Southern Highbush Research Articles

Comparison of Growth Responses of Southern Highbush Blueberry ‘Scintilla’ to Different Growing Types, ‘Evergreen’ and ‘Deciduous’

Comparison of Growth Responses of Southern Highbush Blueberry ‘Scintilla’ to Different Growing Types, ‘Evergreen’ and ‘Deciduous’

Contribution to the knowledge of the anatomy, histochemistry, and phenolic composition of leaf and stems of bilberry (Vaccinium myrtillus L.) cultivated in Tucumán, Argentina.

The Vaccinium genus, with over 200 species, is prized for its fruits and traditional medicinal uses. Introduced to South America in the 1980s, it has become a significant crop, particularly in Tucumán, Argentina. Southern highbush blueberries are the most cultivated. Recent research suggests that theleaves and stems of these speciescontain higher levels of beneficial compounds compared to fruits. This study explores the potential of V. myrtillus L. leaves and stems, typically discarded as agricultural waste, as sources of bioactive compounds. It provides the first detailed analysis of their anatomy and chemical composition, revealing high levels of phenolic compounds with antioxidant properties. Leaf extracts show stronger antioxidant activity compared to stems. Toxicity tests on Artemia salina indicate their safety for further exploration. These findings suggest that V. myrtillus L. waste by-productscould be valuable as sources of bioactive compounds, promoting their application in pharmaceuticals, food, or cosmetics industries.

Preparing a Southern Highbush Blueberry Field for Machine Harvesting

Blueberries are grown commercially in Florida for the early-season fresh fruit market. The majority of Florida’s blueberry crop is currently harvested by hand to ensure high quality standards for fresh fruit production. However, hand harvesting is the single greatest annual production cost for Florida blueberry growers, and mechanization of berry harvests could greatly reduce production costs. This is particularly important when considering the volume of fruit imported into the United States from countries where labor rates are significantly lower. Also, at times the availability of harvest labor when needed may be an issue for Florida growers; mechanization could help address that issue. This publication provides information for commercial blueberry growers interested in adopting machine harvesting.

Management of the Blueberry Gall Midge in Florida’s Southern Highbush Blueberries

The blueberry gall midge (BGM) is one of the most important pests of southern highbush blueberries in Florida. Monitoring for BGM using clear sticky traps or bucket traps should begin as early as November. Chemical control should be applied right before bud break and then ten days after bud break, or when at least two BGM are found on traps. Other management practices include the use of younger mulch, using potentially resistant cultivars, and chemical control such as Movento with Induce and Apta in rotation to avoid resistance development. Applications should also be timed with larval and adult emergence for optimal insecticide efficacy.

Targeted Anthocyanin Profiling of Fruits from Three Southern Highbush Blueberry Cultivars Propagated in Colombia.

The blueberry, a deciduous shrub in the Ericaceae family, is celebrated for its delightful flavor, sweetness, and abundance of anthocyanins and antioxidants, qualities that have garnered significant attention for their potential health benefits. Blueberries grown in diverse environments and exhibit varied anthocyanin profiles, often influenced by factors such as altitude and climate. Varietal groups worldwide have been bred and categorized based on their growth habits and specific cold requirements, particularly with southern highbush cultivars thriving in temperate climates, demonstrating tolerance to higher altitudes or cooler climates-a result of hybridizations involving various Vaccinium species. In the Colombian Andes, southern highbush blueberries thrive in unique high-altitude conditions, leading to exceptional quality due to the region's cool climate and specific soil characteristics. In this context, this study aimed to chemically characterize and differentiate three southern highbush blueberry cultivars (i.e., 'Biloxi,' 'Legacy' and 'Sharpblue') cultivated in a Colombian Andean plateau and compare them to three commercially available highbush blueberries. This comprehensive evaluation involved examining total phenols, flavonoids, anthocyanin content, and DPPH· free-radical scavenging capacity, as well as conducting anthocyanin-targeted profiling via HPLC-DAD-HRMS. Through supervised multivariate analyses such as sPLS-DA, this study delved into the pattern recognition of those anthocyanins that could potentially serve as markers for quality and cultivar-related chemical trait determination. These findings locate blueberry-derived anthocyanins in a metabolic context and afford some insights into southern highbush blueberry cultivar differentiation to be used for further purposes.

Phytophthora Root Rot on Southern Highbush Blueberry in Florida

Roots serve the vital function of water and nutrient uptake for plants. Healthy roots provide the foundation for productive blueberry bushes and require the right horticultural inputs and soil environment to thrive. Less-than-ideal conditions can result in unhealthy, rotten roots, sometimes caused by disease. The most common and destructive root rot disease of southern highbush blueberry (SHB) in Florida is Phytophthora root rot (PRR), caused by the oomycete pathogen Phytophthora cinnamomi Rands. Oomycetes, or “water molds,” favor water-saturated environments. The distinction between oomycetes and fungi is important for disease management, because many fungicides work for only one group, not both. Worldwide, P. cinnamomi is a devastating pathogen of approximately 5,000 woody plant host species. For blueberry growers in Florida, PRR is a persistent problem that is currently managed through careful site selection, preparation, and routine Phytophthora-specific fungicide applications.

Introduction to Southern Highbush Blueberry Cultivation in Containers

Blueberry bushes prefer well drained, acidic soils with high organic matter content. These soil characteristics are not common in many parts of the world. Thus, blueberries are traditionally grown in soils amended with pine bark and elemental sulfur. The need to create optimum conditions for the roots of blueberry bushes has recently led to blueberry cultivation in containers filled with soilless substrates. The intended audience for this publication is commercial blueberry growers. The purpose of this publication is to complement existing information sources by introducing the materials and practices used for blueberry cultivation on container-based farms.

Detection and Characterization of Xylella fastidiosa subsp. fastidiosa in Rabbiteye Blueberry in South Carolina.

Xylella fastidiosa causes bacterial leaf scorch in southern highbush (Vaccinium corymbosum interspecific hybrids) and is also associated with a distinct disease phenotype in rabbiteye blueberry (V. virgatum) cultivars in the southeastern United States. Both X. fastidiosa subsp. fastidiosa and X. fastidiosa subsp. multiplex have been reported to cause problems in southern highbush blueberry, but so far only X. fastidiosa subsp. multiplex has been reported in rabbiteye cultivars in Louisiana. In this study, we report detection of X. fastidiosa in rabbiteye blueberry plants in association with symptoms of foliar reddening and shoot dieback. High throughput sequencing of an X. fastidiosa-positive plant sample and comparative analyses identified the strain in one of these plants as being X. fastidiosa subsp. fastidiosa. We briefly discuss the implications of these findings, which may spur research into blueberry as a potential inoculum source that could enable spread to other susceptible fruit crops in South Carolina.

EFFECT OF APPLYING BIO-INPUTS ON PRODUCTION OF HIGH BUSH BLUEBERRY (Vaccinium corymbosum L.) cv. biloxi IN BRAZIL'S FEDERAL DISTRICT

Blueberry production is increasing in Brazil, and growers are turning to bio-inputs or biostimulants to be used on their growth. This has been due to the growing concern about sustainability in the food production chain and the necessity to increase the yield. The current experiment aimed at evaluating the effects of Samurai King, EM-1 and Brutal Plus (Minhofértil) biostimulants on the cultivation of Southern Highbush blueberries (V. corymbosum L.), cultivar 'Biloxi'. The parameters evaluated were plant height (cm), diameter of the main stem (mm), number of shoots, chlorophyll content, total number of leaves, leaf length and width. The total mass, number of fruits, average mass per fruit, the transversal and longitudinal diameters, and the total sugars (°Brix) were also measured. In 2020, the treatment of Samurai King + EM-1 showed the highest efficiency for the studied parameters related to fruits and yield but with no significant difference as compared to the other treatments. Regarding the plant growth, treatments 1 (Brutal Plus) and 5 (Brutal Plus + EM-1) were the most efficient. In 2021, treatment 7 (Brutal Plus + Samurai King + EM-1) had the highest yields, except for average mass per fruit and total sugars. In the two years of evaluation, although treatments obtained lower averages than the control, the effect observed was generally positive, revealing the efficiency of products containing microorganisms for the growth of blueberry plants. In conclusion, these bioproducts could remarkably affect plant biomass, production and fruit quality, resulting in better yields.

Genome-wide association study and transcriptome analysis reveal candidate genes for off-season flowering in blueberry

Off-season flowering in daylength-sensitive plants is an intriguing characteristic that represents an opportunity to expand crop's production timing and regions, and potentially speed up breeding. Southern Highbush Blueberry (SHB) is classified as a short-day plant, with a blooming period in the northern hemisphere ranging from late winter through spring. In Florida, some blueberry genotypes have consistently bloomed during the fall season, suggesting that flower bud initiation occurred during the summer. Such a characteristic indicates a facultative response to daylength or day-neutrality capacity, leading to the off-season flowering observed. To understand the genetic basis of off-season flowering in SHB, we performed a genome-wide association study (GWAS), followed by transcriptomic analysis of contrasting genotypes. Among the 536 genotypes evaluated, 14 % bloomed during the fall, of which seven presented consistently high scores for off-season flowering capacity. The GWAS revealed 12 single nucleotide polymorphisms (SNPs) significantly associated with the off-season flowering trait, which together accounted for 17 % of the phenotypic variance. A gene homologous to an RNA helicase and reported to modulate florescence formation and flowering time in other plant species, was identified within a genomic region associated with the off-season flowering. This gene was up-regulated in a fall-flowering blueberry genotype. Additionally, we detected down-regulation of flowering repressors and up-regulation of MADS-box transcription factors known to be involved in the fate of floral meristems. Our findings provide insights into the genetic and molecular basis of this complex trait in blueberry. These results can be useful for marker-assisted selection and further functional gene validation to accelerate the development of blueberry varieties suitable for off-season production.

Evidence of Xylella fastidiosa Infection and Associated Thermal Signatures in Southern Highbush Blueberry (Vaccinium corymbosum Interspecific Hybrids).

Xylella fastidiosa, a gram-negative bacterium vectored to plants via feeding of infected insects, causes a number of notorious plant diseases throughout the world, such as Pierce's disease (grapes), olive quick decline syndrome, and coffee leaf scorch. Detection of Xf in infected plants can be challenging because the early foliar disease symptoms are subtle and may be attributed to multiple minor physiological stresses and/or borderline nutrient deficiencies. Furthermore, Xf may reside within an infected plant for one or more growing seasons before traditional visible diagnostic disease symptoms emerge. Any method that can identify infection during the latent period or pre-diagnostic disease progress state could substantially improve the outcome of disease control interventions. Because Xf locally and gradually impairs water movement through infected plant stems and leaves over time, infected plants may not be able to effectively dissipate heat through transpiration-assisted cooling, and this heat signature may be an important pre-diagnostic disease trait. Here, we report on the association between thermal imaging, the early stages of Xf infection, and disease development in blueberry plants, and discuss the benefits and limitations of using thermal imaging to detect bacterial leaf scorch of blueberries.

Photosynthetic Response of Blueberries Grown in Containers.

Recently, there has been increased interest in container blueberry production as a viable alternative to open-field blueberry planting. Container production of blueberries offers numerous advantages, among these, a lack of limitation by suboptimal soil conditions in the open field and the ability to control substrate pH, drainage, and organic matter. The photosynthetic response for three container-grown Southern highbush blueberry (interspecific Vaccinium hybrids) cultivars including 'Jewel', 'Meadowlark', and 'Victoria' and a rabbiteye blueberry (Vaccinium virgatum) 'Baldwin', were measured during the spring and summer of 2022. It was hypothesized that the three cultivars evaluated would have different photosynthetic responses. The objective of this study was to determine the photosynthetic activity of different blueberry cultivars during the first year of crop establishment. A series of measurements were conducted every 2 h throughout the day and for different dates using a gas exchange data analyzer on newly matured fully expanded leaves located in the top middle section of the canopy for each cultivar. The response curves showed that net photosynthesis (A) became saturated at moderate light, with saturation occurring at a photosynthetic photon flux density (PPFD) of 1932 µmol m-2 s-1. At this point, the rate of CO2 assimilation was approximately 16.84 µmol CO2 m-2 s-1. No differences in (A) were found among cultivars. Overall, the attained values of photosynthesis provide a strong conceptual basis for understanding the cultivar variation response when grown in containers; therefore, the containerized system may serve as a production system for early fruiting blueberries in Alabama, USA.

Hydrogen Cyanamide Application Accelerates Vegetative Bud Break and Causes Earlier Yield in ‘Optimus’ and ‘Colossus’ Southern Highbush Blueberry

Southern highbush blueberry (Vaccinium corymbosum interspecific hybrid) cultivation is a major industry in subtropical regions where low winter temperatures are infrequent and inconsistent. In Florida and other subtropical areas, growers use hydrogen cyanamide (HC) applications during endodormancy to mitigate the negative effects of low chill accumulation. Hydrogen cyanamide is a synthetic plant growth regulator that increases and expediates dormancy release and budbreak. However, southern highbush blueberry cultivars differ in their sensitivity to HC. Optimus and Colossus are two recently released cultivars from the University of Florida blueberry breeding program. The effects of HC in these cultivars are unknown. This research aimed to describe responses to HC applications at different rates for these new varieties. Experiments took place in a commercial farm in Waldo, FL, on 3- to 4-year-old deciduous blueberry bushes. HC was applied at rates of 3.8 g·L−1 (0.38%), 5.1 g·L−1 (0.50%), and 6.4 g g·L−1 (0.63%) in ‘Optimus’ and 3.8 g·L−1 (0.38%), 5.1 g·L−1 (0.50%), 6.4 g·L−1 (0.63%), and 7.7 g·L−1 (0.75%) in ‘Colossus’. In both cultivars, the control treatment was not sprayed. Vegetative bud count, and flower bud development, flower bud mortality, and yield were determined. HC application thinned reproductive buds and increased vegetative budbreak. Although seasonal yield was not increased, HC advanced fruit ripening early in the season.

Establishment and Optimization of Micropropagation System for Southern Highbush Blueberry

The optimization of micropropagation for blueberries is crucial due to the growing blueberry industry and demand for plantlets. This study focused on four stages: explant sterilization, in vitro establishment, in vitro proliferation, and ex vitro rooting, aiming to establish an efficient in vitro propagation system for southern highbush blueberry cultivar ‘ZY09’. The most effective explant sterilization method was a 60 s treatment with 75% ethanol and a 5 min treatment with 4% NaClO. During the establishment of the in vitro culture, the modified woody plant medium was found to be suitable. The replacement of NH4NO3 in woody plant medium with (NH4)2SO4 facilitated the proliferation of blueberry microshoots. The optimal combination of plant growth regulators for the in vitro proliferation of blueberry microshoots was indole-3-butyric acid (0.1 mg·L−1), thidiazuron (0.0005 mg·L−1), and zeatin (1 mg·L−1). Perlite was the most suitable substrate for ex vitro rooting. The best ex vitro rooting performance was observed without immersion in growth regulators. Indole-3-butyric acid enhances root formation and suppresses root elongation in blueberries. The findings of this study can be applied to large-scale in vitro propagation of southern highbush blueberry and provide a reference for the genetic transformation of blueberries.

In Vitro Propagation of the Blueberry 'Blue Suede™' (Vaccinium hybrid) in Semi-Solid Medium and Temporary Immersion Bioreactors.

The production of blueberries for fresh and processed consumption is increasing globally and has more than doubled in the last decade. Blueberry is grown commercially across a variety of climates in over 30 countries. The major classes of plants utilized for the planting and breeding of new cultivars are highbush, lowbush, half-high, Rabbiteye, and Southern highbush. Plants can be propagated by cuttings or in vitro micropropagation techniques. In vitro propagation offers advantages for faster generation of a large number of disease-free plants independent of season. Labor costs for in vitro propagation can be reduced using new cultivation technology and automation. Here, we test and demonstrate successful culture conditions and medium compositions for in vitro initiation, multiplication, and rooting of the Southern highbush cultivar 'Blue Suede™' (Vaccinium hybrid).

Miticidal Tools for Management of Southern Red Mites Infesting Southern Highbush Blueberries.

Tetranychid outbreaks have been detected since 2016 in southern highbush blueberries (SHB); however, it was not until 2019 that the southern red mite (SRM), Oligonychus ilicis (Acari: Tetranychidae) was confirmed as the pest causing severe bronzing and stunting, in multiple Florida and Georgia commercial blueberry plantings. To date, only three miticides (fenazaquin, fenpyroximate, and acequinocyl) have been registered for use in SHB and there are no clear guidelines on how to manage SRM in SHB. Similarly, there is no knowledge regarding the existence of natural enemies of SRM in SHB. This is the first report of naturally occurring predatory mites (Amblyseius sp. and Neoseiulus ilicis) associated with SRM in SHB. Predatory mites were recorded in blueberry bushes after treatment with seven miticides used to suppress SRM populations including spiromesifen, acequinocyl, sulfur, sulfur + molasses, bifenazate, fenpyroximate, and fenazaquin. The number of SRM recorded per leaf and averaged plant damage ratings (0 = no bronzing-4 = 100% bronzing) were used to evaluate miticide efficacy. Additionally, the presence or absence of predatory mites per sample was recorded. Fenpyroximate used as the standard miticide, significantly reduced mite numbers seven days after application, as well as acequinocyl and fenazaquin. Fenpyroximate and fenazaquin demonstrated the best performance for managing O. ilicis on SHB and treated bushes demonstrated significantly less bronzing compared with the control plants. These miticides were also safe to naturally occurring predatory mites. Lastly, the level of growers' awareness regarding SRM was assessed using surveys in 2020 to design adequate educational materials available to the grower community.

Impacts of Hurricane Damage on Southern Highbush Blueberries

This publication discusses the types of hurricane damage that can be incurred in blueberry production operations, the impacts of these damages, preparations to make before the storm arrives, and suggestions on best management practices in the aftermath of a storm.

Blueberries as a Source of Energy: Physical Chemistry Characterization of Their Anthocyanins as Dye-Sensitized Solar Cells’ Sensitizers

This work aimed to show the possibility of applying anthocyanins extracted from blueberries following a straightforward path as potential impregnation dyes in dye-sensitized solar cells (DSSCs), particularly in the presence of co-adsorbents, such as silver nanoparticles, as an alternative in order to profit from large amounts of discarded fruits. Following a simple procedure, anthocyanins (mainly delphinidin-3-glucoside) were obtained from blueberries (Southern Highbush type). Complete characterization was carried out in order to prove the utility of delphinidin-3-glucoside as a sensitizer in DSSCs. The analyzed anthocyanin is suitable for sensitizing because of its high molar absorptivity values within the visible region of the light spectra, the adsorption ability to a FTO/TiO2 electrode (FTO, fluorine-doped tin oxide) as confirmed by Fourier transform infrared (FTIR) as well as thermogravimetry coupled to differential scanning calorimetry (TG-DSC), a potential oxidation value near 1 V, and adequate thermal as well as light stabilities. Moreover, the cell’s conversion efficiency is improved in the presence of silver nanoparticles, reaching 0.24% (nearly a 25% increase). The sum of all these characteristics points to the application of delphinidin-3-glucoside as a sensitizer in DSSCs, offering a technological use with potential interest for countries where agricultural production offers an abundant origin of extraction.

Zinc Oxide-Based Nanoformulation Zinkicide Mitigates the Xylem-Limited Pathogen Xylella fastidiosa in Tobacco and Southern Highbush Blueberry.

The xylem-limited pathogen Xylella fastidiosa causes severe economic losses worldwide, and no effective antimicrobial disease management options are available. The goal of this study was to evaluate the efficacy of a novel ZnO-based nanoparticle formulation, Zinkicide TMN110 (ZnK), against X. fastidiosa in vitro and in planta. In vitro, minimum bactericidal concentration (MBC) of ZnK analyzed in Pierce's Disease 2 medium was estimated at approximately 60 ppm. Time-kill kinetics assay showed a 100% reduction of culturable X. fastidiosa in less than 1 h after ZnK treatment. Microfluidic chambers assays showed that ZnK also inhibits X. fastidiosa cell aggregation and growth under flow conditions. Phytotoxicity assessments in the greenhouse demonstrated that ZnK can be applied as a soil drench in 50 ml at 500 ppm/plant/week up to four times to tobacco and blueberry without causing visible damage. ZnK was also evaluated for disease control in the greenhouse using tobacco infected with X. fastidiosa subsp. fastidiosa strain TemeculaL. ZnK soil drench weekly applications at concentrations of 500 followed by 1,000 ppm (500/1,000) and 500/500/1,000 ppm (in 50 ml each), reduced X. fastidiosa populations by >2 to 3 log10 units and disease severity by approximately 57 and 76%, respectively, compared with the untreated control. Similarly, when blueberry plants infected with X. fastidiosa subsp. multiplex strain AlmaEm3 were soil drenched with ZnK at concentrations 1,000/1,000 ppm and 1,000/1,000/500 ppm (in 200 ml each), the bacterial population was reduced by approximately 1 to 2 log10 units, and disease severity decreased by approximately 39 and 43%, respectively. Overall, this study shows antibacterial activity of ZnK against X. fastidiosa and its effectiveness in plants to reduce disease symptoms under controlled conditions.

Cuticular waxes affect fruit surface color in blueberries

Societal Impact StatementIn blueberry, fruit color is one of the most important quality traits affecting consumers' choices. Both pigments and waxes impact fruit color; however, their roles have not been clearly elucidated. Here, the contributions of waxes and anthocyanins to fruit color are characterized. A higher content of β‐diketones—the second largest wax group in blueberries—determines a lighter fruit color; hence revealing that, at harvest, waxes contribute more than anthocyanins in determining variations in fruit color among blueberry varieties.Summary Fruit color is one of the major quality traits determining the marketability of fruits by affecting consumers' choices. In blueberries, although fruit surface color is mainly determined by pigments (e.g., anthocyanins), cuticular waxes also play a role in modulating the surface color, and a lighter color given by a dense wax bloom is normally preferred by consumers. This study investigated the content and composition of cuticular waxes and their roles in modulating fruit surface color in 12 (seven northern highbush, three southern highbush, and two hybrids) blueberry genotypes at harvest (H1, representing the first commercial pick, and H2, representing the second commercial pick). The ultrastructural morphology of cuticular waxes was analyzed in four selected genotypes by scanning electron microscopy. The level and profile of anthocyanins and their contributions to the color were also assessed. Total cuticular wax content ranged from 27.7 to 95.8 μg cm−2 among genotypes at H1 and decreased by an average of 23.9% from H1 to H2. Triterpenoids (62.5% of the total cuticular waxes on average) and β‐diketones (22.9% on average) were the first and second largest wax groups in all genotypes, respectively. β‐Diketones were previously proven to affect leaf surface color in wheat; in this study, their content strongly correlated with the lightness of the blueberry surface. Scanning electron microscopy revealed distinct wax morphologies among genotypes. No significant relationships were found between total or individual anthocyanin concentrations and fruit surface color. Our results suggest that, at harvest, variation in the fruit surface color among blueberry genotypes is more closely related to the content and composition of cuticular waxes than the level and profile of anthocyanins, with β‐diketones being particularly important. This study provides new insights for blueberry breeding programs aiming to improve the surface color in order to meet the market demand.