Triploid Interspecific Hybrids Research Articles

Peculiarities of plant adaptation of interspecific hybrid Betula ex vitro

Microclonal propagation as one of the methods of biotechnology allows obtaining genetically homogeneous plants during the year from a minimum amount of donor material. Adaptation of plants ex vitro to environmental conditions is the final and important stage of microclonal propagation. The purpose of the study is to determine the optimal mode of plant adaptation of triploid interspecific hybrid Betula ex vitro to environmental conditions. Biotechnological (microclonal propagation) and statistical (arithmetic mean, standard error, one-way analysis of variance (ANOVA)) methods were used for research. The study was carried out in the research of Plant Biotechnology Laboratory of the Separated Subdivision of National University of Life and Environmental Sciences of Ukraine “Boyarka Forest Research Station” during 2019-2023. According to research, the MS nutrient medium with the addition of 0.25 mg∙l -1 of kinetin stimulated the active proliferation of microshoots and root system. Optimum plant development took place on the nutrient medium vitro for a 25-30- day cycle of cultivation, which contributed to successful adaptation to environmental conditions. The proportion of adapted Betula ex vitro hybrid plants on agroperlite substrate was more than 60% for 30 days. Significant plant viability (more than 80%) was obtained under the conditions of preliminary exposure of the plant root system in auxin solution (1.0 mg/lIAA, 1.0 mg/l NAA, 1.0 mg/lIBA) for 25-30 minutes followed by daily spraying of leaves with 20% glycerin for 15-20 days. Adapted plants had typical pigmentation without signs of chlorosis and vitrification. In the spring, the survival rate of plants under environmental conditions was more than 80% and indicated a high level of adaptability after in vitro. The developed protocol for the adaptation of the Betula ex vitro hybrid allows obtaining high plant survival in environmental conditions. The practical value of the research is obtaining plants adapted to environmental conditions ex vitro, which in the future can be used to qualitatively enrich the range of artificial plantings in settlements

New introgressive forms of cultivated barley obtained on the basis of interspecific hybrids <i>Hordeum vulgare</i> L. × <i>Hordeum bulbosum</i> L.

Background. The use of alien genetic material of bulbous barley Hordeum bulbosum L. to increase the diversity of cultivated barley Hordeum vulgare L. is an important task, since H. bulbosum is characterized by a number of valuable traits. One of the ways to use the genetic potential of bulbous barley is the interspecific hybridization and obtaining fertile introgressive lines of H. vulgare based on interspecific hybrids. The aim of the study was to obtain new introgressive forms of spring barley using interspecific triploid (HvHbHb) and tetraploid (HbHbHvHv) hybrids of cultivated barley with bulbous barley to expand the collection of introgressive lines of H. vulgare. Materials and methods. To create new introgressive forms, diploid barley H. vulgare (2x) cv. ‘Roland’, was crossed with interspecific hybrids H. vulgare cv. ‘Roland’(2x) × H. bulbosum W851 (4х) (HvHbHb), and H. bulbosum A17 (4x) × H. vulgare ‘Borwina’ (4x) (HbHbHvHv). Cultivated barley forms with introgression of the bulbous barley genetic material were selected from the offspring from these crosses; then the selection was continued in two progenies from self-pollination of selected BC1 plants with three alien introgressions. Identification and localization of introgressions was carried out using the method of fluorescent in situ hybridization (GISH and FISH with chromosome-specific markers). Results. The crossing of cultivated barley with triploid and tetraploid interspecific hybrids H. vulgare × H. bulbosum yielded new forms of cultivated barley with recombinant chromosomes, among which two plants with three terminal introgressions of the genetic material of bulbous barley were identified. The first plant, derived from a triploid hybrid, showed introgressions in chromosomes 5HL, 1HL and 3HS. When two homologues with the 5HL introgression of the initial size are combined in the karyotype, the lethality of seedlings is observed in the offspring plants. In the second plant obtained on the basis of a tetraploid hybrid introgression was revealed in chromosomes 5HL, 2HL, and 7HS. In the offspring from self-pollination of this form, the presence of the 2HL introgression of the original size in both homologues led to plant sterility. Forms with a change in size of the introgression in 5HL and 3HS in the offspring of the first plant and with a change in size of the introgression in 2HL in the offspring of the second plant were detected, which indicated that meiotic recombination had occurred in those chromosome regions in BC1 plants. Conclusions A barley plant with the introgression of bulbous barley chromatin into chromosomes 1HL, 5HL, and 3HS of cultivated barley was identified in the offspring from a cross of cultivated barley with a triploid interspecific hybrid H. vulgare × H. bulbosum. In crosses with a tetraploid interspecific hybrid, a barley plant with the introgression into chromosomes 2HL, 5HL, and 7HS was found. On the basis of ‘Roland’ spring barley cultivar, two series of new introgressive forms of H. vulgare with various combinations of recombinant chromosomes have been created.

Nonadditive gene expression is correlated with nonadditive phenotypic expression in interspecific triploid hybrids of willow (Salix spp.).

Many studies have highlighted the complex and diverse basis for heterosis in inbred crops. Despite the lack of a consensus model, it is vital that we turn our attention to understanding heterosis in undomesticated, heterozygous, and polyploid species, such as willow (Salix spp.). Shrub willow is a dedicated energy crop bred to be fast-growing and high yielding on marginal land without competing with food crops. A trend in willow breeding is the consistent pattern of heterosis in triploids produced from crosses between diploid and tetraploid species. Here, we test whether differentially expressed genes are associated with heterosis in triploid families derived from diploid Salix purpurea, diploid Salix viminalis, and tetraploid Salix miyabeana parents. Three biological replicates of shoot tips from all family progeny and parents were collected after 12 weeks in the greenhouse and RNA extracted for RNA-Seq analysis. This study provides evidence that nonadditive patterns of gene expression are correlated with nonadditive phenotypic expression in interspecific triploid hybrids of willow. Expression-level dominance was most correlated with heterosis for biomass yield traits and was highly enriched for processes involved in starch and sucrose metabolism. In addition, there was a global dosage effect of parent alleles in triploid hybrids, with expression proportional to copy number variation. Importantly, differentially expressed genes between family parents were most predictive of heterosis for both field and greenhouse collected traits. Altogether, these data will be used to progress models of heterosis to complement the growing genomic resources available for the improvement of heterozygous perennial bioenergy crops.

Heterosis for Biomass-Related Traits in Interspecific Triploid Hybrids of Willow (Salix spp.)

Species hybridization is key for the improvement of shrub willow (Salix spp.) bioenergy crops because hybrids often display heterosis for yield. The development of high-yielding genotypes requires numerous broad attempts at hybridization followed by field evaluation and selection for stable performance. Selection of improved shrub willow varieties for use as a bioenergy crop involves evaluation of full-sib progeny in family-based selection trials. Improving the accuracy of evaluation through the use of components of yield would greatly improve the efficiency of selection. Heterosis for biomass yield in intra- and interspecific F1 and F2 shrub willow crosses, made between Salix sections and ploidy, was examined by utilizing a suite of morphological, physiological, and chemical composition traits collected over the course of 12 weeks in the greenhouse and over 3 years in the field. Triploid families generated from diploid S. viminalis and tetraploid S. miyabeana displayed the greatest levels of heterosis for harvestable biomass and biomass-related growth traits in the greenhouse and in the field. While intraspecific S. purpurea diploids exhibited low levels of heterosis for these traits, interspecific diploids produced moderate levels of heterosis in greenhouse experiments. Differences between greenhouse and field trial results can largely be explained by pest damage, which negatively impacted interspecific diploids. Heterosis for the traits that form the basis for biomass yield, including stem growth, foliar, and physiological traits, was quantified, and family-level differences are discussed.

Variable impacts on growth of deficit irrigation on Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt Davy and Poa pratensis L

AbstractAs average global temperatures rise, Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt Davy (triploid interspecific hybrid bermudagrass; HBG) may be increasingly suited for traditionally cooler climates where Poa pratensis L. (Kentucky bluegrass; KB) is common. The objective of this study is to evaluate growth for two HBG cultivars (‘DT‐1’ and ‘NorthBridge Turf Bermudagrass’) compared with KB in all combinations of deficit, moderate, and high irrigation. The HBG had significantly more shoot and root biomass and root depth than KB, with the latter having a higher shoot to root ratio. Differing responses to deficit irrigation were also observed between the two HBG cultivars. When drought stressed, NorthBridge Turf Bermudagrass seems to send roots deeper into the soil to capture the water stored there while DT‐1 grows thicker masses of roots at a shorter depth to maximize its ability to capture water near the surface. These data provide a direct comparison of HBG and KB—quantifying the response for root and shoot growth under deficit irrigation when grown under cool‐season conditions. These data suggest that irrigation needs, especially in regions with increasing water scarcity, will likely be less for HBG than KB as a function of more extensive root systems.

Visualizing Meiotic Chromosome Pairing and Segregation in Interspecific Hybrids of Rice by Genomic in situ Hybridization

Meiotic disturbances in F1 hybrids and their progenies are still major problems in wide hybridization. To investigate the genome affinity reflected in chromosome pairing and segregation, we studied chromosome behaviors during meiosis in two interspecific F1 hybrids [O. minuta×O. australiensis (Om×Oa, BCE genome) and Oa×O. ridleyi (Or, EHJ genome)] by using both traditional staining methods and genomic in situ hybridization (GISH). GISH analysis has been successfully performed on mitotic chromosomes to distinguish different Oryza genomes, but relatively fewer systematic analyses of meiotic chromosomes of interspecific hybrids have been reported. In the hybrids, highly irregular chromosome behaviors through meiosis resulted in producing microspores with unbalanced genome. At diakinesis of these two hybrids, most chromosomes present as univalent, with low frequency as bivalents and occasionally as trivalents. In a pollen mother cell, 2 to 8 bivalents and 0 to 4 trivalents were observed in the hybrid Oa×Or, and 1 to 8 bivalents and 0 to 5 trivalents were observed in the hybrid Om×Oa. GISH results indicated that 51.52% bivalents in Oa×Or and 79.65% bivalents in Om×Oa involved allosyndetic association, which indicates that recombination and introgression should be possible if viable backcrosses can be recovered even from triploid hybrids. In this study, we revealed that the meiotic disturbance due to low affinities between parental genomes is the major reason for the sterility of these two triploid interspecific hybrids. The two hybrids showing vigor in reproductive growth are potential genetic resources in future breeding programs. A better understanding of genomic affinities between these distant Oryza species can facilitate planning an effective breeding program by using wide hybridization, and efficient and routine GISH analysis is helpful to monitor alien introgression in the process.

Spontaneous natural formation of interspecific hybrids within the Festuca-Lolium complex

Interspecific and intergeneric hybridization within the Festuca-Lolium complex is frequently used in forage plant breeding. However, little is known about the natural occurrence and competitiveness of such hybrids. We collected naturally formed hybrids between Festuca apennina, Festuca pratensis, and Lolium perenne in different habitats of Switzerland and the British Isles and studied their origin, the ease of their spontaneous formation, and their competitiveness with parental species. A special attention was paid to the largely sterile triploid forms and their rare sexual progeny. The triploid hybrid F. apennina × F. pratensis proved to be widespread and often highly competitive in Swiss permanent pastures. The majority of these hybrids originated from F. apennina as the seed parent although little or no F. apennina grew nearby. In an experimental setting with ample F. pratensis pollen provided by neighbouring plants, up to 20 % of seeds from open pollinated F. apennina plants were interspecific hybrids; among seeds collected in natural habitats, only 0.35 % were hybrids. At an experimental site at 1 000 m altitude, these triploid hybrids grew much more vigorously than corresponding tetraploid pure F. apennina, confirming their great competitiveness at such altitudes in permanent grasslands. The triploid hybrids were only marginally fertile suggesting that vegetative propagation by rhizomes is the cause of their competitive success in grassland. Moreover, triploid progeny retained the chromosome constitution of their mother plants indicating the possibility of apomixis. Natural triploid F. pratensis × L. perenne hybrids were partially female fertile (a seed set of 0.1 % or less) whereas diploid hybrids did not produce any viable seeds. Progenies of these triploids showed considerable chromosome alterations, such as loss of a genome or recombination due to homoeologous pairing, and only rarely the chromosome constitution of the triploid mother plant was retained. It was concluded that natural triploid interspecific hybrids could expand the range of their progenitor species and might function as bridges transferring genes between them.

Interspecific hybrid confirmation in wide crosses of cotton (Gossypium spp) through morphological, cytological and molecular analysis

Interspecific triploid hybrids were developed between tetraploid cultivated species Gossypium barbadense cv. Suvin and TCB 37 and diploid wild species Gossypium armourianum. The F1 hybridity was confirmed by morphological, cytological and molecular approaches. The ploidy level of interspecific F1 hybrid was triploid and completely male sterile. Female parents Suvin and TCB 37 had erect growth habit, yellow petals, palmate leaves, green stem, thick and prominent leaf veins, but Suvin had dense yellow anthers while TCB 37 was with dense creamy anthers whereas male parent has a spreading growth habit, yellow petals, cordate leaves, reddish green stem, medium dense yellow anthers, thin leaf veins, protruded stigma and glabrous plant body. The growth habit, petal colour, leaf shape and size of interspecific F1 hybrid were intermediate. Plant stem colour, hairyness, leaf pubescence and anther colour of Gossypium armourianum were observed to be dominant as hybrid fully resembled Gossypium armourianum for these characters. Petal spot was observed in both male and female parents but F1 hybrids had different intensity of petal spot in their petals. Variable expression of petal spot, anther colour and filament colour was observed in the F1 hybrids. Gossypium barbadense cv. Suvin and TCB 37 had 52 chromosomes, Gossypium armourianum had 26 chromosomes and the interspecific F1 was with 39 chromosomes. Significant differences were observed between pollen size, pollen fertility of parents and their hybrids. The F1 interspecific hybrid having more than 97% of sterile pollen grains. Out of 6 polymorphic SSR markers between parents, 3 markers unambiguously confirmed the hybrid status of interspecific hybrid. This hybrid may serve as useful genetic resource for the transfer of jassid resistance gene to Gossypium barbadense cultivars.

Новые генетические источники для селекции видов Prunus L. на полиплоидном уровне

This research is aimed at studying of the chromosomal number distribution within the new, in vitro cultured, amitotic
 clonal lines of Prunus species, at comparing of the fertility and size of pollen for triploid and hexaploid amitotic clones and
 at identifying of new genetic sources and their subsequent use in breeding. Methods. The standard cytological and statistical
 methods were used in this scientific work. Results. The regularities of induced polyploids output both from the initial number
 of chromosomes and from the origin and individual characteristics of the original genotypes were established. For amitotic
 hexaploid genotypes of hybrid cherry, high pollen quality was discovered at the level of 81,8–92,6 % of fertility (in triploids
 the 4,6–18,8 % of such pollen was found), therefore, the studied 4 clonal cherry genotypes (12-1-1Т2, 12-1-1Т6, 12-1-2Т3,
 12-1-2Тv) are recommended for breeding of resistant to fungal diseases varieties. No significant differences were found in the
 diameter of fertile pollen (46.3–47.8 μm) between cherry amitotic triploids and hexaploids. Therefore, in all likelihood, fertile
 pollen in triploids carries an unreduced triploid set of chromosomes. Prime scientific novelty. A completely new and original
 selection material for the genus Prunus L. – polyploid hybrids of P. fruricosa Pall. with rare East-Asiatic cherry species P. serrulata Lindl., P. canescens Bois., P. incisa. Thoub. were studied. The arguments in favor of a positive breeding prospect for the
 transfer of new cherries varieties to the hexaploid level (2n = 48), including an in vitro culture method of chromosome number
 doubling for the sterile triploid interspecific hybrids, have been obtained. The first created tetraploid (2n = 32) amitotic clonal
 lines of microcherry P. pumila L. must be tested in crosses with thorns and hybrids of thorns.

Centromere localization in medaka fish based on half-tetrad analysis

Gene-centromere (G-C) mapping provides insight into vertebrate genome composition, structure and evolution. Although medaka fish are important experimental animals, no genome-wide G-C map of medaka has been constructed. In this study, we used 112 interspecific triploid hybrids and 152 DNA markers to make G-C maps of all 24 linkage groups (LGs). Under the assumption of 50% interference, 24 centromeres were localized onto all corresponding medaka LGs. Comparison with 21 centromere positions deduced from putative centromeric repeats revealed that 19 were localized inside the centromeric regions of the G-C maps, whereas two were not. Based on the centromere positions indicated in the G-C maps and those of centromeric repeats on each LG, we classified chromosomes as either biarmed or monoarmed; n = 24 = 10 metacentrics/submetacentrics + 14 subtelocentrics/acrocentrics, which is consistent with the results of previous karyological reports. This study helps to elucidate genome evolution mechanisms, and integrates physical and genetic maps with karyological information of medaka.

Presence/absence of a CACTA transposon in the CYC2c gene of two genotypes of Helianthus × multiflorus cv. “Meteor” characterized by a radiate inflorescence with different shape of disk flower corollas

Helianthus × multiflorus is a triploid (2n = 51) interspecific hybrid derived from the cross of H. decapetalus with H. annuus that exists in radiate and ligulate inflorescence types. The H. × multiflorus “Soleil d’Or” has a ligulate inflorescence, with actinomorphic corolla of disk flowers converted in zygomorphic ray-like corollas. In “Soleil d’Or”, a truncated CACTA transposable element (TE), named CTEHM1, is integrated in the HmCYC2c gene, a key player controlling zygomorphism in the Helianthus genus. Here, we showed that H. × multiflorus “Meteor”, originated from a mutation of “Soleil d’Or”, exists in two different types of radiate inflorescence, here named “Meteor 1” and “Meteor 2”. Notably, in “Meteor 1”, which displayed a corolla of disk flowers typical for the Helianthus genus, CTEHM1 was transposed from the HmCYC2c gene. In contrast, the CTEHM1 TE was still present in the HmCYC2c gene of “Meteor 2”. In this genotype, the largest corolla of the disk flowers shows some features of the ray flowers giving rise to a radiate inflorescence unusual for the Helianthus genus. The in silico analysis of CTEHM1 also highlights the presence of a 202 bp CpNpG island, which is a putative target of methylation. Interestingly, the gene expression of the HmCYC2c gene was significantly higher in disk flowers of “Meteor 2” compared to “Meteor 1”. Stated these results, we suggest that both the excision of a TE and an epigenetic regulation of gene expression generate the two-inflorescence types of H. × multiflorus, “Meteor 1” and “Meteor 2”.

Development of Allotriploid Embryos Produced by Crossing Female Starry Flounder Platichthys stellatus and Male Stone Flounder Kareius bicoloratus

We investigated the development of allotriploid embryos derived from a cross between female starry flounder Platich thys stellatus and male stone flounder Kareius bicoloratus. The second cleavage, mid-blastula, gastrula, and Kupffer’s vesicle appearance stages, and hatching of embryos began 3.7, 25.6, 45.7, 87.7, and 213.2 h after cold shock at 6°C, respectively. The hatching and development time of triploid interspecific hybrid eggs was approximately the same as those of diploid starry flounder eggs at the same incubation temperature.

Sexual introgression of the late blight resistance gene Rpi-blb3 from a Mexican wild diploid species Solanum pinnatisectum Dunal into potato varieties

Solanum pinnatisectum Dunal (2n = 2x = 24) is a tuber-bearing Mexican wild species that has an extremely high level of resistance to late blight (Phytophthora infestans). However, this species is distantly related and isolated from cultivated potato species by a strict sexual reproduction barrier. Previously, we successfully obtained triploid interspecific hybrids between chromosome-doubled S. pinnatisectum and a South American diploid clone carrying the S locus inhibitor gene (Sli). In this study, chromosome doubling of triploid hybrids was done to produce hexaploids used as the recurrent and donor parents in the successive backcrossing scheme. In a BC2 population consisting of 198 genotypes, P. infestans was inoculated. Ninety-six genotypes were resistant, and 102 were susceptible. The presence of the Rpi-blb3–specific marker band perfectly matched the resistance phenotype, verifying that the Rpi-blb3 gene controlled resistance. BC1 and BC2 progenies were relatively easy to reciprocally cross with cultivars. Therefore, the Rpi-blb3 gene derived from S. pinnatisectum could be used in practical breeding to confer a high level of late blight resistance to potato varieties with the aid of the gene-specific marker.

A mixed model approach for evaluating yield improvements in interspecific hybrids of shrub willow, a dedicated bioenergy crop

Lignocellulosic bioenergy crops such as shrub willow (Salix spp.) are expected to have a significant role in climate mitigation strategies. Yield is perhaps the most important trait for genetic selection and development of biomass feedstocks, but the selection process is complicated by the strong influence that environmental factors has on cultivar performance. Understanding the genotype-by-environment interactions using regional yield trials of shrub willow will inform future breeding efforts and improve the ability to make regionally-specific cultivar recommendations. We analyzed two yield trial datasets containing genotypes from successive rounds of breeding using a series of mixed models. Stability variance parameters were used together with overall yields to identify genotypes with stable yields or specific adaptation. Analysis of the first dataset revealed a group of triploid interspecific hybrid cultivars with exceptional performance and specific adaptation to either poor or good quality environments. The best performing cultivar showed a 14% yield improvement over the mean of the check cultivars. In the second dataset, new selections were assessed along with the top performing cultivars from dataset 1. New triploid hybrids had yields 19 to 27% greater than the check cultivar and exhibited similar patterns of specific adaptation as some of the selections from the first dataset. Partial least squares regression analysis indicated that top-yielding genotypes were favored in environments with higher temperatures and greater growing degree days. This analysis demonstrates incremental improvements in yield with successive rounds of breeding through the development of interspecific triploid hybrids.

Chromosome segregation in an allotetraploid banana hybrid (AAAB) suggests a translocation between the A and B genomes and results in eBSV-free offsprings

Many banana cultivars (including the Plantain type) are triploid interspecific hybrids between Musa acuminata (A genome) and Musa balbisiana (B genome). M. balbisiana contains endogeneous Banana streak virus sequences (eBSVs) that can, in interspecific genome context, spontaneously release infectious viral genomes. We analyzed, a triploid progeny of 184 individuals from a cross between a tetraploid AAAB breeding accession (CRBP39) and the diploid AA accession (Pahang) with 38 SSR and eBSV-specific PCR markers. The results showed that (1) most of the alleles are found/transmitted in the expected frequency to the progeny with only 10 % biased; (2) 70 % of the loci displayed a tetrasomic allele segregation and (3) interspecific intrachromosomal recombinations occurred for all the chromosome segments surveyed. However, half of the offspring obtained resulted from maternal unbalanced gametes transmission. Analysis of gamete composition and marker association suggested the presence of a large translocation between A and B genome involving chromosome 1 and 3. The two infectious eBSVs present in the maternal parent CRBP39 are located on chromosome 1B and appeared in a higher proportion than expected in the progeny. Interestingly, we showed that both eBSVs were absent from 24 offspring that represent promising material for breeding.

Combined Use of Molecular Markers and High-Resolution Melting (HRM) to Assess Chromosome Dosage in Potato Hybrids.

In plants, the most widely used cytological techniques to assess parental genome contributions are based on in situ hybridization (FISH and GISH), but they are time-consuming and need specific expertise and equipment. Recent advances in genomics and molecular biology have made PCR-based markers a straightforward, affordable technique for chromosome typing. Here, we describe the development of a molecular assay that uses single-copy conserved ortholog set II (COSII)-based single nucleotide polymorphisms (SNPs) and the high-resolution melting (HRM) technique to assess the chromosome dosage of interspecific hybrids between a Solanum phureja-S. tuberosum diploid (2n = 2x = 24) hybrid and its wild relative S. commersonii. Screening and analysis of 45 COSII marker sequences allowed S. commersonii-specific SNPs to be identified for all 12 chromosomes. Combining the HRM technique with the establishment of synthetic DNA hybrids, SNP markers were successfully used to predict the expected parental chromosome ratio of 5 interspecific triploid hybrids. These results demonstrate the ability of this strategy to distinguish diverged genomes from each other, and to estimate chromosome dosage. The method could potentially be applied to any species as a tool to assess paternal to maternal ratios in the framework of a breeding program or following transformation techniques.

Discovery of Natural Interspecific Hybrids Between Miscanthus Sacchariflorus and Miscanthus Sinensis in Southern Japan: Morphological Characterization, Genetic Structure, and Origin

Natural Miscanthus grasses are useful for improving biomass production. We found a population of putative triploid interspecific hybrids between Miscanthus sacchariflorus and Miscanthus sinensis in southern Kyushu, Japan. This study aims to investigate its morphological variation, genetic structure, and origin. Miscanthus plants were collected from 114 points, mainly beside a river along a distance of 2.8 km in the Tashiro–Fumoto area. They resembled M. sacchariflorus but showed morphology intermediate between the two species. They had a nuclear DNA content corresponding to that of a hybrid between tetraploid M. sacchariflorus and diploid M. sinensis, and had species-specific alleles from both species revealed by DNA marker analysis. This indicates that the plants are triploid hybrids between M. sacchariflorus and M. sinensis. Genotyping using simple sequence repeat markers revealed only four genotypes among the hybrid population, of which two accounted for most plants. The genotypes showed mostly discrete geographical distributions. The two major genotypes showed contrasting phenotypes in pollen viability and in frequency of awns in florets. Some seeds collected from the population germinated and the seedlings showed a wide range of nuclear DNA content from diploid to tetraploid. In this area, many M. sinensis plants also grew, but we could not find M. sacchariflorus. The hybrid Miscanthus might be selected due to its improved adaptability introduced from M. sinensis. Furthermore, genetic and phenotypic characterization suggests the polyphyletic origin and clonal propagation of this population. Such partially fertile hybrids could be interesting for the improvement of Miscanthus as a biomass crop.

Eutrema racemosum (Eutremeae, Brassicaceae), a new tetraploid species from southwest China

The new species Eutrema racemosum is described, and its relationship to the closely related E. heterophyllum and E. edwardsii are discussed based on morphological, cytological, and molecular data. The novelty differs from E. heterophyllum by having elongated racemes and from E. edwardsii by somewhat reflexed fruiting pedicels. Four chloroplast DNA fragments and nuclear ITS region were sequenced for multiple individuals of each species. Three species show distinct and stable sequence variations. Eutrema racemosum and E. heterophyllum form a clade sister to that of E. edwardsii in phylogenetic analyses of sequence variations. Our cytological studies revealed that E. heterophyllum is a diploid with the small genome size, while E. racemosum is a tetraploid with duplicate genomes. These available data support the recognition of E. racemosum as a distinct species well differentiated morphologically and genetically, as well as well-isolated reproductively from its sister species E. heterophyllum. We further found some interspecific triploid hybrids between tetraploid E. racemosum and diploid E. heterophyllum, which seem to be sterile according to our germination experiments.

"A draft Musa balbisiana genome sequence for molecular genetics in polyploid, inter- and intra-specific Musa hybrids".

BackgroundModern banana cultivars are primarily interspecific triploid hybrids of two species, Musa acuminata and Musa balbisiana, which respectively contribute the A- and B-genomes. The M. balbisiana genome has been associated with improved vigour and tolerance to biotic and abiotic stresses and is thus a target for Musa breeding programs. However, while a reference M. acuminata genome has recently been released (Nature 488:213–217, 2012), little sequence data is available for the corresponding B-genome.To address these problems we carried out Next Generation gDNA sequencing of the wild diploid M. balbisiana variety ‘Pisang Klutuk Wulung’ (PKW). Our strategy was to align PKW gDNA reads against the published A-genome and to extract the mapped consensus sequences for subsequent rounds of evaluation and gene annotation.ResultsThe resulting B-genome is 79% the size of the A-genome, and contains 36,638 predicted functional gene sequences which is nearly identical to the 36,542 of the A-genome. There is substantial sequence divergence from the A-genome at a frequency of 1 homozygous SNP per 23.1 bp, and a high degree of heterozygosity corresponding to one heterozygous SNP per 55.9 bp. Using expressed small RNA data, a similar number of microRNA sequences were predicted in both A- and B-genomes, but additional novel miRNAs were detected, including some that are unique to each genome. The usefulness of this B-genome sequence was evaluated by mapping RNA-seq data from a set of triploid AAA and AAB hybrids simultaneously to both genomes. Results for the plantains demonstrated the expected 2:1 distribution of reads across the A- and B-genomes, but for the AAA genomes, results show they contain regions of significant homology to the B-genome supporting proposals that there has been a history of interspecific recombination between homeologous A and B chromosomes in Musa hybrids.ConclusionsWe have generated and annotated a draft reference Musa B-genome and demonstrate that this can be used for molecular genetic mapping of gene transcripts and small RNA expression data from several allopolyploid banana cultivars. This draft therefore represents a valuable resource to support the study of metabolism in inter- and intraspecific triploid Musa hybrids and to help direct breeding programs.

Dysfunction of mitotic cell division at shoot apices triggered severe growth abortion in interspecific hybrids between tetraploid wheat and Aegilops tauschii

Common wheat is an allohexaploid species, derived through endoreduplication of an interspecific triploid hybrid produced from a cross between cultivated tetraploid wheat and the wild diploid relative Aegilops tauschii. Hybrid incompatibilities, including hybrid necrosis, have been observed in triploid wheat hybrids. A limited number of A. tauschii accessions show hybrid lethality in triploid hybrids crossed with tetraploid wheat as a result of developmental arrest at the early seedling stage, which is termed severe growth abortion (SGA). Despite the potential severity of this condition, the genetic mechanisms underlying SGA are not well understood. Here, we conducted comparative analyses of gene expression profiles in crown tissues to characterize developmental arrest in triploid hybrids displaying SGA. A number of defense-related genes were highly up-regulated, whereas many transcription factor genes, such as the KNOTTED1-type homeobox gene, which function in shoot apical meristem (SAM) and leaf primordia, were down-regulated in the crown tissues of SGA plants. Transcript accumulation levels of cell cycle-related genes were also markedly reduced in SGA plants, and no histone H4-expressing cells were observed in the SAM of SGA hybrid plants. Our findings demonstrate that SGA shows unique features among other types of abnormal growth phenotypes, such as type II and III necrosis.