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Recent climate change has resulted in warmer temperatures. Warmer temperatures from autumn to spring has negatively affected dormancy progression, cold (de)acclimation, and cold tolerance in various temperate fruit trees. In Japan, a physiological disorder known as flowering disorder, which is an erratic flowering and bud break disorder, has recently emerged as a serious problem in the production of the pome fruit tree, Japanese (Asian) pear ( Pyrus pyrifolia Nakai). Due to global warming, the annual temperature in Japan has risen markedly since the 1990s. Surveys of flowering disorder in field-grown and greenhouse-grown Japanese pear trees over several years have indicated that flowering disorder occurs in warmer years and cultivation conditions, and the risk of flowering disorder occurrence is higher at lower latitudes than at higher latitudes. Susceptibility to flowering disorder is linked to changes in the transcript levels of putative dormancy/flowering regulators such as DORMANCY-ASSOCIATED MADS-box ( DAM ) and FLOWERING LOCUS T ( FT ). On the basis of published studies, we conclude that autumn–winter warm temperatures cause flowering disorder through affecting cold acclimation, dormancy progression, and floral bud maturation. Additionally, warm conditions also decrease carbohydrate accumulation in shoots, leading to reduced tree vigor. We propose that all these physiological and metabolic changes due to the lack of chilling during the dormancy phase interact to cause flowering disorder in the spring. We also propose that the process of chilling exposure rather than the total amount of chilling may be important for the precise control of dormancy progression and robust blooming, which in turn suggests the necessity of re-evaluation of the characteristics of cultivar-dependent chilling requirement trait. A full understanding of the molecular and metabolic regulatory mechanisms of both dormancy completion (floral bud maturation) and dormancy break (release from the repression of bud break) will help to clarify the physiological basis of dormancy-related physiological disorder and also provide useful strategies to mitigate or overcome it under global warming.

Ultraviolet-B (UV-B) light (280–315 nm) is an important environmental signal that regulates plant development and photomorphogenesis, while also affecting the flavonoid pathway, including anthocyanin biosynthesis. Regarding the effects of UV-B radiation on fruits, the effects of a short-term or postharvest irradiation on fruit quality have been well-documented, but the effects of a long-term preharvest UV-B irradiation on fruit growth and coloration remain unclear. Thus, in this study, we investigated the effects of a long-term treatment involving an environmentally relevant UV-B dose on highbush blueberry (Vaccinium corymbosum) fruit. The preharvest UV-B treatment quickly promoted fruit growth and sugar accumulation, which is not commonly observed in other fruit tree species. The UV-B exposure also accelerated fruit ripening and coloration. The dual-luciferase assay proved that in blueberries, expression of VcUFGT encoding anthocyanin biosynthesis key enzyme, is positively and negatively regulated by VcMYBA1 and VcMYBC2, respectively. Throughout the fruit development stage, the UV-B treatment up-regulated VcMYBPA1 expression, which increased VcUFGT expression via VcMYBA1. In the green fruit stage, the UV-B treatment increased HY5 encoding UV receptor, which up-regulates VcMYBPA1 and down-regulates VcMYBC2, thereby promotes the accumulation of anthocyanins. On the other hand, excessive anthocyanin synthesis was inhibited by increased VcMYBC2 levels in mature fruits when exposed to UV-B light through HY5-independent pathway. In conclusion, anthocyanin-related MYB activators and repressor may coordinately balance the accumulation of anthocyanins in blueberry fruits, with UV-B treatments possibly influencing their effects in a stage-specific manner. The potential utility of preharvest UV-B treatments for improving blueberry fruit quality is discussed herein.

Most deciduous fruit trees cultivated in the temperate zone require a genotype-dependent amounts of chilling exposure for dormancy release and bud break. In Japanese apricot (Prunus mume), DORMANCY-ASSOCIATED MADS-box 6 (PmDAM6) may influence chilling-mediated dormancy release and bud break. In this study, we attempted to elucidate the biological functions of PmDAM6 related to dormancy regulation by analyzing PmDAM6-overexpressing transgenic apple (Malus spp.). We generated 35S:PmDAM6 lines and chemically inducible overexpression lines, 35S:PmDAM6-GR. In both overexpression lines, shoot growth was inhibited and early bud set was observed. In addition, PmDAM6 expression repressed bud break competency during dormancy and delayed bud break. Moreover, PmDAM6 expression increased abscisic acid levels and decreased cytokinins contents during the late dormancy and bud break stages in both 35S:PmDAM6 and 35S:PmDAM6-GR. Our analysis also suggested that abscisic acid levels increased during dormancy but subsequently decreased during dormancy release whereas cytokinins contents increased during the bud break stage in dormant Japanese apricot buds. We previously revealed that PmDAM6 expression is continuously down-regulated during dormancy release toward bud break in Japanese apricot. The PmDAM6 expression pattern was concurrent with a decrease and increase in the abscisic acid and cytokinins contents, respectively, in dormant Japanese apricot buds. Therefore, we hypothesize that PmDAM6 represses the bud break competency during dormancy and bud break stages in Japanese apricot by modulating abscisic acid and cytokinins accumulation in dormant buds.

Interspecific hybridization is a common breeding approach for introducing novel traits and genetic diversity to breeding populations. Southern highbush blueberry (SHB) is a blueberry cultivar group that has been intensively bred over the last 60 years. Specifically, it was developed by multiple interspecific crosses between northern highbush blueberry [NHB, Vaccinium corymbosum L. (2n = 4x = 48)] and low-chill Vaccinium species to expand the geographic limits of highbush blueberry production. In this study, we genotyped polyploid blueberries, including 105 SHB, 17 NHB, and 10 rabbiteye blueberry (RE) (Vaccinium virgatum Aiton), from the accessions planted at Poplarville, Mississippi, and accessions distributed in Japan, based on the double-digest restriction site-associated DNA sequencing. The genome-wide SNP data clearly indicated that RE cultivars were genetically distinct from SHB and NHB cultivars, whereas NHB and SHB were genetically indistinguishable. The population structure results appeared to reflect the differences in the allele selection strategies that breeders used for developing germplasm adapted to local climates. The genotype data implied that there are no or very few genomic segments that were commonly introgressed from low-chill Vaccinium species to the SHB genome. Principal component analysis-based outlier detection analysis found a few loci associated with a variable that could partially differentiate NHB and SHB. These SNP loci were detected in Mb-scale haplotype blocks and may be close to the functional genes related to SHB development. Collectively, the data generated in this study suggest a polygenic adaptation of SHB to the southern climate, and may be relevant for future population-scale genome-wide analyses of blueberry.

In 2010, a major scientific milestone was achieved for tree fruit crops: publication of the first draft whole genome sequence (WGS) for apple ( Malus domestica ). This WGS, v1.0, was valuable as the initial reference for sequence information, fine mapping, gene discovery, variant discovery, and tool development. A new, high quality apple WGS, GDDH13 v1.1, was released in 2017 and now serves as the reference genome for apple. Over the past decade, these apple WGSs have had an enormous impact on our understanding of apple biological functioning, trait physiology and inheritance, leading to practical applications for improving this highly valued crop. Causal gene identities for phenotypes of fundamental and practical interest can today be discovered much more rapidly. Genome-wide polymorphisms at high genetic resolution are screened efficiently over hundreds to thousands of individuals with new insights into genetic relationships and pedigrees. High-density genetic maps are constructed efficiently and quantitative trait loci for valuable traits are readily associated with positional candidate genes and/or converted into diagnostic tests for breeders. We understand the species, geographical, and genomic origins of domesticated apple more precisely, as well as its relationship to wild relatives. The WGS has turbo-charged application of these classical research steps to crop improvement and drives innovative methods to achieve more durable, environmentally sound, productive, and consumer-desirable apple production. This review includes examples of basic and practical breakthroughs and challenges in using the apple WGSs. Recommendations for “what’s next” focus on necessary upgrades to the genome sequence data pool, as well as for use of the data, to reach new frontiers in genomics-based scientific understanding of apple. Genetics: Apple genome sequencing begins to bear fruit Almost 10 years since the first draft of the apple genome was published, the insights it has afforded are being used to improve crops, while next generation DNA sequencing is enabling the breeding value of individual plants to be more rapidly assessed. In this review, Cameron Peace at Washington State University in Pullman, US, and colleagues describe the impact whole genome sequencing of the Golden Delicious apple has had on our understanding of how cultivated apples evolved, and the genomic regions controlling fruit firmness and flavor, tree growth dynamics, responses to water and nutrient availability, and other such traits. These early discoveries have also paved the way for trait-predictive tests which should further accelerate the breeding of improved apple trees, and epigenetic studies to better understand how environmental factors trigger heritable changes in apple characteristics.

‘Monthong’ is one of the most popular durian cultivars in Thailand and international markets because of its good taste, mild aroma, firm texture, and long shelf life. Premium-grade durians are expensive and in high demand, but clear criteria are still limited. In this study, ‘Monthong’ that won prizes in competitions were selected to examine their characteristics. The common traits found in the winning fruits were considered as potential indicators of premium quality. It was found that all winning durians had a pulp dry matter (DM) content of at least 36%. Moreover, pulp DM also showed a positive correlation with flavor (r = 0.59, P = 0.038). Nevertheless, results from a public sensory test showed that pulp DM ≥36% alone was not enough to define premium quality (χ² = 0.120, P > 0.05). Principal component analysis implied that sweetness, nuttiness, aroma, and low fiber content also influenced consumer preference. When DM ≥36% was combined with these favorable sensory traits, consumers could identify premium durians more accurately. In this case, 76.3% correctly identified premium-quality fruit. These findings suggest that a DM of ≥36% with key sensory traits serves as a reliable criterion for defining the premium quality of ‘Monthong’ durian.

In support, quantitative trait loci for vegetative and flower buds were differentially located in Japanese apricot (Prunus mume) (Kitamura et al., 2018). [...]temporal suspension of developmental arrest in sweet cherry (P. avium) flower buds was linked to the specific morphological stage regardless of the bud break capacity of dormant buds, which is generally linked to the vegetative bud dormancy depth (Fadón et al., 2018;Goeckeritz and Hollender, 2021;Yamane et al., 2021). [...]warming in fall, winter and spring due to climate change is expected to impact bud dormancy release, timing and intensity of growth resumption and bloom progression, all of which may threaten the stability of fruit and timber production and disrupt the sustainability of the ecosystem (Luedeling, 2012). While recent molecular studies have improved our understanding of the mechanisms that regulate and execute the bud dormancy cycle in woody perennials including fruit trees (Falavigna et al., 2019;Yang et al., 2021;Nilsson, 2022), a complete picture is still elusive. [...]our ability to develop powerful and reliable means to control timing and intensity of dormancy, flower primordia development, bud break and bloom is still limited. HereAndré et al.reported that SVL also contributes to the regulation of short day-induced growth cessation and bud set through its expression in leaves. [...]SVL represses FT2 transcription and decreases active GAs amounts by repressing the transcription of GA20 OXIDASE.

Bud dormancy is an important developmental stage affecting blooming date and leafing date (LD) in Japanese apricot (Prunus mume), but the genetic factors controlling the chilling requirement (CR) and heat requirement (HR) for dormancy release and bud burst time remain to be elucidated. Here, a quantitative trait locus (QTL) analysis using two F1 segregating populations was conducted to identify loci affecting these traits. The genotyping-by-sequencing technique was used to construct two high-density genetic maps, one for NKSC, a population derived from high-chill ‘Nanko’ crossed with low-chill ‘SC’, covering 660.2 cM with 408 markers, and one for NINK, a population derived from low-chill ‘Ellching’ crossed with ‘Nanko’, covering 1314.2 cM with 718 markers. We observed four traits: CR and HR for dormancy release, blooming date, and LD over several years. To identify the QTL controlling the downregulation of DORMANCY-ASSOCIATED MADS-box6 (PmDAM6) in January’s leaf buds, in which PmDAM6 could act as a dose-dependent inhibitor of bud break, its transcript levels in leaf buds were determined. All traits segregated in the analyzed seasons in both populations. For leaf bud dormancy, CR and LD were highly correlated across years and traits in the NKSC population, while HR, LD, and PmDAM6 expression were highly correlated in the NINK population. The QTL analyses localized the significant QTLs controlling leaf bud CR and HR, LD, and PmDAM6 expression in leaf buds to a region in linkage group 4, which suggests that this locus controls dormancy release, bud break, and PmDAM6’s downregulation in Japanese apricot leaf buds.

Bud endodormancy in woody plants plays an important role in their perennial growth cycles. We previously identified a MADS box gene, DORMANCY-ASSOCIATED MADS (PmDAM6), expressed in the endodormant lateral buds of Japanese apricot (Prunus mume), as a candidate for the dormancy-controlling gene. In this study, we demonstrate the growth inhibitory functions of PmDAM6 by overexpressing it in transgenic poplar (Populus tremula X Populus tremuloides). Transgenic plants constitutively expressing PmDAM6 showed growth cessation and terminal bud set under environmental conditions in which control transformants continued shoot tip growth, suggesting the growth inhibitory functions of PmDAM6. In the Japanese apricot genome, we identified six tandemly arrayed PmDAM genes (PmDAM1-PmDAM6) that conserve an amphiphilic repression motif, known to act as a repression domain, at the carboxyl-terminal end, suggesting that they all may act as transcriptional repressors. Seasonal expression analysis and cold treatment in autumn indicated that all PmDAMs were repressed during prolonged cold exposure and maintained at low levels until endodormancy release. Furthermore, PmDAM4 to PmDAM6 responses to a short period of cold exposure appeared to vary between low-and high-chill genotypes. In the highchill genotype, a short period of cold exposure slightly increased PmDAM4 to PmDAM6 expression, while in the low-chill genotype, the same treatment repressed PmDAM4 to PmDAM6 expression. Furthermore, PmDAM4 to PmDAM6 expression was negatively correlated with endodormancy release. We here discuss the genotype-dependent seasonal expression patterns of PmDAMs in relation to their involvement in endodormancy and variation in chilling requirements.

Fruit quality represents the major constraints to consumer acceptance of new blueberry cultivars. However, breeding for fruit quality is challenging due to its complex inheritance and genotype × environment interaction. Despite previous efforts to detect quantitative trait loci (QTL) associated with fruit quality traits, most of the identified QTL explain only a fraction of the total variability or lack stability across multiple environments. In this study, we investigated multiple fruit quality traits and phenology-related traits of 187 diverse southern highbush blueberry germplasm over 2–4 years. Significant phenotypic variation across observation years was detected for most traits. Genome-wide association study (GWAS) failed to identify stable peaks supported by multiple observation years, indicating complex control of fruit-related traits. To elucidate factors contributing to phenotypic variation, the relationship between observed phenotypic values and the stability measure of these values was examined. Significant correlations were found between the variation of phenology-related traits and the stability of fruit-related traits; it was found that early blooming and ripening accessions tended to exhibit variable firmness over the years. Additionally, size variability was influenced by the fruit size itself: accessions producing smaller fruit tended to show more variation in size over the years. Furthermore, GWAS conducted on the stability indices identified novel marker–trait associations that were not detected using normalized phenotypic values only, and their effects on fruit-related traits were similarly dependent on environment (observation year). Collectively, these findings deepen our understanding of variability in fruit-related traits and provide insights into their genetic control, thereby advancing breeding for superior cultivars with stable phenotypic performance.