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In blueberries (Vaccinium spp), 2n pollen production has been identified in both diploid and tetraploid populations. High 2n pollen producers from diploid V. elliotti, diploid V. darrowi, and tetraploid V. pallidum were chosen for meiotic studies. Cytological examination revealed spindle abnormalities, including parallel spindles and tripolar spindles, as well as synaptic irregularities. These aberrations would result in gametes having the genetic equivalent of first division restitution near the centromere and in portions of the chromosome that are not recombinant. Such gametes would be expected to transmit a high level of heterozygosity to resulting progeny. Reciprocal diploid by tetraploid cultivar crosses were made to evaluate the viability of the 2n gametes in the diploids, and to assess the usefulness of the diploids as parents in a breeding program.
Abstract
‘Georgiagem’, a new low-chilling cultivar. is the first highbush blueberry (Vacciniwn corymbosum L.) cultivar developed from the cooperative blueberry breeding program of the Georgia Agricultural Experiment Station and the USDA. Although ‘Georgiagem’ originated mostly from tetraploid highbush blueberry parentage, it obtained adaptation to the southern U.S. environment from the diploid species, V. darrowi, selected from the wild in Florida (2). ‘Georgiagem’ is early ripening, moderately productive, and has fruit of medium size with good color, small stem scar, firmness, and pleasant flavor.
Abstract
Native highbush blueberries (Vaccinium corymbosum L.) from the flatwoods of Alachua County (North-central), Florida and from Highlands County (Central peninsula) were surveyed for chromosome number and crossability with breeding lines derived from northern highbush cultivars. The Alachua County population was predominately tetraploid; a diploid component differed in leaf serration and glandulation. Tetraploid plants were fully cross-fertile with highbush cultivars and breeding lines. Diploid plants from the Alachua County population were cross fertile with both V. elliottii and V. darrowi. V. corymbosum from Highlands County was diploid.
Mode of inheritance of cold hardiness (CH) in woody perennials is not wellunderstood. This study was undertaken to determine the mode of inheritance and gene action of CH in blueberry (Vaccinium section Cyanococcus). Two testcross populations (segregating for CH) derived from interspecific hybrids of V. darrowi (drw) × V. caesariense (csr) were used. Plants were cold-acclimated by a 4-week exposure to 4°C. Bud CH (LT50) was defined as the temperature causing 50% injury (visual) when subjected to controlled freeze–thaw. Results show that the drw and csr parents had an LT50 of –13° and –20°C, respectively. The F1 population exhibited mean LT50 of –14.7°C. The csr and drw testcross populations had a mean LT50 of –18° (39 individuals) and –14°C (33 individuals), respectively. Individuals of each population were distributed between parental values with center of distribution skewed toward the testcross parent. Since individuals having LT50s as same as the recurrent parents were present in each population of only 33–39 plants, data suggest that CH is determined by relatively few genes. To determine gene action, the estimates for various genetic parameters (calculated from joint scaling test) were used in generation means analysis to test various models. Results indicate that CH in blueberry can be best explained by simple-additive dominance model, whereas models including epistatic components did not satisfactorily explain the data.
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.
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.
Pollen from six southern highbush blueberry cultivars derived from Vaccinium corymbosum L. and one or more other species (V. darrowi Camp, V. ashei Reade, and V. angustifolium Aiton) was incubated on nutrient agar to determine tetrad viability, pollen tube growth rates, and incidence of multiple pollen tube germinations. `Avonblue' pollen had a significantly lower tetrad germination percentage than `Georgiagem', `Flordablue', `Sharpblue', `Gulfcoast', or `O'Neal', all of which had >90% viable tetrads. The in vitro growth rate of `O'Neal' pollen tubes was significantly higher than the growth rates of `Sharpblue' and `Georgiagem pollen tubes. Of those tetrads that were viable, more than two pollen tubes germinated from 83% and 91% of the `Gulfcoast' and `Sharpblue' tetrads, respectively, while only 11% of the `Flordablue' tetrads produced more than two pollen tubes. The total number of pollen tubes germinated per 100 tetrads ranged from 157 (`Flordablue') to 324 (`Sharpblue'), resulting in actual pollen grain viabilities ranging from 39% to 81%. Genetic differences in pollen vigor, as indicated by pollen viability, pollen tube growth rates, and multiple pollen tube germinations, may influence blueberry growers' success in optimizing the beneficial effects of cross-pollination on fruit development.
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.
Most genetic variation in blueberries is quantitative. However, after a decade of exploration among Florida's native blueberry populations and more than 100,000 seedlings grown in nursery plots, several qualitative variants have been found. An allele for anthocyanin-free foliage in Vaccinium elliottii is recessive to wildtype. A second recessive allele at a different locus in the same species depletes anthocyanin in the fruit but not the foliage. A recessive allele in V. ashei produces white, pink, or purple berries when homozygous, the color depending on the clone that is made homozygous for the allele. A dominant allele in V. darrowi produces pink fruit and is nonallelic with the fruit anthocyanin deficiency allele in V. elliottii. Two V. elliottii clones with a weeping to prostrate growth habit have been found in west Florida. This phenotype is maintained by clonal propagation, but its inheritance has not been determined. A V. ashei plant with compact growth habit transmits this phenotype to a small percentage of its F-1 progeny when crossed with most V. ashei cultivars.
Variability in sucrose levels and metabolism in ripe fruit of several Vaccinium species were examined. The objective was to determine if sufficient variability for fruit sucrose accumulation was present in existing populations to warrant attempts to breed for high-sucrose fruit, which potentially would be less subject to bird predation. Three-fold differences in fruit sucrose concentration were found among species, ranging from 19 to 24 mg·(g fw)-1 in V. stamineum and V. arboreum to about 7 mg·(g fw)-1 in cultivated blueberry (V. ashei and V. corymbosum) and V. darrowi. Soluble acid invertase activity was negatively correlated with fruit sucrose concentration. There was no apparent correlation between fruit sugar concentration and either sucrose phosphate synthase or sucrose synthase activities, both of which were low for all species studied. The degree of variability in fruit sucrose accumulation among Vaccinium species supports the feasibility of developing high sucrose fruit, which would be a potentially valuable addition to current strategies of minimizing crop losses to birds.