Irrigation Practices for Southern Highbush Blueberry in Florida

This new 4-page publication of the UF/IFAS Horticultural Sciences Department provides guidance on irrigation requirements and practices to Florida Southern highbush blueberry growers. Written by Douglas A. Phillips and Jeffrey G. Williamson.https://edis.ifas.ufl.edu/hs1432

Preplant Fertilization Increases Substrate Microbial Respiration But Does Not Affect Southern Highbush Blueberry Establishment in a Coconut Coir-based Substrate

Coconut coir is widely used as a substrate component for southern highbush blueberry [(SHB) Vaccinium corymbosum L. interspecific hybrids] cultivation in containers. Coconut coir-based substrates can exhibit high potassium (K), sodium (Na), and chlorine (Cl) concentrations. Sodium in the substrate is particularly problematic because it can cause salinity stress and nutritional imbalances in young blueberry plants. Thus, Na removal is important to ensure transplant success. We hypothesized that preplant fertilization with large volumes of nutrient solution can reduce substrate salinity, replace Na with nutritional cations, and enhance blueberry establishment. We tested this hypothesis in a greenhouse experiment with ‘Snowchaser’ SHB grown in rhizoboxes filled with a 7:3 mix of coconut coir and perlite. Four different treatments were delivered every 24 hours starting 72 hours before transplant. Treatments included 1.75 g⋅L–1 calcium nitrate (CN), 2.38 g⋅L–1 monoammonium phosphate (MAP), deionized water, and well water. One rooted cutting was transplanted to each rhizobox. Rhizoboxes were fertigated during the 7-week cultivation period. We found that preplant fertilization increased nitrogen (N), phosphorus (P), and calcium (Ca) concentrations in the substrate without replacing Na. Thus, preplant fertilization increased substrate salinity. Preplant fertilization also promoted microbial respiration in the substrate at the start of the experiment. Treatments did not affect SHB root architecture, leaf area index, leaf greenness, or biomass accumulation, likely because nutrients delivered by the fertigation solution provided the plants with homogeneous optimal conditions. These findings suggest that preplant fertilization with large volumes of nutrient solution does not enhance blueberry establishment in coconut coir-based substrates.

High-quality reference genome and annotation aids understanding of berry development for evergreen blueberry (Vaccinium darrowii)

Vaccinium darrowii Camp (2n = 2x = 24) is a native North American blueberry species and an important source of traits such as low chill requirement in commercial southern highbush blueberry breeding (Vaccinium corymbosum, 2n = 4x = 48). We present a chromosomal-scale genome of V. darrowii generated by the combination of PacBio sequencing and high throughput chromatin conformation capture (Hi–C) scaffolding technologies, yielding a total length of 1.06 Gigabases (Gb). Over 97.8% of the genome sequences are scaffolded into 24 chromosomes representing the two haplotypes. The primary haplotype assembly of V. darrowii contains 34,809 protein-coding genes. Comparison to a V. corymbosum haplotype assembly reveals high collinearity between the two genomes with small intrachromosomal rearrangements in eight chromosome pairs. With small RNA sequencing, the annotation was further expanded to include more than 200,000 small RNA loci and 638 microRNAs expressed in berry tissues. Transcriptome analysis across fruit development stages indicates that genes involved in photosynthesis are downregulated, while genes involved in flavonoid and anthocyanin biosynthesis are significantly increased at the late stage of berry ripening. A high-quality reference genome and accompanying annotation of V. darrowii is a significant new resource for assessing the evergreen blueberry contribution to the breeding of southern highbush blueberries.

Ion-specific Limitations of Sodium Chloride and Calcium Chloride on Growth, Nutrient Uptake, and Mycorrhizal Colonization in Northern and Southern Highbush Blueberry

Excess salinity is becoming a prevalent problem for production of highbush blueberry (Vaccinium L. section Cyanococcus Gray), but information on how and when it affects the plants is needed. Two experiments, including one on the northern highbush (Vaccinium corymbosum L.) cultivar, Bluecrop, and another on the southern highbush (V. corymbosum interspecific hybrid) cultivar, Springhigh, were conducted to investigate their response to salinity and assess whether any suppression in growth was ion specific or due primarily to osmotic stress. In both cases, the plants were grown in soilless media (calcined clay) and fertigated using a complete nutrient solution containing four levels of salinity [none (control), low (0.7–1.3 mmol·d−1), medium (1.4–3.4 mmol·d−1), and high (2.8–6.7 mmol·d−1)] from either NaCl or CaCl2. Drainage was minimized in each treatment except for periodic determination of electrical conductivity (EC) using the pour-through method, which, depending on the experiment, reached levels as high as 3.2 to 6.3 dS·m−1 with NaCl and 7.8 to 9.5 dS·m−1 with CaCl2. Total dry weight of the plants was negatively correlated to EC and, depending on source and duration of the salinity treatment, decreased linearly at a rate of 1.6 to 7.4 g·dS−1·m−1 in ‘Bluecrop’ and 0.4 to 12.5 g·dS−1·m−1 in ‘Springhigh’. Reductions in total dry weight were initially similar between the two salinity sources; however, by the end of the study, which occurred at 125 days in ‘Bluecrop’ and at 111 days in ‘Springhigh’, dry weight declined more so with NaCl than with CaCl2 in each part of the plant, including in the leaves, stems, and roots. The percentage of root length colonized by mycorrhizal fungi also declined with increasing levels of salinity in Bluecrop and was lower in both cultivars when the plants were treated with NaCl than with CaCl2. However, leaf damage, which included tip burn and marginal necrosis, was greater with CaCl2 than with NaCl. In general, CaCl2 had no effect on uptake or concentration of Na in the plant tissues, whereas NaCl reduced Ca uptake in both cultivars and reduced the concentration of Ca in the leaves and stems of Bluecrop and in each part of the plant in Springhigh. Salinity from NaCl also resulted in higher concentrations of Cl and lower concentrations of K in the plant tissues than CaCl2 in both cultivars. The concentration of other nutrients in the plants, including N, P, Mg, S, B, Cu, Fe, Mn, and Zn, was also affected by salinity, but in most cases, the response was similar between the two salts. These results point to ion-specific effects of different salts on the plants and indicate that source is an important consideration when managing salinity in highbush blueberry.

Dissecting the subtropical adaptation traits and cuticle synthesis pathways via the genome of the subtropical blueberry Vaccinium darrowii

Vaccinium darrowii is a subtropical wild blueberry species, which was used to breed economically important southern highbush cultivars. The adaptation traits of V. darrowii to subtropical climate would provide valuable information for breeding blueberry and perhaps other plants, especially against the background of global warming. Here, we assembled the V. darrowii genome into 12 pseudochoromosomes using Oxford Nanopore long reads complemented with Hi-C scaffolding technologies, and predicted 41 815 genes using RNAseq evidence. Syntenic analysis across three Vaccinium species revealed a highly conserved genome structure, with the highest collinearity between V. darrowii and V. corymbosum. This conserved genome structure may explain the high fertilization during crossbreeding between V. darrowii and other blueberry cultivars. Gene expansion and tandem duplication analysis indicated possible roles of defense and flowering associated genes in adaptation of V. darrowii to the subtropics. The possible SOC1 genes in V. darrowii were identified with phylogeny and expression analysis. Blueberries are covered in a thick cuticle layer and contain anthocyanins, which confer their powdery blue color. Using RNA-sequencing, the cuticle biosynthesis pathways of Vaccinium species were delineated here in V. darrowii. This result could serve as a reference for breeding berries with customer-desired colors. The V. darrowii reference genome, together with the unique traits of this species, including diploid genome, short vegetative phase, and high compatibility in hybridization with other blueberries, make V. darrowii a potential research model for blueberry species.

Harvest of Southern Highbush Blueberry with a Modified, Over-the-Row Mechanical Harvester: Use of Soft-Catch Surfaces to Minimize Impact Bruising

Harvest of fresh market, southern highbush blueberries (SHB) is labor intensive and costly, leading to a demand for alternative harvest methods. Recent research has shown potential for mechanically harvesting blueberries with minimal bruising by using a modified over-the-row (OTR) harvester. For two harvests, SHB cultivars Optimus and Vireo were either hand-harvested (HH) or mechanically harvested (MH) by two commercial harvesters, one unmodified with standard hard-catch surfaces (HCS) or by the other modified with soft-catch surfaces (SCS). For Harvest 1, fruit from all harvest methods were hand-sorted into the following categories: blue fruit (marketable), red fruit, green fruit and culls. Samples from each cultivar and treatment were then held at 24 °C overnight, and the following day firmness and impact bruise severity were determined. Harvest 2 had identical harvest treatments; however, the fruit were sorted on a commercial packing line prior to packing in clamshells (n = 16). A subsample was held overnight as in Harvest 1 for bruise severity rating, while the remaining fruit were stored at 1 °C for 14 days (d). Although percent marketable fruit was more affected by cultivar than harvest method, determination of bruise severity revealed the benefit of harvest with SCS over HCS for both cultivars. The former had 16–26% severe bruising, compared to 27–40% for the latter; HH had 1–4%. During storage, HH fruit remained firmer than HCS and SCS, which were similar. After 14 d, firmness for “Optimus” was 239 N (HH), 157 N (HCS and SCS) and for “Vireo” it was 189 (HH), 155 N (HCS and SCS). Fruit weight loss increased during storage (1.1–4.4%), but there was no difference due to catch plate surface. SSC, TTA and Ratio were not affected by catch surface type or storage period within cultivar. Using modifications such as “soft” catch surfaces on currently available OTR harvesters reduces impact bruise damage; however, impacts incurred during commercial packing operations can negate this effect. MH for fresh market blueberries may provide an economical alternative for blueberry growers; however, with current technology, the fruit should be utilized within a week of harvest.

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

Background Blueberry (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. Results V. 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. Conclusions These 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.