Southern Highbush Blueberry Cultivars Research Articles

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.

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.

Inoculation with Oidiodendron maius BP Improves Nitrogen Absorption from Fertilizer and Growth of Vaccinium corymbosum during the Early Nursery Stage.

Blueberry roots are inefficient in taking up water and nutrients, a fact partially related to their scarcity of root hairs, but they improve nutrient uptake by associating with ericoid mycorrhizal and endophytic fungi. However, the benefits of this association are both cultivar- and fungus-dependent. Our objective was to assess the effect of inoculation with three native fungal strains (Oidiodendron maius A, O. maius BP, and Acanthomyces lecanii BC) on plantlet growth, plantlet survival, and nitrogen (N) absorption of the southern highbush blueberry (SHB) cultivars Biloxi and Misty. The fungal strains were inoculated into the peat-based substrate for growing blueberry cultivars, and plantlets produced by micropropagation were transplanted and grown for four months. The three inoculated strains positively affected the survival percentage in at least one of the cultivars tested, whereas O. maius BP positively affected plant biomass, N derived from fertilizer absorption, N content, and plant N recovery (%) in both Biloxi and Misty. Our results show that the O. maius BP strain may prove useful as a bio-inoculant to improve blueberry production during the nursery stage.

The seasonal progression of the reproductive phenology of two southern highbush blueberry (V. corymbosum L. interspecific hybrids) cultivars in the Western Cape, South Africa

• The reproductive phenology of SHB cultivars ‘8-42’ and ‘9-02’ was documented for the first time in such depth and per whole plant. • The timing and peaks of the phenological stages quantified on individual plant basis were similar between the two locations - for both cultivars. • The duration of the phenological stages was influenced by micro climate. • The intensity of bud development was accurately illustrated per cultivar and location. • The differences in the intensity of phenological development on bud and plant level will serve as baseline for further studies on carbohydrate allocation to explain the differences in yield. The objective of this study was to evaluate the timing and duration of selected flower bud phenological stages of two southern highbush blueberry (SHB) cultivars in a Mediterranean climate to optimize the management of commercial production systems. The experiment was conducted in commercial orchards during the 2020 growing season, in the Hex River and Wolseley production areas, Western Cape, South Africa. The timing (date) and duration (days) of selected flower bud stages were recorded on individual plants, from April to November 2020 for bud swell, bud break, tight cluster, closed flower, open flower, petal fall, green fruit, colouring fruit, and fruit harvest respectively. Standard commercial management practices were followed on both sites. Cultivar 8-42 flowered from April to mid-October, with a peak during early August. Cropping occurred from early August to mid-November, and volumes peaked in October, at both sites. Cultivar 9-02 flowered from April to late October, with a peak during early August at the Wolseley site, whereas flowering for this cultivar only peaked during late September, at the Hex River site, indicating a possible climate related response. Subsequently, harvest started two weeks later at the Hex River site for ‘9-02’, while the highest yield volumes were obtained during October to early November, at both sites. This paper provides a first report on the phenological categorization of the reproductive development of commercial SHB blueberry cultivars, as produced in the Western Cape, South Africa. As all major management decisions in blueberry cultivation depend on the phenological phases of the crop, this information will contribute towards decision making regarding production, but also via quantifying the progression of each stage in addition to the peaks, allowing for additional logistical management. The influence of growing conditions on the phenological development of these cultivars was also explored and indicated the need for supplemental research considering the influence of micro-environmental conditions in driving evergreen production blueberry systems.

Agricultural Water Footprint of Southern Highbush Blueberry Produced Commercially with Drip Irrigation and Sprinkler Frost Protection

A study was conducted from 2010 to 2017 to determine the water footprint for producing blueberries in the Entre Ríos province of Argentina. Three cultivars of southern highbush blueberry (hybrid cross of Vaccinium sp.) were evaluated in the study, including “Star”, “Emerald”, and “Snowchaser”. In each case, the plants were irrigated by drip and protected from frost using overhead sprinklers. Water requirements for irrigation and frost protection varied among the cultivars due to differences in the timing of flowering and fruit development. The annual water footprint for fruit production in each cultivar is expressed in units of cubic meters of water used to produce one ton of fresh fruit and ranged from 212 - 578 m3∙t−1 for “Star”, 296 - 985 m3∙t−1 for “Emerald”, and 536 - 4066 m3∙t−1 for “Snowchaser”. “Snowchaser” flowered earlier than the other cultivars and, therefore, needed more water for frost protection. “Star”, on the other hand, ripened the latest among the cultivars and required little to no water for frost protection. Frost protection required a minimum of 30 m3∙h−1 of water per hectare and in addition to drip irrigation was a major component of the water footprint.

Hummingbirds, honeybees, and wild insect pollinators affect yield and berry quality of blueberries depending on cultivar and farm’s spatial context

The contribution of wild pollination service to global agriculture is increasingly recognized. Still, biotic pollination demand is mainly covered by managed species, whereas implementing ecological intensification practices to promote wild pollination service remain less common. In this study, we evaluated (i) the effect of wild and managed pollinators and the richness of pollinator functional groups (RPFG) on production quality (i.e., fruit size) and quantity (i.e., crop yield), of two southern highbush blueberry (Vaccinium corymbosum) cultivars, and (ii) how wild pollinator service and crop production correlate with farm’s land cover. We found that pollination service supply and the spatial context interact with the blueberry cultivar to determine yield and fruit size. The abundance of big-sized wild bees and hummingbirds positively affected fruit size and crop yield, but the relationship's significance was cultivar-dependent. In contrast, the increase in honeybees visitation rate was detrimental to the average fruit size of blueberries, but the effect was not generalizable between cultivars. The amount of forested area affected positively wild pollinator abundance and RPFG only in one cultivar, whereas grassland and hedgerow had adverse effects for pollinators in the other. Consistently, the relation between blueberry fruit size and the farm’s land cover was subordinate to the cultivar. That is, despite all significant relations had the same sign between cultivars, their coefficients were statistically different. Our results support the idea that wild pollinators contribute to producing higher yields and larger berries in blueberry crops. Moreover, we found that the retention of natural forest at a 200 m radius within the farm may increase pollination service supply. However, the significance of every effect was contingent on the blueberry cultivar. This cultivar-dependent response points out that a robust assessment of pollinator benefits not only should include multiple production metrics, but also must incorporate within-crop variation, particularly in systems where growers use a mosaic of cultivars with different pollination requirements.

Southern Highbush Blueberry Cultivars from the University of Florida

This publication provides historical background on southern highbush blueberries (SHB), and information on specific UF/IFAS cultivars that can be a helpful resource for SHB growers. Written by D. A. Phillips, J. G. Williamson, P. M. Lyrene, and P. R. Munoz, and published by the UF/IFAS Horticultural Sciences Department, revised September 2022.

Bark Inclusions in Canes of Southern Highbush Blueberry and Their Impact on Cane Union Strength and Association with Botryosphaeria Stem Blight

Bark inclusions are an understudied structural defect in trees and shrubs. They consist of areas of bark on adjacent parts of stems or scaffolds, typically on the inner faces of a narrow fork, which become overgrown and internalized to occupy part of the wood between the stems. Here, bark inclusions are described for the first time to occur in cane unions at the crown of southern highbush blueberry (Vaccinium corymbosum interspecific hybrids) cultivars ‘Farthing’ and ‘Meadowlark’, both of which are characterized by a narrow, vase-shaped architecture at the base of the plant, leading to crowding of the canes. When affected canes were dissected at their bases, bark inclusions were visible internally as a line of compressed bark within the wood of adjoining canes, or as bark invaginations and fissures across part of or the entire cross-section of the cane. Externally, blueberry crowns with included bark were characterized by either an inward ridgeline of bark between canes of similar diameters emerging from the crown at a narrow angle from each other, or by the presence of girdling roots. Bark inclusions were observed in plants of all ages, from the nursery to mature production fields. The internal length of the bark inclusion correlated strongly with the external length of the inward stem bark ridgeline symptom as measured by destructive sampling in the field (r = 0.916, p < 0.0001, n = 20). When plants with and without bark inclusions were subjected to a winch test in the field, the probability of breakage for canes without included bark was significantly lower (p < 0.0002) than for those with included bark, and at the maximum applied force of 972.4 N, 95.2% of the canes with bark inclusions failed (i.e., broke at the crown), compared with only 52.6% for canes without included bark. In a survey across three fields, the number of bark inclusions per plant was significantly associated with an index of cane crowding (r = 0.286. p = 0.0267, n = 60), suggesting that plants with tight, crowded bases had more bark inclusions. In addition, there was a significant association (p < 0.0001) between the presence or length of bark inclusions and the intensity of Botryosphaeria stem blight in these fields. This study showed that bark inclusions occur commonly in certain southern highbush blueberry cultivars in the production conditions of Georgia and Florida, with negative implications for cane integrity and plant health.

The Xenia Effect Promotes Fruit Quality and Assists in Optimizing Cross Combinations in ‘O’Neal’ and ‘Emerald’ Blueberry

Cross-pollination can improve the fruit set and quality of blueberry (Vaccinium spp.) for growers and consumers. However, the xenia effect in southern highbush blueberry remains unclear. Therefore, we selected eight cultivars of southern highbush blueberry (Vaccinium corymbosum L., interspecific hybrids) and applied pollination treatments (i.e., artificial self-pollination, artificial pollination with mixed pollen, or artificial pollination with individual cultivar pollen) to explore the xenia effects on the fruit set and quality of ‘O’Neal’ and ‘Emerald’. Pollen viability tests indicated that all of the cultivars are capable of fertilization. The highest fruit set came from ‘Bluerain’ pollen for ‘O’Neal’, while ‘Gulfcoast’ pollen increased fruit set the most in ‘Emerald’. Principal component analysis revealed that the cross combinations ‘Emerald’ × ‘Gulfcoast’ and ‘O’Neal’ × ‘Gulfcoast’ optimized the external and interior quality of the fruit. SSR was applied to determine which pollen source yielded the most seedlings. Results indicated that ‘Emerald’ × ‘Gulfcoast’ and ‘O’Neal’ × ‘Bluerain’ increased seedling production. Our results demonstrate that the xenia effects of ‘Gulfcoast’ pollen may increase ‘Emerald’ yields and promote fruit quality, while pollen from ‘Bluerain’ or ‘Jewel’ can improve ‘O’Neal’ fruit quality and seed number. Hence, these cross combinations may be utilized in blueberry production to increase fruit set, yield, and quality.

Identification of Fungi in the Botryosphaeriaceae Family Associated with Stem Blight of Vaccinium spp. in the Southeastern United States

Stem blight is a major disease of blueberry caused by Botryosphaeriaceae fungi. Chemical and cultural management options are limited, putting emphasis on breeding efforts to identify sources of resistance. The efficacy and durability of host resistance could be impacted by the species composition of the pathogen population in a region and by the isolates employed in the screenings used to identify the resistance. Samples (365) were collected from southern highbush (SHB) and rabbiteye blueberry (REB) cultivars from 28 sites in the southeastern US (AL, FL, GA, NC, and SC). Colony morphology identified 86% of the isolates as Botryosphaeriaceae. Conidia morphology and Maximum Likelihood analysis of the Internal Transcribed Spacer rDNA regions (ITS), translation elongation factor one alpha (tef1-α), and β-tubulin were used to identify isolates at genera or species level. A PCR-restriction fragment length polymorphism (PCR-RFLP) test was used to identify isolates to genus. Neofusicoccum and Lasiodiplodia were the predominant genera. N. kwambonambiense, N. ribis, L. theobromae and L. pseudotheobromae were the most common species isolated. Phylogenies conducted with a limited number of isolates indicated non-clonal and potentially diverse populations occur on blueberry that warrant additional study. Botryosphaeria corticis, B. dothidea, and Diplodia seriata were isolated infrequently.

Transcriptomic and Physiological Analysis Reveals the Responses to Auxin and Abscisic Acid Accumulation During Vaccinium corymbosum Flower Bud and Fruit Development.

Blueberry (Vaccinium corymbosum) is reputed as a rich source of health-promoting phytonutrients, which contributes to its burgeoning consumer demand and production. However, blueberries are much smaller and have lower yields than most domesticated berries, and the inherent regulatory mechanisms remain elusive. In this study, the cytological and physiological changes, as well as comparative transcriptomic analysis throughout flower and fruit development in the southern highbush blueberry cultivar ‘O’Neal’ were performed. ‘O’Neal’ hypanthium and fruit exhibited a distinctive cell proliferation pattern, and auxin accumulation was unusual throughout development, while abscisic acid (ABA) levels rapidly increased in association with anthocyanin accumulation, total phenolic reduction and fruit maturation. Transcriptomic data showed that many differentially expressed genes (DEGs) were specifically expressed at each flower bud and fruit developmental stage. Further weighted gene co-expression network analysis (WGCNA) revealed numerous DEGs that correlated with the cell numbers of outer mesocarp and columella, showed two distinctive expression patterns. Most of the DEGs involved in auxin biosynthesis, transportation and signal transduction were upregulated, and this upregulation was accompanied by cell expansion, and flower bud and fruit development. However, individual members of VcSAUR50 and VcIAA9 families might be insensitive to auxin, suggesting that these genes play a distinctive role in the growth and development of blueberry fruits. These results will support future research to better understand the flower and fruit development of southern highbush blueberry.

Exploring environmental and storage factors affecting sensory, physical and chemical attributes of six southern highbush blueberry cultivars

Blueberry (Vaccinium spp.) is a specialty crop with expanding production and consumption worldwide. Southern Highbush Blueberries (SHB) require few chilling hours and include early-ripening cultivars which can be harvested in an early market window making the crop more profitable for growers in sub-tropical regions. To expand the marketability of the crop, fruit breeders are seeking to meet the current demand for fruit quality. To this end, this study gathered sensory measurements (firmness, sweetness, sourness, blueberry flavor, green flavor and off-flavors), chemical (pH, titratable acidity and soluble solids concentration), and physical attributes (compression force) on six SHB cultivars, in order to understand how fruit quality traits are affected by environmental conditions such as storage duration, year and harvest date. Differences across environmental conditions for all attributes were observed. Indigocrisp and Keecrisp were the firmest cultivars and maintained firmness over time in storage. Additionally, Indigocrisp was the sweetest and had the most blueberry and green flavors among the cultivars. On the other hand, Arcadia was the softest, as measured by sensory and compression force, but varied with year and harvest. Arcadia and Emerald were the least sweet and most sour of the cultivars, and Endura and Patrecia were intermediate for all sensory attributes. In general, sensory descriptors were well explained by instrumental measurements. Variations across seasons and storage were inconsistent among cultivars, but Indigocrisp was the most stable cultivar for the quality traits evaluated. In the end, all fruit quality traits assayed in this study were influenced by environmental conditions throughout the season.

High-density linkage map construction and identification of loci regulating fruit quality traits in blueberry

Fruit quality traits play a significant role in consumer preferences and consumption in blueberry (Vaccinium corymbosum L). The objectives of this study were to construct a high-density linkage map and to identify the underlying genetic basis of fruit quality traits in blueberry. A total of 287 F1 individuals derived from a cross between two southern highbush blueberry cultivars, ‘Reveille’ and ‘Arlen’, were phenotyped over three years (2016–2018) for fruit quality-related traits, including titratable acidity, pH, total soluble solids, and fruit weight. A high-density linkage map was constructed using 17k single nucleotide polymorphisms markers. The linkage map spanned a total of 1397 cM with an average inter-loci distance of 0.08 cM. The quantitative trait loci interval mapping based on the hidden Markov model identified 18 loci for fruit quality traits, including seven loci for fruit weight, three loci for titratable acidity, five loci for pH, and three loci for total soluble solids. Ten of these loci were detected in more than one year. These loci explained phenotypic variance ranging from 7 to 28% for titratable acidity and total soluble solid, and 8–13% for pH. However, the loci identified for fruit weight did not explain more than 10% of the phenotypic variance. We also reported the association between fruit quality traits and metabolites detected by Proton nuclear magnetic resonance analysis directly responsible for these fruit quality traits. Organic acids, citric acid, and quinic acid were significantly (P < 0.05) and positively correlated with titratable acidity. Sugar molecules showed a strong and positive correlation with total soluble solids. Overall, the study dissected the genetic basis of fruit quality traits and established an association between these fruit quality traits and metabolites.

Comparative anatomical and transcriptomic insights into Vaccinium corymbosum flower bud and fruit throughout development

BackgroundBlueberry (Vaccinium spp.) is characterized by the production of berries that are smaller than most common fruits, and the underlying mechanisms of fruit size in blueberry remain elusive. V. corymbosum ‘O’Neal’ and ‘Bluerain’ are commercial southern highbush blueberry cultivars with large- and small-size fruits, respectively, which mature ‘O’Neal’ fruits are 1 ~ 2-fold heavier than those of ‘Bluerain’. In this study, the ontogenetical patterns of ‘O’Neal’ and ‘Bluerain’ hypanthia and fruits were compared, and comparative transcriptomic analysis was performed during early fruit development.ResultsV. corymbosum ‘O’Neal’ and ‘Bluerain’ hypanthia and fruits exhibited intricate temporal and spatial cell proliferation and expansion patterns. Cell division before anthesis and cell expansion after fertilization were the major restricting factors, and outer mesocarp was the key tissue affecting fruit size variation among blueberry genotypes. Comparative transcriptomic and annotation analysis of differentially expressed genes revealed that the plant hormone signal transduction pathway was enriched, and that jasmonate-related TIFYs genes might be the key components orchestrating other phytohormones and influencing fruit size during early blueberry fruit development.ConclusionsThese results provided detailed ontogenetic evidence for determining blueberry fruit size, and revealed the important roles of phytohormone signal transductions involving in early fruit development. The TIFY genes could be useful as markers for large-size fruit selection in the current breeding programs of blueberry.

A comparative analysis on the anthocyanin composition of 74 blueberry cultivars from China

Blueberries are rich in anthocyanins and studied for their numerous beneficial effects on human health. The present study aimed to evaluate the anthocyanin composition of 74 blueberries collected in the south of China as well as analyze the phytochemical relationships among cultivars. Rabbiteye, southern highbush, northern highbush, half-highbush and lowbush blueberry cultivars were analyzed. Delphinidin, cyanidin, petunidin, and malvidin had three glycoside forms including galactoside, glucoside, and arabinoside, while peonidin had only galactoside form. The anthocyanin profile was similar among cultivars but amounts of individual compound differed. Malvidin, delphinidin and petunidin were the major contributors to total anthocyanin content (TAC), and malvidin-3-O-galactoside had the highest content among the 74 blueberry cultivars. Gardenblue had the highest TAC (2,235.51 ± 54.18 μg cyanidin 3-glucoside equivalent g−1 wet weight). In general, rabbiteye had significantly higher TAC than other categories analyzed in this study.

Endophytic fungi in blueberry cultivars, in three production areas of Argentina

Blueberries develop a shallow and fibrous root system, with sparse root hairs, normally colonized by mycorrhizal fungi. The presence of endophytic fungi in blueberry roots has been studied mainly in the area of origin of each species. The aims of the present study were to determine the occurrence of endophytic fungi in the roots of southern highbush blueberry (SHB) cultivars, in the three most important blueberry production areas of Argentina, and identify them. Soil samples with blueberry rootlets were obtained and endophytic fungi were isolated from them. Some of them by classical taxonomy identification, and, when this was not possible, PCR amplified material were sequenced (Macrogen laboratory), DNA fragments were analyzed with the Basic Local Alignment Search Tool (BLAST) and identified, through GenBank. Blueberry roots were found to be colonized by a large number of fungal genera, which varied greatly among locations and cultivars. Some of the endophytic fungi identified have pathogenic function, others are only plant hosts, and some of them have mycorrhizal function as is the case of genus Oidiodendron where we found O. maius and O. echinulatum. We may conclude that SHB is associated with local ericoid fungi, some of which are mycorrhizal and some dark septate endophytes, which, in most cases, do not match with those found in production regions of their native area, but same of them are important to promote blueberry growth.

Three-dimensional photogrammetry with deep learning instance segmentation to extract berry fruit harvestability traits

Fruit cluster characteristics such as compactness, maturity, berry number, and berry size, are important phenotypic traits associated with harvestability and yield of blueberry genotypes and can be used to monitor berry development and improve crop management. The goal of this study was to develop a complete framework of 3D segmentation for individual blueberries as they develop in clusters and to extract blueberry cluster traits. To achieve this goal, an image-capturing system was developed to capture blueberry images to facilitate 3D reconstruction and a 2D-3D projection-based photogrammetric pipeline was proposed to extract berry cluster traits. The reconstruction was performed for four southern highbush blueberry cultivars (‘Emerald’, ‘Farthing’, ‘Meadowlark’ and ‘Star’) with 10 cluster samples for each cultivar based on photogrammetry. A minimum bounding box was created to surround a 3D blueberry cluster to calculate compactness as the ratio of berry volume and minimum bounding box volume. Mask R-CNN was used to segment individual blueberries with the maturity property from 2D images and the instance masks were projected onto 3D point clouds to establish 2D-3D correspondences. The developed trait extraction algorithm was used to segment individual 3D blueberries to obtain berry number, individual berry volume, and berry maturity. Berry maturity was used to calculate cluster maturity as the ratio of the mature berry (blue colored fruit) number and the total berry (blue, reddish, and green colored fruit) number comprising the cluster. The accuracy of determining the fruit number in a cluster is 97.3%. The linear regression for cluster maturity has a R2 of 0.908 with a RMSE of 0.068. The cluster berry volume has a RMSE of 2.92 cm3 compared with the ground truth, indicating that the individual berry volume has an error of less than 0.292 cm3 for clusters with a berry number greater than 10. The statistical analyses of the traits for the four cultivars reveals that, in the middle of April, ‘Emerald’ and ‘Farthing’ were more compact than ‘Meadowlark’ and ‘Star’, and the mature berry volume of ‘Farthing’ was greater than ‘Emerald’ and ‘Meadowlark’, while ‘Star’ had the smallest mature berry size. This study develops an effective method based on 3D photogrammetry and 2D instance segmentation that can determine blueberry cluster traits accurately from a large number of samples and can be used for fruit development monitoring, yield estimation, and harvest time prediction.

Blue Light Does Not Affect Fruit Quality or Disease Development on Ripe Blueberry Fruit During Postharvest Cold Storage

Blueberry fruit are perishable after harvesting due to fruit softening, water loss and susceptibility to pathogens. Light, especially blue light, increases the accumulation of anthocyanins and reduces postharvest decay in some fruits, but the effect of blue light on postharvest fruit quality attributes in blueberries is unknown. In this study, we evaluated the effect of blue light on fruit quality, anthocyanin accumulation and disease development during postharvest cold storage (2 °C–4 °C) in two experiments with southern highbush blueberry ‘Star’ and rabbiteye blueberry ‘Alapaha’. Overall, diurnal blue light did not affect postharvest fruit quality attributes, such as visual defects, fruit compression, skin puncture, total soluble solid content and titratable acidity, in the two cultivars compared with their respective controls (diurnal white light or continuous darkness). Further, there was no effect of blue light on fruit color and anthocyanin accumulation. Fruit disease incidence in ‘Star’ ranged from 19.0% to 27.3% after 21 days and in ‘Alapaha’ from 44.9% to 56.2% after 24 days in postharvest storage, followed by 4 days at room temperature, but blue light had no consistent effect on postharvest disease incidence for either cultivar. Disease progression following artificial inoculations with Alternaria tenuissima and Colletotrichum acutatum in ‘Star’ was not influenced by light treatment prior to inoculation and during fruit storage. In a separate experiment, we tested the effect of blue light on color development in ‘Farthing’, a southern highbush blueberry cultivar with fruit prone to non-uniform ripening, whereby the stem-end remains green as the rest of the fruit turns blue. Although green stem-end spots turned blue over time, there was no statistically significant effect of the blue light treatment. Overall, these data indicate that blue light does not affect fruit quality attributes or disease development in ripe blueberry fruit during postharvest storage in the conditions investigated here.