Genome composition of 'Elatior'-begonias hybrids analyzed by genomic in situ hybridisation

Interspecific hybridization of various tuberous Begonia species hybrids with Begonia socotrana results in so-called 'Elatior'-begonias hybrids (B. x hiemalis Fotsch). In our study, genomic in situ hybridization (GISH) has been employed to assess the genome composition in eleven 'Elatior'-begonias hybrids and their ancestor genotypes. Genomic DNA of tuberous Begonia was sonicated to 1-10-kb fragments, labelled by nick translation with digoxigenin-11-dUTP and used as a probe whereas B. socotrana DNA was autoclaved to 100 bp fragments and used as block. The genome of tuberous Begonia was clearly pronounced in 'Elatior'-begonias when the probe concentration was similar to 3.75 ng/mu l (150 ng/slide), with 30 times the excess of B. socotrana blocking DNA and stringency of post hybridization washings at 73% (0.1x SSC at 42A degrees C). In 'Elatior'-begonias hybrids GISH distinguished two groups comprising short (0.6-1.03 mu m in length) and relatively longer chromosomes (1.87-3.88 mu m) which represent B. socotrana and tuberous Begonia genomes, respectively. The number of chromosomes derived from tuberous Begonia ranged from 14 to 56 and for B. socotrana from 7 to 28 which suggest the presence of different ploidy levels in analyzed 'Elatior'-begonia hybrids. Intergenomic recombination has not been detected through GISH in hybrids analyzed. Genomic in situ hybridization turned out to be useful to identify the genome constitution of 'Elatior'-begonia hybrids and thus gain an insight into the origins of these cultivars. This knowledge on the ploidy level and genome composition is essential for further progress in breeding Begonias

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

Breeding and Cytogenetics in the Genus Tulipa

Tulip (Tulipa) is one of the most important ornamental bulbous plants, which has been cultivated for cut flower, potted plant, garden plant and for landscaping. Species from the different sections display complementary agronomic characteristics and breeding techniques are used to combine desired features. The main goals of modern tulip breeding are the introgression of resistance against Tulip Breaking Virus (TBV), Botrytis tulipae and Fusarium oxysporum (bulb-rot), and also characteristics such as a short forcing period, good flower longevity and new flower colours and flower shapes into the commercial assortment of T. gesneriana. T. gesneriana has been crossed successfully with only 12 out of the approximately 55 tulip species by using conventional breeding methods. Many successful crosses have been made between T. gesneriana cultivars and TBV resistant T. fosteriana cultivars resulting in highly resistant Darwin hybrids tulips. The majority of tulip cultivars are diploid (2n = 2x = 24) however, there have been many attempts to obtain polyploid tulips. The production of tetraploids was described in the late sixties when young ovaries were treated, under pressure, with laughing gas (N2O). In breeding of polyploid tulip laughing gas has also been used to induce 2n gametes. Several new tetraploids were also obtained by making crosses between tetraploid lines. Polyploids have been derived from interploidy crosses between diploid, triploid, and tetraploid cultivars. Several other polyploids have resulted from 2n gametes, spontaneously produced by diploid F1 hybrids. Molecular cytogenetic tools such as FISH and GISH permitted detailed studies of genome composition and chromosome recombination in the progenies of interspecific hybrids. In this context, tulip breeding and the use of cytogenetic techniques for genome analysis of hybrids are discussed

Breeding and Cytogenetics in the Genus Tulipa

Tulip (Tulipa) is one of the most important ornamental bulbous plants, which has been cultivated for cut flower, potted plant, garden plant and for landscaping. Species from the different sections display complementary agronomic characteristics and breeding techniques are used to combine desired features. The main goals of modern tulip breeding are the introgression of resistance against Tulip Breaking Virus (TBV), Botrytis tulipae and Fusarium oxysporum (bulb-rot), and also characteristics such as a short forcing period, good flower longevity and new flower colours and flower shapes into the commercial assortment of T. gesneriana. T. gesneriana has been crossed successfully with only 12 out of the approximately 55 tulip species by using conventional breeding methods. Many successful crosses have been made between T. gesneriana cultivars and TBV resistant T. fosteriana cultivars resulting in highly resistant Darwin hybrids tulips. The majority of tulip cultivars are diploid (2n = 2x = 24) however, there have been many attempts to obtain polyploid tulips. The production of tetraploids was described in the late sixties when young ovaries were treated, under pressure, with laughing gas (N2O). In breeding of polyploid tulip laughing gas has also been used to induce 2n gametes. Several new tetraploids were also obtained by making crosses between tetraploid lines. Polyploids have been derived from interploidy crosses between diploid, triploid, and tetraploid cultivars. Several other polyploids have resulted from 2n gametes, spontaneously produced by diploid F1 hybrids. Molecular cytogenetic tools such as FISH and GISH permitted detailed studies of genome composition and chromosome recombination in the progenies of interspecific hybrids. In this context, tulip breeding and the use of cytogenetic techniques for genome analysis of hybrids are discussed

Breeding and Cytogenetics in the Genus Tulipa

Tulip (Tulipa) is one of the most important ornamental bulbous plants, which has been cultivated for cut flower, potted plant, garden plant and for landscaping. Species from the different sections display complementary agronomic characteristics and breeding techniques are used to combine desired features. The main goals of modern tulip breeding are the introgression of resistance against Tulip Breaking Virus (TBV), Botrytis tulipae and Fusarium oxysporum (bulb-rot), and also characteristics such as a short forcing period, good flower longevity and new flower colours and flower shapes into the commercial assortment of T. gesneriana. T. gesneriana has been crossed successfully with only 12 out of the approximately 55 tulip species by using conventional breeding methods. Many successful crosses have been made between T. gesneriana cultivars and TBV resistant T. fosteriana cultivars resulting in highly resistant Darwin hybrids tulips. The majority of tulip cultivars are diploid (2n = 2x = 24) however, there have been many attempts to obtain polyploid tulips. The production of tetraploids was described in the late sixties when young ovaries were treated, under pressure, with laughing gas (N2O). In breeding of polyploid tulip laughing gas has also been used to induce 2n gametes. Several new tetraploids were also obtained by making crosses between tetraploid lines. Polyploids have been derived from interploidy crosses between diploid, triploid, and tetraploid cultivars. Several other polyploids have resulted from 2n gametes, spontaneously produced by diploid F1 hybrids. Molecular cytogenetic tools such as FISH and GISH permitted detailed studies of genome composition and chromosome recombination in the progenies of interspecific hybrids. In this context, tulip breeding and the use of cytogenetic techniques for genome analysis of hybrids are discussed

Meiotic polyploidization in Darwin hybrid tulips

In our study, 2n gamete producing F1 hybrids of Darwin hybrids (T. gesneriana × T. fosteriana) have been selected and used as pollen donor with the aim of producing of polyploid tulips. In total, 308 one-year-old BC1 seedlings resulting from crosses between diploid and triploid T. gesneriana cultivars and diploid 2n gametes producers have been tested by flow cytometry analysis. Complementary, chromosome number and genome composition was evaluated for selected genotypes through genomic in situ hybridization (GISH) analysis. The progenies from crosses at diploid level (2x × 2x) were mostly diploids, whereas a few seedlings were triploids. In crosses 3x × 2x, 81 genotypes were tetraploids and 25 seedlings were pentaploids. Cytological analyses using GISH of the sexual polyploid progenies have shown considerable amounts of intergenomic recombination in the BC1 generations which is desirable for introgression breeding

The Significance of Polyploidy for Bulbous Ornamentals: A Molecular Cytogenetic Assessment

Most of the bulbous crops, viz., Crocus, Narcissus, Tulipa, Alstroemeria and Lilium that are commercially important, share certain common characteristics. The present day cultivars are all derived from hybrids between distantly related species, and in almost all cases spontaneous polyploidization has played a prominent role and there is a tendency to replace diploids by polyploid cultivars. Molecular cytogenetic techniques such as genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH), along with other techniques, have greatly facilitated our understanding of the modes of origins of polyploids. Because the bulbous crops generally have large chromosomes, the parental genomes, individual chromosomes, as well as intergenomic recombinant chromosomes, can be accurately identified in the interspecific hybrids and their backcross progenies. This enables an assessment of the potential genetic variation that might occur in the progenies as well as the extent of introgression. Although the superiority of polyploids as compared to their diploid parents is beyond doubt, the actual explanation for their superiority is still elusive. Of the several explanations, chromosome dosage, optimal amounts of 4C DNA values of the complements, heterozygosity and favourable gene interactions transmitted by the 2n gametes to polyploid progenies are some of the factors that might be considered at present. Undoubtedly, more studies on the bulbous ornamental crops using molecular techniques might be rewarding

A Molecular Cytogenetic Analysis of Introgression in Backcross Progenies of Intersectional Lilium Hybrids

The genus Lilium is comprised of about 100 species and has been divided into seven taxonomic sections. The abundance and diversity of species within the genus Lilium offers numerous and rewarding possibilities to lily breeders. Species within the same section can be crossed by conventional hybridization and this has led to different hybrid groups of great commercial importance such as Longiflorum, Asiatic and Oriental lilies. On the other hand, the divergence of species between various taxonomic sections causes considerable difficulties for intersectional crosses. Such difficulties include crossing incompatibility barriers, embryo abortion, sterility and reduced fertility in intersectional hybrids. For these reasons, various pollination techniques followed by in vitro embryo (sac) rescue and ovary culture, chromosome doubling, and 2n gametes are used frequently to obtain progeny between parents from different sections. Being the largest genome in the plant kingdom, lily is used as a model plant for cytogenetic analysis. The genome composition of the hybrids and backcross progenies were monitored through genomic in situ hybridization (GISH). The progress in molecular cytogenetic studies has been associated with the analysis of introgression of chromosomal segments in backcross progenies of various interspecific hybrids, contribution of individual genome in the resultant progenies, and the mechanism of 2n gamete formation. Based on the cytological analysis of progenies derived from the use of both haploid and 2n gametes, cytological maps of three different genomes have been constructed and the relevance of these analyses for introgression in Lilium is demonstrated