2n Pollen Research Articles

Utilisation de marqueurs SSR pour étudier le mécanisme de formation du pollen 2n chez Populus × euramericana (Dode) Guinier et P. × popularis

• Using cytological methods and SSR DNA marker analysis, this study revealed the formation mechanisms and the genetic constitutions of the 2n pollen in Populus × euramericana (Dode) Guinier and P. × popularis. • In P. × euramericana (Dode) Guinier, four abnormalities in microsporogenesis were observed: parallel spindle, fused spindle, tripolar spindle and premature cytokinesis. The first three can lead to first-division restitution (FDR) 2n pollen formation and the last one can form second-division restitution (SDR) 2n pollen. The SSR marker analysis results of parents and their tetraploidy filial generation confirmed that the genetic constitution of 2n pollen produced by P. × euramericana (Dode) Guinier was FDR. • In P. × popularis, three of these abnormalities were observed: parallel spindle, fused spindle and premature cytokinesis. The SSR marker analysis results showed the genetic constitution of 2n pollen produced by P. × popularis was SDR. Natural 2n female gametes in P. × euramericana (Dode) Guinier are reported for the first time. SSR analysis indicated that natural 2n female gametes of P. × euramericana (Dode) Guinier did exist and were fertile, which could be FDR genetic constitution. • The results from this study showed a great potential for using 2n gametes to produce polyploid poplar clones, which can be used effectively for polyploid breeding for poplar species in the section Aigeiros.

Field performance and resistance to tuber soft rot of potato clones derived from sexual polyploidization

Unilateral sexual polyploidization through 4x x 2x crosses is widely used to introgress genes from the diploid gene pool to the tetraploid cultivated potato Solanum tuberosum. Clones of eight 4x x 2x families, from crosses between four tetraploid cultivated potatoes and two diploid S. phureja - S. tuberosum hybrids, produc- ing 2n pollen, were evaluated for yield performances and resistance to tuber soft rot. Significant differences in terms of tuber yield and number were found between families and clones, with several clones outyielding their tetraploid parents. The source of variation due to females (4x females GCA) was significant for both tuber yield and number. A number of clones displayed inheritance of resistance to tuber soft rot. No relationship was found between agronomic traits and resistance to soft rot. Results suggest that the genotypes produced represent genet- ic material with good potentiality in the constitution of new genotypes with interesting trait combinations.

Studies on unreduced gamete formation in hybrids between tetraploid wheats and Aegilops squarrosa L.

Five accessions of Aegilops squarrosa L. were crossed to nine of tetraploid wheat, and 18 combinations of normal F1 hybrids were obtained. Their meiosis and the frequency of unreduced gamete formation were observed. From cytological observations, unreduced gametes were formed as follows; restitution of the first meiotic division, and normal second division followed by formation of dyads which developed into two fertile 2n pollen grains. Unreduced gametes were formed with high frequency in the following cases; (1) when Triticum carthlicum Nevski was used as female and Ae. squarrosa ssp. strangulata Eig or var. meyeri Griseb. was used as male; (2) when spikes headed relatively later; (3) in spikes of secondary or subsequent tillers. The high frequency of unreduced gamete formation in F1 hybrids between T. carthlicum and ssp. strangulata or var. meyeri is genetically controlled.

Occurrence and cytological mechanism of 2n pollen formation in Chinese Diospyros spp. (Ebenaceae) staminate germplasm

SummarySome Diospyros spp. (Ebenaceae) staminate germplasm (2n = 6x = 90) recently found in Hubei Province, China, was of potential value for breeding. This study evaluated the natural rate of occurrence and cytological mechanism responsible for the formation of 2n pollen in this staminate germplasm. The frequencies of giant pollen, dyads, and triads detected in all accessions were 0 – 2.3%, 0.8 – 2.2%, and 2.3 – 4.3%, respectively. The correlation coefficient (r = 0.98**; P < 0.01) between the frequency of giant pollen and those of dyads and triads was highly significant, which strongly suggests that the giant pollen was 2n pollen. Cytological analysis of pollen mother cell meiosis showed that the main cytological mechanisms responsible for the formation of 2n pollen were tripolar spindles and fused spindles, instead of parallel spindles and vertical spindles. In addition, an abnormal disintegration of sister chromatids, which also produced 2n pollen in the end, was occasionally found at metaphase II. Diploid (2n) pollen produced by tripolar spindles and fused spindles was equivalent to first division restitution (FDR) gametes. Therefore, this Diospyros spp. staminate germplasm may have value for sexual polyploidisation in breeding programmes of Japanese persimmon.

Male fertility and occurrence of 2n gametes in East African Highland bananas (Musa spp.)

The quantity and quality of pollen produced by a genotype are important attributes to be considered in the selection of male parents for breeding. The objective of this research was to determine the quantity and quality of pollen in 13 selected East African Highland bananas (EAHB) in relation to six diploids commonly used as male parents. Pollen quantity was scored on a scale of 0–6 while the variation of pollen stainability along the rachis was determined using acetocarmine glycerol jelly. Actual male fertility was determined by using pollen from the EAHB varieties on M. acuminata spp. burmannicoides, ‘Calcutta 4’, as the female. The diameter of 200 viable pollen grains was measured under a microscope with the aid of a graduated eyepiece. Significant differences were obtained for mean pollen stainability and pollen diameter. The pollen stainability for diploids was higher than that for the EAHB. Node numbers contributed significantly to variation of pollen stainability in EAHB (P ≤ 0.01) and ‘Pisang lilin’ (P ≤ 0.001). ‘Pisang lilin’ and the EAHB varieties had about 100 nodes as opposed to about 200 in other diploids. The EAHB varieties produced less pollen than most of the diploids. The actual male fertility of EAHB varieties was low (1 seed/bunch), compared to that of ‘Calcutta 4’ (223.3 seeds/bunch) and ‘Pisang lilin’ (13.7 seeds/bunch). Although the production of 2n pollen in EAHB varieties was low (0–7%), the potential exists for using them in new breeding approaches.

Cytological mechanisms of 2n pollen formation in the wild potato Solanum okadae and pollen-pistil relations with the cultivated potato, Solanum tuberosum

Solanum okadae Hawkes et Hjert is a wild diploid potato species endemic to Argentina and Bolivia, of potential breeding value. However, no genetic studies have been carried out with this species and its crossability relations with the common tetraploid potato, S. tuberosum L. ssp. tuberosum, are unknown. Furthermore, accessions from both countries differed in their morphological phenotypes. To ascertain the feasibility of incorporating this wild germplasm into cultivated potato, 2n pollen screening was carried out in 10 accessions and families derived from crosses between accessions; also, pollen-pistil compatibility relations were studied in reciprocal interspecific crosses. Plants of four of the 10 accessions produced 2n pollen (0.1 to 5.0%) and 4n pollen (0.0 to 3.0%). Parallel and tripolar spindles at Anaphase II were the cytological mechanisms involved in 2n pollen formation; lack of chromosome migration in both meiotic divisions originated the 4n pollen. Both full compatibility and incompatibility at various sites along the pistil were observed in the S. tuberosum × S. okadae combinations; most reciprocal combinations were incompatible. Compatible genotypes produced 2n pollen. However, only a few seeds were obtained and chromosome counts could not be carried out in the hybrid progeny because seedlings died at an early stage. The pollen-pistil barriers are incomplete and can be circumvented by the appropiate choice of parents. The identification of the post-zygotic barriers will be the focus of further studies.

Genetic Positioning of Centromeres Using Half-Tetrad Analysis in a 4x–2xCross Population of Potato

From biological and genetic standpoints, centromeres play an important role in the delivery of the chromosome complement to the daughter cells at cell division. The positions of the centromeres of potato were determined by half-tetrad analysis in a 4x-2x population where the male parent produced 2n pollen by first-division restitution (FDR). The genetic linkage groups and locations of 95 male parent-derived amplified fragment length polymorphism markers could be determined by comparing their position on a 2x-2x highly saturated linkage map of potato. Ten centromere positions were identified by 100% heterozygosity transmitted from the 2n heterozygous gametes of the paternal parent into the tetraploid offspring. The position of these centromeric marker loci was in accordance with those predicted by the saturated 2x-2x map using the level of marker clustering as a criterion. Two remaining centromere positions could be determined by extrapolation. The frequent observation of transmission of 100% heterozygosity proves that the meiotic restitution mechanism is exclusively based on FDR. Additional investigations on the position of recombination events of three chromosomes with sufficient numbers of markers showed that only one crossover occurred per chromosome arm, proving strong interference of recombination between centromere and telomere.

Production of 2n pollen of Asiatic hybrid lilies by nitrous oxide treatment

Tetraploid varieties of lilies have superior agronomic traits such as large flowers and resistance to physiological disorders. In the present study, we attempted to induce 2n pollen of Asiatic hybrid lilies by arresting the meiotic process with nitrous oxide (N2O) gas. To determine which meiotic stage is optimal for induction of 2n pollen, plants with attached buds at different meiotic stages were treated with N2O for 24 h in a pressure-tolerant cylinder. A few 2n pollen grains were induced using plants with anthers in prophase I, whereas mixed pollen grains of differing size were produced using plants undergoing meiotic metaphase predominantly in anthers. Although normal lily pollen grains are elliptical, nitrous oxide exposure induced giant pollen grains that appeared spherical. Flow cytometry analysis showed that the giant pollen grains were diploid. When mixed pollen that included normal and giant pollen was crossed to tetraploid cultivars, the resulting seedlings were tetraploid and aneuploid, indicating that the giant pollen grains were diploids that could generate tetraploid seedlings through fusion to diploid eggs supplied from a tetraploid female parent. Thus, treatment with N2O is useful for the production of 2n lily pollen and may provide a new approach for tetraploid lily breeding.

Incidence and molecular markers of 2n pollen in Populus tomentosa Carr.

Microscopic examination, amplified fragment length polymorphism (AFLP) and SCAR (sequence-characterized amplified region) molecular markers were employed to determine the incidence of 2n pollen (unreduced pollen) in Chinese white poplar (Populus tomentosa Carr.) and to identify related molecular markers. The presence of a parallel and tripolar spindle at metaphase II and the absence of cytokinesis at telophase II were found to be determining factors in 2n pollen formation. A group of 298 clones that originated from their indigenous areas were investigated for the production of 2n pollen based on pollen size differences, both within a clone and between n and 2n pollen. Pollen grains were collected from 224 of the clones, six of which were subsequently determined to produce only normal pollen; the remainder produced 2n pollen at different frequencies (0.6–21.9%). The frequency at which 2n pollen was produced was significantly and highly significantly different among and within indigenous populations, respectively. Clones produced by the six normal and twenty-two 2n pollen clones were selected for AFLP analysis. Following an initial screening with 55 primer combinations, the E50-M38 (CAT/ACT) primer was identified: it generated a PCR fragment (246 bp) from the normal clones, but not from the 2n pollen producers. In addition, the E31-M50 (AAA/CAT)-amplified DNA fragment (204 bp) was present in 2n pollen producers, and absent in normal clones. These two discriminating AFLP markers were developed into easily detectable SCAR (sequence characterized amplified region) markers which can be used in combination with previously developed AFLP markers to distinguish between normal and 2n pollen clones.

Efficacy of Colchicine and Trifluralin in Creating In Vitro Autotetraploid Gaura lindheimeri Engelm. and Gray

Gaura lindheimeri is a diploid herbaceous perennial species native to Texas and Louisiana and winter hardy only to USDA hardiness zone 5. A potential source of winter hardiness is G. coccinea Pursh., a polyploid widely distributed in North America; of particular interest are autotetraploid populations of G. coccinea from Minnesota. To facilitate interspecific hybridization, a tetraploid G. lindheimeri would be advantageous. Two G. lindheimeri genotypes, MN selections 443-1 and 01G-02, were treated with two different antimitotic agents at two concentrations, trifluralin—15 and 30 μm and colchicine—0.25 and 1.25 mm, along with appropriate controls, to determine the frequency of chromosome doubling. Two-node stem sections were treated for 12, 24, or 48 h and then rooted and grown to flowering. Pollen diameter was measured as an indicator of chromosome doubling in cell layer LII, and morphologic characteristics (days to flower, flower size, plant height, inflorescence height, and plant width) were recorded for all plants. Chromosome doubling was not observed in any plant treated with trifluralin. Based on pollen diameter, genotype 443–1 only had chromosome doubling in the colchicine 1.25 mm concentration when treated for 12 h. All durations of colchicine at 1.25 mm were successful for genotype 01G-02 as well as a small percent treated with colchicine at 0.25 mm treated for 48 h. Autotetraploid plants (2n = 4x = 28) had larger flowers in both genotypes, and autotetraploid derivatives of genotype 01G-02 flowered earlier and were taller than diploid plants. Conformation changes from three-lobed to four-lobed pollen grains were observed when pollen diameter approached that expected of 2n pollen. Visual screening of pollen for conformation changes can quickly determine if chromosome doubling in cell layer LII has occurred. With the autotetraploid G. lindheimeri derived from colchicine application, crosses can be performed with autotetraploid G. coccinea to introgress cold tolerance. Additional breeding can also be done at the tetraploid level to develop new autotetraploid cultivars of G. lindheimeri.

Direct and indirect detection of 2n eggs in hybrid diploid families derived from haploid tbr × wild species crosses

The analytic-synthetic scheme makes use of haploidization and 2n gametes-mediated sexual polyploidization to incorporate genetic diversity from wild related species in potato breeding. Whereas 2n pollen can be directly screened by microscopy, 2n eggs are routinely screened indirectly by interploid crosses, a time-consuming and inaccurate technique. In five haploid tbr × wild diploid species families with variability for agronomic characters, 2n eggs were screened indirectly to incorporate this germplasm into a useful form and directly by microscopy to establish the feasibility of this approach. For the indirect screening, at least 15 flowers of each of 49 genotypes/family were crossed with a commercial cultivar. Eighty-five fruits were produced; only 15 of them had seeds (1–25). Chromosome numbers were determined in a random sample of five seeds/fruit, resulting diploid in two genotypic combinations and tetraploid in another two. For the direct screening, eight combinations of staining and destaining (times and concentrations) were evaluated in detached ovules to adjust a clarification technique. The best combination was one day of staining and one day of destaining in 0.5 % acetic acid. In an indirectly detected diplogynoid, the average diameters of the central cell nuclei (CCN) and nucleoli (CCNu) were, respectively, 9.3 μ and 3.4 μ. Gametophytes with diametres 1.26 times the average were considered 2n. By crosses, eleven seeds were obtained in one fruit of this clone whereas the 2n egg frequency determined by microscopy was 7%. The direct technique is easy to carry out once the eye is trained and its results better reflect actual 2n gamete frequencies.

The production of 2n pollen in rose

Based on the size differences found between haploid and diploid pollen produced by diploid and tetraploid rose cultivars, respectively, 2n pollen producers were identified in a population of 53 diploid hybrids from a cross between a dihaploid rose, derived from the haploidization of a tetraploid modern cultivar and the diploid species R. wichuraiana. Frequency of 2n pollen producers was estimated in 2002, 2003 and 2004. Highly variable frequencies were found i) within population; ii) during years of observation (between years and between different months in the same year). The variation of 2n pollen production could be related to environmental fluctuations. A cytological analysis of male meiosis was carried out in 10 hybrids randomly chosen. Among meiotic abnormalities leading to 2n pollen formation, triads (containing a 2n microspore at one pole and two n microspores at the other) resulting from abnormal spindle geometry were frequently observed. The mode of 2n pollen formation is genetically equivalent to a First Division Restitution (FDR) mechanism. FDR 2n pollen transmits a high percentage of the heterozygosity from the diploid parent – 2n pollen producer-to the tetraploid offspring.

Nitrous oxide (N2O) induces 2n gametes in sterile F1 hybrids between Oriental × Asiatic lily (Lilium) hybrids and leads to intergenomic recombination

Eight different genotypes of the F1 hybrids between Oriental × Asiatic lily (Lilium) hybrids (2n = 2x = 24) were treated with nitrous oxide (N2O) gas under pressure for 24 and 48 hours. At the time of treatment, all plants possessed early meiotic stages in the anthers of the oldest flower buds. The mature flowers from treated plants were monitored for fertility through pollen germination in vitro as well as by using them in crosses with diploid Asiatic hybrids (2n = 2x = 24) both as male and female parents. In five out of the eight genotypes of OA hybrids there was evidence for the production of 2n pollen which germinated in vitro from either one or both treatments. The 2n pollen from three genotypes was successfully used in crosses. In two cases, the treated plants were successfully used as female parents which indicated the formation of 2n (or 2x) egg cells. From an analysis of 41 sexual polyploid progenies obtained from N2O treated plants it was shown that they were all euploids consisting of 34 triploids (2n = 3x = 36) and seven tetraploids (2n = 4x = 48). A detailed cytological analysis of 12 progeny plants through genomic in situ hybridization (GISH) proved that N2O had induced first division restitution gametes in most cases and in two cases they produced gametes through indeterminate meiotic restitution. There was evidence for intergenomic recombination in three cases.

GENOTYPIC AND ENVIRONMENTAL VARIATION IN PRODUCTION OF 2N-GAMETES OF ORIENTAL x ASIATIC LILY HYBRIDS

It is attractive to use 2n gametes in breeding for three reasons: a) they can overcome the sterility of F1 hybrids between distantly related species, b) facilitate homoeologous recombination between alien chromosomes and c) generate a large number of different genotypes of 2n gametes from a single F1 hybrid. Such genetic variation can be potentially useful for breeding. However, there is one drawback of using 2n gametes in breeding. The frequency of 2n gamete-producing genotypes OA-hybrids, is very low. By producing a large number of interspecific hybrids followed by careful screening, we have selected few 2n gamete producing F1 hybrids between different groups of Lilium species. This screening for 2n pollen production revealed enormous variation in 2n pollen production frequencies between the different genotypes and between the same genotypes grown in different environments. The fluctuations in greenhouse temperature appeared to influence 2n gametes frequency considerably. To study this during several years, four normally complete sterile genotypes were exposed to a heat shock treatment in phytotron. Three out of the four genotypes produced viable 2n pollen. In total 2% of the treated flowers became fertile due to this temperature-induced stimulation of 2n pollen formation.

NEW ASPECTS OF TULIP BREEDING: EMBRYO CULTURE AND POLYPLOID

In order to improve bulb productivity and ornamental characteristics in tulips, it is necessary to increase genetic variation by using breeding techniques such as overcoming of interspecific barrier, embryo rescue of abortive embryos and induction of polyploids. To identify interspecific barrier between species, crossing experiments have been studied about fifty years ago and recently embryo rescue technique just has been attempted in Holland. In polyploid breeding, colchicine treatment is a common technique to produce polyploids, whereas nitrous oxide has been applied to zygotes as a polyploidizing agent in various crops. This paper reviews some of the literature and our results regarding to embryo rescue technique and also reports on the usefulness of 2n pollen induced with nitrous gas in tulip breeding.

Occurrence of 2n gametes in the F1 hybrids of Oriental × Asiatic lilies (Lilium): Relevance to intergenomic recombination and backcrossing

Cytological modes of the origin of 2n gametes were investigated in six different genotypes of F1 hybrids between Oriental and Asiatic (OA) lilies (Lilium, 2n = 2x = 24). Chromosome pairing between the parental genomes was very low, the average frequency range from 0.3 to 1.2 bivalents per cell among the genotypes. Within a genotype the frequency of bivalents varied from 0 to 6 in some cases. The normally occurring haploid pollen grains were totally sterile. In contrast, in different genotypes, variable percentages of 2n pollen were found and shown to be fertile as estimated from pollen germination. A cytological analysis of Metaphase I and subsequent stages of meiosis using genomic in situ hybridization (GISH) revealed that there was intergenomic recombination between the alien genomes. Following Metaphase I stage, three different types of abnormal cytological events led to the formation of 2n pollen: (i) Post-Metaphase I division (PMI), (ii) Post-Metaphase II division (PMII) and (iii) Asymmetric Cytokinesis of the pollen mother cell followed by chromosome division. All three cytological events led to first division restitution (FDR) gametes. Based on in vitro pollen germination it was proved for two genotypes that 2n pollen was viable only during the first day of anthesis. It was possible to use 2n pollen successfully for backcrossing. Implications of 2n pollen for intergenomic recombination in BC1 progenies are discussed.

Induction of 2n pollen in tulips by arresting the meiotic process with nitrous oxide gas

Triploid tulips have agronomically desirable traits such as vigorous growth and large flower size, but only a portion of all cultivated tulips is triploid. To apply 2n pollen to polyploid breeding of tulips, the polyploidizing agent, nitrous oxide gas (N2O), was applied to bulbs. In tulips, meiosis in anthers occurs inside the bulbs from mid- to late-October. When meiosis in anthers (excised from bulbs) reached metaphase I, we treated other bulbs of the same clones with N2O for 24–48 h. Most of the treated plants produced pollen grains with a wide-ranging or bimodal size distribution, indicating a mixture of n, 2n and aneuploid pollen grains. The use of pollen containing a relatively high proportion of giant pollen grains tended to yield larger numbers of triploids in the progeny. The number of giant pollen grains could be increased when N2O-treated pollen grains were suspended in 10% sucrose and then sieved through a nylon mesh. Very few polyploids were observed in some cross combinations, even those involving pollen with a relatively high proportion of giant grains. Even so, this low polyploid yield most likely is due to a triploid block, because the capsules obtained in the crosses of the diploid×N2O-treated plants contained some abnormal seeds, which were mostly triploid. Embryo culture was useful in rescuing abnormal embryos. The present study reveals that 2n pollen can be produced at high frequency using N2O during tulip breeding.

Trifluralin-mediated polyploidization of Rosa chinensis minima (Sims) Voss seedlings

Many diploid rose species and cultivars possess valuable traits that can be introgressed into modern tetraploid cultivars. Interspecific, interploidy crosses are possible, but triploid hybrids typically have limited fertility, hindering further breeding and selection. Tetraploidizing diploids before mating with tetraploids can alleviate fertility barriers. The efficiency of trifluralin was investigated for polyploidization of Rosa chinensis minima (2n = 2x = 14) seedlings. Treatments were trifluralin at 0.086% and 0.0086%, colchicine (0.5%), and distilled water and contained 2% dimethyl sulfoxide and a surfactant. Approximately 5 μl of the treatment solution was applied to the apical meristem of seedlings (N = 337, 82–85 per treatment) in the process of cotyledon expansion. Guard cell length, pollen diameter, and root tip squashes of rooted cuttings were used to detect polyploidy in meristematic layer (L)I, LII, and LIII, respectively. Trifluralin (0.086%) was the most effective treatment for polyploidization (LI 20.2%, LII 12.9%, LIII 12.9%), followed by trifluralin (0.0086%) (LI 10.6%, LII 7.1%, LIII 4.7%) and colchicine (LI 2.4%, LII 0%, LIII 0%). Polyploidization consistently occurred from LI inward. Polyploids as a group had reduced pollen stainability and a lower leaflet length to width ratio than diploids. In addition, two diploid seedlings were identified which produce 2n pollen. Considerations in selecting germplasm and generating somatically-induced polyploids from seedlings versus clones for use in breeding are discussed.

IDENTIFICATION AND EVALUATION OF DIPLOGYNY IN CLEMENTINE (CITRUS CLEMENTINA) FOR USE IN BREEDING

Seedlessness is an important trait in citrus cultivars for the fresh fruit market. It can be obtained by selection of self-incompatibility and sterility genes or by triploid methodology. Auto-incompatibility phenomena induce sterility but cross pollinations restore fertility. INRA and CIRAD-FLHOR are exploring triploid methodology to create new hybrids for diversification of the easy peeler citrus group. One of the possibilities is to select for spontaneous triploids occurring naturally in citrus progenies. These result from gametic cell fusions between a haploid gamete and an unreduced diploid gamete. We crossed three selections of clementine and a mandarin with different citrus species. Considering that the unbalanced level of ploidy between endosperm cells and embryo cells could affect seed development, we screened seeds, and extracted embryos which were then cultivated in vitro. From 99 triploid hybrids, we saved 88 by macro-grafting. We determined the parental origin of diplogamy for 72 triploid hybrids using isozymes. We have found that 2n ovum production (diplogyny) is very frequent, and 2n pollen production (diploandry) is a rare event (less than 2%). A few triploid hybrids have started to fruit. Comparison of seed yield per fruit for triploid hybrids and their genitors showed a dramatic decrease of female fertility leading most of the time to total sterility. Pollen of triploid hybrids was totally sterile. (Resume d'auteur)

Use of 2n gametes for the production of sexual polyploids from sterile Oriental x Asiatic hybrids of lilies (Lilium).

Sixteen Oriental and 12 Asiatic cultivars were crossed in 158 different combinations. A total of 708 F1 hybrids were obtained from 86 of the different combinations of 15 Oriental and 11 Asiatic cultivars. Because the Lilium cultivars (2n=2x=24) used for the production of these hybrids belong to two different taxonomic sections-Archelirion (0) and Sinomartagon (A), respectively-the F1 hybrids (OA) could be obtained only through embryo, embryo sac rescue, ovary slice or ovule culture. Most of the F, hybrids were highly sterile (did not produce viable n gametes) due to the failure of chromosome pairing. However, in a few cases F1 plants were found that produced viable 2n pollen at variable frequencies. These 2n pollen grains were successfully used for the production of backcross progenies. Using genomic in situ hybridization we found intergenomic recombinant chromosomes in the sexual polyploid progenies. These results indicate that there are effective prospects for combining important horticultural traits from the two main groups of cultivars of lilies through sexual polyploidization.