Entomopathogenic Nematodes for the Management of Plum Curculio in Highbush Blueberry

Conotrachelus nenuphar Herbst (Coleoptera: Curculionidae) is a key pest of stone and pome fruits in the United States. Application of certain entomopathogenic nematode (EPN) species has shown efficacy in some crops when targeting the larval stage of C. nenuphar in soil. To date, however, no EPNs have been tested for the control of this pest in highbush blueberries. In 2020, laboratory and field studies were conducted to: (1) determine the persistence of Steinernema riobrave, S. carpocapsae, S. feltiae, and Heterorhabditis bacteriophora in acidic blueberry soil; (2) compare the virulence of these EPNs to C. nenuphar larvae and pupae; and (3) compare the efficacy of these EPN species to control this pest in blueberry fields. The greatest persistence in blueberry soil was exhibited by S. riobrave followed by S. carpocapsae. Superior virulence was observed in S. riobrave against C. nenuphar larvae and pupae. Promising levels of virulence were also observed in S. carpocapsae and S. feltiae against the larvae, but S. scarabaei had low virulence. In the field, S. riobrave provided significantly higher levels of C. nenuphar suppression (90%) than the other EPNs. The field efficacy of S. riobrave against C. nenuphar at low and high rates was confirmed in 2021. Steinernema riobrave has the potential to become an important component in the management of C. nenuphar in highbush blueberry.

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.

Changes in Anthocyanin and Antioxidant Contents during Maturation of Australian Highbush Blueberry (Vaccinium corymbosum L.) Cultivars

The Australian blueberry industry is worth over $300 million, but there is limited information on factors influencing their chemical composition, particularly their ripeness and harvest stage. This pilot study investigated changes in total monomeric anthocyanin content (TMAC; measured using the pH-differential method) and total antioxidant capacity (TAC; measured with the cupric reducing antioxidant capacity assay) of four Australian highbush blueberry cultivars (Denise, Blue Rose, Brigitta and Bluecrop) at four time points and three maturity stages (unripe, moderately ripe and fully ripe). The TAC of most cultivars decreased by 8–18% during ripening, although that of the Blue Rose cultivar increased markedly. However, the TAC of ripe fruit from this cultivar also fluctuated markedly throughout the harvest season (between 1168–2171 mg Trolox equivalents 100 g−1). The TMAC increased sharply between the medium-ripe and fully ripe maturity stages, with the Blue Rose cultivar showing the highest TMAC values (211 mg 100 g−1, compared to 107–143 mg 100 g−1 for the remaining varieties). The TMAC of ripe fruit from this cultivar also rose steadily throughout the harvest season, in contrast to most other cultivars where the TMAC fell slightly over time. These results indicate that the levels of health-benefitting compounds in Australian-grown highbush blueberries may depend not only on the cultivar, but also upon the time of harvest.

Honey bee (Apis mellifera) colony strength and its effects on pollination and yield in highbush blueberries (Vaccinium corymbosum)

Many pollination studies with honey bees have examined the effect of colony density on crop yield and yet overlook the effect of variation in the population size of these colonies. High colony density in northern highbush blueberry has been met with concerns from beekeepers who feel higher densities will intensify outbreaks of European foulbrood (EFB, Melissococcus plutonius, Truper and dé Clari), a honey bee brood disease. The purpose of this study was to confirm the prevalence of EFB in colonies pollinating blueberries and to determine whether field-level variation in the population of adult workers in colonies explained variation in blueberry fruit set and/or yield. We addressed these objectives over the course of two production seasons at 13 commercial blueberry fields in Oregon, USA, stocked with identical densities of 10 colonies/ha. We confirmed that all colonies had negligible symptoms of EFB at the start of blueberry pollination, but 53% of colonies in 2019 and 41% in 2020 had symptoms immediately following the pollination season. We also validated a method for rapidly assessing adult honey bee colony populations, namely by counting the rate of foragers returning to colonies, and it was found to be strongly correlated to true internal adult bee population independent of year and ambient temperature at the time of evaluation. Using returning forager counts, we determined there was considerable variation in the average population of colonies at each field, ranging from an estimated 10,300 to 30,700 adult worker bees per colony. While average colony strength did not predict variation in fruit set, it was related to variation in yield, independent of year. Our linear model of flight count (as a proxy for colony strength) predicts estimated yield increases of up to 25,000 kg/ha of blueberries could be achieved by colonies stronger than the recommended six frame minimum, suggesting that higher pollination benefits could be achieved without increasing hive density if stronger colonies are promoted.

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.

Accumulation of sugars and associated gene expression in highbush blueberries differ by cultivar, ripening stage, and storage temperature

BACKGROUND: The sweetness of highbush blueberries is a sensory quality standard for consumers. Changes in metabolites and expression of associated genes induce variation in the sensory quality of blueberries. OBJECTIVE: This work investigated the ripening mechanism of blueberries by measuring changes in organic acids and sugar content as well as the gene expression levels associated with sugar accumulation, such as β amylase, invertase, sucrose phosphate synthase, and tonoplast monosaccharide transporter genes, before and after harvesting. METHODS: We used three different blueberry cultivars (Duke, Sierra, and Elizabeth) that we harvested at two ripening stages in a randomized complete block design and then kept at room temperature or 4°C for 7 days. The organic acids and sugar content were measured via HPLC, and gene expression levels were analyzed by qPCR. RESULTS: Cultivars, ripening stage, and storage conditions affected the synthesis of sugars and degradation of organic acids to determine the sweetness in blueberries and the expression of tagged genes and analyses of compounds involved in the metabolic mechanism. CONCLUSIONS: The results provide insights into the mechanism underlying the ripening and the postharvest quality. This study may support the selection of suitable blueberry cultivars that meet customer demand.

Research in biologically active substances of the volatile fraction from Highbush blueberry vegetative organs

Ukraine ranked second in the world after Peru in the pace of laying new Highbush blueberry plantations. Experts estimate that in 2018, in Ukraine, from 0.7 thousand hectares to 1.0 thousand hectares of new Highbush blueberry plantations were laid. Over the past 12 years, previously little-known product, Highbush blueberries have become one of the main berry crops. At present, commercial plantations blueberries take the 3rd place after black currants and strawberries. Zhytomyr region boasts the biggest areas planted with Highbush blueberries in Ukraine, followed by Volyn and Kyiv. According to estimates, the export of blueberries from Ukraine may increase to 20 thousand tons in 5 years. In addition to the use of Highbush blueberries in the food industry, they are a promising source of BAS for pharmaceutical and medical use, so their study is a promising area of pharmaceutical science. In Ukraine, there are no domestic standardized medicines manufactured from Highbush blueberries, and there are only foreign dietary and functional supplements. Abroad, Highbush blueberry medicines are used to improve vision and as astringents for colitis, enterocolitis and diarrhoea. In this regard, the development of domestic standardized medicines based on Highbush blueberries raw materials is an urgent task for modern pharmacy. The aim of the research was to study the phytochemical profile of the volatile fraction of Highbush blueberry vegetative organs (leaves, stems and fruits). Materials and methods. The objects of research were the leaves, fruits and stems of Highbush blueberry (Vaccinium corymbosum L.), in which the composition of the the volatile fraction components was studied by chromato-mass spectrometry on a gas chromatograph Agilent Technologies 6890 with a mass spectrometric detector 5973. Results. Chromato-mass spectrometry in the composition of volatile fractions of leaves, fruits and stems of Highbush blueberries revealed 65 substances. 49 substances were identified in the Highbush blueberry leaves, of which 36 substances of terpene nature, 13 organic acids, and 2 compounds were not identified. In the Highbush blueberries fruits, 47 substances were found, of which 36 substances are of terpene nature, 14 are organic acids and 3 were not identified. In the Highbush blueberries stems, 50 substances were found, of which 33 substances are of terpene nature, 14 are organic acids and one was not identified. Conclusions. As a result of phytochemical studies, it is for the first time that the component composition of volatile fractions of leaves, stems and fruits of Highbush blueberries from the flora of Ukraine was established. The content of 65 substances was identified and established, including 14 organic acids and 39 terpene compounds.

Transcriptome based genetic resources from Rabbiteye and Southern Highbush blueberries

BACKGROUND: Blueberry is among the fastest growing fruit crops in the world, which is beneficial to human health and attracts extensive interests. In contrast to its rapid development and utilization, availability of molecular and genetic resources for blueberries are still scarce. OBJECTIVE: In present report, transcriptomic profiling of four widely cultivated varieties of Rabbiteye and Southern Highbush blueberries were characterized to assist the breeding programs. METHODS: Both de novo and reference-based assembly were conducted to generate the genetic resources that can be used in the further functional and breeding studies. RESULTS: De novo and reference-based assembly found average 136,350 and 158,123 non-redundant transcripts, respectively. Average 57,668 de novo assembled transcripts can be functionally annotated by homology search with different databases. We further detected 6,268 polymorphic simple sequence repeats, 566,913 high-quality single nucleotide polymorphisms and 88,662 insertion and deletions among the four varieties with comparison to a recently released reference genome of blueberry. Differentially expressed genes analysis showed that varieties of same species show less differences within species but larger differences between species. CONCLUSIONS: These comprehensive and high-quality genetic resources will contribute to a wide range of genetics and molecular breeding studies in blueberries.