2n Pollen Research Articles

The use of <i>in vitro</i> androgenesis for the involvement of interspecific hybrids between <i>Solanum tuberosum</i> L. and wild allotetraploid potato species <i>Solanum stoloniferum</i> Schltdl. et Bouché into breeding

Wild allotetraploid potato species Solanum stoloniferum Schltdl. & Bouché from Mexico is regarded as a valuable source of resistance genes for use in breeding. However, introgression of its resistance genes into breeding material is hampered by a set of reproductive barriers. The genomic difference between S. stoloniferum (genome ААВВ) and S. tuberosum L. (AAAA) is one of them. This makes questionable the possibility of transferring a variety of valuable genes of the wild species localized on the chromosomes of its genome B into the genome of cultivated potatoes. It is proposed to produce tetraploid (4x, AAAB) interspecific hybrids of S. stoloniferum, which are regarded as more promising for homoeological recombination than pentaploid (5x, ААААВ) hybrids commonly used in the introgression schemes. However, the effective ploidy of tetraploid hybrids (3EBN) hinders their backcrossing to cultivated potatoes (4 EBN). For instance, our attempts to involve the tetraploid hybrid of S. stoloniferum IGC16/36.1 obtained by us into hybridization with potato varieties were unsuccessful for a number of years. To solve this problem, we suggested a technique based on the production of 4x plants obtained in anther culture of this hybrid. The present research was aimed at assessing the efficiency of this approach.Thirty-one plants were obtained in anther culture (androgenic clones, androclones) of the hybrid IGC16/36.1 in 2018. Most of them exceeded the initial hybrid in habitus strength and flowering intensity. As a result of crosses made in 2019, 1039 hybrid seeds were obtained from crossing 21 androclones with the ‘Lemhi Russet’ variety (8.7 seeds/pollination), 1017 seeds (7.5 seeds/pollination) from crosses of 23 androclones with the ‘Quarta’ variety, and 716 seeds (12.3 seeds/pollination) from crosses of 11 androclones and a diploid potato line IGC 17n8 capable of producing fertile unreduced (2n) pollen. The hybrid seeds had good germination rate of 70-90%. Among the androclones that gave progeny in crosses with potato varieties, we identified genotypes carrying DNA markers of late blight (LB) resistance genes Rpi-sto1, R2 and R3b, PVY resistance genes Ryadg, Rysto and Rychc, and potato wart disease resistance gene Sen2 (these markers were found in the initial accession of S. stoloniferum PI 205522 and in the IGC 16/36.1 hybrid). Despite the complex nature of inheritance of the analyzed markers in progenies of backcrosses of androclones, a number of isolated hybrids carried several markers, including those of the Rpi-sto1, a broad-spectrum gene for high resistance to late blight. Hybrids with relatively high tuber productivity, features of cultivated potatoes such as regularly shaped tubers with small eyes, and high field resistance to late blight were selected.The prospects for using androclones of the tetraploid interspecific hybrid IGC 16/36.1 for increasing the frequency of homoeologous A/B recombination of chromosomes are discussed.

Comparative assessment of morphological, cytological, and reproductive characteristics of the spontaneous mixoploid ‘MM 2×/4×’ and its diploid counterpart ‘Miss Manilla’ in Bougainvillea (Bougainvillea × buttiana Honlttum & Standl.)

Polyploidization-triggered chromosome multiplication typically leads to improved agronomic and ornamental characteristics in plants. However, mixoploidy may sometimes occur in spontaneous and artificially induced polyploidization events, and the deficiency of basic information about mixoploidy limits its application in breeding. In this study, the ploidy stability of spontaneous mixoploidy Bougainvillea × buttiana ‘Miss Manila’ (‘MM 2×/4×’) was validated through chromosome counting and flow cytometry analysis. Compared with its diploid counterpart ‘MM 2×’, ‘MM 2×/4×’ exhibited significantly larger size in the morphological characters related to leaf, bract, thorn, and perianth tube. The average length, width, and density of stomata in ‘MM 2×/4×’ were also significantly larger than in ‘MM 2×’, while the stomatal density of mesophyll cells decreased. The anthers of ‘MM 2×/4×’produced both 1n and 2n pollen grains, which in vitro germinated reached 8.92 %, significantly higher than ‘MM 2×’ (0.36 %). The seed setting rate of the crossing combinations ‘MM 2×/4×’ × ‘Chitra’, ‘Chitra’ × ‘MM 2×/4×’ and ‘MM 2×/4×’ × ‘Bixi’ were 65.47 %, 32.36 %, and 53.17 %, respectively, and the ploidy levels among different offspring individuals of the same genetic population are relatively consistent. While ‘MM 2×’ could not be hybrid with either the tetraploid ‘Chitra’ or diploid ‘Bixi’. Therefore, the mixoploid ‘MM 2×/4×’ partially restored the fertility of gametes and might be employed for both ploidy breeding directly and creating hybrid segregation populations in bougainvillea for trait genetic dissection.

High temperature treatment induced production of unreduced 2n pollen in Camellia oleifera

Unreduced gametes through chromosome doubling play a major role in the process of plant polyploidization. Our previous work confirmed that Camellia oleifera can produce natural 2n pollen, and it is possible to induce the 2n pollen formation by high temperature treatment. This study focused on the optimization of the 2n pollen induction technique and the mechanisms of high temperature-induced 2n pollen formation in C. oleifera. We found that the optimal protocol for inducing 2n pollen via high temperature was to perform 45 °C with 4 h at the prophase I stage of the pollen mother cells (PMCs). Meanwhile, high temperature significantly decreased the yield and fertility of 2n pollen. Through the observation of meiosis, abnormal chromosome and cytological behaviour was discovered under high-temperature treatment, and we confirmed that the formation of 2n pollen is caused by abnormal cell plate. Based on weighted gene co-expression network analysis, fifteen hub genes related to cell cycle control were identified. After male flower buds were exposed to heat shock, polygalacturonase gene (CoPGX3) was significantly upregulated. We inferred that high temperature causes the CoPGX3 gene to be overexpressed and that CoPGX3 is redistributed into the cytosol where it degrades cytoplasmic pectin, which leads to an abnormal cell plate. Furthermore, abnormal cytokinesis resulted in the formation of dyads and triads, and PMCs divided to produce 2n pollen. Our findings provide new insights into the mechanism of 2n pollen induced by high temperature in a woody plant and lay a foundation for further ploidy breeding of C. oleifera.

A case study of potato germplasm enhancement using distant late blight resistant wild relatives

AbstractImproving potato late blight (LB) resistance is essential for ensuring food security, particularly using wild relatives endemic to Phytophthora infestans‐prone regions. However, reproductive barriers can impede the transfer from potato wild relatives (PWR) to the cultivated genepool. This study sought to incorporate potentially novel LB resistance from wild diploid accessions of Series Piurana (Solanum chiquidenum, Solanum paucissectum, and Solanum piurae), Tuberosa (Solanum cajamarquense), and Megistracroloba (Solanum sogarandinum) into tetraploid potato. Trough rescue pollination, 699 diploid interspecific hybrids were obtained, of which 385 displayed LB resistance in two endemic environments. Based on a comprehensive evaluation, including assessing 2n pollen production, 14 diploid interspecific hybrids were selected to continue the introgression process. These pre‐bred stocks were then used in interploidy (4x‐2x) crosses to incorporate their LB resistance in the cultivated tetraploid background. Assessment of 1978 genotypes resulting from interploidy crosses under endemic disease pressure yielded 717 hybrids with moderate to high levels of LB resistance. Evaluation of pollen viability and ploidy revealed moderate fertility and predominantly tetraploid genotypes. Reassessment of LB resistance on this new subset of hybrids further identified 214 genotypes with sustained resistance. Among them, 12 tetraploid hybrids with low glycoalkaloid content, favorable agronomic, and post‐harvest attributes were identified as crossing‐friendly stocks. Notably, 11 of these hybrids were derived from S. cajamarquense and one from S. sogarandinum. These promising 4x hybrids are now primed to be incorporated into potato breeding programs.

The Hybridization Barrier between Herbaceous Medicago sativa and Woody M. arborea Is Weakened by Reproductive Abnormalities in M. sativa Seed Parents.

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.

Gibberellins as a novel mutagen for inducing 2n gametes in plants.

The plant hormone gibberellin (GA) regulates many physiological processes, such as cell differentiation, cell elongation, seed germination, and the response to abiotic stress. Here, we found that injecting male flower buds with exogenous gibberellic acid (GA3) caused defects in meiotic cytokinesis by interfering with radial microtubule array formation resulting in meiotic restitution and 2n pollen production in Populus. A protocol for inducing 2n pollen in Populus with GA3 was established by investigating the effects of the dominant meiotic stage, GA3 concentration, and injection time. The dominant meiotic stage (F = 41.882, P < 0.001) and GA3 injection time (F = 172.466, P < 0.001) had significant effects on the frequency of induced 2n pollen. However, the GA3 concentration (F = 1.391, P = 0.253) did not have a significant effect on the frequency of induced 2n pollen. The highest frequency of GA3-induced 2n pollen (21.37%) was observed when the dominant meiotic stage of the pollen mother cells was prophase II and seven injections of 10 μM GA3 were given. Eighteen triploids were generated from GA3-induced 2n pollen. Thus, GA3 can be exploited as a novel mutagen to induce flowering plants to generate diploid male gametes. Our findings provide some new insight into the function of GAs in plants.

Meiocyte size is a determining factor for unreduced gamete formation in Arabidopsis thaliana.

Polyploidy, the presence of more than two sets of chromosomes within a cell, is a widespread phenomenon in plants. The main route to polyploidy is considered through the production of unreduced gametes that are formed as a consequence of meiotic defects. Nevertheless, for reasons poorly understood, the frequency of unreduced gamete formation differs substantially among different plant species. The previously identified meiotic mutant jason (jas) in Arabidopsis thaliana forms about 60% diploid (2n) pollen. JAS is required to maintain an organelle band as a physical barrier between the two meiotic spindles, preventing previously separated chromosome groups from uniting into a single cell. In this study, we characterized the jas suppressor mutant telamon (tel) that restored the production of haploid pollen in the jas background. The tel mutant did not restore the organelle band, but enlarged the size of male jas tel meiocytes, suggesting that enlarged meiocytes can bypass the requirement of the organelle band. Consistently, enlarged meiocytes generated by a tetraploid jas mutant formed reduced gametes. The results reveal that meiocyte size impacts chromosome segregation in meiosis II, suggesting an alternative way to maintain the ploidy stability in meiosis during evolution.

Two pathways of 2n gamete formation and differences in the frequencies of 2n gametes between wild species and interspecific hybrids

Epidendrum produces 2n gametes with high frequency. This paper is the first to report on multiple pathways for forming 2n gametes, meiotic defeats, and pre-meiotic chromosome doubling. Unreduced 2n reproductive cells are predominantly involved in pathways that lead to polyploid plants. Although one of the most common pathways for inducing 2n gametes is through meiotic defects, a small set of isolated species alternatively generates 2n gametes from tetraploid pollen mother cells in the pre-meiotic phase. Hence, determining the mechanisms underlying 2n gamete formation is critical to improving breeding programmes and understanding plant evolution. We investigated sporads to reveal the pathway(s) accounting for the formation and frequencies of 2n gametes in wild species and interspecific hybrids in the genus Epidendrum. We investigated different types of sporads with varying frequencies, sizes, and viability in the wild species and hybrids of the genus Epidendrum. Large tetrad-estimated pre-meiotic chromosome doubling was observed in wild species. The Epidendrum is unique in that it forms 2n pollens via two pathways, namely, meiotic defects and pre-meiotic chromosome doubling. These two pathways of 2n pollen formation could influence the high diversity generation of polyploidy with different degrees of heterozygosity and genetic backgrounds in the genus Epidendrum. Therefore, these findings are proposed to influence polyploid breeding of Epidendrum via 2n pollen, helping us understand evolution and speciation via unreduced 2n gamete formation in Orchidaceae.

Induction of 2n pollen by colchicine during microsporogenesis to produce polyploids in herbaceous peony (Paeonia lactiflora Pall.)

Polyploid breeding is an effective way to improve ornamental traits of horticultural plants. Colchicine, an anti-mitotic agent, is widely used to induce 2n gametes in horticultural plants, allowing for the production of polyploid plants through sexual hybridization. Based on an understanding of flower bud development and meiosis in pollen mother cells (PMCs) of Paeonia lactiflora cv. ‘Fen Yu Nu’, 2n pollen were obtained by injecting different concentrations of colchicine (0.1, 0.2, 0.3, 0.4 or 0.5%) into flower buds multiple times (once, twice or three times with a 24-h interval in between). External morphology, viability and possible hybridization of colchicine-induced 2n pollen were observed. Finally, P. lactiflora cv. ‘Lian Tai’ was pollinated with colchicine-induced pollen from ‘Fen Yu Nu’. Polyploids were identified among offspring by flow cytometry, chromosome counting, and molecular assessment using simple sequence repeats (SSR). Flower bud diameter of herbaceous peony was related with meiosis in PMCs. The most suitable period to induce 2n pollen was when most PMCs were in prophase I of meiosis, and when flower buds were about 11-12 mm in diameter. The highest induced incidence (%) of 2n pollen was 47.39% following treatment with 0.4% colchicine solution injected twice. The average diameter of 2n pollen was 46.01 μm, which was 1.53-fold wider than haploid pollen. SEM results indicated that 2n pollen were considerably different from haploid pollen in terms of external shape and surface decoration, and 2n pollen were mostly spherical or with an irregular shape. Induced 2n pollen could germinate in vitro and on the stigma of the female parent, but abnormalities such as pollen tube bifurcation or thickening were observed in both germinated states. The percentage of germinated 2n pollen in vitro was 12.78%. In addition, two tetraploids (2n = 4x = 20) were obtained by 2n pollen hybridization. SSR analysis indicated that tetraploids were produced by the spontaneous fusion of 2n female gametes with colchicine-induced 2n male gametes. This indicates that colchicine did not entirely inactivate 2n pollen. The production of few polyploids may be due to the abnormal germination of 2n pollen and obstacles in ploidy hybridization. Our findings fortify the foundation for Paeonia polyploid breeding.

Advances and Perspectives for Polyploidy Breeding in Orchids.

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.

Heat shock-induced failure of meiosis I to meiosis II transition leads to 2n pollen formation in a woody plant.

The formation of diploid gametes through chromosome doubling is a major mechanism of polyploidization, diversification, and speciation in plants. Unfavorable climate conditions can induce or stimulate the production of diploid gametes during meiosis. Here, we demonstrated that heat shock stress (38°C for 3 or 6 h) induced 2n pollen formation, and we generated 42 triploids derived from heat shock-induced 2n pollen of Populus canescens. Meiotic analysis of treated pollen mother cells revealed that induced 2n pollen originated from the complete loss of meiosis II (MII). Among the 42 triploids, 38 triploids derived from second division restitution (SDR)-type 2n pollen and 4 triploids derived from first division restitution-type 2n pollen were verified using simple sequence repeats(SSR) molecular markers. Twenty-two differentially expressed genes related to the cell cycle were identified and characterized by expression profile analysis. Among them was POPTR_0002s08020g (PtCYCA1;2), which encodes a type A Cyclin CYCA1;2 that is required for the meiosis I (MI) to MII transition. After male flower buds were exposed to heat shock, a significant reduction was detected in PtCYCA1;2 expression. We inferred that the failure of MI-to-MII transitions might be associated with downregulated expression of PtCYCA1;2, leading to the formation of SDR-type 2n pollen. Our findings provide insights into mechanisms of heat shock-induced 2n pollen formation in a woody plant and verify that sensitivity to environmental stress has evolutionary importance in terms of polyploidization.

Production of Triploid Germplasm by Inducing 2n Pollen in Longan

Longan (Dimocarpus longan Lour.) is of great economic significance in South China for its unique taste and nutritional properties. However, longan breeding is mainly based on seedling selection, which generally results in small fruits, low flesh recovery, and few seedless germplasm. Triploid breeding is a central way to improve these problems. In this study, microspore chromosomes were doubled by colchicine and high-temperature treatment to create triploids in longans. The relationship between the development process of male gametophyte of longans and the morphological changes of male flower buds was established. Cytological observation showed that when the male flower buds were in stage I (when the diameter of the flower bud is 1.4–2.0 mm), most of the microspores were at the pachytene to diakinesis stage of meiosis, and the chromosome doubling induction effect was the best at this stage. The results showed that the 2n pollen rate induced by a high temperature of about 38 °C was higher than that induced by colchicine treatment. The highest 2n pollen rate was 5.7% and 5.5% based on the microscopic measurement method and the abnormal separation in tetrad stage estimation method, respectively. Four triploids were successfully obtained from artificial pollination with 2n pollen, with a triploid induction rate of 0.6%. This study will promote ploidy breeding in longan.

Cytological Study of 2n Pollen Formation in Musa

Current Musa breeding strategies are complex and time consuming involving the selection of tetraploids from 3x - 2x crosses. Secondary triploids are then obtained by crossing these tetraploids with diploids. Considering the very low hybrid seed set, routine embryo rescue procedures of hybrid seeds and the long growth cycle of banana, it takes approximately 10 - 12 years to produce an acceptable banana hybrid. The banana breeding process could benefit tremendously if triploid bananas could be obtained directly from 2x - 2x crosses through the process of unilateral sexual polyploidization. There are few reports on the mechanisms through which Musa species produce 2n pollen. This study investigated the type of meiotic irregularities that lead to 2n pollen formation in diploid, triploid and tetraploid Musa accessions using cytological analyses. The results showed that aberrations in cytokinesis and karyokinesis during microsporogenesis are possible mechanisms for 2n pollen formation in Musa. The meiotic aberrations described in this study have implications for Musa breeding. It appears that 2n pollen formation in Musa occurs via both first division restitution (FDR) and second division restitution (SDR). FDR is said to be more promising in transferring more heterozygosity from parents to offspring.

Induction of 2n pollen with colchicine during microsporogenesis in Phalaenopsis.

The induction of 2n pollen is an important technique for breeding polyploid plants. Here, we observed meiosis in the pollen mother cells (PMCs) of six Phalaenopsis cultivars and attempted to induce 2n pollen. The meiotic stage was related to flower bud length. During meiosis, Phalaenopsis cultivars with flower widths of approximately 20-40 mm and 50-60 mm had bud lengths of approximately 3-8 mm and 5-13 mm, respectively. The duration of meiosis ranged from 4.2 to 14 d. This was the first study to characterize meiosis of the PMCs of Phalaenopsis. The natural generation frequency of 2n pollen varied from 0.68% to 1.78%. Meiotic stage and colchicine concentration significantly affected the induction of 2n pollen. The most effective treatment for obtaining 2n pollen was 0.05% colchicine in the leptotene to zygotene stage for 3 d, which achieved a 2n pollen frequency of 10.04%.

Desvendando mecanismos relacionados a anormalidades meióticas em Crotalaria spectabilis Roth

ABSTRACT The identification of epigenetic marks associated with problems in the meiotic process can enlighten the mechanisms underlying the irregularities and the impacts in the genetic constitution of gametes. Therefore, this study aimed to verify the relationship between the pattern of phosphorylation in serine 10 of histone H3 (H3S10ph), a (peri) centromeric epigenetic mark, with meiotic abnormalities in a wild population of Crotalaria spectabilis Roth. The main abnormalities observed were transfer of genetic material through cytoplasmatic connections, DNA elimination and abnormal spindle array. Different forms of elimination (chromatin fragmentation, ring formation, lagging chromosomes and micronuclei) were observed from the early phases until tetrad formation. The eliminated chromatin was either positive or negative for the immunosignal of H3S10ph, so it may be occurring elimination of acentric fragments, as well as of chromosomes with active or inactive centromeres. Therefore, dysfunctional centromere is not the only candidate cause for elimination. The transfer of genetic material and the abnormal spindle arrays are evidence that this population can produce aneuploid gametes and 2n pollen grains.

Colchicine induced manifestation of abnormal male meiosis and 2n pollen in Trachyspermum ammi (L.) Sprague (Apiaceae)

Unreduced gametes are the key source for the natural polyploidization in plants, but process of its formation is very low in nature. Meiotic mutants are second source for the formation of 2n pollen. In this cytological investigation, the meiotic aberrations and its impact on post-meiotic products were analysed in autotetraploid Trachyspermum ammi (L.) Sprague (4n=36). The seedlings of T. ammi (L.) Sprague were treated with 3 different concentrations of colchicine (0.2, 0.4 and 0.5%, w/v) for 3 different durations. Six polyploid plants were induced which was confirmed on the basis of cytological analysis. Colchicine, an anti-microtubular drug induced different meiotic and post-meiotic abnormalities such as chromosomal bridges, lagging chromosomes, scattering, precocious, fragments, dyads, triads, and polyads. The formation of several abnormal sporads clearly signifies the meiotic restitution. The tendency of univalents to scattered in the cytoplasm at metaphase was identified as a peculiar aberration asynapsis. Pollen variability and fusion of pollen walls was reported and pollen fertility was calculated. The morphological analysis of the pollen allowed us to confirm the occurrence of 2n pollen.

Consequences of whole genome duplication for 2n pollen performance

The vegetative cell of the angiosperm male gametophyte (pollen) functions as a free-living, single-celled organism that both produces and transports sperm to egg. Whole-genome duplication (WGD) should have strong effects on pollen because of the haploid to diploid transition and because of both genetic and epigenetic effects on cell-level phenotypes. To disentangle historical effects of WGD on pollen performance, studies can compare 1n pollen from diploids to neo-2n pollen from diploids and synthetic autotetraploids to older 2n pollen from established neo-autotetraploids. WGD doubles both gene number and bulk nuclear DNA mass, and a substantial proportion of diploid and autotetraploid heterozygosity can be transmitted to 2n pollen. Relative to 1n pollen, 2n pollen can exhibit heterosis due to higher gene dosage, higher heterozygosity and new allelic interactions. Doubled genome size also has consequences for gene regulation and expression as well as epigenetic effects on cell architecture. Pollen volume doubling is a universal effect of WGD, whereas an increase in aperture number is common among taxa with simultaneous microsporogenesis and pored apertures, mostly eudicots. WGD instantly affects numerous evolved compromises among mature pollen functional traits and these are rapidly shaped by highly diverse tissue interactions and pollen competitive environments in the early post-WGD generations. 2n pollen phenotypes generally incur higher performance costs, and the degree to which these are met or evolve by scaling up provisioning and metabolic vigor needs further study.

Meiotic behaviour and pollen fertility of F1, F2 and BC1 progenies of Iris dichotoma and I. domestica

Abstract Pollen characteristics are very important for Iris interspecific hybridisation. In this study, the pollen viability and male meiosis were studied in yellow-flowered Iris dichotoma (Y2), I. domestica (S3) and their hybrids F1, F2 and BC1 (BC1-Y and BC1-S). The BC1-Y hybrids showed higher pollen viability than that of F1, F2 and BC1-S hybrids, which were between I. dichotoma (26.1%) and I. domestica (35.1%). Two sterile hybrids, F2-1 and BC1-S-1, exhibited more meiotic abnormalities (57.3% and 58.7%) than other individuals. During the first meiotic division, a diffuse diplotene stage was observed for the first time in the genus Iris. The meiotic abnormalities included non-congressed chromosomes, chromosome bridges, lagging chromosomes, unequal division, abnormally oriented spindle fibres, nonsynchronous division and polyad, and resulted in reduced pollen fertility. The relatively high frequency of 2n pollen grains was found in hybrids of BC1-Y-2, BC1-Y-1, BC1-S-2, BC1-S-3 and BC1-S-4. Our research provides a new resource for meiotic behaviour and pollen fertility of the genus Iris.

Cytological and morphology characteristics of natural microsporogenesis within Camellia oleifera.

The online version contains supplementary material available at 10.1007/s12298-021-01002-5.

Colchicine induction of 'Old Blush' 2n pollen for the hybridization and breeding of tetraploid rose.

Obtaining 2n pollen from the diploid Chinese old rose ‘Old Blush’ through artificial induction is one important means of hybridizing and breeding modern tetraploid roses. We used colchicine-induced 2n pollen to assess normal viability during hybridization and fructification. The results showed that the pollen mother cell had lagging chromosomes and parallel spindles at meiosis I stage, following which the 2n pollen was produced from dyads and triads with doubled chromosomes. We obtained 4.30% viable 2n pollen, which was significantly higher than the yield of the spontaneous 2n pollen (1.00%) using an optimal treatment combination of induction for 24 h with 0.50% colchicine. There was no significant difference between the external morphology of the induced 2n pollen and the spontaneous 2n pollen, whereas both types of 2n pollen possessed finer furrows, and fewer and smaller pores than the 1n pollen, and the external morphology of 2n pollen was more evolved. In terms of in vitro germination rate and pollen tube length, the induced 2n pollen did not differ significantly from the spontaneous 2n pollen. The survival rate of the floral buds was significantly decreased with increased colchicine concentration and treatment time.