Search Results (25)

Hybridization between sugarcane (Saccharum spp.) and its wild relative Erianthus rockii offers a promising route to broadening the narrow genetic base of modern cultivars, but the authenticity and chromosome inheritance patterns of such hybrids remain poorly understood. In this study, we combined molecular marker (tetra-primer ARMS-PCR) and cytogenetic (genomic in situ hybridization, GISH) approaches to verify hybridity and track chromosome transmission in 24 F₁ and 12 BC₁ progeny. The F₁ hybrids exhibited a strict n + n transmission pattern, receiving exactly 15 chromosomes from E. rockii. When F₁ plants were used as the male parent in backcrosses, no BC₁ seeds were obtained due to complete pollen sterility. Remarkably, when F₁ plants served as the female parent, all 12 BC₁ clones retained the entire set of 15 E. rockii chromosomes intact, following an unconventional 2n + n pattern. These findings reveal a strong parent-of-origin effect and, for the first time, demonstrate that the whole E. rockii chromosome complement can be stably transmitted into backcross progeny without loss or recombination. This opens a direct route for introgressing complete wild genomes into sugarcane breeding lines, preserving complex polygenic traits and guiding rational crossing strategies. Full article

This review examines the reproductive biology of Limonium, mainly L. sinuatum and L. perezii, and explores the breeding strategies employed for these species. Limonium is one of the 20 most cultivated genera in the ornamental plant industry worldwide, with novelty sought in traits such as flower color, stem quality and disease resistance. Approximately 85% of the species in this genus present pollen/stigma dimorphism and self-incompatibility, presenting both challenges and opportunities for breeding. Breeding strategies such as interspecific hybridization, ploidy manipulation and chromosomal mutation have been used to increase the diversity of material available to breeders. In this review, we highlight how insights into reproductive biology, combined with advanced breeding techniques, can accelerate the development of fertile interspecific hybrids and broaden the genetic base for future Limonium breeding programs. Full article

A typical seed of rice (Oryza sativa L.) gives rise to a single seedling. In contrast, seeds from multiple embryos may develop into two or more seedlings, one of which is generated via sexual reproduction, while the others are likely to originate through apomictic pathways. Therefore, the occurrence of multiple embryos is often considered a hallmark of apomixis in rice. Apomixis refers to an asexual reproductive strategy wherein unreduced gametes form through modified meiosis (apomeiosis) without fertilization, thereby generating clonal offspring generally genetically identical to the maternal plant. This process is of great relevance in fixing heterosis in hybrid rice breeding. This review discusses the origin, frequency, genetic regulation, and candidate genes related to multiple embryos in rice and provides a systematic summary of the latest research advances in rice apomixis. The insights presented in this study provide a theoretical foundation for the application of apomixis in rice breeding. Full article

Polyploids are essential in plant evolution and species formation, providing a rich genetic reservoir and increasing species diversity. Complex polyploids with higher ploidy levels often have a dosage effect on the phenotype, which can be highly detrimental to gametes, making them rare. In this study, offspring plants resulting from an autoallotetraploid (RRRC) derived from the interspecific hybridization between allotetraploid Raphanobrassica (RRCC, 2n = 36) and diploid radish (RR, 2n = 18) were obtained. Fluorescence in situ hybridization (FISH) using C-genome-specific repeats as probes revealed two main genome configurations in these offspring plants: RRRCC (2n = 43, 44, 45) and RRRRCC (2n = 54, 55), showing more complex genome configurations and higher ploidy levels compared to the parental plants. These offspring plants exhibited extensive variation in phenotypic characteristics, including leaf type and flower type and color, as well as seed and pollen fertility. Analysis of chromosome behavior showed that homoeologous chromosome pairing events are widely observed at the diakinesis stage in the pollen mother cells (PMCs) of these allopolyploids, with a range of 58.73% to 78.33%. Moreover, the unreduced C subgenome at meiosis anaphase II in PMCs was observed, which provides compelling evidence for the formation of complex allopolyploid offspring. These complex allopolyploids serve as valuable genetic resources for further analysis and contribute to our understanding of the mechanisms underlying the formation of complex allopolyploids. Full article

Potato is the most important non-cereal crop worldwide, and, yet, genetic gains in potato have been traditionally delayed by the crop’s biology, mostly the genetic heterozygosity of autotetraploid cultivars and the intricacies of the reproductive system. Novel site-directed genetic modification techniques provide opportunities for designing climate-smart cultivars, but they also pose new possibilities (and challenges) for breeding potato. As potato species show a remarkable reproductive diversity, and their ovules have a propensity to develop apomixis-like phenotypes, tinkering with reproductive genes in potato is opening new frontiers in potato breeding. Developing diploid varieties instead of tetraploid ones has been proposed as an alternative way to fill the gap in genetic gain, that is being achieved by using gene-edited self-compatible genotypes and inbred lines to exploit hybrid seed technology. In a similar way, modulating the formation of unreduced gametes and synthesizing apomixis in diploid or tetraploid potatoes may help to reinforce the transition to a diploid hybrid crop or enhance introgression schemes and fix highly heterozygous genotypes in tetraploid varieties. In any case, the induction of apomixis-like phenotypes will shorten the time and costs of developing new varieties by allowing the multi-generational propagation through true seeds. In this review, we summarize the current knowledge on potato reproductive phenotypes and underlying genes, discuss the advantages and disadvantages of using potato’s natural variability to modulate reproductive steps during seed formation, and consider strategies to synthesize apomixis. However, before we can fully modulate the reproductive phenotypes, we need to understand the genetic basis of such diversity. Finally, we visualize an active, central role for genebanks in this endeavor by phenotyping properly genotyped genebank accessions and new introductions to provide scientists and breeders with reliable data and resources for developing innovations to exploit market opportunities. Full article

Banana breeding faces numerous challenges, such as sterility and low seed viability. Enhancing our understanding of banana genetics, notably through next-generation sequencing, can help mitigate these challenges. The genotyping datasets currently available from genebanks were used to decipher cultivated bananas’ genetic makeup of natural cultivars using genome ancestry mosaic painting. This article presents the application of this method to breeding materials by analyzing the chromosome segregation at the origin of ‘Gold Finger’ (FHIA-01), a successful improved tetraploid variety that was developed in the 1980s. First, the method enabled us to clarify the variety’s intricate genetic composition from ancestral wild species. Second, it enabled us to infer the parental gametes responsible for the formation of this hybrid. It thus revealed 16 recombinations in the haploid male gamete and 10 in the unreduced triploid female gamete. Finally, we could deduce the meiotic mechanism lying behind the transmission of unreduced gametes (i.e., FDR). While we show that the method is a powerful tool for the visualization and inference of gametic contribution in hybrids, we also discuss its advantages and limitations to advance our comprehension of banana genetics in a breeding context. Full article

Polyploidy is a significant evolutionary process in plants that involves the duplication of genomic content and has been recognized as a key mechanism driving plant diversification and adaptation. In natural populations, polyploids frequently arise from unreduced gametes, which subsequently fuse with reduced or unreduced gametes, resulting in triploid or tetraploid offspring, respectively. Cannabis sativa L. is a diploid species, but recent work using artificially induced polyploidy has demonstrated its potential advantages in an agricultural setting. Further, recent work has identified that some elite clonal cultivars, vis. Mac1, are triploid, with no indication that they were artificially produced. The current study was conducted to determine if polyploidy is a naturally occurring phenomenon in cannabis and to estimate the frequency of this phenomenon across populations. To do this, the presence of natural triploid individuals was evaluated in 13 seedling populations of cannabis using a flow cytometry analysis. Among the examined populations, natural triploids were identified in 10 groups with an average frequency of approximately 0.5%. The highest frequency of natural triploids was observed in a self-pollinated population at 2.3%. This research demonstrates that polyploidy is a naturally occurring event in cannabis and triploids are present at an average of approximately 0.5%, or 1 in 200 plants. These data shed light on the natural variation in ploidy within cannabis populations and contribute valuable insights to the understanding of cannabis genetics and breeding practices. Full article

Medicago sativa (2n = 4x = 32) and M. arborea (2n = 4x = 32) were thought to be reproductively isolated until hybrids (Alborea) were produced by sexual reproduction for the first time in 2003 in Wisconsin. The hybrids were asymmetric, at or near 2n = 4x = 32, and with a predominance of the alfalfa genome. Only M. sativa seed parents with reproductive abnormalities, including unreduced eggs, have produced hybrids; where M. arborea has been used as the seed parent, no hybrids have resulted. Pedigree selection within derivatives of the two original M. sativa seed parents (MB and M8) has been successful in increasing the frequency of hybrids produced. While Alborea individuals more closely resemble M. sativa, a number of M. arborea-specific traits have been observed across different hybrid individuals. These include single-coil flat pods, large seeds, yellow flowers, indeterminate growth, a minimal crown, lodging, frost resistance, and anthracnose resistance. These M. arborea traits have the potential to restructure alfalfa to increase its versatility and utilisation. There is emerging evidence from North and South America and Australia that some Alborea selections have the capacity to complement adapted alfalfa cultivars for yield. Work is continuing to introgress M. arborea traits of value into alfalfa. Full article

Historically, crosses between Medicago sativa (alfalfa) and M. arborea with alfalfa as the seed parent failed, as did crosses using M. arborea as the seed parent. Thus, a reproductive barrier kept the two species isolated until early in this century. The breakthrough came when alfalfa seed parents were identified in Wisconsin USA and Queensland AU that produced partial hybrids (hereafter hybrids). The hybrids were obtained by making large numbers of crosses on selected alfalfa parents. This was the first level of weakening the crossing barrier as reported in Plants in 2013. Further weakening of the barrier is reported herein whereby more hybrids were obtained with fewer crosses. This was accomplished by pedigree selection for new alfalfa seed parents and by using a product of the first hybrids called Alborea. New alfalfa seed parents were crossed with M. arborea, and Alborea parents were backcrossed to M. arborea. Hybrid plants were produced with fewer crosses in both cases. These hybrids, like the first hybrids, have mostly alfalfa traits but also have traits from M. arborea. It was theorized early on that the alfalfa component could be explained by 2n eggs in the alfalfa parents that were fertilized by normal n gametes from M. arborea. Evidence that the Wisconsin alfalfa and Alborea seed parents did in fact produce 2n eggs was reported in Plants in 2022. Moreover, they produced 2n eggs at approximately the same frequency that they produced hybrids. As reported herein, Alborea parents produced the highest frequency of hybrids and thus had the weakest barrier. Importantly, they also have the highest frequency of 2n eggs. It was determined that alfalfa and Alborea parents that produce 2n eggs and hybrids, also produce 2n pollen. In effect, an experiment was undertaken in reverse showing that 2n pollen could be used to screen for plants that produce hybrids. In the thousands of crosses made over the years, fertilization of normal n eggs in alfalfa parents always failed. Normal meiosis appears to be the main barrier to producing interspecific hybrids in our case. Fertilization of abnormal 2n eggs ensures sufficient alfalfa genetic material to continue embryogenesis. Evidently, the meiotic abnormality of 2n eggs is the major factor that weakens the crossing barrier. Full article

The role of apomeiosis, parthenogenesis, and pseudogamy in the asexual reproduction of some plant groups has not been fully elucidated in relation to species diversification. Quantitative analyses of seed origin may help in gaining better understanding of intercytotypic interactions. Asexual reproduction associated with polyploidy and frequent hybridization plays a crucial role in the evolutionary history of the genus Crataegus in North America. In Europe, the genus represents a taxonomically complex and very difficult species group not often studied using a modern biosystematic approach. We investigated the reproduction pathways in mixed-cytotype populations of selected taxa of Crataegus in eastern Slovakia, Central Europe. The investigated accessions were characterized by seed production data and the ploidy level of mature plants as well as the embryo and endosperm tissues of their seeds determined via flow cytometry. Diploid and polyploid hawthorns reproduce successfully; they also produce high numbers of seeds. An exception is represented by an almost sterile triploid. Diploids reproduce sexually. Polyploids shift to asexual reproduction, but pseudogamy seems to be essential for regular seed development. In rare cases, fertilization of unreduced gametes occurs, which offers opportunity for the establishment of new polyploid cytotypes between diploid sexuals and polyploid asexuals. Opposite to sexual diploids, triploids are obligate, and tetraploids almost obligate apomicts. Apomixis is considered to help stabilize individual weakly differentiated polyploid microspecies. Pseudogamy is a common feature and usually leads to unbalanced maternal to paternal contribution in the endosperm of triploid accessions. Parental contribution to endosperm gene dosage is somehow relaxed in triploids. Our Crataegus plant system resembles reproduction in the diploids and polyploids of North American hawthorns. Our data provide support for the hypothesis that polyploidization, shifts in reproduction modes, and hybridization shape the genus diversity also in Central Europe. Full article

Polyploid induction is of utmost importance in horticultural plants for the development of new varieties with desirable morphological and physiological traits. Polyploidy may occur naturally due to the formation of unreduced gametes or can be artificially induced by doubling the number of chromosomes in somatic cells. In this experiment, a protocol for in vitro polyploid induction of highbush blueberry (Vaccinium corymbosum L.) leaf tissues was studied by using different concentrations of colchicine and oryzalin. Oryzalin was found to be highly toxic to this species, while the adventitious shoot organogenesis media enriched with 25 and 250 µM colchicine was able to induce polyploidization, with significant differences among the treatments used. Higher concentrations of both antimitotic agents led to the browning and death of the leaf tissues. The polyploids obtained showed several morphological differences when compared with the diploid shoots. Flow cytometry analysis was used to confirm the ploidy level of the regenerated shoots, demonstrating that a total of 15 tetraploids and 34 mixoploids were obtained. The stomatal sizes (length and width) of the tetraploids were larger than those of the diploids, but a reduced stomatal density was observed as compared to the controls. These shoots will be acclimatized and grown until they reach the reproductive phase in order to test their potential appeal as new varieties or their use for breeding and genetic improvement. Full article

Bouquet formation is believed to be involved in initiating homologous chromosome pairings in meiosis. A bouquet is also formed in the absence of chromosome pairing, such as in F₁ wheat–rye hybrids. In some hybrids, meiosis is characterized by a single, mitotic-like division that leads to the formation of unreduced gametes. In this study, FISH with the telomere and centromere-specific probe, and immunoFISH with ASY1, CENH3 and rye subtelomere repeat pSc200 were employed to perform a comparative analysis of early meiotic prophase nuclei in four combinations of wheat–rye hybrids. One of these, with disomic rye chromosome 2R, is known to undergo normal meiosis, and here, 78.9% of the meiocytes formed a normal-appearing telomere bouquet and rye subtelomeres clustered in 83.2% of the meiocytes. In three combinations with disomic rye chromosomes 1R, 5R and 6R, known to undergo a single division of meiosis, telomeres clustered in 11.4%, 44.8% and 27.6% of the meiocytes, respectively. In hybrids with chromosome 1R, rye subtelomeres clustered in 12.19% of the meiocytes. In the remaining meiocytes, telomeres and subtelomeres were scattered along the nucleus circumference, forming large and small groups. We conclude that in wheat–rye hybrids with mitotic-like meiosis, chromosome behavior is altered already in the early prophase. Full article

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. Full article

The orchid market is a dynamic horticultural business in which novelty and beauty command high prices. The two main interests are the development of flowers, from the miniature to the large and showy, and their fragrance. Overall organ size might be modified by doubling the chromosome number, which can be accomplished by careful study of meiotic chromosome disjunction in hybrids or species. Meiosis is the process in which diploid (2n) pollen mother cells recombine their DNA sequences and then undergo two rounds of division to give rise to four haploid (n) cells. Thus, by interfering in chromosome segregation, one can induce the development of diploid recombinant cells, called unreduced gametes. These unreduced gametes may be used for breeding polyploid progenies with enhanced fertility and large flower size. This review provides an overview of developments in orchid polyploidy breeding placed in the large context of meiotic chromosome segregation in the model plants Arabidopsis thaliana and Brassica napus to facilitate molecular translational research and horticultural innovation. Full article

Selected genotypes of alfalfa (Medicago sativa) produce partial hybrids in sexual crosses with Medicago arborea, as reported in Plants (2013). The hybrids contain mostly alfalfa DNA and traits, but also contain DNA and traits from M. arborea. It was proposed in 2008 that the partial hybrids could be explained by fertilization of 2n eggs in alfalfa by normal pollen from M. arborea, followed by partial loss of M. arborea chromosomes during embryogenesis. In this paper, we confirm the presence of 2n eggs in the first alfalfa parents that produced hybrids. The test for 2n eggs involved pollinating 4x alfalfa with pollen from 8x alfalfa. The production of 8x progeny in the cross proved that selected alfalfa parents produced 2n eggs. Thus, 2n eggs appear to explain how the partial hybrids (hereafter hybrids) contain mostly alfalfa DNA and traits. However, two of the six alfalfa plants that did not hybridize with M. arborea also had 2n eggs. Thus, although 2n eggs explain the alfalfa content of hybrids, 2n eggs are not the only factor involved in weakening the hybridization barrier, and in transferring genes to alfalfa from M. arborea. Full article