Ornamental Plant Breeding Research Articles

Protocol for Pre-Selection of Dwarf Garden Rose Varieties

Ornamental plant breeding enables the selection of cultivars with desired features from numerous genotypes; however, this process is time-consuming and resource-demanding. Aiming to establish a pre-selection protocol that can facilitate the selection of dwarf rose varieties, the connection between anatomical and histological characteristics and the vegetative growth of rose cultivars was examined. To assess the adaptive potential of the studied cultivars, intra-annual cambial dynamics were explored relative to the observed meteorological fluctuations during the growing season. The investigation included six garden rose cultivars from the ‘Reka’ and ‘Pixie’ collections, bred under semi-arid open-field conditions in Serbia. Plant height ranged from 20 to 68 cm, with differing growth habits and types. Vegetative growth was significantly correlated with the xylem/phloem ratio, the proportion of total vessel area relative to cross-sectional and xylem areas, vessel-related features, and porosity (correlation coefficients up to 0.78). Regeneration via cambial activity and the formation of false rings were observed in five of the six cultivars studied, with meteorological analysis suggesting that precipitation and temperature triggered cambial reactivation. This approach effectively targets key parameters in the selection of dwarf and climate-resilient rose cultivars, facilitating the development of reliable pre-selection criteria.

OfLCYB positively regulates drought and heat tolerance by modulating ROS scavenging in Osmanthus fragrans

Osmanthus fragrans is an important tree in Asia, widely used in gardening and landscaping. As the global climate changes, the tree's growth and development are significantly affected by drought and heat stresses. Lycopene β-cyclase (LCYB) is a pivotal enzyme in the carotenoid pathway and plays an important role in abiotic stress responses. However, the function of the OfLCYB gene in the regulation of drought and heat tolerance is still unclear. In O. fragrans, OfLCYB expression was significantly induced by drought and heat treatments, and OfLCYB localized in the chloroplasts. Meanwhile, GUS staining of OfLCYB promoter showed that its promoter activity was dramatically activated by drought and heat treatments. Functional analysis showed that OfLCYB overexpression significantly improved the drought and heat tolerance of yeast cells, O. fragrans calli, and Arabidopsis. And the decrease of H2O2 concentration was found in the OfLCYB-overexpressing O. fragrans calli and Arabidopsis leaves. Furthermore, RNA-seq was performed and revealed that ROS scavenging-related genes were upregulated in the OfLCYB-overexpressing O. fragrans calli, especially the expression of APX, CAT, GPX, and PRX genes were significantly induced by drought and heat stresses. Therefore, we speculated that the OfLCYB gene contributes to the improvement of drought and heat tolerance by reducing the H2O2 accumulation through activating the expression of reactive oxygen species (ROS) scavenging-related genes in O. fragrans. Our results provide valuable insights into the role of the OfLCYB gene in the regulation of abiotic stress tolerance, with implications for future molecular breeding of ornamental plants.

Ornamental plant breeding is tools for new generation

Ornamental plant breeding is tools for new generation

The catalytic role of glutathione transferases in heterologous anthocyanin biosynthesis

Anthocyanins are ubiquitous plant pigments used in a variety of technological applications. Yet, after over a century of research, the penultimate biosynthetic step to anthocyanidins attributed to the action of leucoanthocyanidin dioxygenase has never been efficiently reconstituted outside plants, preventing the construction of heterologous cell factories. Through biochemical and structural analysis, here we show that anthocyanin-related glutathione transferases, currently implicated only in anthocyanin transport, catalyse an essential dehydration of the leucoanthocyanidin dioxygenase product, flavan-3,3,4-triol, to generate cyanidin. Building on this knowledge, introduction of anthocyanin-related glutathione transferases into a heterologous biosynthetic pathway in baker’s yeast results in >35-fold increased anthocyanin production. In addition to unravelling the long-elusive anthocyanin biosynthesis, our findings pave the way for the colourants’ heterologous microbial production and could impact the breeding of industrial and ornamental plants.

Chromosome-scale genome assembly provides insights into flower coloration mechanisms of Canna indica

Canna indica, which produce conspicuous and colorful flowers, are widely appreciated as ornamental plants. We used Pacific Biosciences sequencing (PacBio) and chromosome conformation capture (Hi-C) genome scaffolding to build a high-quality chromosome-scale genome assembly of C. indica and the genome assembly was 821Mb with a contig N50 of 48Mb assembled into nine chromosomes. The genome of C. indica was predicted to contain 31,130 genes and 30,816 genes were functionally annotated. Genome annotation identified 522 Mb (63.59 %) as repetitive sequences. Genome evolution analysis showed that whole-genome duplication occurred 53.4 million years ago. Transcriptome analysis revealed that petal coloration was linked with the expression of genes encoding enzymes involved in anthocyanin biosynthesis, carotenoid biosynthesis, and the methylerythritol phosphate (MEP) pathway. Furthermore, modules of co-expressed genes and hub genes were identified via weighted gene co-expression network analysis. These results suggested that, in Canna indica, deep red petal coloration was regulated by CHS2 and yellow petal coloration was associated with expression of ARF6 and NAC14. Considered together, the current study revealed a high-quality reference genome which may provide new insights into the molecular basis of flower coloration in Canna indica and help enhance the conservation and breeding of ornamental plants in general.

DBALM: A novel method for identifying ornamental flowering plants based on DNA barcodes–leaf morphology

AbstractWhereas the presence of flowers on ornamental flowering plants is essential for their identification via traditional methods, ornamental flowering plants cannot be reliably identified in non‐flowering stages likewise. Here, DBALM (DNA Barcodes–Leaf Morphology), a new approach that combines DNA barcoding data with micromorphological features of the leaf epidermis and that is not limited by the flowering stage, was used to identify 16 evergreen rhododendron cultivars. First, the sequences of DNA barcodes, ITS, matK, psbA‐trnH, and rbcL, were obtained from the DNA of leaves. Phylogenetic analysis was conducted to clarify the groupings among all the samples based on the four markers. Then, microscopic features of the leaf epidermis were used to further distinguish individuals from the same clade. DNA barcoding permitted the 16 cultivars to be divided into eight groups. The microscopic features of the leaf epidermis permitted cultivars within the same clade to be distinguished. The matK + psbA‐trnH combination was the most effective barcode combination in this study. In addition, the new primer matK‐Rh_R was designed, and it increased the amplification rate of evergreen rhododendron cultivars to 100%. In sum, DBALM was capable of accurately identifying the 16 evergreen rhododendron cultivars using data collected from a single leaf in the vegetative growth stage. This method can greatly facilitate the identification and breeding of ornamental flowering plants.

Volatile metabolome and transcriptome reveal fragrance release rhythm and molecular mechanisms of Rosa yangii

Rose is a highly significant ornamental plant with substantial edible and medicinal value, cultivated worldwide primarily for perfume production. Recently, Rosa yangii, a new species found in northwestern Yunnan, China, has drawn attention due to its strong sweet scented flowers. In this study, the floral components of R. yangii were extracted at different flowering stages using solid phase micro extraction (SPME) and analyzed through gas chromatography–mass spectrometry (GC–MS). A total of 131 volatile organic compounds (VOCs) were detected from R. yangii, including 69 odor compounds. The production and release of floral VOCs were the highest during the initial-open stage, making it the most suitable time for harvesting as a significant number of floral components were synthesized and preserved. The analysis of the odor activity values (OAV) highlighted several key aromatic ingredients of R. yangii, such as eugenol, methyleugenol, benzeneacetaldehyde and phenylethylalcohol, heptanal, decanal, (E)-2-hexen-1-yl acetate, caryophyllene, and others. Metabolome and time-order gene co-expression networks (TO-GCN) revealed that VOCs and benzenoids/phenylpropanoids, along with associated genes, played a pivotal role in the overall floral regulatory network of R. yangii. MYB and bHLH were identified as the essential regulatory factors governing the regulation of eugenol synthase (EGS) and isoeugenol synthase (IGS), consequently influencing the sweet scent of R. yangii. The findings of this study provide a scientific foundation for enhancing fragrance through molecular breeding of ornamental plants. Furthermore, the study facilitated the development and utilization of this new plant’s essential oil material in various industries, including food storage, aromatherapy, cosmetic, and perfumery.

Over-expression of CcMYB24, encoding a R2R3-MYB transcription factor from a high-leaf-number mutant of Cymbidium, increases the number of leaves in Arabidopsis.

Ornamental foliage plants have long been cultivated for their attractive leaves. Variation in leaf traits of ornamental foliage plants is one of the goals in breeding. MYB transcription factors regulate many aspects of leaf development, and thus influence morphological traits of leaves. However, little is known about the function of MYB transcription factors in leaf development of Cymbidium, one of the most economically important ornamental plants in the world. In the present study, a MYB transcription factor, CcMYB24, was identified and the corresponding gene cloned from a new orchid mutant, TRIR-2, which produces more leaves than control plants. The CcMYB24 showed a higher expression level in 'TRIR-2' than in control plants, and the protein was located in the nucleus. The sequence of CcMYB24 showed a high similarity with RAX2-like genes which belong to the R2R3-MYB gene family in other Cymbidium plants. Overexpression of CcMYB24 resulted in a phenotype with an increased number of leaves, elevated chlorophyll content, and decreased contents of carotenoids and flavonoids in Arabidopsis. These results provide functional evidence for the role of CcMYB24 in promoting the production of leaves in 'TRIR-2'. Understanding the role of CcMYB24 in Cymbidium will be beneficial for the molecular breeding of ornamental foliage plants.

The past and future of Hungarian annual and perennial ornamental plant breeding

The past and future of Hungarian annual and perennial ornamental plant breeding

Exploring Genetic Diversity in an Ilex crenata Breeding Germplasm

Knowledge of genetic identity, genetic relationships, ploidy level, and chromosome numbers can enhance the efficiency of ornamental plant breeding programs. In the present study, genome sizes, chromosome numbers, and genetic fingerprints were determined for a collection of 94 Ilex accessions, including 69 I. crenata. The genome size of the entire collection ranged from 1.50 ± 0.03 to 8.01 ± 0.18. Within the species of I. crenata, genome sizes varied (mean ± sd) between 1.98 ± 0.08 and 2.30 ± 0.04, with three outliers: 3.06 ± 0.04, 4.04 ± 0.09, and 4.19 ± 0.08. The chromosome counting results showed 2n = 40 for I. crenata accessions and confirmed the outliers as one triploid and two tetraploids. A high intra-specific genetic diversity in Ilex crenata was found, after genetic fingerprinting using genotyping-by-sequencing (GBS). The species I. crenata was separated into three clades, which coincided with intraspecific differences in genome sizes (mean ± sd) of 2.09 ± 0.006, 2.07 ± 0.05, and 2.19 ± 0.06 pg/2C per clade as mean values for the diploids. Applying a principal coordinate analysis (PCoA) to the genetic fingerprinting data of all species in the collection revealed a wide genetic variation, which has not yet been commercially exploited. These findings could form the basis for selectively breeding parents, in order to create more genetic diversity via intra- and interspecific crosses.

Responses of the tree peony (Paeonia suffruticosa, Paeoniaceae) cultivar ‘Yu Hong’ to heat stress revealed by iTRAQ-based quantitative proteomics

Horticulture productivity has been increasingly restricted by heat stress from growing global warming, making it far below the optimum production capacity. As a popular ornamental cultivar of tree peony, Paeonia suffruticosa ‘Yu Hong’ has also been suffering from heat stress not suitable for its optimal growth. To better understand the response mechanisms against heat stress of tree peony, investigations of phenotypic changes, physiological responses, and quantitative proteomics were conducted. Phenotypic and physiological changes indicated that 24 h of exposure to heat stress (40 °C) was the critical duration of heat stress in tree peony. The proteomic analyses revealed a total of 100 heat-responsive proteins (HRPs). According to bioinformatic analysis of HRPs, the heat tolerance of tree peony might be related to signal transduction, synthesis/degradation, heat kinetic proteins, antioxidants, photosynthesis, energy conversion, and metabolism. Our research will provide some new insights into the molecular mechanism under the response against the heat stress of tree peony, which will benefit the future breeding of heat-resistant ornamental plants.

Transcriptome and chemical analyses revealed the mechanism of flower color formation in Rosa rugosa.

Rosa rugosa is a famous Chinese traditional flower with high ornamental value and well environmental adapt ability. The cultivation of new colorful germplasms to improve monotonous flower color could promote its landscape application. However, the mechanism of flower color formation in R. rugosa remains unclear. In this study, combined analyses of the chemical and transcriptome were performed in the R. rugosa germplasms with representative flower colors. Among the identified anthocyanins, cyanidin 3,5-O-diglucoside (Cy3G5G) and peonidin 3,5-O-diglucoside (Pn3G5G) were the two dominant anthocyanins in the petals of R. rugosa. The sum content of Cy3G5G and Pn3G5G was responsible for the petal color intensity, such as pink or purple, light- or dark- red. The ratio of Cy3G5G to Pn3G5G was contributed to the petal color hue, that is, red or pink/purple. Maintaining both high relative and high absolute content of Cy3G5G may be the precondition for forming red-colored petals in R. rugosa. Cyanidin biosynthesis shunt was the dominant pathway for anthocyanin accumulation in R. rugosa, which may be the key reason for the presence of monotonous petal color in R. rugosa, mainly pink/purple. In the upstream pathway of cyanidin biosynthesis, 35 differentially expressed structural genes encoding 12 enzymes co-expressed to regulate the sum contents of Cy3G5G and Pn3G5G, and then determined the color intensity of petals. RrAOMT, involved in the downstream pathway of cyanidin biosynthesis, regulated the ratio of Cy3G5G to Pn3G5G via methylation and then determined the color hue of petals. It was worth mentioning that significantly higher delphinidin-3,5-O-diglucoside content and RrF3’5’H expression were detected from deep purple-red-flowered 8-16 germplasm with somewhat unique and visible blue hue. Three candidate key transcription factors identified by correlation analysis, RrMYB108, RrC1, and RrMYB114, might play critical roles in the control of petal color by regulating the expression of both RrAOMT and other multiple structural genes. These results provided novel insights into anthocyanin accumulation and flower coloration mechanism in R. rugosa, and the candidate key genes involved in anthocyanin biosynthesis could be valuable resources for the breeding of ornamental plants in future.

Melhoramento de plantas ornamentais: entrando em uma nova era?

Abstract During the last century, plant breeding of crops and ornamentals has become an important business. Mendel’s principles of inheritance of traits laid the foundation of today’s modern genetics. Although intra- and interspecific cross breeding, chromosome doubling and mutation breeding still form the cornerstone of ornamental plant breeding, the speed of plant breeding has significantly increased since Mendel’s time. New genomic tools now offer possibilities for advanced precision breeding and selection towards more difficult to assess or quantitative traits. Today’s ornamental plant breeding is a complicated exercise, characterized by new and rapidly-changing challenges. Partnerships between industry and research will be essential to implement available technologies in minor crops.

Effects of Polyploidization on Morphology, Photosynthetic Parameters and Sucrose Metabolism in Lily.

Polyploidization is widely used in ornamental plant breeding. The polyploids usually produce greater amounts of biomass. However, the alternations to sucrose metabolism that occur in lily during development after polyploidization induced using colchicine are poorly understood. In this study, compared with their allodiploid counterparts, allotetraploid lilies presented a larger total leaf area per plant and slightly delayed flowering time. Moreover, photosynthetic parameter measurements revealed a higher net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and maximum Pn for allotetraploids than for allodiploids. Compared with allodiploids, allotetraploids also showed higher nonstructural carbohydrate (NSC) contents during development according to HILIC-CAD results. The expression levels of sucrose metabolism-related genes were higher in allotetraploids than in allodiploids at the same time points. The expression profiles of several target genes in allotetraploids were distinctly different from those in allodiploids. Susy2/3 exhibited opposite expression profiles in allotetraploids and allodiploids, and the expression profiles of SPS3 and Susy2 were significantly correlated with sucrose content change trends in allodiploids and allotetraploids, respectively.

Induction of dwarf and early flowering phenotypes in Tricyrtis sp. by ectopic expression of LEAFY from Arabidopsis thaliana.

LEAFY (LFY), which encodes a plant-specific transcription factor, plays an important role in the transition from vegetative to reproductive development. Ectopic expression of LFY has been reported to induce dwarfism and early flowering in some model plants. In order to examine the possibility of using LFY for molecular breeding of ornamental plants, we produced and characterized transgenic plants ectopically expressing LFY from Arabidopsis thaliana (AtLFY) in the liliaceous ornamental plant Tricyrtis sp. Nine independent transgenic plants have been obtained, and all of them exhibited dwarf phenotypes compared with the vector control. These transgenic plants could be classified into three types according to the degree of dwarfism: one showed an extreamly dwarf phenotype with smaller leaves (Type I); two showed moderately dwarf phenotypes (Type II); and six showed slightly dwarf phenotypes (Type III). All of Type I, Type II and Type III transgenic plants produced flower buds 1-3 weeks earlier than the vector control. Vector control and Type III transgenic plants produced 1-4 apical flower buds, whereas Type I and Type II transgenic plants produced only a single apical flower bud. Type I and Type II transgenic plants often produced non-fully-opened flowers. Quantitative real-time reverse transcription-polymerase chain reaction analysis showed that the AtLFY expression level generally correlated with the degree of dwarfism. These results indicate that morphological alterations observed in the transgenic plants was induced by ectopic expression of AtLFY. Lower levels of ectopic expression of LFY may be valuable for producing dwarf and early flowering ornamental plants.

An Aux/IAA Family Member, RhIAA14, Involved in Ethylene-Inhibited Petal Expansion in Rose (Rosa hybrida).

Flower size, a primary agronomic trait in breeding of ornamental plants, is largely determined by petal expansion. Generally, ethylene acts as an inhibitor of petal expansion, but its effect is restricted by unknown developmental cues. In this study, we found that the critical node of ethylene-inhibited petal expansion is between stages 1 and 2 of rose flower opening. To uncover the underlying regulatory mechanism, we carried out a comparative RNA-seq analysis. Differentially expressed genes (DEGs) involved in auxin-signaling pathways were enriched. Therefore, we identified an auxin/indole-3-acetic acid (Aux/IAA) family gene, RhIAA14, whose expression was development-specifically repressed by ethylene. The silencing of RhIAA14 reduced cell expansion, resulting in diminished petal expansion and flower size. In addition, the expressions of cell-expansion-related genes, including RhXTH6, RhCesA2, RhPIP2;1, and RhEXPA8, were significantly downregulated following RhIAA14 silencing. Our results reveal an Aux/IAA that serves as a key player in orchestrating petal expansion and ultimately contributes to flower size, which provides new insights into ethylene-modulated flower opening and the function of the Aux/IAA transcription regulator.

Exploiting Unreduced Gametes for Improving Ornamental Plants.

The formation of gametes with somatic chromosome number or unreduced gametes (2n gametes) is an important process involved in the origin of polyploid plants in nature. Unreduced gametes are the result of meiotic mutations occurring during micro- and mega-sporogenesis. 2n gametes have been identified or artificially induced in a large number of plant species. Breeding of plants through 2n gametes can be advantageous because it combines genetic effects of polyploidy with meiotic recombination and sexual hybridization to produce tremendous genetic variation and heterosis. 2n gametes also occur in ornamental plants, but the potential of using 2n gametes in ornamental plant breeding has not been extensively exploited. Ornamental plants are primarily produced for their esthetic appearance and novelty, not for food and yield, and they can be readily propagated through vegetative means. Triploids, tetraploids, and plants with even higher ploidy levels produced through 2n gametes can be propagated through tissue culture to fix their phenotypes, thus leading to the development of new cultivars. In this review article, we intend to discuss the mechanisms underlying the formation of 2n gametes, techniques for 2n gamete identification, methods for enhancing 2n gamete formation, and the current status in the use of 2n gametes for development of novel ornamental plants. We believe that polyploidy breeding through 2n gametes represents a viable way of developing new cultivars, new species, and even new genera of ornamental plants.

Near-Hexaploid and Near-Tetraploid Aneuploid Progenies Derived from Backcrossing Tetraploid Parents Hibiscus syriacus × (H. syriacus × H. paramutabilis).

Hibiscus syriacus, azalea, is an important woody ornamental shrub planted throughout many temperate and subtropical regions of the world. However, flower size is smaller in this species than some of its relatives. To increase flower size, interspecific hybridization has been used, and such hybrid cultivars are usually characterized by larger flowers, increased vigor, diverse leaf shapes, and reduced fertility. Our earlier studies have shown that these hybrid cultivars could backcross with H. syriacus when used as male parents. To understand the breeding potential of these hybrid cultivars, two popular tetraploid hybrid cultivars, ‘Lohengrin’ and ‘Resi’, were used as pollen parents to backcross several tetraploid H. syriacus cultivars. As a result, 28.76% and 64.4% of ‘Lohengrin’ and ‘Resi’ progenies exhibited larger flowers than both of their parents. Interestingly, 14 of 18 progenies of ‘Resi’ were putative hexaploids, whereas 19 tested ‘Lohengrin’ progenies were tetraploid. Because putative hexaploid progenies were only observed among progenies of ‘Resi’, this hybrid cultivar appears to produce unreduced gametes. In addition, among the 14 putative hexaploids derived from ‘Resi’, 11 had larger flowers than both of their parents and their tetraploid siblings (p < 0.05). The 45S rDNA and 5S rDNA locus segregation among those BC1F1 progenies was tested by fluorescent in situ hybridization (FISH), and the wide range of 45S rDNA signal numbers among siblings indicated that these aneuploids resulted from unequal segregation or chromosome rearrangement. Chromosome counting confirmed aneuploidy among BC1F1 progenies. Ploidy diversity and aneuploidy have been known to contribute to various elements of morphological diversity, such as larger flower size and reduced fertility, which are important in ornamental plant breeding. The present study demonstrated the breeding potential of interspecific Hibiscus cultivars for increasing ploidy level and flower size.

Analysis of Photosynthetic Pigment Content and Leaf Structure of Pteroceltis Tatarinowii Mutant with Yellow Leaf

The relationship betweenleaf variation characteristics and leaf structure characteristics of Pteroceltistatarinowii with yellow leaf was explored to provide a theoretical basisfor the breeding of other ornamental plants. In this study, the differences inpigment content, leaf structure, and chloroplast ultrastructure in leaves of Pteroceltistatarinowii mutant with yellow leaf 'Huiguang' and its original species'Lingyansi No. 1’ were studied. The results showed that the chlorophyll in'Huiguang' leaves decreased significantly, and the carotenoids-totalchlorophyll ratio increased greatly. The palisade tissue cells in 'Huiguang'leaves are short, thick, and loosely structured, while the sponge tissue cellsare irregular in shape and loosely arranged. In addition, the chloroplasts of'Huiguang' leaves were irregular in shape and the grana lamellae were looselyarranged, broken, and missing, with more osmiophilic granules and fewer starchgranules. These anomalies in leaf pigment content and chloroplast structureaffect leaf photosynthesis and chlorophyll accumulation, thereby affecting leaf color changes.

SMRT and Illumina RNA-Seq Identifies Potential Candidate Genes Related to the Double Flower Phenotype and Unveils SsAP2 as a Key Regulator of the Double-Flower Trait in Sagittaria sagittifolia.

Double flowers are one of the important objectives of ornamental plant breeding. Sagittaria sagittifolia is an aquatic herb in the Alismataceae family that is widely used as an ornamental plant in gardens. However, the reference genome has not been published, and the molecular regulatory mechanism of flower formation remains unclear. In this study, single molecule real-time (SMRT) sequencing technology combined with Illumina RNA-Seq was used to perform a more comprehensive analysis of S. sagittifolia for the first time. We obtained high-quality full-length transcripts, including 53,422 complete open reading frames, and identified 5980 transcription factors that belonged to 67 families, with many MADS-box genes involved in flower formation being obtained. The transcription factors regulated by plant hormone signals played an important role in the development of double flowers. We also identified an AP2 orthologous gene, SsAP2, with a deletion of the binding site for miR172, that overexpressed SsAP2 in S. sagittifolia and exhibited a delayed flowering time and an increased number of petals. This study is the first report of a full-length transcriptome of S. sagittifolia. These reference transcripts will be valuable resources for the analysis of gene structures and sequences, which provide a theoretical basis for the molecular regulatory mechanism governing the formation of double flowers.