Tetraploid Cultivars Research Articles

An extracted tetraploid wheat harbouring the BBAA component of common wheat shows anomalous shikimate and sucrose metabolism

BackgroundThe BBAA subgenomes of hexaploid common wheat are structurally intact, which makes it possible to extract the BBAA subgenomes to constitute a novel plant type, namely, extracted tetraploid wheat (ETW). ETW displays multiple abnormal phenotypes such as massively reduced biomass and abnormal spike development, compared to extant tetraploid wheat with a BBAA genome. The genetic, biochemical and physiological basis underlying the phenotypic abnormality of ETW remains unknown.ResultsTo explore the biochemical basis of these phenotypic abnormalities, we analysed the metabolomic and proteomic profiles and quantified 46 physiological traits of ETW in comparison with its common wheat donor (genome BBAADD), and a durum tetraploid wheat cultivar (genome BBAA). Among these three types of wheat, ETW showed a saliently different pattern of nutrient accumulation and seed quality, markedly lower concentrations of many metabolites involved in carbohydrate metabolism, and higher concentrations of many metabolites related to amino acids. Among the metabolites, changes in shikimate and sucrose were the most conspicuous. Higher levels of shikimate and lower levels of sucrose influence many metabolic processes including carbohydrate and amino acid metabolism, which may contribute to the phenotypic abnormalities. Gene expression assay showed downregulation of a shikimate degradation enzyme (5-enolpyruvylshikimate-3-phosphate synthase) coding gene and upregulation of several genes coding for the sucrose hydrolysis enzyme, which could explain the higher levels of shikimate and lower levels of sucrose, respectively.ConclusionsOur results suggest that significant and irreversible biochemical changes have occurred in the BBAA subgenomes of common wheat during the course of its co-evolution with the DD subgenome at the hexaploid level.

Seed yield in red clover is associated with meiotic abnormalities and in tetraploid genotypes also with self-compatibility

Red clover (Trifolium pratense L.) is a major forage legume crop with diploid and tetraploid cultivars. Seed yield is an important trait in red clover, but the underlying reasons for low seed yield in individual genotypes are not well known. Here we investigated direct associations between seed yield and ovule abortion, male meiotic abnormalities, and pollen quality in well-characterized, diploid and tetraploid red clover genotypes with contrasting seed yields. Ovule development was studied after manual pollinations: in most genotypes, high rates of embryo abortion occurred between 7 and 14 days after pollination. However, the frequencies of developing, underdeveloped and shrivelled ovules were similar in diploid and tetraploid genotypes and were not associated with seed yield. Surprisingly, self-pollination only took place in tetraploid genotypes with high seed yield (83% self-pollination on average). The frequencies of meiotic abnormalities during microsporogenesis were investigated, in addition to pollen viability and pollen germination capacity. Tetraploid genotypes displayed more meiotic abnormalities (17.3% and 7.0% respectively) and lower pollen germination (39% and 63% respectively) than diploids. A negative trend was present between meiotic abnormalities and seed yield. In conclusion, our study reveals that high seed yield was associated with a low degree of abnormalities in male meiosis in diploid and tetraploid genotypes, and with the ability to self-pollinate in the tetraploid genotypes investigated. In certain genotypes, defective male meiosis may be a primary cause of low pollen quality and low seed yield.

Variation in Genome Size, Ploidy, Stomata, and rDNA Signals in Althea

Althea (Hibiscus syriacus) is a shrub prized for its winterhardiness and colorful summer flowers. Altheas are tetraploids (2n = 4x = 80); however, breeders have developed hexaploids and octoploids. Previous studies report anatomical variation among polyploids, including stomata size. The purpose of this study was 4-fold. First, identify genome size and ploidy variation in cultivars via flow cytometry and chromosome counts. Second, create a ploidy series consisting of 4x, 5x, 6x, and 8x cytotypes. Third, investigate the ploidy series for variation in stomatal guard cell lengths, stomatal density, and copy number of fluorescent ribosomal DNA (rDNA) signals. Fourth, investigate segregation patterns of rDNA signals in a subset of pentaploid seedlings. Flow cytometry revealed most cultivars to be tetraploid with holoploid 2C genome sizes from 4.55 ± 0.02 to 4.78 ± 0.06 pg. Five taxa (‘Aphrodite’, ‘Pink Giant’, ‘Minerva’, Azurri Satin®, and Raspberry Smoothie™) were hexaploids (6.68 ± 0.13 to 7.05 ± 0.18 pg). Peppermint Smoothie™ was a cytochimera with tetraploid cells (4.61 ± 0.06 pg) and octoploid cells (8.98 ± 0.13 pg). To create pentaploids, reciprocal combinations were made between hexaploid ‘Pink Giant’ and tetraploid cultivars. To create octoploids, seedlings were treated with agar solutions containing 0.2% colchicine or 125 μM oryzalin. Guard cell lengths were significantly different among the four cytotypes: 4x (27.36 ± 0.04 μm), 5x (30.35 ± 1.28 μm), 6x (35.59 ± 0.63 μm), and 8x (40.48 ± 1.05 μm). Measurements of stomatal density revealed a precipitous decline in average density from the 4x cytotype (398.22 ± 15.43 stomata/mm2) to 5x cytotype (194.06 ± 38.69 stomata/mm2) but no significant difference among 5x, 6x, and 8x cytotypes. Fluorescent in situ hybridization (FISH) revealed an increase in 5S and 45S rDNA signals that scaled with ploidy: 4x (two 5S + four 45S), 6x (three 5S + six 45S), and 8x (four 5S + eight 45S). However, pentaploid (5x) seedlings exhibited random segregation of rDNA signals between the 4x and 6x cytotypes, including all six possible combinations (two 5S, three 5S) × (four 45S, five 45S, six 45S).

Nutritive characteristics of perennial ryegrass cultivars: have they changed over time?

Improvement in nutritive characteristics resulting from breeding perennial ryegrass (PRG) cultivars used in Australia from the 1970s to the present day was quantified in a grazed field experiment in south-western Victoria. The experiment was sown in May 2014 with measurements undertaken over 3 years. The experiment contained 36 PRG treatments (cultivar–endophyte combinations), which were replicated four times, with herbage nutritive characteristics measured at each grazing. The treatments differed in estimated metabolisable energy (ME), crude protein and neutral detergent fibre (NDF) concentrations at each harvest date. The decade of cultivar release had little effect on the ME or the NDF concentration of the cultivars released from 1970s onward. Early season diploids had a lower ME concentration than did later-maturing diploid cultivars (11.0 vs 11.4 MJ/kg DM), predominantly due to a lower ME concentration in late spring and early summer (10.3 vs 11.1 MJ/kg DM). The tetraploid cultivars had a higher ME concentration (11.8 vs 11.4 MJ/kg DM) and a lower NDF (480 vs 505 g/kg DM) concentration than did the mid- and late-season diploid cultivars. These differences are likely to be of economic importance at the farm level.

Does the "high sugar" trait of perennial ryegrass cultivars express under temperate climate conditions?

The objective was to evaluate water‐soluble carbohydrate (WSC) and crude protein (CP) concentration of perennial ryegrass (PRG) cultivars with different genetic potential for producing WSC under two contrasting agronomic managements in temperate climate (southern Chile). A 4 × 2 factorial design was randomly allocated to 24 plots (31 m2 each, three blocks): four PRG cultivars (diploid standard cultivar, “2nSt”; tetraploid standard cultivar, “4nSt”; diploid high sugar cultivar developed in New Zealand, “2nHSNZ”; and tetraploid high sugar cultivar developed in Europe, “4nHSEU”) and two agronomic managements (“favourable,” defoliations at three leaves per tiller and nitrogen (N) fertilization rate of 83.3 kg N ha−1 year−1; “unfavourable,” defoliations at two leaves per tiller and N fertilization rate of 250 kg N ha−1 year−1). Herbage samples were collected in early spring, spring, summer and autumn. Concentration of WSC did not differ among cultivars in spring and summer, averaging 194 and 251 g/kg DM, respectively. The cultivar 4nHSEU had the greatest WSC concentration in early spring and autumn (187 and 266 g/kg DM, respectively) and the greatest CP concentration across samplings (average 230 g/kg DM). Favourable management improved WSC concentrations in early spring and summer and decreased CP in spring, summer and autumn. Annual DM yield did not vary with cultivar or management, averaging 8.43 t/ha. Within a 12‐month study at one site in a temperate environment in southern Chile, PRG cultivars have not shown a consistent expression of the “high sugar” trait, where a genetic × environment interaction might be operating.

QTLs Location of Calyx-related Traits in Tetraploid Dendrobium

In order to identify QTL locus of calyx-related traits in Dendrobium, 190 F1 individuals derived from the crossbreed of tetraploid Dendrobium cultivars D. Mangosteen x D. Burana Pink No.2 were used as materials. Through three years observation of four characteristics of calyx (length of dorsal sepal, width of dorsal sepal, length of lateral sepal, width of lateral sepal), the QTL was located on the two genetic maps of parents which had been already constructed. The result showed that the four characteristics were quite different among the individuals of F1 generation, and the observed values of all the characteristics were all positive distribution, which was suitable for QTL analysis. Nine QTLs were detected on the maternal ‘D. Mangosteen’ genetic linkage map, including 1 QTL for dorsal sepal length, 3 QTLs for dorsal sepal width, 2 QTLs for lateral length and 3 QTLs for lateral width, with the genetic contribution rate ranging from 11.9% to 16.8%. Also, two tight linkage markers were acquired (M10E3-146, M8E8-284). A total of 6 QTLs were detected on the paternal ‘D. Burana Pink No.2’ linkage map, including 2 QTLs for dorsal sepal length, 1 QTL for dorsal sepal width, 2 QTLs for lateral length and 1 QTL for lateral width, with the genetic contribution rate ranging from 11.8% to 17.3%. This result of study could provide reference for Dendrobium molecular marker assisted breeding and precise location of correlation gene.

QTLs Location of Calyx-related Traits in Tetraploid <i>Dendrobium</i>

In order to identify QTL locus of calyx-related traits in Dendrobium, 190 F1 individuals derived from the crossbreed of tetraploid Dendrobium cultivars D. Mangosteen x D. Burana Pink No.2 were used as materials. Through three years observation of four characteristics of calyx (length of dorsal sepal, width of dorsal sepal, length of lateral sepal, width of lateral sepal), the QTL was located on the two genetic maps of parents which had been already constructed. The result showed that the four characteristics were quite different among the individuals of F1 generation, and the observed values of all the characteristics were all positive distribution, which was suitable for QTL analysis. Nine QTLs were detected on the maternal ‘D. Mangosteen’ genetic linkage map, including 1 QTL for dorsal sepal length, 3 QTLs for dorsal sepal width, 2 QTLs for lateral length and 3 QTLs for lateral width, with the genetic contribution rate ranging from 11.9% to 16.8%. Also, two tight linkage markers were acquired (M10E3-146, M8E8-284). A total of 6 QTLs were detected on the paternal ‘D. Burana Pink No.2’ linkage map, including 2 QTLs for dorsal sepal length, 1 QTL for dorsal sepal width, 2 QTLs for lateral length and 1 QTL for lateral width, with the genetic contribution rate ranging from 11.8% to 17.3%. This result of study could provide reference for Dendrobium molecular marker assisted breeding and precise location of correlation gene.

Changes in estimated value of perennial ryegrass cultivar/ endophyte combinations in the DairyNZ Forage Value Index when metabolisable energy contents specific to culitvar groups are included

Further development of the DairyNZ Forage Value Index (FVI) requires accounting for genetic variation in the nutritive value of ryegrass herbage in addition to the current weightings on dry matter production traits. Performance values for metabolisable energy content (PV ME) have been identified as the most appropriate variables to use for this purpose. In this study an assessment was made of the effect of including cultivar group (mid-heading date diploid, late-heading date diploid and tetraploid) PV ME in FVI ranking calculations of eligible perennial ryegrass (Lolium perenne) cultivars. Incorporation of the seasonal ME trait into the FVI has resulted in changes in rankings of those cultivars. Although correlations were strong (0.74 for Upper South Island to 0.92 for Upper North Island) between rankings of cultivars using the current FVI and the FVI with cultivar group PV ME, marked improvements have been made in the rankings of tetraploid cultivars. On-farm persistence implications (not yet included in the FVI) of selecting tetraploid cultivars will need to be included if the ME trait is included in the FVI.

Protocol for Agrobacterium-Mediated Transformation and Transgenic Plant Production of Switchgrass.

Switchgrass (Panicum virgatum L.) is one of the most important bioenergy crops for lignocellulose ethanol production. Molecular breeding provides a powerful tool to supplement conventional switchgrass breeding by introducing or editing genes of interest. In this chapter, we describe Agrobacterium tumefaciens-mediated transformation protocols for lowland tetraploid switchgrass cultivar Alamo.

Multiple haploids, triploids, and tetraploids found in modern-day \u201cliving fossil\u201d Ginkgo biloba

Ginkgo biloba, the last extant representative of a lineage of Mesozoic gymnosperms, is one of the few seed plants with an exceptionally long (~300 Myr) evolutionary history free of genome-wide duplications (polyploidy). Despite this genome conservatism, we have recently found a viable spontaneous tetraploid Ginkgo sapling during routine screening of several plants, demonstrating that natural polyploidy is possible in Ginkgo. Here we provide a much wider flow cytometry survey of ploidy in some European Ginkgo collections, and own seedlings (>2200 individuals and ~200 cultivars). We found a surprisingly high level of ploidy variation in modern-day Ginkgo and documented altogether 13 haploid, 3 triploid, and 10 tetraploid Ginkgo plants or cultivars, most of them being morphologically distinct from common diploids. Haploids frequently produced polyploid (dihaploid) buds or branches. Tetraploids showed some genome size variation. The surveyed plants provide a unique resource for future Ginkgo research and breeding, and they might be used to accelerate the modern diversification of this nearly extinct plant lineage.

Linkage Disequilibrium and Evaluation of Genome-Wide Association Mapping Models in Tetraploid Potato.

Genome-wide association studies (GWAS) have become a powerful tool for analyzing complex traits in crop plants. The current study evaluates the efficacy of various GWAS models and methods for elucidating population structure in potato. The presence of significant population structure can lead to detection of spurious marker-trait associations, as well as mask true ones. While appropriate statistical models are needed to detect true marker-trait associations, in most published potato GWAS, a ‘one model fits all traits’ approach has been adopted. We have examined various GWAS models on a large association panel comprising diverse tetraploid potato cultivars and breeding lines, genotyped with single nucleotide polymorphism (SNP) markers. Phenotypic data were generated for 20 quantitative traits assessed in different environments. Best Linear Unbiased Estimates (BLUEs) for these traits were obtained for use in assessing GWAS models. Goodness of fit of GWAS models, derived using different combinations of kinship and population structure for all traits, was evaluated using Quantile-Quantile (Q-Q) plots and genomic control inflation factors (λGC). Kinship was found to play a major role in correcting population confounding effects and results advocate a ‘trait-specific’ fit of different GWAS models. A survey of genome-wide linkage disequilibrium (LD), one of the critical factors affecting GWAS, is also presented and our findings are compared to other recent studies in potato. The genetic material used here, and the outputs of this study represent a novel resource for genetic analysis in potato.

Meiotic irregularities in diploid and tetraploid plants of Lolium multiflorum Lam.

The genus Lolium comprises several species of economical importance in temperate countries, mostly due to their high nutritional value and adaptability to cold environments, including southern regions of Brazil. Recently, several diploid cultivars and populations, as well as synthetic tetraploid cultivars have been explored. In order to viabilize or to direct crossings, it is important that the accessions present regular meiosis, thus, producing viable pollen grains. In this way, this study aimed at investigating the meiosis of nine accessions of Lolium multiflorum used in breeding programs, seeking to evaluate its viability in future crossings. The meiosis of diploid plants (2n = 2× = 14) is more regular than the artificially tetraploidized genotypes (2n = 4× = 28). In the tetraploids, univalent, bivalent, and multivalent configurations were observed. The irregularities were associated to mixoploidy, irregular segregation of chromosomes, spindle disorders, asynchrony, micronuclei, and cellular fusion and formation of syncyte. The abnormalities affected the meiotic index of tetraploid cultivars, characterizing them as unstable. Nevertheless, both diploid and tetraploid genotypes are considered able to participate in crossings because, although there are abnormalities, they do not occur at levels that could affect the production of viable pollen grains.

Nitrogen partitioning differs in sheep offered a conventional diploid, a high sugar diploid or a tetraploid perennial ryegrass cultivar at two feed allowances

Grazing sheep on ryegrass based pasture with elevated water soluble carbohydrate (WSC) concentration might improve N use efficiency and reduce N excretion into the environment. Diploid ryegrasses with elevated WSC have been bred and released as a high-sugar cultivars (HSG), and tetraploid ryegrass (TRG) generally has elevated WSC compared to conventional diploid ryegrass (CRG). The objective of the current study was to determine N partitioning in sheep fed HSG, TRG, and CRG offered at two feed allowances. Three N partitioning trial periods (Sep 2013, March 2014 and Nov 2014) were conducted with 30 Romney wethers (different sheep in each period) over 5 d of excreta collection measurements per period. For each period, three perennial ryegrass types (HSG, CRG and TRG) were each offered at two allowances (0.7 and 1.0 kg DM/d) (6 treatments × 5 sheep). As a proportion of N intake, urinary-N excretion was greater (P = 0.016) for sheep fed TRG compared with sheep fed CRG, and intermediate for sheep fed HSG. There was an interaction between cultivars and feed allowance levels for N retained as a proportion of N intake (P = 0.04) with retained-N being similar among cultivars at the high feed allowance, while sheep fed CRG had a greater retained-N as proportion of N intake than sheep fed TRG at low feed allowance, with HSG fed sheep intermediate. The ratio of urinary-N:faecal-N was lower (P < 0.001) for sheep fed CRG and HSG compared with sheep fed TRG. The ratio of digestible N to organic matter (OM) was greater (P = 0.003) for sheep fed TRG than sheep fed HSG, with sheep fed CRG intermediate. Forage WSC concentration and WSC:Crude protein and WSC:Neutral Detergent Fibre ratios correlated negatively (r −0.46 to −0.56) with urinary-N as proportion of N intake. Offering a higher forage allowance was, however, a more effective strategy to decrease N excretion and increase retained N, both as a proportion of N intake. In conclusion, urinary-N as proportion of N intake was lower for sheep fed CRG than for sheep fed TRG, with sheep fed HSG intermediate, and it was lower at a the higher feed allowance.

The Capacity to Buffer and Sustain Imbalanced D-Subgenome Chromosomes by the BBAA Component of Hexaploid Wheat Is an Evolved Dominant Trait.

Successful generation of pentaploid wheat (genome, BBAAD) via interspecific hybridization between tetraploid wheat (BBAA) and hexaploid wheat (BBAADD) holds great promise to mutually exchange desirable traits between the two cultivated wheat species, as well as providing a novel facet for evolutionary studies of polyploid wheat. Taking advantage of the viable and fertile nature of an extracted tetraploid wheat (ETW) with a BBAA genome that is virtually identical with the BBAA component of a hexaploid common wheat, and a synthetic hexaploid wheat, we constructed four pentaploid wheats with several distinct yet complementary features, of which harboring homozygous BBAA subgenomes is a common feature. By using a combined FISH/GISH method that enables diagnosing all individual wheat chromosomes, we precisely karyotyped a larger number of cohorts from the immediate progenies of each of the four pentaploid wheats. We found that the BBAA component of hexaploid common wheat possesses a significantly stronger capacity to buffer and sustain imbalanced D genome chromosomes and appears to harbor more structural chromosome variations than the BBAA genome of tetraploid wheat. We also document that this stronger capacity of the hexaploid BBAA subgenomes behaves as a genetically controlled dominant trait. Our findings bear implications to the known greater than expected level of genetic diversity in, and the remarkable adaptability of, hexaploid common wheat as a staple crop of global significance, as well as in using pentaploidy as intermediates for reciprocal introgression of useful traits between tetraploid and hexaploid wheat cultivars.

Genetic fingerprinting of diploid and tetraploid cotton cultivars by retrotransposon-based markers

Cotton (Gossypium spp.) is the most important natural fiber and oil source worldwide. The genus Gossypium has 45 diploid and 5 allotetraploid species. Currently cotton has only 4 cultivated species, two tetraploid species [G. hirsutum L. and G. barbadense L., (2n = 4x = 52)] and two diploid species [G. arboreum L. and G. herbaceum L., (2n = 2x = 26]. Continuous artificial selection and cultivation of available cotton cultivars has led to genetic erosion and loss of useful genetic loci from the available cotton germplasm. Different molecular markers used in genetic fingerprinting of cottons, revealed narrow genetic variability. In order to provide data on genetic diversity present in our cotton germplasm collection, we carried out genetic fingerprinting study of 17 diploid and tetraploid cotton accessions by inter retrotransposon amplified polymorphism markers. The results showed low-moderate genetic variability (0.0–18%) among the studied cultivars. However, we obtained high genetic variability within each species (45–80%). Moreover, some specific bands (alleles) were identified in these species. Such moderate to high genetic variability in cotton germplasm is of high importance for choosing parental plants for hybridization. Inter retrotransposon amplified polymorphism markers could efficiently differentiate the cultivars and the studied diploid species from tetraploids. Therefore, these are suitable molecular markers for fast screening and genetic fingerprinting of large cotton germplasm.

Comparison of perennial ryegrass,Lolium perenneL., ploidy and white clover,Trifolium repensL., inclusion for herbage production, utilization and nutritive value

AbstractIncreasing herbage dry‐matter (DM) production and utilization on‐farm improves efficiency and sustainability. The objective of this study was to investigate the effect of perennial ryegrass,Lolium perenneL., ploidy and white clover,Trifolium repensL., inclusion on herbageDMproduction and utilization in an intensive animal grazing system, with high nitrogen (N) inputs (250 kg N ha−1) and a high stocking rate (2.75 livestock units ha−1). The study was a 2 × 2 factorial design, consisting of diploid and tetraploid cultivars sown as grass‐only and grass‐white clover to give four sward treatments (diploid‐only, tetraploid‐only, diploid‐white clover, tetraploid‐white clover). These were evaluated at each grazing occasion (8–10 per year) for 3 years (2014–2016). Tetraploid‐white and grass‐white clover swards had a lower sward density (−9 and −8 kg DM cm−1, respectively) and perennial ryegrass tiller density (−820 and −1,436 tillers m−2, respectively) leading to lower postgrazing sward heights (−0.15 and −0.41 cm, respectively), and maintained a superior nutritive value when compared with diploid‐only and grass‐only swards respectively. White clover inclusion resulted in higher productivity characterized by increased herbageDMproduction (+1,468 kg DM ha−1), improved nutritive value and increased utilization across the three grazing seasons. Varying sward composition with perennial ryegrass ploidy led to improved nutritive value and favourable grazing characteristics in tetraploid swards.

Maximization of Markers Linked in Coupling for Tetraploid Potatoes via Monoparental Haploids

Haploid potato populations derived from a single tetraploid donor constitute an efficient strategy to analyze markers segregating from a single donor genotype. Analysis of marker segregation in populations derived from crosses between polysomic tetraploids is complicated by a maximum of eight segregating alleles, multiple dosages of the markers and problems related to linkage analysis of marker segregation in repulsion. Here, we present data on two monoparental haploid populations generated by prickle pollination of two tetraploid cultivars with Solanum phureja and genotyped with the 12.8 k SolCAP single nucleotide polymorphism (SNP) array. We show that in a population of monoparental haploids, the number of biallelic SNP markers segregating in linkage to loci from the tetraploid donor genotype is much larger than in putative crosses of this genotype to a diverse selection of 125 tetraploid cultivars. Although this strategy is more laborious than conventional breeding, the generation of haploid progeny for efficient marker analysis is straightforward if morphological markers and flow cytometry are utilized to select true haploid progeny. The level of introgressed fragments from S. phureja, the haploid inducer, is very low, supporting its suitability for genetic analysis. Mapping with single-dose markers allowed the analysis of quantitative trait loci (QTL) for four phenotypic traits.

Challenges of Breeding Rose Rosette–resistant Roses

Rose rosette disease (RRD) whose causal agent, the Emaravirus Rose rosette virus (RRV), was only recently identified has caused widespread death of roses in the midwestern and eastern sections of the United States. A national research team is working on the detection and best management practices for this highly damaging disease. Unfortunately, little is known about the host plant resistance to either the causal viral agent or its vector, the eriophyid mite Phyllocoptes fructiphilus. Thus far, the only confirmed resistance is among Rosa species. Of the over 600 rose cultivars observed, only 7% have not exhibited symptoms of RRD. Replicated trials are in progress to confirm resistance and/or susceptibility of ≈300 rose accessions in Tennessee and Delaware. Rose is a multispecies cultivated complex that consists of diploid, triploid, and tetraploid cultivars. The basic breeding cycle is 4 years with a 3-year commercial trial coupled with mass propagation before release. Thus, if only one breeding cycle is needed, a new cultivar could be produced in 7 years. Unfortunately, for the introgression of a new trait such as disease resistance from a related species into the commercial rose germplasm, multiple generations are required which can easily take two decades from the first cross to cultivar release. Research is ongoing to develop a rapid selection procedure for resistance to RRD with the aid of molecular markers associated with the resistance. Such an approach has the potential of reducing the breeding cycle time by 50% and increasing the efficiency of seedling and parental selection manifold, leading to commercially acceptable rose cultivars with high RRD resistance in less time and with less expense.

Acquisition of triploid germplasms by controlled hybridisation between diploid and tetraploid in Chinese jujube

ABSTRACT‘Chenguang’ is the first released tetraploid cultivar (2n = 4x = 48) of Chinese jujube (Ziziphus jujuba Mill.) induced by colchicine. The purpose of this study was to create triploid germplasms by using ‘Chenguang’ as a parent. The controlled crosses between autotetraploid ‘Chenguang’ and diploid ‘Dongzao’ were carried out from 2013 to 2015 by maintaining the 2 parents in a nylon net and employing bees as pollinator. A total of 606 fruits were produced, yet only 17 seeds were obtained from ‘Dongzao’ and none from ‘Chenguang’. Direct sowing of the seeds in greenhouse showed a higher seedling rate than embryo culture. Four progeny plants were eventually obtained in the greenhouse and all of them were confirmed as authentic hybrids by SSR marker technique. At last, 3 triploids and 1 diploid were identified by flow cytometric analysis. Consequently, tetraploid ‘Chenguang’ with high pollen vitality and pollen number per anther could be used as a reliable 2n pollen provider, and the 2x × 4x cross combination type is more suitable for triploid creation in Chinese jujube. This is the first successful production of triploid hybrids by controlled cross between diploids and tetraploids in jujube.

Differential growth response to fertilization of ten elite shrub willow (Salix spp.) bioenergy cultivars

Shrub willow triploid hybrid cultivars obtained the greatest aboveground biomass compared to diploid and tetraploid cultivars, and greater biomass was highly correlated with leaf traits and rapid early stem elongation. Shrub willow (Salix L. spp.) is a strong candidate for use as a dedicated bioenergy crop in moist, temperate climates due to high growth rates, excellent regenerative properties and relatively low nutrient demand. Large discrepancies exist in the literature as to the benefits of fertilization for improving biomass production. Controlled environment fertilization studies can remove some confounding edaphic and climatic factors present in field studies. Ten top-performing commercial or pre-commercial cultivars, mostly bred in the US, were assessed for response to five fertilization levels by measuring 20 biomass and growth traits. Triploid hybrid Salix viminalis × S. miyabeana cultivars had the greatest total aboveground biomass, as well as high stem biomass. There was a strong relationship between early stem growth and final aboveground biomass, but only under adequate fertilization. Different strategies for high biomass production among cultivars are discussed in the context of nitrogen investment in leaves. Comparing field trial results and this greenhouse experiment indicates that while the yield ranking is generally preserved, the greenhouse results diverged greatly for two cultivars.