Vaccinium Section Cyanococcus Research Articles

Continuous-Flow High-Pressure Homogenization of Blueberry Juice Enhances Anthocyanin and Ascorbic Acid Stability during Cold Storage.

Blueberries (Vaccinium section Cyanococcus) have a wealth of bioactive compounds, including anthocyanins and other antioxidants, that offer significant health benefits. Preserving these compounds and maintaining the sensory and nutritional qualities of blueberry products such as juice during cold market storage is critical to meet consumer expectations for nutritious, safe, and minimally processed food. In this study, we compared the effects of two preservation processing techniques, high-temperature short-time (HTST) and continuous flow high-pressure homogenization (CFHPH), on blueberry juice quality during storage at 4 °C. Our findings revealed that inlet temperature (Tin) of CFHPH processing at 4 °C favored anthocyanin retention, whereas Tin at 22 °C favored ascorbic acid retention. After 45 days of storage, CFHPH (300 MPa, 1.5 L/min, 4 °C) juice retained up to 54% more anthocyanins compared to control at 0 day. In contrast, HTST treatment (95 °C, 15 s) initially increased anthocyanin concentrations but led to their subsequent degradation over time, while also significantly degrading ascorbic acid. Furthermore, CFHPH (300 MPa, 4 °C) juice had significantly lower polyphenol oxidase activity (>80% less than control), contributing to the overall quality of the juice. This innovative processing technique has the potential to improve commercial blueberry juice, and help meet the rising demand for healthy and appealing food choices.

Genomic and evolutionary relationships among wild and cultivated blueberry species

BackgroundBlueberries (Vaccinium section Cyanococcus) are an economically important fruit crop in the United States. Understanding genetic structure and relationships in blueberries is essential to advance the genetic improvement of horticulturally important traits. In the present study, we investigated the genomic and evolutionary relationships in 195 blueberry accessions from five species (comprising 33 V. corymbosum, 14 V. boreale, 81 V. darrowii, 29 V. myrsinites, and 38 V. tenellum) using single nucleotide polymorphisms (SNPs) mined from genotyping-by-sequencing (GBS) data.ResultsGBS generated ~ 751 million raw reads, of which 79.7% were mapped to the reference genome V. corymbosum cv. Draper v1.0. After filtering (read depth > 3, minor allele frequency > 0.05, and call rate > 0.9), 60,518 SNPs were identified and used in further analyses. The 195 blueberry accessions formed three major clusters on the principal component (PC) analysis plot, in which the first two PCs accounted for 29.2% of the total genetic variance. Nucleotide diversity (π) was highest for V. tenellum and V. boreale (0.023 each), and lowest for V. darrowii (0.012). Using TreeMix analysis, we identified four migration events and deciphered gene flow among the selected species. In addition, we detected a strong V. boreale lineage in cultivated blueberry species. Pairwise SweeD analysis identified a wide sweep (encompassing 32 genes) as a strong signature of domestication on the scaffold VaccDscaff 12. From this region, five genes encoded topoisomerases, six genes encoded CAP-gly domain linker (which regulates the dynamics of the microtubule cytoskeleton), and three genes coded for GSL8 (involved in the synthesis of the cell wall component callose). One of the genes, augustus_masked-VaccDscaff12-processed-gene-172.10, is a homolog of ArabidopsisAT2G25010 and encodes the protein MAINTENANCE OF MERISTEMS-like involved in root and shoot growth. Additional genomic stratification by admixture analysis identified genetic lineages and species boundaries in blueberry accessions. The results from this study indicate that V. boreale is a genetically distant outgroup, while V. darrowii, V. myrsinites, and V. tenellum are closely related.ConclusionOur study provides new insights into the evolution and genetic architecture of cultivated blueberries.

Admixture Analysis Using Genotyping-by-Sequencing Reveals Genetic Relatedness and Parental Lineage Distribution in Highbush Blueberry Genotypes and Cross Derivatives.

Blueberries (Vaccinium section Cyanococcus) are perennial shrubs widely cultivated for their edible fruits. In this study, we performed admixture and genetic relatedness analysis of northern highbush (NHB, primarily V. corymbosum) and southern highbush (SHB, V. corymbosum introgressed with V. darrowii, V. virgatum, or V. tenellum) blueberry genotypes, and progenies of the BNJ16-5 cross (V. corymbosum × V. darrowii). Using genotyping-by-sequencing (GBS), we generated more than 334 million reads (75 bp). The GBS reads were aligned to the V. corymbosum cv. Draper v1.0 reference genome sequence, and ~2.8 million reads were successfully mapped. From the alignments, we identified 2,244,039 single-nucleotide polymorphisms, which were used for principal component, haplotype, and admixture analysis. Principal component analysis revealed three main groups: (1) NHB cultivars, (2) SHB cultivars, and (3) BNJ16-5 progenies. The overall fixation index (FST) and nucleotide diversity for NHB and SHB cultivars indicated wide genetic differentiation, and haplotype analysis revealed that SHB cultivars are more genetically diverse than NHB cultivars. The admixture analysis identified a mixture of various lineages of parental genomic introgression. This study demonstrated the effectiveness of GBS-derived single-nucleotide polymorphism markers in genetic and admixture analyses to reveal genetic relatedness and to examine parental lineages in blueberry, which may be useful for future breeding plans.

Control of Insect Pests and Diseases in an Ohio Fruit Farm with a Laser-guided Intelligent Sprayer

Laser-guided variable-rate intelligent spray technology is designed to significantly reduce pesticide use with a positive impact on the environment. However, there have been no reports on applying this technology to commercial fruit farms. Comparative experiments of intelligent variable-rate and conventional constant-rate spray applications for pesticide use and pest control were conducted at a fruit farm in Ohio during two consecutive growing seasons. Apple (Malus pumila), peach (Prunus persica), blueberry (Vaccinium section Cyanococcus), and black raspberry (Rubus occidentalis) were used for the tests. Pest severity of codling moth (Cydia pomonella), oriental fruit moth (Grapholitha molesta), scab (Venturia inaequalis), and powdery mildew (Podosphaera leucotricha) in apple; oriental fruit moth, brown rot (Monilinia fructicola), and powdery mildew (Podosphaera pannosa) in peach; spotted wing drosophila (Drosophila suzukii), mummy berry (Monilinia vaccinii-corymbosi), and phomopsis (Phomopsis vaccinii) in blueberry; and anthracnose (Elsinoe veneta) in black raspberry were assessed. There was equal severity of pests between intelligent and conventional spray applications, whereas the intelligent spray reduced pesticide use by 58.7%, 30.6%, 47.9%, and 52.5% on average for apple, peach, blueberry, and black raspberry, respectively. These results illustrate that intelligent spray technology is more environmentally friendly than conventional standard spray technology and equally or more effective for control of insect and disease pests in fruit production.

MYBA From Blueberry (Vaccinium Section Cyanococcus) Is a Subgroup 6 Type R2R3MYB Transcription Factor That Activates Anthocyanin Production.

The Vaccinium genus in the family Ericaceae comprises many species, including the fruit-bearing blueberry, bilberry, cranberry, huckleberry, and lingonberry. Commercially, the most important are the blueberries (Vaccinium section Cyanococcus), such as Vaccinium corymbosum (northern highbush blueberry), Vaccinium virgatum (rabbiteye blueberry), and Vaccinium angustifolium (lowbush blueberry). The rising popularity of blueberries can partly be attributed to their “superfood” status, with an increasing body of evidence around human health benefits resulting from the fruit metabolites, particularly products of the phenylpropanoid pathway such as anthocyanins. Activation of anthocyanin production by R2R3-MYB transcription factors (TFs) has been characterized in many species, but despite recent studies on blueberry, cranberry, and bilberry, no MYB anthocyanin regulators have been reported for Vaccinium. Indeed, there has been conjecture that at least in bilberry, MYB TFs divergent to the usual type are involved. We report identification of MYBA from blueberry, and show through sequence analysis and functional studies that it is homologous to known anthocyanin-promoting R2R3-MYBs of subgroup 6 of the MYB superfamily. In transient assays, MYBA complemented an anthocyanin MYB mutant of Antirrhinum majus and, together with a heterologous bHLH anthocyanin regulator, activated anthocyanin production in Nicotiana benthamiana. Furthermore anthocyanin accumulation and anthocyanin structural gene expression (assayed by qPCR and RNA-seq analyses) correlated with MYBA expression, and MYBA was able to transactivate the DFR promoter from blueberry and other species. The RNA-seq data also revealed a range of other candidate genes involved in the regulation of anthocyanin production in blueberry fruit. The identification of MYBA will help to resolve the regulatory mechanism for anthocyanin pigmentation in the Vaccinium genus. The sequence information should also prove useful in developing tools for the accelerated breeding of new Vaccinium cultivars.

Population Structure of the Blueberry Pathogen Monilinia vaccinii-corymbosi in the United States.

The fungus Monilinia vaccinii-corymbosi causes disease of blueberry (Vaccinium section Cyanococcus) shoots, flowers, and fruit. The objective of our research was to examine the population biology and genetics of M. vaccinii-corymbosi in the United States. A total of 480 samples of M. vaccinii-corymbosi were collected from 18 blueberry fields in 10 states; one field in Georgia, Massachusetts, Maine, Michigan, Mississippi, New Jersey, New York, Oregon, and Washington and nine fields in North Carolina. Analysis with 10 microsatellite markers revealed 247 unique multilocus haplotypes (MLHs), with 244 MLHs detected within 11 fields in the Northeast, Northwest, Midwest, and Southeast and three MLHs detected within seven fields in the Southeast United States. Genetic similarity and low genetic diversity of M. vaccinii-corymbosi isolates from the seven fields in the Southeast United States suggested the presence of an expansive, self-fertile population. Tests for linkage disequilibrium within 10 fields that contained ≥12 MLHs supported random mating in six fields and possible inbreeding and/or self-fertilization in four fields. Analysis of molecular variance, discriminate analysis of principal components, and Bayesian cluster analysis provided evidence for population structure and restricted gene flow among fields. This research represents the first comprehensive investigation of the genetic diversity and structure of field populations of M. vaccinii-corymbosi.

Exobasidium maculosum, a new species causing leaf and fruit spots on blueberry in the southeastern USA and its relationship with other Exobasidium spp. parasitic to blueberry and cranberry

Exobasidium leaf and fruit spot of blueberry (Vaccinium section Cyanococcus) is an emerging disease that has rapidly increased in prevalence throughout the southeastern USA. To determine whether this disease is caused by a new species of Exobasidium, we studied the morphology and phylogenetic relationship of the causal fungus compared with other members of the genus, including the type species E. vaccinii and other species that parasitize blueberry and cranberry (V. macrocarpon). Both scanning electron microscopy and light microscopy were used for morphological characterization. For phylogenetic analyses, we sequenced the large subunit of the rDNA (LSU) from 10 isolates collected from leaf or fruit spots of rabbiteye blueberry (V. virgatum), highbush blueberry (V. corymbosum) and southern highbush blueberry (Vaccinium interspecific hybrid) from Georgia and North Carolina and six isolates from leaf spots of lowbush blueberry (V. angustifolium) from Maine and Nova Scotia, Canada. LSU was sequenced from isolates causing red leaf disease of lowbush blueberry and red leaf spot (E. rostrupii) and red shoot (E. perenne) of cranberry. In addition, LSU sequences from GenBank, including sequences with high similarity to the emerging parasite and from Exobasidium spp. parasitizing other Vaccinium spp. and related hosts, were obtained. All sequences were aligned and subjected to phylogenetic analyses. Results indicated that the emerging parasite in the southeastern USA differs morphologically and phylogenetically from other described species and is described herein as Exobasidium maculosum. Within the southeastern USA, clustering based on host species, host tissue type (leaf or fruit) or geographic region was not detected; however, leaf spot isolates from lowbush blueberry were genetically different and likely represent a unique species.

Patterns of simple sequence repeats in cultivated blueberries (Vaccinium section Cyanococcus spp.) and their use in revealing genetic diversity and population structure

Blueberry (Vaccinium section Cyanococcus) is an important small fruit crop native to North America. Relationships among the primary species known as ‘blueberry’ has been a source of speculation due to the out-breeding nature of the crop, the use of intra-specific hybridization and open-pollinated selection in breeding programs, and the lack of genomic resources to adequately address the issue. The objectives of this study were to characterize simple sequence repeats (SSRs) from an emerging genomic draft sequence, develop useful molecular markers and provide an in-depth analysis of genetic diversity and population structure in blueberry using a broad range of cultivated blueberry accessions representing multiple species, ploidy levels and sources of origin. Genomic scaffolding was assembled from the whole-genome sequencing of a diploid V. corymbosum accession ‘W8520.’ From the assembled 358 Mb sequence, a total number of 43,594 SSRs were identified (122 per Mb). Among genomic regions, SSRs were longest and occurred most frequently in predicted 5′ untranslated regions (5′ UTR), while SSRs were shortest and least common in the predicted coding sequences. AG/CT and AAG/CTT were the most frequent motifs while CG/CG and CCG/CGG motifs were the rarest di- and trinucleotide motifs, respectively. For analysis of genetic diversity and population structure, 42 genomic SSR and EST–SSR markers with an average of 14.2 alleles and 56.0 allele phenotypes per locus were used to genotype a diverse blueberry population of 150 accessions. Cluster analysis grouped the 150 accessions in a manner consistent with known information regarding species, ploidy levels and pedigree. The analysis of population structure among blueberry accessions revealed inter- and intra-specific levels of stratification. Rabbiteye blueberry (V. virgatum) represents a genetically distinct subgroup within Cyanococcus. Three additional subpopulations were detected among highbush varieties that are largely attributable to distinctions between northern and southern highbush and founder effects of a single cultivar (‘Weymouth’). The identification of substructure that correlates with known pedigree information, and the availability of new genomic molecular markers will facilitate future evolutionary and genetic studies in blueberry.

Fertility and Other Characteristics of F1 and Backcross1 Progeny from an Intersectional Blueberry Cross [(highbush cultivar × Vaccinium arboreum) × highbush cultivar

Fertility and morphological traits were studied in the F1 and BC1 generations of intersectional crosses between tetraploid highbush blueberry cultivars (Vaccinium section Cyanococcus) and colchicine-induced tetraploid V. arboreum (Vaccinium section Batodendron). The goal of the introgression project was to combine desirable plant characteristics from V. arboreum with the large fruit and high fruit quality of highbush cultivars. Highbush × V. arboreum crosses were hard to make, but large numbers of BC1 seedlings were easily obtained using the most fertile F1 plants as parents in backcrosses to highbush. Anther awns, a character from V. arboreum, were present in all F1 seedlings, but fruit sclerids, another V. arboreum trait, were absent in most seedlings. Berry size in the BC1 generation was twice as large as in the F1 generation and was twice as large in the F1 as in V. arboreum. The BC1 generation was extremely variable in vigor and berry quality. Although berries of most BC1 plants were smaller, darker, and less desirable in texture and flavor than highbush berries, the high fertility of BC1 plants and the high variability among plants indicate that useful clones could be selected or developed by further breeding.

The Use of Inter-Sectional Hybrids in Blueberry Breeding

The tetraploid species in Vaccinium section Cyanococcus and tetraploid V. uliginosum in section Vaccinium are autotetraploid. The same is probably true of the tetraploid species in other sections of the genus. Chromosome pairing at metaphase I in these species is normally regular and bivalent, but each gamete contains two homologous chromosomes for each of the 12 basic chromosome types (x = 12 in Vaccinium). Thus, F1 hybrids between tetraploid plants from different Vaccinium sections can have regular bivalent chromosome pairing during meiosis and high fertility, even though diploid hybrids involving the same sections are highly sterile. Such fertile tetraploid hybrids are called amphidiploids. Amphidiploidy can give rise to new species; several important crop species are domesticated amphidiploids. The conditions for amphidiploid formation are narrow. The two species that hybridize must be divergent enough to insure faithful homologous bivalent chromosome pairing in the hybrid, where each bivalent consists of chromosomes derived from the same parent species. However, the parent species must be closely enough related to permit formation of vigorous hybrids. The first indication that amphidiploidy could be useful in blueberry breeding was a report by Rousi in 1963 of vigorous, fertile hybrids between tetraploid V. uliginosum (section Vaccinium) and tetraploid V. corymbosum (section Cyanococcus). In Florida, crosses of colchicine-induced tetraploid V. arboreum (section Batodendron) with tetraploid highbush cultivars and with tetraploid Florida V. myrsinites (section Cyanococcus) indicate that Vaccinium sections Batodendron and Cyanococcus also have the right degree of divergence to produce vigorous, fertile tetraploid hybrids. The feasibility of producing other intersectional tetraploid combinations in Vaccinium, and the vigor and fertility of the hybrids, can best be determined by trial and error.

Hybridization of two diploid Vaccinium section Cyanococcus species with diploid Vaccinium arboreum in section Batodendron

Several characteristics from sparkleberry (V. arboreum) would be useful if transferred to highbush blueberry cultivars, but to date all direct crosses have failed. The purpose of this research was to see whether crosses of diploid V. darrowii and diploid V. fuscatum (both section Cyanococcus) with diploid V. arboreum (section Batodendron) could be made and to assess the possibility of transferring traits from V. arboreum into cultivated blueberries of section Cyanococcus. Many crosses were successful and easy to make. Crosses were more productive when V. arboreum was the pollen parent, but some hybrids were also obtained with V. arboreum as seed parent. Pollen stainability of F1 (V. darrowii × V. arboreum) hybrids was low, ranging from 0.9 to 23.7%. Numerous meiotic abnormalities were found in the F1 hybrids. These led to a high percentage of incomplete and unstained tetrads and probably to the production of unreduced gametes.

Major differences observed in transcript profiles of blueberry during cold acclimation under field and cold room conditions

Our laboratory has been working toward increasing our understanding of the genetic control of cold hardiness in blueberry (Vaccinium section Cyanococcus) to ultimately use this information to develop more cold hardy cultivars for the industry. Here, we report using cDNA microarrays to monitor changes in gene expression at multiple times during cold acclimation under field and cold room conditions. Microarrays contained over 2,500 cDNA inserts, approximately half of which had been picked and single-pass sequenced from each of two cDNA libraries that were constructed from cold acclimated floral buds and non-acclimated floral buds of the fairly cold hardy cv. Bluecrop (Vaccinium corymbosum L.). Two biological samples were examined at each time point. Microarray data were analyzed statistically using t tests, ANOVA, clustering algorithms, and online analytical processing (OLAP). Interestingly, more transcripts were found to be upregulated under cold room conditions than under field conditions. Many of the genes induced only under cold room conditions could be divided into three major types: (1) genes associated with stress tolerance; (2) those that encode glycolytic and TCA cycle enzymes, and (3) those associated with protein synthesis machinery. A few of the genes induced only under field conditions appear to be related to light stress. Possible explanations for these differences are discussed in physiological context. Although many similarities exist in how plants respond during cold acclimation in the cold room and in the field environment, there are major differences suggesting caution should be taken in interpreting results based only on artificial, cold room conditions.

A Novel Method to Quantify Transport of Self- and Cross-pollen by Bees in Blueberry Plantings

Blueberry species (Vaccinium section Cyanococcus) benefit from cross-pollination. Outcrossing increases fruit set, berry size, and ripening rate. Although knowledge of pollen dispersal is essential for maximizing cross-pollination and achieving optimal planting designs, this process has not been quantified previously in blueberry plantings. A novel method was developed to estimate the proportion of self- and cross-pollen transported by blueberry pollinators. The proposed technique requires a consistent difference in pollen size between two cultivars to predict the composition of a pollen mixture based on frequency distributions of pollen diameter. Vaccinium ashei Reade `Brightwell' and `Climax' were chosen for this study because they produce pollen tetrads of different size. Tetrad diameter and number were analyzed with a particle counter. The technique was validated by predicting the proportion of `Brightwell' in pollen mixtures where the cultivar composition was known, and predicted and actual values were linearly correlated (r = 0.995, P < 0.0001). The technique was then applied to pollen samples extracted from the bodies of pollinators that were collected in a mixed `Brightwell' and `Climax' blueberry plot. Numbers of blueberry tetrads extracted per bumblebee (Bombus spp.) averaged 4595 and 797 in 2003 and 2004, respectively, which was considered adequate to make accurate predictions based on frequency distributions of tetrad diameter. The proportion of `Brightwell' pollen carried by bumblebees changed with the phenology of the crop following an expected pattern, indicating that the method performed well under field conditions. This technique could potentially be used to quantify the likelihood for outcrossing and establish the effect of cultivar arrangements on pollen dispersion, as well as to examine pollen collection and manipulation, and cultivar preference by bees.

Unilateral cross compatibility in Vaccinium elliottii × V. arboreum, an intersectional blueberry hybrid

Vaccinium elliottii Chapmn., a diploid blueberry in Vacciniumsection Cyanococcus, was crossed with V. arboreum Marsh, a diploid blueberry insection Batodendron. The goal was toproduce hybrids that could be used toincorporate traits from these species intotetraploid southern highbush cultivars. The crosses were made reciprocally usingtwo clones of each species. A recessiveseedling marker gene for anthocyanin-freecotyledons in the V. elliottii clonesused as female parents permitted thetesting of mentor pollination. For thementor pollinations, V. elliottiiplants that were homozygous for therecessive marker allele were pollinatedwith a small amount of viable V.elliottii pollen carrying the recessivemarker mixed with a large amount of V.arboreum pollen carrying the dominantmarker. Thousands of intersectional hybridseedlings were obtained when V.elliottii was the seed parent, both withand without mentor pollination, but nohybrids were obtained from 2735 flowerspollinated in the reciprocal crosses. Theseeds that gave rise to hybrid embryos weresmaller than normal V. elliottiiseeds, but germinated well. Hybridseedlings grew slowly at first, buteventually produced some vigorous plants inthe field, although many plants remainedmuch smaller than normal seedlings of thetwo parental species. Some of the hybridsproduced numerous flowers during the 6years they were observed in the field, buteven with many diploid, tetraploid, andhexaploid section Cyanococcus blueberryplants growing nearby that could haveprovided pollen for their flowers, thehybrids produced no viable seed.

Results of multiple pollination in blueberry (Vaccinium elliottii Chapm.)

Blueberry (Vaccinium section Cyanococcus, family Ericaceae) is a shrub that produces multiple-seeded berries in which only a fraction of the ovules develop into viable seeds. A recessive yellowleaf marker gene was used to evaluate the efectiveness of a single pollination versus multiple pollinations in producing seeds in Vaccinium elliottii Chapm. A multiple-pollination experiment was conducted to see if the first pollen applied or the second produced more progeny, and to see if multiple pollinations increased the number of seedlings produced. Flowers of diploid yellowleaf Vaccinium elliottii were pollinated from one to four times at daily intervals. Pollen from redleaf and yellowleaf plants was used to produce two types of seedlings that could be distinguished visually. Generally, percent berry set, seeds per berry, and seed germination were not increased by multiple pollination. After multiple pollination, the pollen applied first always produced the most seedlings. Prior pollination greatly reduced seed set from subsequent pollination, but subsequent pollination caused little or no decrease in the number of seeds set by the first pollination.

Genetic analysis of freezing tolerance in blueberry (Vaccinium section Cyanococcus)

An understanding of the genetic control of freezing tolerance (FT) in woody perennials is important for the effective selection and development of plants with a broader climatic adaptation. This study was undertaken to examine the inheritance and gene action of FT in segregating populations of a woody perennial blueberry (Vaccinium, section Cyanococcus). Two backcross populations were derived from interspecific hybrids of the diploid species Vaccinium darrowi andVaccinium caesariense, which are widely divergent in their FT. The bud FTs of uniformly cold acclimated plants of parental, F1, and two backcross populations were evaluated with a laboratory controlled freeze-thaw regime, followed by a visual assessment of injury. FT (LT50) was defined as the temperature causing 50% of the flower buds to be injured. Data indicate that the two parents were homozygous for genes for low or high FT. Freezing-tolerance values of the parental and F1 populations indicate that freeze-sensitivity is a partially dominant trait. Results from reciprocal crosses revealed that there was no significant maternal influence on freezing tolerance. Parental phenotypes were fully recovered in 40–42 plants of each testcross population, suggesting that FT is determined by relatively few genes. The degree of dominance and an analysis of generation means revealed that FT in blueberry is controlled largely by additive gene effects and, to a lesser degree, by dominance gene effects. Testing of various genetic models indicated that FT inheritance can be adequately explained by a simple additive-dominance model; however, two epistatic models involving additive-additive and dominance-dominance interactions also fit the data.

Level of Self- and Cross-fertility of Derivatives of Vaccinium arboreum × Vaccinium Section Cyanococcus Hybrids

The extent of self-fertility and self-fruitfulness was studied in Vaccinium arboreum Marsh, V. darrowi Camp, and in seedlings, termed MIKs, from open-pollination of V. darrowi (section Cyanococcus) × V. arboreum (section Batodendron) F1 hybrids. The open pollinations that produced the MIKs occurred in a field containing tetraploid southern highbush selections (based largely on V. corymbosum L.), and the pollen parents of the MIKs are believed to be southern highbush selections. The MIKs that were studied had been selected for high fruit set after open pollination in the field. Both V. arboreum and V. darrowi exhibited very low self-fruitfulness and self-fertility when hand-pollinated in a greenhouse; the former produced no seedlings from more than 600 selfed flowers, and the latter produced only 13. By contrast, southern highbush clones averaged 70 seedlings per 100 pollinated flowers when selfed and 230 when crossed. Self-fertility and self-fruitfulness of the MIKs were higher than those of V. arboreum and V. darrowi but lower than those of southern highbush selections. MIK × MIK crosses gave fewer seedlings per 100 pollinated flowers (84) than highbush × highbush crosses (230), probably reflecting their hybrid ancestry. Although introduction of V. arboreum genes into southern highbush blueberry gives plants of excellent vigor and adaptation to north Florida, several generations of breeding will be needed to obtain cultivars with high fertility and berry quality.

Water Status in Relation to Maintenance and Release from Dormancy in Blueberry Flower Buds

Three blueberry (Vaccinium section Cyanococcus) genotypes, that have different chilling requirements and levels of cold hardiness, were studied. Depth of dormancy was evaluated and water status was determined, using nuclear magnetic resonance (NMR), throughout the accumulation of chilling that leads to release from dormancy. Among the two highbush cultivars studied, `Bluecrop' (Vaccinium corymbosum L.) was the most dormant and `Gulfcoast' (Vaccinium corymbosum L. x Vaccinium darrowi Camp) was the least dormant. The rabbiteye cultivar `Tifblue' (Vaccinium ashei Reade) had an intermediate dormancy. It appeared that the cultivar with the deepest dormancy had also the highest chilling requirement (CR). The NMR results showed that `Bluecrop' buds had the lowest relaxation times (T2), indicating that water was relatively more bound in `Bluecrop' buds than in the buds of the two other cultivars. Whatever the cultivar, no significant variation of T2s and water content of the buds was noted throughout the accumulation of chilling, even after CRs were satisfied. Within 1 day of forcing (24 °C, long day), there was a shift towards freer water but no change in the water content. Forcing was ineffective in freeing water until the plants received enough chilling to satisfy their CRs.

Derivatives of Vaccinium arboreum × Vaccinium Section Cyanococcus: I. Morphological Characteristics

Morphological characteristics of many derivatives from Vaccinium arboreum Marsh × Vaccinium section Cyanococcus crosses were studied. The purpose of the study was to determine if V. arboreum traits were being inherited and expressed in hybrid progeny and to identify characteristics that would enable hybrid field identification. This study focused on the F1 hybrids of V. darrowi Camp × V. arboreum (F1 hybrids) and the open-pollinated progeny of the F1 hybrids [mother is known (MIK)]. Also included in the study were the parents: V. darrowi, V. arboreum, and V. corymbosum L. (pollen parent of the MIKs). Many leaf, flower, and fruit characteristics were measured for all five taxa. Leaf characteristics included length, width, and presence or absence of stalked glands, pubescence, and marginal bump glands. The floral characteristics measured were corolla length and width, corolla aperture, pedicel length, peduncle length, bracteole length and width, and the presence or absence of anther awns and bracteoles. Berry and seed mass were the fruit characteristics investigated. Four unique V. arboreum traits were found to be expressed in the F1 and MIK hybrid populations. These were the presence of anther awns, large seed size, bracteole shape, and marginal glands. These traits should permit field identification of hybrid plants.

Chill‐responsive dehydrins in blueberry: Are they associated with cold hardiness or dormancy transitions?

To survive winters, woody perennials of temperate zones must enter into endodormancy. Resumption of spring growth requires sufficient exposure to low temperature (chill units, CUs) in winter (chilling requirement), which also plays a role in the development of cold hardiness (cold acclimation). Physiological studies on dormancy breaking have focused on identifying markers, such as appearance or disappearance of proteins in response to varying degrees of chill unit accumulation. However, whether these changes are associated with dormancy transitions or cold acclimation is not clear. In the present study, greenhouse‐grown blueberry (Vaccinium section Cyanococcus) plants were used to address this question. Three blueberry cultivars, Bluecrop, Tifblue, and Gulfcoast having chilling requirement of approximately 1 200, 900 and 600 CUs, respectively, were first exposed to 4°C for long enough to provide chill units equivalent to one‐half of their respective chilling requirement. This treatment was expected to result in cold acclimation. A fraction of plants was then subjected to a 15/12°C (light/dark) regime for 2 weeks, a treatment expected to be “dormancy‐neutral” but cause deacclimation. Before and after each treatment, cold hardiness and dormancy status of floral buds were determined; proteins were extracted from the buds collected on the same sampling date, and separated by one‐dimensional SDS‐PAGE. Dehydrin‐like proteins were identified by immunoblotting, using anti‐dehydrin antiserum. Results indicate that the chilling treatment resulted in cold acclimation as indicated by increased bud hardiness in all three cultivars. Data also indicate a distinct accumulation of three dehydrin‐like proteins of 65, 60, and 14 kDa during cold acclimation. The cold hardiness and levels of dehydrin proteins decreased during the exposure to 15/12°C for 2 weeks. Results also confirmed that this treatment had no negative effect on chill unit accumulation. Densitometric scans of protein gels indicated a close association between the abundance of dehydrins and degree of cold hardiness in these cultivars. In addition, levels of the dehydrin proteins and cold hardiness remained about the same between 100% and >100% satisfaction of chilling requirement. These results suggest that changes in dehydrin expression are more closely associated with cold hardiness than with dormancy transitions.