Genomic constitutions of four Chinese endemic Elymus species: E. brevipes, E. yangii, E. anthosachnoides, and E. altissimus (Triticeae, Poaceae).

The objectives of this study were to determine the genomic constitution and to explore the genomic variation within four Chinese endemic Elymus species, i.e., E. brevipes (Keng) L?ve (2n = 4x = 28) and E. yangii B.R. Lu (2n = 4x = 28), E. anthosachnoides (Keng) L?ve (2n = 4x = 28), and E. altissimus (Keng) L?ve (2n = 4x = 28). Intraspecific crosses between different populations of the four Elymus species, as well as interspecific hybridizations among the four target species, and with six analyzer species containing well-known genomes, i.e., E. caninus (L.) L. (2n = 4x = 28, SH), E. sibiricus L. (2n = 4x = 28, SH), E. semicostatus (Lees ex Steud.) Melderis (2n = 4x = 28, SY), E. parviglumis (Keng) L?ve (2n = 4x = 28, SY), E. tsukushiensis Honda (2n = 6x = 42, SHY), and E. himalayanus (Nevski) Tzvelev (2n = 6x = 42, SHY), were achieved through the aid of embryo rescue. Chromosome pairing behaviors were studied in the parental species and their hybrids. Numerical analysis on chromosome pairing was made on the interspecific hybrids. With one exception, each meiotic configuration at metaphase I in the hybrids involving the target taxa and the analyzer species containing the "SH" genomes fit a 2:1:1 model with x-values ranging between 0.91 and 1.00; chromosome pairing in the hybrids involving analyzer parents with the "SY" genomes match a 2:2 model, with x-values between 0.97 and 0.99. All pentaploid hybrids with a genomic formula "SSYYH," except for two crosses having unexpected low c-values, had pairing patterns fitting the 2:2:1 model with x-values varying between 0.96 and 1.00. It is concluded based on hybridization, fertility, and chromosome pairing data that (i) the four target Elymus species are strictly allotetraploid taxa, (ii) they are closely related species, all comprised of the "SY" genomes, (iii) minor genomic structural rearrangements have occurred within the four Elymus species, and (iv) meiotic pairing regulator(s) exists in some of the Elymus taxa studied.     

Genetic relationships among Hylocereus and Selenicereus vine cacti (Cactaceae): evidence from hybridization and cytological studies

BACKGROUND AND AIMS: Hylocereus and Selenicereus are native to tropical and sub-tropical America. Based on its taxonomic status and crossability relations it was postulated that H. megalanthus (syn. S. megalanthus) is an allotetraploid (2n = 4x = 44) derived from natural hybridization between two closely related diploid taxa. The present work aimed at elucidating the genetic relationships between species of the two genera. METHODS: Crosses were performed and the putative hybrids were analysed by chromosome counts and morphological traits. The ploidy level of hybrids was confirmed by fluorescent in situ hybridization (FISH) of rDNA sites. Genomic in situ hybridization (GISH) was used in an attempt to identify the putative diploid genome donors of H. megalanthus and an artificial interploid hybrid. KEY RESULTS: Reciprocal crosses among four diploid Hylocereus species (H. costaricensis, H. monacanthus (syn. H. polyrhizus), H. undatus and Hylocereus sp.) yielded viable diploid hybrids, with regular chromosome pairing. Reciprocal crosses between these Hylocereus spp. and H. megalanthus yielded viable triploid, pentaploid, hexaploid and aneuploid hybrids. Morphological and phenological traits confirm the hybrid origin. In situ detection of rDNA sites was in accord with the ploidy status of the species and hybrid studied. GISH results indicated that overall sequence composition of H. megalanthus is similar to that of H. ocamponis and S. grandiflorus. High sequence similarity was also found between the parental genomes of H. monacanthus and H. megalanthus in one triploid hybrid. CONCLUSIONS: The ease of obtaining partially fertile F1 hybrids and the relative sequence similarity (in GISH study) suggest close genetic relationships among the taxa analysed.     

Genomic distribution of three repetitive DNAs in cultivated hexaploid Diospyros spp. (D. kaki and D. virginiana) and their wild relatives

To understand the genomic organization of Diospyros species with different ploidy levels, we cloned three different repetitive DNAs and compared their genomic distributions in ten Diospyros species, including hexaploid D. kaki and D. virginiana. Genomic Southern hybridization demonstrated that the EcoRV-repetitive DNA was present in tandem in the genomes of D. glandulosa (2n=2x=30), D. oleifera (2n=2x=30), D. lotus (2n=2x=30), D. virginiana (2n=6x=90) and D. kaki (2n=6x=90). All of these species except D. virginiana also contained the HincII-repetitive DNA in tandem. Fluorescent in situ hybridization showed that the EcoRV- and HincII-repetitive DNAs were predominantly located at the proximal or centromeric regions of chromosomes. The DraI-repetitive sequence cloned from D. ehretioides (2n=2x=30) was not found in the other Diospyros species tested. This suggests that D. ehretioides has a genomic organization different from that of the other Diospyros species. Speciation of hexaploid Diospyros species is also discussed with respect to the genomic distribution of the three repetitive DNAs cloned.     

中间偃麦草的GISH分析

以染色体组为E^eE^e的二倍体长穗偃麦草（Thinopyrum elongatum,2n=2x=14)、染色体组为E^bE^b的二倍体比萨偃麦草（Th.bessarabicum,2n=2x=14）、染色体组为StStStSt的四倍体拟鹅冠草（Pseudoroegneiria strigosa,2n=4x=28)的总基因组DNA为探针,对中间偃麦草（Th.intermedium)进行GISH分析。结果表明,中间偃麦草是由2个亲缘关系较近的染色体组、1个亲缘关系较远的染色体组构成;中间偃麦草所含的亲缘关系较近的染色体组分别与二倍长穗偃麦草染色体组E^e、比萨偃麦草染色体组E^b、以及1个亲缘关系较远的染色体组与拟鹅冠草染色体组St基本相似,但不完全一样,因此,中间偃麦草的染色体组用E^etE^etE^btStSt表示。     

The genomic composition of Tricepiro, a synthetic forage crop.

Chromosome in situ hybridization (FISH and GISH) is a powerful tool for determining the chromosomal location of specific sequences and for analysing genome organization and evolution. Tricepiro (2n = 6x = 42) is a synthetic cereal obtained by G. Covas in Argentina (1972), which crosses hexaploid triticale (2n = 6x = 42) and octoploid Trigopiro (2n = 8x = 56). Several years of breeding produced a forage crop with valuable characteristics from Secale, Triticum, and Thinopyrum. The aim of this work is to analyse the real genomic constitution of this important synthetic crop. In situ hybridization using total DNA of Secale, Triticum, and Thinopyrum as a probe (GISH) labelled with biotin and (or) digoxigenin showed that tricepiro is composed of 14 rye chromosomes and 28 wheat chromosomes. Small zones of introgression of Thinopyrum on wheat chromosomes were detected. The FISH using the rye repetitive DNA probe pSc 119.2 labelled with biotin let us characterize the seven pairs of rye chromosomes. Moreover, several wheat chromosomes belonging to A and B genomes were distinguished. Therefore, tricepiro is a synthetic hexaploid (2n = 6x = 42) being AABBRR in its genomic composition, with zones of introgression of Thinopyrum in the A genome of wheat.     

Molecular cytogenetic characterization of Aegilops biuncialis and its use for the identification of 5 derived wheat-Aegilops biuncialis disomic addition lines.

The aim of the experiments was to produce and identify different Triticum aestivum-Aegilops biuncialis disomic addition lines. To facilitate the exact identification of the Ae. biuncialis chromosomes in these Triticum aestivum-Ae. biuncialis disomic additions, it was necessary to analyze the fluorescence in situ hybridization (FISH) pattern of Ae. biuncialis (2n = 4x = 28, U(b)U(b)M(b)M(b)), comparing it with the diploid progenitors (Aegilops umbellulata, 2n = 2x = 14, UU and Aegilops comosa, 2n = 2x = 14, MM). To identify the Ae. biuncialis chromosomes, FISH was carried out using 2 DNA clones (pSc119.2 and pAs1) on Ae. biuncialis and its 2 diploid progenitor species. Differences in the hybridization patterns of all chromosomes were observed among the 4 Ae. umbellulata accessions, the 4 Ae. comosa accessions, and the 3 Ae. biuncialis accessions analyzed. The hybridization pattern of the M genome was more variable than that of the U genome. Five different wheat-Ae. biuncialis addition lines were produced from the wheat-Ae. biuncialis amphiploids produced earlier in Martonvásár. The 2M, 3M, 7M, 3U, and 5U chromosome pairs were identified with FISH using 3 repetitive DNA clones (pSc119.2, pAs1, and pTa71) in the disomic chromosome additions produced. Genomic in situ hybridization (GISH) was used to differentiate the Ae. biuncialis chromosomes from wheat, but no chromosome rearrangements between wheat and Ae. biuncialis were detected in the addition lines.     

Identification of mitotic chromosomes of tuberous and non-tuberous solanum species (Solanum tuberosum and Solanum brevidens) by GISH in their interspecific hybrids.

GISH (genomic in situ hybridization) was applied for the analysis of mitotic chromosome constitutions of somatic hybrids and their derivatives between dihaploid clones of cultivated potato (Solanum tuberosum L.) (2n = 2x = 24, AA genome) and the diploid, non-tuberous, wild species Solanum brevidens Phil. (2n = 2x = 24, EE genome). Of the primary somatic hybrids, both tetraploid (2n = 4x) and hexaploid (2n = 6x) plants were found with the genomic constitutions of AAEE and AAEEEE, respectively. Androgenic haploids (somatohaploids) derived from the tetraploid somatic hybrids had the genomic constitutions of AE (2n = 2x = 24) and haploids originating from the hexaploid hybrids were triploid AEE (2n = 3x = 33 and 2n = 3x = 36). As a result of subsequent somatic hybridization from a fusion between dihaploid S. tuberosum (2n = 2x = 24, genome AA) and a triploid somatohaploid (2n = 3x = 33, genome AEE), second-generation somatic hybrids were obtained. These somatic hybrids were pentaploids (2n = 5x, genome AAAEE), but had variable chromosome numbers. GISH analysis revealed that both primary and second-generation somatic hybrids had lost more chromosomes of S. brevidens than of S. tuberosum.     

Variation in chromosome numbers, CMA bands and 45S rDNA sites in species of Selaginella (Pteridophyta)

BACKGROUND AND AIMS: Selaginella is the largest genus of heterosporous pteridophytes, but karyologically the genus is known only by the occurrence of a dysploid series of n=7-12, and a low frequency of polyploids. Aiming to contribute to a better understanding of the structural chromosomal variability of this genus, different staining methods were applied in species with different chromosome numbers. METHODS: The chromosome complements of seven species of Selaginella were analysed and, in four of them, the distribution of 45S rDNA sites was determined by fluorescent in situ hybridization. Additionally, CMA/DA/DAPI and silver nitrate staining were performed to investigate the correlation between the 45S rDNA sites, the heterochromatic bands and the number of active rDNA sites. KEY RESULTS: The chromosome numbers observed were 2n=18, 20 and 24. The species with 2n=20 exhibited chromosome complement sizes smaller and less variable than those with 2n=18. The only species with 2n=24, S. convoluta, had relatively large and asymmetrical chromosomes. The interphase nuclei in all species were of the chromocentric type. CMA/DA/DAPI staining showed only a weak chromosomal differentiation of heterochromatic bands. In S. willdenowii and S. convoluta eight and six CMA+ bands were observed, respectively, but no DAPI+ bands. The CMA+ bands corresponded in number, size and location to the rDNA sites. In general, the number of rDNA sites correlated with the maximum number of nucleoli per nucleus. Ten rDNA sites were found in S. plana (2n=20), eight in S. willdenowii (2n=18), six in S. convoluta (2n=24) and two in S. producta (2n=20). CONCLUSIONS: The remarkable variation in chromosome size and number and rDNA sites shows that dramatic karyological changes have occurred during the evolution of the genus at the diploid level. These data further suggest that the two putative basic numbers of the genus, x=9 and x=10, may have arisen two or more times independently.     

Genomic in situ hybridization differentiates between A/D- and C-genome chromatin and detects intergenomic translocations in polyploid oat species (genus Avena).

The genomic in situ hybridization (GISH) technique was used to discriminate between chromosomes of the C genome and those of the A and A/D genomes in allopolyploid oat species (genus Avena). Total biotinylated DNA from A. strigosa (2n = 2x = 14, AsAs genome) was mixed with sheared, unlabelled total DNA from A. eriantha (2n = 2x = 14, CpCp) at a ratio of 1:200 (labelled to unlabelled). The resulting hybridization pattern consisted of 28 mostly labelled and 14 mostly unlabelled chromosomes in the hexaploids. Attempts to discriminate between chromosomes of the A and D genomes in A. sativa (2n = 6x = 42, AACCDD) were unsuccessful using GISH. At least eight intergenomic translocation segments were detected in A. sativa 'Ogle', several of which were not observed in A. byzantina 'Kanota' (2n = 6x = 42, AACCDD) or in A. sterilis CW 439-2 (2n = 6x = 42, AACCDD). At least five intergenomic translocation segments were observed in A. maroccana CI 8330 'Magna' (2n = 4x = 28, AACC). In both 'Ogle' and 'Magna', positions of most of these translocations matched with C-banding patterns.     

Centric fusion differences among Oryx dammah, O. gazella, and O. leucoryx (Artiodactyla, Bovidae)

G- and C-banded karyotypes of the genus Oryx were compared using the standard karyotype of Bos taurus. Chromosomal complements were 2n = 56 in O. gazella gazella, 2n = 58 in O. g. beisa and O. g. callotis, 2n = 56-58 in O. dammah, and 2n = 57-58 in O. leucoryx. The number of autosomal arms in all karyotypes was 58. Nearly all variation in diploid number was the result of three independent centric fusions, but one 2n = 57 specimen of O. g. gazella deviated from the normal complement of 2n = 56 due to XXY aneuploidy. A 2;17 centric fusion was fixed in O. g. gazella, whereas O. g. beisa and O. g. callotis lacked this fusion and had indistinguishable karyotypes. Oryx dammah was polymorphic for a 2;15 centric fusion, and O. leucoryx was polymorphic for an 18;19 centric fusion. The five Oryx taxa shared a fixed 1;25 centric fusion; the small acrocentric element involved in the 1;25 fusion was identified by fluorescence in situ hybridization using a cosmid specific to Bos chromosome 25. The X and Y chromosomes were also conserved among the five taxa. Oryx g. gazella differed from the other Oryx species because of the fixed 2;17 centric fusion. This difference reflects an apparently longer period of geographic isolation between O. g. gazella and other populations of Oryx, and it is consistent with the classification of O. gazella and O. beisa as distinct species (see Kingdon, 1997). The lack of monobrachial relationships among the Oryx taxa indicates that sterility barriers between species have not developed. Viability of hybrid offspring constitutes a threat to captive breeding programs designed for endangered species conservation; in the case of Oryx, the 2;15, 2;17, and 18;19 metacentrics could serve as marker chromosomes for assessing hybridization between certain Oryx taxa.     

The use of dna sequencing (ITS and trnL-F), AFLP, and fluorescent in situ hybridization to study allopolyploid Miscanthus (Poaceae)

Two clones of Miscanthus, grown under the names M. ×giganteus and M. sacchariflorus, have been used in biomass trials in Europe, but neither the identity of these clones nor their origin has been established. DNA sequencing, amplified fragment length polymorphism (AFLP), and chromosome studies confirm that M. ×giganteus is an allotriploid (2n = 3x = 57) combining genomes from M. sinensis (2n = 2x = 38) and M. sacchariflorus (2n = 38 or 76). Two alleles of the internal transcribed spacer of 18S-25S nuclear ribosomal DNA (ITS) were discovered in polymerase chain reaction products of M. ×giganteus. Cloning of these revealed that one matched M. sinensis and the other M. sacchariflorus. Plastid trnL intron and trnL-F spacer sequences showed that the maternal lineage of M. ×giganteus was M. sacchariflorus. Fluorescent in situ hybridization, FISH, was used to investigate genome organization in Miscanthus but was unable to differentiate between the different parental genomes present in M. ×giganteus, indicating that two parental genomes are still extremely similar at the repetitive DNA level. This study is an example in which rDNA sequences and AFLP fingerprints permit identification of the parental genomes in a hybrid, but FISH methods, at the repetitive DNA level (including genomic in situ hybridization, GISH), were unable to do so because their sequences remain too similar.     

Mapping the distribution of the telomeric sequence (T(2)AG(3))(n) in rock wallabies,Petrogale (Marsupialia: Macropodidae), by fluorescence in situ hybridization. ii. the lateralis complex

The distribution of the conserved vertebrate telomeric sequence (T(2)AG(3))(n) was examined by fluorescence in situ hybridization in the six Petrogale (rock wallabies) taxa of the lateralis complex. As expected, the (T(2)AG(3))(n) sequence was located at the termini of all chromosomes in all taxa. However, the sequence was also present at several nontelomeric (viz., interstitial and centromeric) sites. The signals identified were associated with either ancient rearrangements involved with the formation of the 2n = 22 plesiomorphic macropodine karyotype or more recent rearrangements associated with karyotypes derived from the 2n = 22 karyotype. Interstitial (T(2)AG(3))(n) signals identified on chromosomes 3 and 4 in all six species of the lateralis complex and a large centromeric signal identified on chromosome 7 in the five subspecies/races of P. lateralis appear to be related to the more ancient rearrangements. Subsequent chromosome evolution has seen these signals retained, lost, or amplified in different Petrogale lineages. Within the lateralis complex, in two submetacentric chromosome derived by recent centric fusions, the telomeric sequence was identified at or near the centromere, indicating its retention during the fusion process. In the two taxa where chromosome 3 was rearranged via a recent centromeric transposition to become an acrocentric chromosome, the telomeric signal was located interstitially.     

秦巴山区重楼属的核型研究

本文报道了陕西秦巴山区几种重楼属植物的核型研究结果。在秦岭(太白山)地区,北楼(Paris verticillata)具有一种核型,其核型公式为 2n=4 x=20=10m+2sm+4st+4t;狭叶重楼(P.polyphylla var.stenophylla)在一个居群内不同的个体间具有两种不同的核型,核型公式分别为2n=2x=10=5m+1sm+4t和2n=2x=10+2B=6m+4t+2B。在秦岭和巴山两地,宽叶重楼(P.polyphylla var.latifolia)和球药隔重楼(P.fargesii)分别具有两种不同的核型,前者的核型公式为2n=2x=10+3B=6m+3t+3B和2n=2x=10=5m+1sm+4t,后者的核型公式为2n=2x=10+2B=4m+2sm+4t+2B和2n=2x=10+2B=6m+4t+2B。这些材料均属2A核型,在核型结构及B染色体的有无和数目上与前人报道的结果不完全相同。     

Introgression mapping of genes for winter hardiness and frost tolerance transferred from Festuca arundinacea into Lolium multiflorum

Genes for winter hardiness and frost tolerance were introgressed from Festuca arundinacea into winter-sensitive Lolium multiflorum. Two partly fertile, pentaploid (2n = 5x = 35) F(1) hybrids F. arundinacea (2n = 6x = 42) x L. multiflorum (2n = 4x = 28) were generated and backcrossed twice onto L. multiflorum (2x). The backcross 1 (BC(1)) and backcross 2 (BC(2)) plants were preselected for high vigor and good fertility, and subsequently, a total of 83 BC(2) plants were selected for winter hardiness after 2 Polish winters and by simulated freezing tests. Genomic in situ hybridization (GISH) was performed on 6 winter-hardy plants selected after the first winter and shown to be significantly (P < 0.05) more frost tolerant than the L. multiflorum control. Among the analyzed BC(2) winter survivors, only diploid (2n = 2x = 14) plants were found. Five plants carried 13 intact L. multiflorum chromosomes and 1 L. multiflorum chromosome with a single introgressed F. arundinacea terminal chromosome segment. The sixth BC(2) winter survivor appeared to be Lolium without any Festuca introgression capable of detection by GISH. A combined GISH and fluorescence in situ hybridization analysis with rDNA probes of the most winter-hardy (after 2 winters) and frost-tolerant BC(2) plant revealed the location of an F. arundinacea introgression on the nonsatellite arm of L. multiflorum chromosome 2, the same chromosome location reported previously as a site for frost tolerance genes in the diploid and winter-hardy species Festuca pratensis.     

Chromosome pairing in triploid intergeneric hybrids ofFestuca pratensis withLolium multiflorum, revealed by GISH

Genomic in situ hybridisation (GISH) was used to reveal chromosome pairing in two partly fertile, triploid (2n = 3x = 21) hybrids obtained by crossing the diploid (2n = 2x = 14) Festuca pratensis Huds. (designated FpFp), used as a female parent, with the autotetraploid (2n = 4x = 28) Lolium multiflorum Lam. (designated LmLmLmLm), used as a male parent. The pattern of chromosome pairing calculated on the basis of the mean values of chromosome configurations identified in all 100 PMCs analysed, was: 0.71I Lm + 2.24I Fp + 2.18II Lm/Lm + 0.54II Lm/Fp + 4.18III Lm/Lm/Fp. A relatively high number of Lm/Lm bivalents and Fp univalents, and a low number of Lm/Fp bivalents and Lm univalents indicated that the pairing was preferential between L. multiflorum chromosomes. Other observations regarding chromosome pairing within the Lm/Lm/Fp trivalents also confirmed this preferential pairing in the analysed triploids, as the Fp chromosome was not randomly located in the chain- and frying-pan-shaped trivalents. The similarities and differences in chromosome pairing at metaphase I and the level of preferential pairing between Lolium chromosomes in the different triploid Lolium-Festuca hybrids are discussed.     

A comparative study on karyotypes of 28 taxa in Rubus sect. Idaeobatus and sect. Malachobatus (Rosaceae) from China

Rubus is a taxonomically difficult group and cytological data are expected hopefully to gain insight into the relationships of the genus. In this study the chromosome numbers and karyotypes of 18 taxa from sect. Idaeobatus and 10 taxa from sect. Malachobatus were investigated. Among them, the chromosome numbers of 10 taxa and karyotypes of 26 taxa were reported for the first time and mixoploidy was observed new in the genus. The chromosomes are small in size with a length of less than 3 µm and metacentric (about 90%) or submetacentric. All taxa have karyotypes of “1A” except R. cockburnianus, R. innominatus and R. ellipticus var. obcordatus, which have karyotypes of “2A”. No aneuploids were found in all the 28 taxa studied. Plants of sect. Idaeobatus have diploids with 2n=2x=14, except R. idaeopsis (2n=3x=21) and R. parvifolius (A mixoploid of 2n=2x=14 and 2n=4x=28). However, plants of sect. Malachobatus have tetraploids with 2n=4x=28, except for R. buergeri with 2n=8x=56. In addition, conspicuous karyotype differences existed within the 18 taxa belonging to 11 of 7 subsections in sect. Idaeobatus, and the differences between some species within subsections are greater than that between subsections, while uniform karyotypes within subsections and variable karyotypes between subsections were observed in six of 13 subsections in sect. Malachobatus represented by 10 taxa. Systematic values of the cytological data were discussed for some cases when applicable to the two sections.     

中国姜花属十九个分类群的细胞学研究

采用压片法对中国姜花属十八个分类群进行了体细胞染色体计数,对白姜花减数分裂终变期I的染色体数目和形态进行了观察。结果显示:包括白姜花在内的十九个分类群中有六个二倍体,一个三倍体,十二个四倍体,其中十二个分类群的体染色体数目为首次报道,显示中国姜花属植物具有较高比例的多倍体类型;姜花属的染色体基数为n=17,染色体组可能是多倍体起源的。     

The genome organization and diversification of maize and its allied species revisited: evidences from classical and FISH-GISH cytogenetic analysis

The present review summarizes our classical and molecular cytogenetic investigations in the genus Zea. The results obtained from the meiotic behavior analysis of Zea species and hybrids, confirm the amphiploid nature of all species in the genus, with a basic number of x = 5 chromosomes. All species with 2n = 20 are diploidized allotetraploids, whereas Z. perennis (2n = 40) is an allooctoploid with four genomes somewhat divergent from one another. These analyses also revealed the existence of postzygotic reproductive isolation among Zea species. Our studies using genomic in situ hybridization (GISH) provide evidence about the evolutionary relationships among maize and its allied species, and reveal remarkable genomic divergences. Particularly, knob sequences were not completely shared between taxa previously considered to be closely related. Our data strongly suggest that the teosinte Z. mays parviglumis is not the only progenitor of cultivated maize. Introgression of Tripsacum into cultivated maize cannot be discarded.     

Genomic in situ hybridization analysis of a trigenomic hybrid involving Solanum and Lycopersicon species.

A 4x potato (+) tomato fusion hybrid (2n = 4x = 48) was successfully backcrossed with a diploid Lycopersicon pennellii (2n = 2x = 24). Genomic in situ hybridization (GISH) on somatic and meiotic chromosomes confirmed that the progenies were triploids (2n = 3x = 36) and possessed three different genomes: potato, tomato, and L. pennellii. Therefore, they have been called trigenomic hybrids. Total genomic probes of both Lycopersicon species were found to hybridize mutually, whereas the potato genome was clearly differentiated. During metaphase I, bivalents were formed predominantly between tomato and L. pennellii chromosomes and the univalents of potato chromosomes were most common. Trivalents in all cases included homoeologous chromosomes of potato, tomato, and L. pennellii. However, the triploids were totally sterile as determined from extensive crossing. On chromosome doubling of triploids by shoot regeneration from callus, hexaploids (2n = 6x = 72) were obtained. Despite exhibiting clear allohexaploid behaviour by forming 36 bivalents at meiosis, these were also completely sterile like their triploid counterparts. In spite of this drawback, the prospects of chromosome pairing between potato L. pennellii and Solanum genomes does open the possibilities for bringing the two genera close.