Low Chilling Requirement Research Articles

Alternative splicing and deletion in S-RNase confer stylar-part self-compatibility in the apple cultivar 'Vered'.

Although self-incompatibility in apples (Malus × domestica Borkh.) is regulated by a single S-locus with multiple S-haplotypes that comprise pistil S (S-RNase) and pollen S genes, it is not desirable in commercial orchards because it requires cross-pollination to achieve stable fruit production. Therefore, it is important to identify and characterize self-compatible apple cultivars. However, little is known about self-compatibility(SC) and its underlying molecular mechanisms in apples. In this study, we discovered that 'Vered', an early maturing and low chilling-requiring apple cultivar, exhibits stable SC, which was evaluated via self-pollination tests. The S-genotype of 'Vered' was designated as S24S39sm. Results of genetic analysis of selfed progeny of 'Vered' revealed that SC is associated with the S39sm-haplotype, and molecular analyses indicated that it is caused by alternative splicing and a 205-bp deletion in S39sm-RNase. These events induce frameshifts and ultimately produce the defective S39sm-RNase isoforms that lack their C-terminal half. These results enabled us to develop a 117-bp DNA marker that can be used to assist in the selection of self-compatible apples with the dysfunctional S39sm-RNase. Thus, analysis of 'Vered' provided insights into the molecular mechanism of the very rare trait of natural stylar-part SC. Moreover, 'Vered' is a valuable genetic resource for breeding cultivars with SC and/or low chilling requirement in apple. Our findings contribute to a better understanding of self-compatible molecular mechanisms in apple and provide for the accelerated breeding of self-compatible apple cultivars.

Origins and Genetic Characteristics of Egyptian Peach.

Peach (Prunus persica), a significant economic fruit tree in the Rosaceae family, is extensively cultivated in temperate and subtropical regions due to its abundant genetic diversity, robust adaptability, and high nutritional value. Originating from China over 4000 years ago, peaches were introduced to Persia through the Silk Road during the Han Dynasty and gradually spread to India, Greece, Rome, Egypt, Europe, and America. Currently grown in more than 80 countries worldwide, the expansion of peach cultivation in Egypt is mainly due to the development and utilization of peach varieties with low chilling requirements. These varieties exhibit unique phenotypic characteristics such as early maturity, reduced need for winter cold temperatures, low water requirements, and high economic value. In this study, a systematic analysis was conducted on the genetic characteristics and kinship relationships of peaches with low chilling requirements in Egypt. We conducted a comprehensive evolutionary and Identity-by-Descent (IBD) analysis on over 300 peach core germplasm resources, including Egyptian cultivars with low chilling requirements, to investigate their origin and genetic characteristics. The evolutionary analysis revealed that 'Bitter almond' is closely related to China's wild relative species Prunus tangutica Batal, while 'Early grand' shares one branch with Chinese ornamental peach cultivars, and 'Nemaguard' clusters with some ancient local varieties from China. The IBD analysis also indicated similar genetic backgrounds, suggesting a plausible origin from China. Similarly, the analysis suggested that 'Swelling' may have originated from the Czech Republic while 'Met ghamr' has connections to South Africa. 'Desert red', 'Early swelling', and 'Florida prince' are likely derived from Brazil. These findings provide valuable insights into the genetic characteristics of Egyptian peach cultivars. They offer a significant foundation for investigating the origin and spread of cultivated peaches worldwide and serve as a valuable genetic resource for breeding low chilling requirement cultivars, which is of considerable significance for the advancement of peach cultivation in Egypt.

Physiological adaptations of the Japanese plum tree for agricultural productivity: A promising crop for high altitude tropics

The Japanese plum tree is of great importance in the productive development of Colombian fruit growers due to its nutritional contribution to human health, its great adaptability in the tropical highlands, and its good yields. This review presents the current investigative state of physiology of this plant and its management in tropical highlands, including aspects such as its ecophysiology, forced production, gas exchange, flowering, pollination, and fruit development. In Colombia, Japanese plum production systems are adapted between 1,670 and 2,900 m a.s.l., average solar brightness of 1,400 h per year, 12 h photoperiods, temperatures between 14 and 20°C during the day and 6 and 8°C during the night, and rainfall between 700 and 1,600 mm per year. Under these conditions, management can be implemented to produce cyclical crops of the Japanese plum. This management consists of the selection of varieties with low chilling requirement, chemical defoliation, proper fertilization, fruit and green pruning, and the application of chemical substances that promote the breaking of flower buds. Flowering and pollination require a high specificity so that they do not present incompatibility. The growth and development of the fruit requires 1,538 degree days until harvest. This review indicates the great adaptability, management, and production of Japanese plum in the Colombian high tropics.

Feasting on the ordinary or starving for the exceptional in a warming climate: Phenological synchrony between spongy moth (Lymantria dispar) and budburst of six European tree species.

Global warming is affecting the phenological cycles of plants and animals, altering the complex synchronization that has co-evolved over thousands of years between interacting species and trophic levels. Here, we examined how warmer winter conditions affect the timing of budburst in six common European trees and the hatching of a generalist leaf-feeding insect, the spongy moth Lymantria dispar, whose fitness depends on the synchrony between egg hatch and leaf emergence of the host tree. We applied four different temperature treatments to L. dispar eggs and twig cuttings, that mimicked warmer winters and reduced chilling temperatures that are necessary for insect diapause and bud dormancy release, using heated open-top chambers (ambient or +3.5°C), and heated greenhouses (maintained at >6°C or >10°C). In addition, we conducted preference and performance tests to determine which tree species the larvae prefer and benefit from the most. Budburst success and twig survival were highest for all tree species at ambient temperature conditions, whereas it declined under elevated winter temperature for Tilia cordata and Acer pseudoplatanus, likely due to a lack of chilling. While L. dispar egg hatch coincided with budburst in most tree species within 10 days under ambient conditions, it coincided with budburst only in Quercus robur, Carpinus betulus, and, to a lesser extent, Ulmus glabra under warmer conditions. With further warming, we, therefore, expect an increasing mismatch in trees with high chilling requirements, such as Fagus sylvatica and A. pseudoplatanus, but still good synchronization with trees having low chilling requirements, such as Q. robur and C. betulus. Surprisingly, first instar larvae preferred and gained weight faster when fed with leaves of F. sylvatica, while Q. robur ranked second. Our results suggest that spongy moth outbreaks are likely to persist in oak and hornbeam forests in western and central Europe.

Feasible strategies for efficient propagation system of Paeonia lactiflora ‘Hang Baishao’: In vitro culture of embryos

Herbaceous peony (Paeonia lactiflora Pall.) is a renowned traditional Chinese flower, which has been cherished by people since ancient times. It holds significant value as both an agricultural cash crop and an ornamental and medicinal plant. However, the lack of in vitro propagation system has been long hindered the commercial production of this species and the development of new cultivars. In this study, the low chilling requirement cultivar Paeonia lactiflora ‘Hang Baishao’ that originated from low latitudes of China, was used to study the in vitro culture of embryos. The results of our experiment showed that the optimal medium for in vitro culture of embryos was a 1/2 Murashige and Skoog (MS) medium supplemented with 1.0 mg/L 6-benzyladenine (6-BA), 1.0 mg/L gibberellic acid (GA3) and 2.0 g/L polyvinyl pyrrolidone (PVP). Additionally, histological observations revealed the crucial role of vascular bundle development in the survival of transplants. Plants with well-developed vascular tissue exhibited better transplanting success. This study presents, for the first time, a protocol for embryos propagation and transplanting of ‘Hang Baishao’, a cultivar with low chilling requirement (CR) during winter. This study provides an efficient method for in vitro culture of ‘Hang Baishao’, and makes it possible for large-scale production, utilization, and germplasm preservation of this species.

Bud endodormancy – a familiar but still unknown key adaptive trait in extratropical woody plants

In autumn, the buds of extratropical trees are in a state of endodormancy, since regardless of the prevailing environmental conditions, growth cannot be activated in these buds because the dormancy is caused by physiological factors in the buds. In natural conditions the growth-arresting physiological factors are removed by prolonged exposure to low chilling temperatures. This phenomenon is a key adaptive trait, for it prevents ‘false spring’, i.e., untimely bud burst during mild spells in autumn and winter, which would lead to cold damage during subsequent cold periods. Traditionally, endodormancy and the chilling requirement have been important in practical horticulture, as cultivars with low and high chilling requirements have been bred for locations in warm and cool climates, respectively. More recently, endodormancy and the chilling requirement have become major research themes in climate change studies where climatic change impacts are assessed by means of process-based tree phenology models. The dormancy phenomenon has been studied thoroughly at the whole-tree level for a hundred years, and several genes and genetic pathways involved have recently been identified in tree species such as hybrid aspen, apple, and pear. There is an urgent need, however, to integrate molecular physiological studies with modelling studies so as to understand the impact of climate change on the regulation of dormancy. To that end, we shall provide an overview of bud endodormancy research.

A Study of the Molecular Regulatory Network of VcTCP18 during Blueberry Bud Dormancy.

BRANCHED1 (BRC1) is a crucial member of the TEOSINTE BRANCHED1/CYCLOIDEA/PCF (TCP) gene family and is well known for playing a central role in shoot branching by controlling buds' paradormancy. However, the expression characteristics and molecular regulatory mechanism of BRC1 during blueberry bud dormancy are unclear. To shed light on these topics, shoots of three blueberry cultivars with different chilling requirements (CRs) were decapitated in summer to induce paradormancy release and subjected to different levels of chilling in winter to induce endodormancy release. The results showed that the high-CR cultivar 'Chandler' had the strongest apical dominance among the three cultivars; additionally, the expression of VcTCP18, which is homologous to BRC1, was the highest under both the decapitation treatment and low-temperature treatment. The 'Emerald' cultivar, with a low CR, demonstrated the opposite trend. These findings suggest that VcTCP18 plays a negative regulatory role in bud break and that there may be a correlation between the CR and tree shape. Through yeast 1-hybrid (Y1H) assays, we finally screened 21 upstream regulatory genes, including eight transcription factors: zinc-finger homeodomain protein 1/4/5/9, MYB4, AP2-like ethylene-responsive transcription factor AINTEGUMENTA (ANT), ASIL2-like, and bHLH035. It was found that these upstream regulatory genes positively or negatively regulated the expression of VcTCP18 based on the transcriptome expression profile. In summary, this study enriched our understanding of the regulatory network of BRCl during bud dormancy and provided new insights into the function of BRC1.

Exploitation of genotypic variation in chilling and heat requirements for flowering in Prunus armeniaca and Prunus persica (L.) Batsch cultivars

In a rapidly changing climate resulting in warmer winters, knowledge on the chilling and heat requirements of deciduous fruit tree cultivars is a pre-requisite for adaptation; however little is known on commercially available P. armeniaca (apricot) and P. persica (L.) Batsh (peach/nectarine) cultivars. We quantified the chilling and heat requirements of 50 apricot, and 49 peach/nectarine cultivars commercially grown, evaluated the consistency of results over different years, and relationships with bloom dates. The range of chilling requirements was similar in the apricot and the peach/nectarine cultivars studied (43–73 Chilling Portions, 807–1473 Chill Units), yet a greater portion of apricot and non-melting peach cultivars were categorized under the high chilling requirement group. Apricot cultivars had a later day of breaking dormancy, but similar full bloom day compared with the peach/nectarine cultivars, which are related to having lower heat requirements for flowering (mean 3783 vs. 5100 Growing Degree Hours, respectively). Only few apricot (‘Anegat’ and ‘Pluot’) and peach/nectarine (‘Carla’, ‘Tastired’, ‘Royal Queen’, ‘Crimson Lady’ and ‘Ferlate’) cultivars attain combination of low or medium chilling requirements, and high heat requirements, linked with better resilience to warm winters, and ensuring late bloom time to avoid frost damages. Measured values of chilling requirements were higher in the high− chill year, in apricot, but not in peach/nectarine cultivars. The chill accumulation during the 2016–2022 experimental autumn/winter periods ranged from 72 to 86 Chilling Portions. Under the current climate conditions in Naoussa, and considering recent predictions, chilling accumulation will be insufficient for the ‘High’ chill cultivars of both species, therefore choosing the appropriate cultivars and breeding efforts are required for adaptation.

MADS-box protein PpDAM6 regulates chilling requirement-mediated dormancy and bud break in peach.

Bud dormancy is crucial for winter survival and is characterized by the inability of the bud meristem to respond to growth-promotive signals before the chilling requirement (CR) is met. However, our understanding of the genetic mechanism regulating CR and bud dormancy remains limited. This study identified PpDAM6 (DORMANCY-ASSOCIATED MADS-box) as a key gene for CR using a GWAS (Genome-Wide Association Study) analysis based on structural variations (SVs) in 345 peach (Prunus persica (L.) Batsch) accessions. The function of PpDAM6 in CR regulation was demonstrated by transiently silencing the gene in peach buds and stably overexpressing the gene in transgenic apple (Malus × domestica) plants. The results showed an evolutionarily conserved function of PpDAM6 in regulating bud dormancy release, followed by vegetative growth and flowering, in peach and apple. The 30-bp deletion in the PpDAM6 promoter was substantially associated with reducing PpDAM6 expression in low-CR accessions. A PCR marker based on the 30-bp indel was developed to distinguish peach plants with non-low and low CR. Modification of the H3K27me3 marker at the PpDAM6 locus showed no apparent change across the dormancy process in low- and non-low-chilling requirement cultivars. Additionally, H3K27me3 modification occurred earlier in low-CR cultivars on a genome-wide scale. PpDAM6 could mediate cell-cell communication by inducing the expression of the downstream genes PpNCED1 (9-cis-epoxycarotenoid dioxygenase 1), encoding a key enzyme for ABA biosynthesis, and CALS (CALLOSE SYNTHASE), encoding callose synthase. We shed light on a gene regulatory network formed by PpDAM6-containing complexes that mediate CR underlying dormancy and budbreak in peach. A better understanding of the genetic basis for natural variations of CR can help breeders develop cultivars with different CR for growing in different geographical regions.

Research on Chilling Requirements and Physiological Mechanisms of Prunus mume

Low temperature plays a vital role in the growth and development of woody plants. In this research, based on the ability of artificial low temperatures to break dormancy, the Utah model was used to determine the chilling requirements (CR) of four early flowering Prunus mume Sieb. et Zucc. (Rosaceae) cultivars, which are widely found in the Henan area of China. In addition, changes in the carbohydrates, antioxidant enzyme activities, and endogenous hormone contents of the flower buds (FBs) of the above-mentioned P. mume cultivars were measured during the low-temperature storage process, and the physiological changes of the four cultivars during the low-temperature induction period were explored. The main research conclusions are as follows: (1) the CRs of ‘Gulihong’, ‘Nanjing gongfen’, ‘Zaoyudie’, and ‘Zaohualve’ were 408CU, 396CU, 372CU, and 348CU, respectively. All the P. mume cultivars belonged to cultivars with a low chilling demand. They also bloomed 4 months earlier, and (2) during the process of releasing dormancy at low temperatures, the contents of soluble sugar (SS) in the osmoregulation system of the four Prunus mume cultivars showed an upward trend, while the content of starch (ST) basically showed an opposite trend to the increase in chilling. The superoxide dismutase (SOD) activity in the FBs of each cultivar gradually decreased with the increase in cold and remained at a low level, while the peroxidase (POD) activity showed an opposite trend, and the dynamic changes of the catalase (CAT) activity generally showed a trend of first increasing and then decreasing. The content of abscisic acid (ABA) showed a trend of increasing first and then decreasing as a whole. The changing trend of gibberellin (GA3) content was similar to that of ABA. In addition, it was found that before dormancy was released, the SS and Pro contents of cultivars with lower CRs and early FB germination were significantly higher than those of other cultivars with higher CRs and the contents of ST and SP were lower. The cultivars with higher CRs and late FB germination had higher ABA content, lower GA3 contents, and their enzyme activities were significantly higher than those of the cultivars with lower CR. Therefore, the changes in the content of various substances in FBs are related to the amount of cooling required by the cultivar and at what point the FBs germinate, and the changes in their contents can be used as one of the indicators for judging the dormancy process of FBs.

Ppe.CR.1 DNA test for predicting chilling requirement in peach

Chilling requirement (CR) is an important agronomic trait controlling the floral bud break for proper flowering in peach. Even though it has been widely researched and several peach CR quantitative trait loci (QTLs) have been identified, no diagnostic DNA tests validated in the U.S. peach breeding germplasm are available for this trait. Breeders and growers need a simple DNA test to predict the CR of peach cultivars for their particular environment. Therefore, we developed a quick and reliable Kompetitive Allele Specific PCR (KASP) DNA test using haplotype information from 9K IPSC genotype data of the U.S. peach germplasm integrating four CR-associated SNP markers from the previously reported CR QTL region on linkage group 1. Four KASP assays (Ppe.CR.1-1 to -4) were developed and validated on 77 peach cultivars, and nine accessions from two F2 populations, with 96 and 74% accuracy in determining expected CR genotype (compared to SNP array) and predicting phenotype, respectively. Furthermore, the Ppe.CR.1 showed 80% accuracy in predicting the precise CR phenotype in the Clemson University peach breeding material. Only one Ppe.CR.1 KASP assay (Ppe.CR.1-1) is needed to distinguish between haplotypes with CR lower and higher than 800 chilling hours, and two Ppe.CR.1 assays (Pp.CR.1-1 and -4), are capable of distinguishing low, moderate, and high CR alleles. Coupled with the crude DNA extraction, the Ppe.CR.1 DNA test provides a low-cost option for breeders and growers to predict CR in peach material with more than 70% accuracy.

Inbreeding and founder cultivars contributions in low chill requirement peaches and nectarines

Inbreeding and founder cultivars contributions in low chill requirement peaches and nectarines

Development of new nectarine cultivars with low chilling requirements, adapted to climate change

Development of new nectarine cultivars with low chilling requirements, adapted to climate change

Global Methylation Analysis Using MSAP Reveals Differences in Chilling-Associated DNA Methylation Changes during Dormancy Release in Contrasting Sweet Cherry Varieties

Dormancy is an adaptive strategy developed by temperate perennial crops to protect overwinter tissues from unfavorable environmental conditions. Sweet cherry (Prunus avium L.), a member of the Rosaceae family, requires chilling to overcome dormancy. The time of harvest is directly correlated with chilling requirements in sweet cherries. Consequently, early and late season varieties have low and high chilling requirements, respectively. There is evidence that the expression of dormancy-related genes is regulated by DNA methylation. In this work, methylation-sensitive amplified polymorphism (MSAP) was applied to study genome-wide DNA methylation changes associated with dormancy in two low-chill varieties, ‘Royal Dawn’ and ‘Glen Red’, and one high-chill variety, ‘Kordia’. Our primary results suggest that the occurrence of progressive DNA demethylation is associated with chilling accumulation during dormancy in the three varieties, independent of their chilling requirements. Genes were identified with different methylation status changes, detected by MSAP, related to cell wall remodeling and energy metabolism. Several MSAP profiles among the varieties were observed, suggesting that fine epigenetic control is required to coordinate hormonal and environmental signals that induce dormancy and its release.

Adaptation of white spruce to climatic risk environments in spring: Implications for assisted migration

The timing of spring dormancy release and bud break in trees is an adaptive trait with potentially important management implications. Depending on how spring phenology is controlled, climate warming may disrupt the synchronization of bud break with the available growing season. Further, addressing climate change through human assisted migration in reforestation programs could cause additional problems if phenology triggers of source and target locations differ. Here, we assess how phenology is controlled by heat sum and chilling requirements for a widespread and commercially important boreal tree species, white spruce (Picea glauca) in a range-wide common garden experiment. We find significant genetic population differentiation in heat sum requirements ranging from 390 to 450 degree days among regions (±12 average SE), and from 375 to 500 (±16) degree days among populations within regions. The most northern populations showed the lowest heat sum requirements, which could be explained by frost avoidance or growth optimization strategies. Our data favors a frost avoidance hypothesis, although the explanations are not mutually exclusive. Chilling requirements in white spruce were also found (approx. 15 degree days), but they showed no geographic population differentiation. Due to generally low chilling requirements, we do not anticipate de-synchronization of spring phenology with the growing season under climate warming in spruce. Synthesizing results from this study and other research on additional growth and adaptive traits, we conclude that assisted migration northward, compensating for approximately 2° C warming, is safe and yields higher growth rates for white spruce.

Genetic Pool of the Cultivated Pear Tree (Pyrus spp.) in the Canary Islands (Spain), Studied Using SSR Molecular Markers

The Canary Islands have an enormous richness of crops and varieties, many of them traditional or local, selected for decades by farmers based on the most desirable characteristics. Pear trees were introduced to the Canary Islands presumably in the first years after their Conquest in the 15th century, reaching a high degree of diversification. In this study, to determine the genetic identity of the genus Pyrus in the Canary Islands for conservation purposes, 266 pear accessions from the islands of Tenerife, La Palma and Gran Canaria were characterized with 18 SSRs, in addition to 190 genotypes from Galicia, Asturias, wild and commercial varieties as references to detect possible synonyms, genetic relationships and the possible genetic structure. We identified 310 unique genotypes, both diploid and putative triploid, 120 of them present only in the Canary Islands (39%, with 50% clonality). The population structure of the genotypes was analyzed by STRUCTURE 2.3.4 software (Pritchard Lab, Stanford University, Stanford, CA, USA). The dendrogram, by using the Jaccard coefficient and principal component analysis (PCoA), separated the analyzed genotypes into stable groups. One of these groups was formed only by Canarian varieties present at lower altitudes, showing adaptation to low chilling requirements with a significant positive correlation (0.432, p < 0.01). This first study of the pear germplasm in the Canary Islands reflects the importance of the group of local cultivars and their need for conservation given they are adapted to their peculiar climatic conditions and have a low number of chill units.

Apple mutant trees with low chilling requirements: Proximal, genetic and DNA methylation analyses

In Arteaga, Coahuila, Mexico, different apple mutants derived from the Golden Delicious cultivar have been identified. They are characterized by their low chilling requirements (350–650 Chilling units (CU)) for breaking dormancy, and high flower production. The aim of this study was to determine the bromatological, genetic, and DNA methylation differences among ten apple mutants, and the wild-type Golden Delicious cultivar. The bromatological analyses showed that there are slight differences between some apple mutants with respect to control (Golden Delicious); in most cases, mutants were similar to each other. On the other hand, the genetic diversity among apple genotypes accessed by ISSR markers showed 57.12% of polymorphism among the 11 apple genotypes. The methylation assay showed that the Verde mutant from the Huachichil location had the highest values of DNA methylation (87.49%), even higher than the control (Golden Delicious). Furthermore, in the San Antonio of Alazanas location, the Tunal and Vigas II mutants showed the highest values of DNA methylation (62.85 and 87.61, respectively), however, the chilling requirements between these two cultivars are very different (340 and 750 CU, respectively), so it was concluded that a higher chilling requirement, is not always caused by a higher percentage of methylation. The study of these mutants may allow development of apple tree cultivars with desirable characteristics under warm winter conditions.

Comparative Study on Physiological Responses and Gene Expression of Bud Endodormancy Release Between Two Herbaceous Peony Cultivars (Paeonia lactiflora Pall.) With Contrasting Chilling Requirements.

With the global temperature increase, diverse endogenous factors and environmental cues can lead to severe obstacles to bud endodormancy release for important economic plants, such as herbaceous peony (Paeonia lactiflora Pall.). Knowing the underlying mechanism in bud endodormancy release is vital for widely planting herbaceous peony at low latitudes with warm winter climates. A systematic study was carried out between the southern Chinese cultivar ‘Hang Baishao’ with low-chilling requirement (CR) trait and the northern cultivar ‘Zhuguang’ with high-CR trait. Peony buds were sampled at regular intervals under natural cold during the crucial bud endodormancy release stage. Physiology and morphology of the buds were observed, and the roles of reactive oxygen species (ROS) and relevant genes in the regulation of bud endodormancy release were also highlighted, which has been rather rare in previous bud dormancy studies of both herbaceous and tree peonies. The expression of the starch metabolism- and sucrose synthesis-related genes PlAMY PlSPS and PlSUS was lower in the high-CR ‘Zhuguang’ and corresponded to a lower content of soluble sugars. The expression of polyamine oxidase gene PlPAO2 correlated with a higher level of hydrogen peroxide (H2O2) in high-CR ‘Zhuguang’ than in low CR ‘Hang Baishao’ during bud endodormancy. Expression of PlMAPKKK5, an intermediate gene in the abscisic acid (ABA) response to ROS signaling, correlated with ROS levels and ABA content. We present the hypothesis that accumulation of ROS increases ABA content and decreases GA3 content and signal transduction leading to reduced expression of PlSVP and PlSOC1. Reduced cell division and increased cellular damage which probably blocked bud endodormancy release were also observed in high-CR ‘Zhuguang’ through histological observation and related genes expression. This study provides a comparative analysis on physiological responses and gene expression patterns of bud dormancy of geophytes in an increasingly unsuitable environment.

The genome of low-chill Chinese plum "Sanyueli" (Prunus salicina Lindl.) provides insights into the regulation of the chilling requirement of flower buds.

Chinese plum (Prunus salicina Lindl.) is a stone fruit that belongs to the Prunus genus and plays an important role in the global production of plum. In this study, we report the genome sequence of the Chinese plum "Sanyueli", which is known to have a low-chill requirement for flower bud break. The assembled genome size was 282.38Mb, with a contig N50 of 1.37Mb. Over 99% of the assembly was anchored to eight pseudochromosomes, with a scaffold N50 of 34.46Mb. A total of 29,708 protein-coding genes were predicted from the genome and 46.85% (132.32Mb) of the genome was annotated as repetitive sequence. Bud dormancy is influenced by chilling requirement in plum and partly controlled by DORMANCY ASSOCIATED MADS-box (DAM) genes. Six tandemly arrayed PsDAM genes were identified in the assembled genome. Sequence analysis of PsDAM6 in "Sanyueli" revealed the presence of large insertions in the intron and exon regions. Transcriptome analysis indicated that the expression of PsDAM6 in the dormant flower buds of "Sanyueli" was significantly lower than that in the dormant flower buds of the high chill requiring "Furongli" plum. In addition, PsDAM6 expression was repressed by chilling treatment. The genome sequence of "Sanyueli" plum provides a valuable resource for elucidating the molecular mechanisms responsible for the regulation of chilling requirements, and it is also useful for the identification of the genes involved in the control of other important agronomic traits and molecular breeding in plum.

Micropropagation of Vaccinium virgatum ‘Delite’: a rabbiteye cultivar adapted to mild winters

ABSTRACT Blueberries have large amounts of antioxidant and anti-inflammatory compounds, playing an important role in improving health. In vitro culture is a possible method for vegetative propagation overcoming the problems of pathogen infection. Most studies on the in vitro culture of blueberries focus on highbush and lowbush cultivars. However, blueberry rabbiteye cultivars have lower chilling requirements and are more adapted to mild winter regions. Our objective was to develop a micropropagation protocol through axillary shoot growth, with reduced risks of somaclonal variation in ‘Delite’ rabbiteye blueberry. In vitro establishment was tested with single-node segments. The most promising results were using 2.5 µM zeatin. Multiplication through axillary shoot growth, starting with two-node stem segments were more successful in the concentration of 2.5 µM zeatin (70% of explants with axillary shoot growth). In vitro and ex vitro rooting with acclimatization were compared. In vitro rooting was achieved with immersion in 500 mg L−1 IBA (indole-3-butyric acid). Different substrates and mineral salts were also compared in ex vitro rooting. The results in vermiculite with WPM mineral salts were superior (68% rooting). In conclusion, this study provides techniques for micropropagation through axillary shoots of ‘Delite’ rabbiteye blueberry concerning establishment, multiplication, rooting, and acclimatization of plants.