range of soils, with or without the addition of peatmoss, and seedlings of blueberry progenies were used in an outdoor pot study to examine the adaptability of blueberries to upland soil conditions with controlled fertilizer additions and trickle irrigation. Blueberry progenies ranged from essentially pure highbush (Vaccinium corymbosum L.) to interspecific hybrids containing varying amounts of evergreen (V. darrowi Camp), lowbush (V. angustifolium Aiton), black highbush (V. atrococcum Heller), and rabbiteye (V. ashei Reade) blueberry germplasm. The soils represented the 3 physiographic regions of the eastern United States with Berryland sand used as a comparative control. Leaf analysis for N, P, K, Ca, and Mg showed significant effects of soil, but no consistent effect of peatmoss addition or fertilizer source in the 2 years of the experiment. There were significant differences among progenies. Foliar Fe, B, Al, Zn, and Cu concentrations varied independent of soil material, progeny, or fertilizer source. Leaf Mn was significantly increased from solid 10N-4P-8K fertilizer and a significant soil by progeny interaction existed. Those progenies containing some V. angustifolium tended to have increased foliar Mn levels. The reduced vigor of the blueberry progenies grown on soils other than the Berryland sand was tentatively ascribed to induced nutrient imbalances, involving Ca, Fe, and Mn, possibly being governed by soil cation exchange capacity and organic matter reactivity.
Interspecific blueberry (Vaccinium spp.) progenies were examined to determine combining abilities and genetic variability for seedling root system size and shoot vigor and to establish whether a large root system is correlated with good growth when plants are grown on a mineral soil and exposed to a moderate soil water deficit. General combining ability (GCA) variance components for root system size and shoot vigor and specific combining ability variance components for shoot vigor were significant. US226, a tetraploid hybrid of V. myrtilloides Michaux × V. atrococcum Heller, had the highest GCA effect for root system size and the lowest GCA effect for shoot vigor. US75 (V. darrowi Camp × V. corymbosum L.) had the highest GCA effect for shoot vigor and was second in GCA effect for root system size. Comparison of the crosses containing G111 (V. corymbosum) with those containing G362 (V. corymbosum) indicates that selecting for the best V. corymbosum clone to start a breeding program seems as important as selecting the mineral soil-adapted parent. Root system ratings were highly correlated with total dry weight of field-grown plants (r = 0.89). The method used in this study to evaluate seedlings for root system size and shoot vigor could be used to eliminate the less vigorous plants from a population before field planting and to evaluate mineral soil adaptability.
Vaccinium species collected from the eastern United States were grown and fruited at Castle Hayne, N.C. Harvest season extended from 5 June to 22 Aug. Vaccinium angustifolium Ait. was earliest ripening. Vaccinium myrtilloides Michx., V. elliotti Chap., diploid V. corymbosum L., and tetraploid V. pallidum Ait. populations also contained very early- to early-ripening seedlings. Early-ripening seedlings were not observed in tetraploid V. corymbosum populations and reached peak ripeness around mid-June, about with ‘Bluecrop’. One tetraploid V. corymbosum population continued ripening into early August. Vaccinium ashei Reade populations from Georgia began ripening about 2 weeks earlier than Florida V. ashei or Arkansas V. amoenum Ait. populations. One Georgia V. ashei population was only slightly later than tetraploid V. corymbosum. The Florida V. ashei populations continued ripening into late August. The diploid species V. darrowi Camp, V. tenellum Ait., and V. stamineum L., were all basically late in ripening. The potential utility of these species in breeding for both early- and late-ripening Vaccinium genotypes is discussed.
A new southern highbush blueberry cultivar named `Camellia' was released in 2005 by The University of Georgia and the USDA–ARS. `Camellia' is a hybrid containing mostly Vaccinium corymbosum and a small amount of V. darrowi. The new cultivar was selected in 1996 at the Coastal Plain Experiment Station in Tifton, Ga. from a cross of MS-122 × MS-6, and was tested as TH-621 in plantings at Alapaha, Ga. beginning in 1998. `Camellia' has an estimated chill requirement of 450 to 500 hours (<7 °C). It is an early- to mid-season cultivar, having berries that are large, with a very light blue color, and a small, dry picking scar. Berry firmness is good and flavor is very good. `Camellia' flowers 5 to 8 days after `Star' and `O'Neal' in south Georgia, and ripens 4 to 9 days after `Star', and with `O'Neal'. Plants are highly vigorous, with strong cane growth and an open, upright bush habit and a narrow crown. Yields have been similar to `Star' and greater than `O'Neal'. `Camellia' should be planted with other southern highbush blueberry cultivars with a similar time of bloom for cross-pollination (`Star' and `O'Neal' suggested). It is recommended on a trial basis at this time. `Camellia' requires a license to propagate. For licensing information and/or a list of licensed propagators, contact the Georgia Seed Development Commission, 2420 S. Milledge Avenue, Athens, GA 30606; or visit their website at www.gsdc.com.
To determine if blueberry shoestring virus (BBSSV) is absent in the southern United States due to resistance of cultivars, we mechanically and rub-inoculated 1-year-old rooted microshoots of nine cultivars representing southern rabbiteye (Vaccinium ashei Reade), southern highbush (hybrids of V. corymbosum and V. darrowi Camp), and northern highbush (V. corymbosum L.). Leaves were sampled from plants, and enzyme-linked immunosorbent assay screened for the presence of virus over 15 months. Only a few individuals were infected after aphid inoculation, but many northern and southern cultivars became infected after mechanical inoculation. Northern highbush `Elliot' (50%) and `Blueray' (46.3%) had the highest infection rates, followed by rabbiteye `Climax' (36.3%) and the southern highbush `O'Neal' (12.5%). The lowest rates of infection were found in southern highbush `Georgiagem' (2.5%), `Misty' (2.5%), rabbiteye `Brightwell' (0.0%), and northern highbush `Bluecrop' (2.5%). Since many southern cultivars were infected by the disease, resistance likely has not excluded BBSSV from the southern United States.
The organic acid composition of blueberries of three highbush (Vaccinium corymbosum) cultivars, three rabbiteye (V. ashei cultivars and nine southern highbush (V. corymbosun hybrids) cultivars or selections was determined by HPLC. Species means off the individual acids (citric, malic, succinic, and quinic), expressed as a percentage of total acid, formed profiles or patterns that are thought to be characteristic of the species. Citric (75%) was the predominant acid in highbush fruit with lesser percentages of succinic (13%), quinic (9.6%), and malic (2.7%). The percent composition of rabbiteye berries [quinic (49%), succinic (39%), citric (6.7%), malic (5%)] was distinctly different from highbush. The acid profile of southern highbush fruit reflected their V. corymbosum heritage with an acid profile similar to that of highbush. When related to a clone's pedigree, these results suggest that organic acid profiles may be a useful screening tool for studying the contribution of southeastern native species such as V. darrowi or V. ashei to the inheritance of organic acids.