Gametes with somatic chromosome number and their significance in interspecific hybridization in Fuchsia

Sexual polyploidization has both a theoretical as well as an applied significance. Morphological screening for large pollen grains and shape of pollen produced by the individual, cytological investigation of hybrid progeny, and unbalanced separation of chromosomes at anaphase I in pollen mother cells were used to detect the gametes with somatic chromosome number in Fuchsia. The interspecific hybrids of F. fulgens (sect. Ellobium) × F. magellanica (sect. Quelusia), F. fulgens (sect. Ellobium) × F. splendens (sect. Ellobium), and F. triphylla (sect. Fuchsia) × F. splendens (sect. Ellobium) produced at the University of Auckland, New Zealand, showed both large and normal pollen grains in the same anther indicating the presence of unreduced gametes. Cytological investigation carried out on the hybrid progeny of F. fulgens (diploid, 2n=22, sect. Ellobium) × F. magellanica (tetraploid, 2n=44, sect. Quelusia) and F. triphylla (diploid, sect. Fuchsia) × F. arborescens (diploid, sect. Schufia) revealed unexpected chromosome numbers of 2n=44 and 2n=33, respectively. In general, the hybrids showed low fertility caused by genetically unbalanced gametes resulted from random disjunction of chromosomes at anaphase I. Studies on meiosis together with the presence of different shapes and sizes of pollen grains in Fuchsia proved indirectly that unreduced gametes are the products of first division meiotic nuclear restitution. These unreduced gametes were viable irrespective of pollen shape, their predominance in the hybrids, nuclear DNA amount and species phylogenetic position.     

Molecular cytogenetic evidence of hybridization in the “purple corolla clade of the genus Capsicum” (C. eximium × C. cardenasii)

Abstract

A hybrid individual between two taxa from “the Purple Corolla clade of the genus Capsicum”, C. eximium × C. cardenasii (2n = 24) was found during a cytogenetic study of a population belonging to C. cardenasii cytotype 1, from Bolivia. 5S and 45S rDNA probes were located on mitotic chromosomes by fluorescent in situ hybridization. The hybrid haploid karyotype length was an average value of the two taxa; the hybrid presented 24 45S loci in the diploid complement, 18 45S sites belonged to C. cardenasii cytotype 2, and six came from C. eximium cytotype 2, although this cytotype of C. eximium has been mentioned only for Argentina. Whereas hybrids were previously reported in the purple flower group, their existence has not been cytologically corroborated. This finding constitutes the first molecular cytogenetic evidence of hybridization between two taxa from this group.     

On the diploidization mechanism of the genus Aegilops: meiotic behaviour of interspecific hybrids

Chromosomal pairing of the three diploid hybrids Aegilops uniaristata × Ae. tauschii (ND), Ae. umbellulata × Ae. tauschii (UD) and Ae. comosa × Ae. uniaristata (MN), and a triploid hybrid Ae. cylindrica × Ae. caudata (DCC), was analyzed by electron microscopy in surface-spread-prophase-I nuclei and compared with light-microscopic observations of metaphase-I cells after C-banding and fluorescence in situhybridization. All hybrids showed extensive synapsis and complex multivalents in which up to 14 chromosomes were involved. In the diploid hybrids most metaphase-I chromosomal associations were between homoeologs, their frequencies being dependent on the relationship between the donor genomes. Despite the different overall bound-arm frequencies displayed by ND and MN hybrids at metaphase-I, chromosomes bearing rDNA sequences showed similar mean cell chromosomal association frequencies. In the triploid hybrid preferential associations involving C genomes were predominant. These observations are discussed in relation to the mechanism of diploidization showed by allotetraploid Aegilops species. Received: 13 January 1999 / Accepted: 12 March 1999     

Post-zygotic gametic selection due to endosperm balance number explains unusual chromosome numbers of 3×× 2× progeny in Solanum

 Crosses between triploid and diploid genotypes are usually the best sources of trisomics in potato as well as in several other crop species. However, 3×× 2× crosses between triploid (2n=3×=36; 2EBN) Solanum commersonii-S. tuberosum hybrids and diploid (2n= 2×=24; 2EBN) genotypes gave progenies with a high number of extra chromosomes, 29–36, suggesting that only eggs with 17–24 chromosomes produced embryos that reached full development. Our hypothesis is that although triploids produce eggs with a range of chromosome numbers, 3×× 2× crosses involving a 2×(2EBN) parent favor eggs with a high chromosome number. These eggs have higher probabilities of possessing the same endosperm balance number (EBN) value (i.e. 1) of gametes produced by the 2EBN diploid parent to give the required 2:1 maternal to paternal EBN ratio in the hybrid endosperm. Under this model, trisomics are produced only if the diploid parent has an EBN of 1. Based on our results and those reported in the literature, it is proposed that in 3×(2EBN) × 2×(2EBN) crosses the endosperm balance number exercises negative selection for gametes with a low chromosome number, and a corresponding low EBN, and positive selection for gametes with a high chromosome number and EBN. Received: 2 April 1998 / Revision accepted: 27 October 1998     

Chromosome analysis in coregonid individuals in the interspecific hybridization zone

Artificial spawning (reproduction), a popular method in fisheries, has caused the unintentional hybridization between native European whitefish (Coregonus lavaretus) and introduced peled (Coregonus peled). The resultant hybrids are fertile and their morphological identification is impossible. The study shows the genetic characteristics of the hybrid coregonid fish specimens. Analyses of the number and morphology of chromosomes were based on conventional Giemsa staining. Nucleolar Organiser Regions (NOR) were analysed using CMA₃‐ and Ag‐NOR staining. Metaphases were also investigated by C‐banding methods. Hybrid specimens had a diploid chromosome number (2n) ranging from 76 to 80 and an arm chromosome number ranging from 96 to 100. NORs were observed on the subtelo‐acrocentric and submeta‐metacentric chromosomes. Results of the present study indicate a high level of chromosomal differentiation due to rearrangement taking place in the gene pool of whitefish/peled hybrids.     

Establishment of the diploid gynogenetic hybrid clonal line of red crucian carp × common carp

This study investigated the gynogenetic cytobiological behavior of the third gynogenetic generation (G3), which was generated from the diploid eggs produced by the second gynogenetic generation (G2) of red crucian carp × common carp, and determined the chromosomal numbers of G3, G2×scatter scale carp and G2×allotetraploid hybrids of red crucian carp × common carp. The results showed that the diploid eggs of G2 with 100 chromosomes, activated by UV-irradiated sperm from scatter scale carp and without the treatment for doubling the chromosomes, could develop into G3 with 100 chromosomes. Similar to the first and second gynogenetic generations (G1 and G2), G3 was also diploid (2n=100) and presented the hybrid traits. The triploids (3n=150) and tetraploids (4n=200) were produced by crossing G2 with scatter scale carp and crossing G2 with allotetraploids, respectively. The extrusion of the second polar body in the eggs of G2 ruled out the possibility that the retention of the second polar body led to the formation of the diploid eggs. In addition, we discussed the mechanism of the formation of the diploid eggs generated by G2. The establishment of the diploid gynogenesis clonal line (G1, G2 and G3) provided the evidence that the diploid eggs were able to develop into a new diploid hybrid clonal line by gynogenesis. By producing the diploid eggs as a unique reproductive way, the diploid gyno- genetic progeny of allotetraploid hybrids of red crucian carp × common carp had important signifi- cances in both biological evolution and production application.     

Natural hybridization in JapaneseCalamagrostis

Morphological and pollen studies were made for the collections belonging toCalamagrostis langsdorffii, C. Sachalinensis, C. longiseta, C. nana and various intermediates between these species from central Honshu, the chromosome numbers of which were reported in a previous paper (Tateoka, 1976). Additional collections made from the Akaishi Range in 1976 were also subjected to the present work. The intermediates showed 0%, or nearly 0%, pollen stainability and a mosaic of morphological features of putative parental taxa which can be estimated to occur for F₁ hybrids. This estimation was sustained by a comparison with the pattern of character expressions for the artificially raised F₁ hybrids of various European species ofCalamagrostis as reported by Nygren (1962). These results as well as field observations strongly suggested that the intermediates may be wholly or almost wholly F₁ hybrids. The hybrids were sometimes found in abundance within a limited area, but seemed to have little capacity to migrate from the places where they originated. The following combinations, which were not previously recorded, were disclosed:C. longiseta×C. sachalinensis, C. langsdorffii×C. nana, C. langsdorffii×C. longiseta, C. longiseta×C. nana. Possibilities of introgression in these hybridizing species were discussed. The hybrids were tetraploids except one hexaploid which was discovered in a mixed population ofC. nana, C. longiseta and their putative F₁ hybrids at the tetraploid level. The hexaploid in question, which seemed to have resulted from the participation of an unreduced gamete, was very similar morphologically toC. nana subsp.hayachinensis distributed in the mountain far distant from central Honshu. Geographical distributions of the hybrid plants were surveyed through examination of the herbarium specimens.     

Somatic hybridization between potato and Nicotiana plumbaginifolia

Summary Electrofusion was carried out between mesophyll protoplasts from the transformed diploid S. tuberosum clone 413 (2n=2x=24) which contains various genetic markers (hormone autotrophy, opine synthesis, kanamycin resistance, -glucuronidase activity) and mesophyll protoplasts of a diploid wild-type clone of N. plumbaginifolia (2n=2x=20). Hybrid calli were obtained after continuous culture on selection medium containing kanamycin. Parental chromosome numbers, determined at 2 months after fusion, revealed hybrid-specific differences between the individual calli. On the basis of these differences three categories of hybrids were distinguished. Category I hybrids contained between 8 and 24 potato chromosomes and more than 20 N. plumbaginifolia chromosomes; category II hybrids had between 1 and 20 N. plumbaginifolia chromosomes and more than 24 potato chromosomes; category III hybrids contained diploid or subdiploid numbers of chromosomes from both parents. The hybrids were evenly distributed over the three categories. After a 1-year culture of 24 representative hybrid callus lines on selection medium the karyotype of 10 hybrids remained stable, whereas 8 hybrids showed polyploidization of the genome of one parent, together with no or minor changes of the chromosome numbers of the other parent. Six hybrids showed slight changes in the hybrid karyotype. The elimination of chromosomes of a particular parent was not correlated to their metaphase location. The processes of spontaneous biparental chromosome elimination leading to the production of asymmetric hybrids of different categories are discussed.     

Karyomorphology of Turkish species in Centaurea sections Centaurea and Phalolepis (Asteraceae) and implications for taxonomy

In this paper, 31 mostly endemic and locally distributed Turkish Centaurea taxa belonging to Centaurea and Phalolepis sections were examined in terms of their karyomorphology. The basic chromosome number for all of the studied species was concurringly determined as 9(x = 9) for both sections, excluding C. hierapolitana. We also determined tetraploid and hexaploid species in spite of many species having diploid chromosome numbers. Twelve chromosome counts are reported for the first time and most of the karyotyping analyses are described for the first time via the KAMERAM program. The karyotypes had a predominance of metacentric (m) chromosomes. However, in the karyotyping of six taxa, submetacentric (sm) chromosomes were dominant. Five quantitative asymmetric indices were used to evaluate karyological features of the species. A meaningful dendrogram was carried out to assess the karyotype-symmetry conditions and describe the karyotyping relationships between different taxa.     

Introgression into the allotetraploid coffee ( Coffea arabica L.): segregation and recombination of the C. canephora genome in the tetraploid interspecific hybrid ( C. arabicax C. canephora)

Transfer of desired characters from the diploid relative species such as Coffea canephora into the cultivated allotetraploid coffee species (Coffea arabica L.) is essential to the continued improvement of varieties. Behaviour of the C. canephora genome and its interaction with the C. arabica genome were investigated in tetraploid interspecific hybrids (C. arabica×C. canephora 4x) resulting from a cross between an accession of C. arabica and a tetraploid plant of C. canephora obtained following colchicine treatment. Segregation and co-segregation of restriction fragment length polymorphism (RFLP) and microsatellite loci-markers were studied in two BC₁ populations. These two populations of 28 and 45 individuals, respectively, resulted from the backcross of two tetraploid F₁ plants to C. arabica. The presence in BC₁ plants of specific C. canephora markers was scored for 24 loci (11 RFLP and 13 microsatellites) distributed on at least 7 of the 11 linkage groups identified in C. canephora. At almost all loci analysed, the segregation of C. canephora alleles transmitted by the (C. arabica×C. canephora 4x) hybrids conformed to the expected ratio assuming random chromosome segregation and the absence of selection. The recombination fractions of C. canephora chromosome segments were estimated for seven marker intervals, and compared with the recombination fractions previously observed in C. canephora for the equivalent marker intervals. The recombination frequencies estimated in both plant materials were rather similar, suggesting that recombination in the (C. arabica×C. canephora 4x) hybrid is not significantly restricted by the genetic differentiation between chromosomes belonging to the different genomes. The hybrid (C. arabica×C. canephora 4x) therefore appeared particularly favourable to intergenomic recombination events and gene introgressions. Received: 26 March 2001 / Accepted: 29 June 2001     

Assessment of intergenomic recombination through GISH analysis of F1, BC1 and BC2 progenies of Tulipa gesneriana and T. fosteriana

Using 23 F1 hybrids, 14 BC1 and 32 BC2 progenies, the genome composition of Darwin hybrid tulips was analysed through genomic in situ hybridisation (GISH) of somatic chromosomes. All plants were diploids (2n = 2x = 24) with the exception of one tetraploid BC1 (2n = 4x = 48) and one aneuploid BC2 (2n = 2x + 1 = 25) hybrid. Morphometric analysis in F1 hybrids revealed a difference in the total length of chromosomes representing genomes of T. gesneriana and T. fosteriana, where the percentage of each genome equaled 55.18 ± 0.8 and 44.92 ± 0.6% respectively. GISH distinguished chromosomes from both parent genomes although there was a lack of consistent chromosome labelling in some cases. In both T. gesneriana and T. fosteriana chromosomes some segments of heterochromatin in the telomeric and intercalary regions exhibited a higher intensity of fluorescence. In situ hybridisation with 5S rDNA and 45S rDNA probes to metaphase chromosomes of F1 hybrids showed that these regions are rich in rDNA. A notable feature was that, despite genome differences, there was a considerable amount of intergenomic recombination between the parental chromosomes of the two species as estimated in both BC1 and BC2 offspring. The number of recombinant chromosomes ranged from 3 to 8 in BC1 and from 1 to 7 in BC2 progenies. All recombinant chromosomes possessed mostly a single recombinant segment derived from either a single crossover event or in a few cases double crossover events. This explains the fact that, unlike the situation in most F1 hybrids of other plant species, certain genotypes of Darwin hybrid tulips behave like normal diploid plants producing haploid gametes and give rise to mostly diploid sporophytes.     

Chromosome instability in Hordeum vulgare x H. bulbosum hybrids

Chromosome number in Hordeum vulgare x H. bulbosum hybrids ranged between the haploid and diploid number but with peaks in frequency occurring at the 14 and 7 chromosome level. This was reflected in a gradual change from hybrid morphology to that of haploid H. vulgare. The rate of chromosome elimination differed significantly between hybrids, while within each hybrid, differences in mean chromosome number were recorded between and within individual tillers. An increase in temperature from 25–30° C caused a significant increase in the rate of elimination of H. bulbosum chromosomes.     

Fertility of females of sturgeon hybrids obtained from species with different levels of ploidy (Acipenser ruthenus and A. dauricus) and their cloning

Main purpose of this work is the identification of females of artificial sturgeon hybrids capable to produce unreduced oocytes. The importance of this task is due to the ability to receive clonal all-female lines. Experiments were performed on the previously obtained reciprocal hybrids of sterlet, Acipenser ruthenus (S) with ~120 chromosomes and kaluga, Acipenser dauricus (K) with ~260 chromosomes. Karyotypes of backcross hybrids of (S × K) female (obtained by crossing sterlet female with kaluga male) and sterlet male included 180 – 190 chromosomes. This means that (S × K) female produced eggs with ~125 chromosomes and its karyotype consisted of ~250 chromosomes. This number was confirmed by a comparative analysis of erythrocyte size in this female and species with different ploidy. Karyotype with ~250 chromosomes can occur in (S x K) female only as a result of fertilization of a diploid sterlet egg (120 chromosomes) with kaluga haploid sperm (~130 chromosomes). Eggs of hybrid fertile (S × K) female, inseminated with inactivated sperm of Amur sturgeon and sterlet, developed into viable gynogenetic offspring, confirmed by the analysis of five microsatellite loci in this progeny, (S x K) female, and males used for UV-inactivated sperm. These data allow us to propose a method for obtaining fertile females of sturgeon hybrids from species with different ploidy. For this, experimentally obtained diploidized eggs from diploid 120-chromosome species must be fertilized by 250–270-chromosome male. Karyotypes of backcross hybrids of (K × S) female (obtained by crossing kaluga female with sterlet male) and sterlet male included ~250 chromosomes and hybrids of this female with kaluga male had ~320 chromosomes. These results proved an ability of hybrid (K × S) female to produce unreduced eggs, resulting in triploid backcrosses. The absence of reduction during egg development is well known in clonal forms (species) of vertebrates, which are of hybrid origin, and in artificially created fish hybrids. However, this has not been reported previously for sturgeons. Insemination of eggs of (K × S) female with UV-inactivated sperm of sterlet and Amur sturgeon led to offspring generation for which the genetic identity to their mother was proved using microsatellite analysis. That is, clonal inheritance was observed. These results suggest the possibility of developing a technology to produce all-female offspring. Artificial production of clonal lines in hybrid vertebrates can be also considered as experimental reproduction of the first stages of reticular speciation in nature.     

Introgression of chromosomes of Festuca arundinacea var. glaucescens into Lolium multiflorum revealed by genomic in situ hybridisation (GISH)

An F₁ hybrid (n=4x=28) between the tetraploid species Festuca arundinacea var. glaucescens (GGG′G′) and a synthetic tetraploid Lolium multiflorum (LmLmLmLm) was backcrossed to diploid L. multiflorum to produce triploid (2n=3x=21) BC₁ hybrids (LmLmG). At metaphase I of meiosis the triploids had a preponderance of ring bivalents and univalents with some linear and frying-pan trivalents. Genomic in situ hybridisation (GISH) differentiated the Festuca chromosomes from Lolium and revealed that the bivalents were exclusively between Lolium homologues, while the univalents were Festuca. Despite the limited amount of homoeologous chiasmata pairing in the triploids, some recombinant chromosomes were recovered in the second backcross when the hybrids were further crossed to diploid L. multiflorum. The progeny from the second backcross was predominantly diploid. Genotypes with recombinant chromosomes and chromosome additions involving an extra Festuca chromosome were identified using GISH. Changes in plant phenotype were related to the presence of Festuca chromatin. Received: 20 September 2000 / Accepted: 05 January 2001     

Chromosome numbers of the genusCalamagrostis in Japan

Chromosome counts for 783 collection ofCalamagrostis in Japan are reported. These include the first record forC. tashiroi and the reports of new cytotypes inC. stricta, C. hakonensis andC. longiseta. The geographical distribution of different cytotypes ofC. langsdorffii andC. hakonensis is outlined. Counts are also reported for a number of “intermediates” which are supposed to be interspecific hybrids or hybrid derivatives. A summary of chromosome counts for JapaneseCalamagrostis so far recorded is tabulated. No diploid plants with 2n=14 chromosomes are found. The tetraploid taxa, which are plentiful and seem to have adaptively radiated in Japan, jack any sign suggestive of their recent origin from the diploids. It is suggested that plant with 2n=28 (4X in the traditional sense) may be regarded as semidiploid and having that behavior, and that speciation ofCalamagrostis in Japan has occurred principally at this chromosome level. Speciation by means of amphiploidy may have been scarce. It is also suggested that hybridization and polyploidy have greatly contributed to the formation of complicated internal structure of various species.     

CYTOGENETIC AND EVOLUTIONARY STUDIES IN SECALE. I. SOME NEW DATA ON THE ANCESTRY OF S. CEREALE

Khush , G. S., and G. L. Stebbins . (U. California, Davis.) Cytogenetic and evolutionary studies in Secale. I. Some new data on the ancestry of S. cereale. Amer. Jour. Bot. 48(8): 723–730. Illus. 1961.—Cultivated rye, Secale cereale, was crossed with all 4 wild species of the genus. It crosses readily with S. montanum, S. africanum, and S. vavilovii, but crossability of S. cereale and S. silvestre is extremely low. Meiosis in the hybrid S. cereale × silvestre is characterized by high frequency of univalents at metaphase I, reduced chiasma frequency at metaphase I, high frequency of PMC's with unequal separations and laggards at anaphase I and II, high frequency of microspores with micronuclei, and extremely low pollen fertility. These abnormalities occurred less frequently in other hybrids, and consequently the pollen fertility is fairly high: 19.1% in the hybrid S. cereale × vavilovii and 31.3% and 31.8%, respectively, in the hybrids S. cereale × montanum and S. cereale × africanum. An interesting cytogenetic feature of all these hybrids, however, was the formation of a translocation configuration of 6 chromosomes at metaphase I of meiosis. In the hybrid, S. cereale × silvestre, a translocation configuration of 8 chromosomes was observed in a few cells. It is evident, therefore, that the genome of S. cereale differs from the genomes of wild species by 2 translocations. Another small translocation may differentiate S. cereale and S. silvestre, in addition. Thus, on the basis of chromosome arrangements, no particular wild species is most likely to be ancestral to S. cereale. Similarly, Stutz's hypothesis of hybrid origin of S. cereale seems highly improbable. After considering ecological preferences, breeding habits, geographical distribution, morphological and cytological affinities of wild species and cultivated rye, it is concluded that S. cereale evolved from S. montanum as a result of progressive cytological and morphological differentiation and that this differentiation was facilitated, probably, by adaptive superiority of translocation heterozygotes and rearrangement homozygotes.     

Chromosomal inheritance of parental rDNAs distribution pattern detected by FISH in diploid F1 hybrid progeny of Cobitis (Teleostei,Cobitidae) species has non-Mendelian character

This study was conducted to describe the major and the minor rDNA chromosome distribution in the spined loach Cobitis taenia (2n = 48) and the Danubian loach Cobitis elongatoides (2n = 50), and their laboratory-produced diploid reciprocal F₁ hybrid progeny. It was tested by fluorescence in situ hybridisation (FISH) whether the number of 28s and 5s rDNA sites in the karyotypes of diploid hybrids corresponds to the expectations resulting from Mendelian ratio and if nucleolar organiser regions (NOR)were inherited from both parents or nucleolar dominance can be observed in the induced F₁ hybrid progeny. Ten (females) or twelve (males) 28s rDNA loci were located in nine uniarm chromosomes of C. taenia. Two of such loci terminally bounded on one acrocentric chromosome were unique and indicated as specific for this species. Large 5s rDNA clusters were located on two acrocentric chromosomes. In C. elongatoides of both sexes, six NOR sites in terminal regions on six meta-submetacentric chromosomes and two 5s rDNA sites on large submetacentrics were detected. The F₁ hybrid progeny (2n = 49) was characterised by the intermediate karyotype with the sites of ribosome synthesis on chromosomes inherited from both parents without showing nucleolar dominance. 5s rDNA sites were detected on large submetacentric and two acrocentric chromosomes. The observed number of both 28s and 5s rDNAs signals in F₁ diploid Cobitis hybrids was disproportionally inherited from the two parental species, showing inconsistency with the Mendelian ratios. The presented rDNA patterns indicate some marker chromosomes that allow the species of the parental male and female to be recognised in hybrid progeny. The 5s rDNA was found to be a particularly effective diagnostic marker of C. elongatoides to partially discern genomic composition of diploid Cobitis hybrids and presumably allopolyploids resulting from their backcrossing with one of the parental species. Thus, the current study provides insight into the extent of rDNA heredity in Cobitis chromosomes and their cytotaxonomic character.     

Karyotype analysis in some species of Consolida (Ranunculaceae) from Iran

Consolida (dc .) S. F. Gray belongs to Ranunculaceae. The genus includes about 52 species worldwide. Here we report the diploid chromosome number and chromosome size and morphology for six Consolida species. For C. anthoroidea, C. leptocarpa, C. paradoxa and C. rugulosa the diploid chromosome number is reported for the first time. All investigated species have a diploid chromosome number of 2n = 2x = 16, except for C. persica having 2n = 2x = 14. The karyotypes of all six taxa are asymmetric, consisting of all four major chromosome types: metacentric, submetacentric, subtelocentric and telocentric chromosome type. However, considering the karyotype formula, all six species could be distinguished. In all taxa, metacentric chromosome pair 1 possesses a satellite. The only exception is C. rugulosa having an additional satellite positioned on metacentric chromosome pair 2. Karyotype data allow the separation of Aconitella from Consolida. Karyotype data plus morphological evidence support the reduction of C. paradoxa to formae level of C. rugulosa. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Production of Polyploids and Unreduced Gametes in Lilium auratum × L. henryi Hybrid

Intergenomic F₁ hybrids between L. auratum x L. henryi and their BC₁ progeny were investigated through genomic in situ hybridization technique (GISH) to determine their potential value in lily breeding. We confirmed that F₁ intergenomic hybrids possessed a set of chromosomes (x=12) from both parents and that flowers of the F₁ auratum × henryi hybrid showed an intermediate morphological phenotype. Pollen size, viability and germination ability were measured through microscopic observations. F₁ intergenomic hybrids produced a relevant frequency of 2n-gametes, which were successfully used to perform crosses with Oriental hybrids, resulting in the triploid Oriental Auratum Henryi (OAuH) hybrid. Twenty BC₁ plants were generated by crossing between four different Oriental hybrid cultivars and F₁ AuH hybrids using an in vitro embryo rescue technique, after which the genome constitution and chromosome composition were analyzed by GISH. All plants were triploid, showing 12 from female parents (diploid Oriental hybrid) and 24 from male parents (diploid F₁ AuH hybrid). Overall, 16 out of 20 BC₁ progeny possessed recombinant chromosomes with 1-5 crossover sites per plant. Cytological analysis of 20 BC₁ plants by GISH verified that the occurrence of 2n pollen formation in all F₁ AuH hybrids was derived from the FDR (first division restitution) mechanism, in which the genome composition of all BC₁ plants possess 12 Oriental + 12 L. auratum + 12 L. henryi chromosomes. Allotriploids derived from the AuH hybrid were used as female for crossing with the diploid Oriental hybrid cultivar ''Sorbonne'' and considerable numbers of plants (0-6.5 plants per ovary) were only obtained when female OAuH (BC₁) triploids were used. Taken together, the results of this study indicate that production and analysis of F₁ AuH hybrids and their progeny through sexual polyploidization can be useful for efficient creation of important horticultural traits.