New chromosome numbers for plant taxa endemic to the Balearic Islands

Mitotic chromosome numbers are reported from 25 vascular plant taxa, endemic to the Balearic Islands that are poorly known cytogenetically. The chromosome numbers ofAnthyllis vulneraria subsp.balearica (2n=12),Cymbalaria fragilis (2n=56), andPolygonum romanum subsp.balearicum (2n=40) were determined for the first time. A new chromosome number was found in several populations ofAnthyllis hystrix (2n=70) suggesting that this species is decaploid, in contrast to an earlier work reporting a higher ploidy level (2n=12x=84). The new chromosome number 2n=32 was reported inHypericum hircinum subsp.cambessedesii. It is suggested that the previous count (2n=40) could be explained by the presence of anomalous pentaploid cells in some tissues, contrating with the presence of a regular tetraploid complement (2n=32). Cytogenetic observations suggest thatSibthorpia africana has a diploid chromosome complement of 2n=18, with 0–2 accessory chromosomes. Accessory chromosomes are also reported forPhlomis italica, being the first record of B chromosomes in this genus. Chromosomal instability was found inGalium crespianum andG. friedichii species, with three numbers 2n=44, 55 and 66. Two cytotypes differing in ploidy level were documented within single plants. It is suggested that both species share a regular complement of 2n=44 and that the past hybridization events and formation of regenerating roots from the typical rootstock ofG. crespianum andG. friedrichii could be involved in the genesis of chromosome variants through partial endopolyploidy and concomitant somatic segregation.     

Somatic hybrid plants produced by electrofusion between Solanum melongena L. and Solanum torvum Sw

Summary Somatic hybrid plants between eggplant (Solanum melongena) and Solanum torvum have been produced by the electrofusion of mesophyll protoplasts in a movable multi-electrode fusion chamber. Using hair structure as a selection criteria, we identified a total of 19 somatic hybrids, which represented an overall average of 15.3% of the 124 regenerated plants obtained in the two fusion experiments. Several morphological traits were intermediate to those of the parents, including trichome density and structure, height, leaf form and inflorescence. Cytological analyses revealed that the chromosome numbers of the somatic hybrids approximated the expected tetraploid level (2n=4x=48). Fifteen hybrid plants were homogeneous and had relatively stable chromosome numbers (46–48), while four other hybrids had variable chromosome numbers (35–48) and exhibited greater morphological variation. The hybridity of these 19 somatic hybrid plants was confirmed by analyses of phosphoglucomutase (Pgm) and esterase zymograms.     

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.     

Cytogenetic analysis of Lycopersicon esculentum (+) Solanum etuberosum somatic hybrids and their androgenetic regenerants

The aim of the study was to characterize genomic relationships among cultivated tomato (Lycopersicon esculentum Mill.) (2n=2x=24) and diploid (2n=2x=24) non-tuberous wild Solanum species (S. etuberosum Lindl.). Using genomic in situ hybridization (GISH) of mitotic and meiotic chromosomes, we analyzed intergeneric somatic hybrids between tomato and S. etuberosum. Of the five somatic hybrids, two plants were amphidiploids (2n=4x=48) mostly forming intragenomic bivalents in their microsporocytes, with a very low frequency of multivalents involving the chromosomes of tomato and S. etuberosum (less than 0.2 per meiocyte). Tomato chromosomes showed preferential elimination during subsequent meiotic divisions of the amphidiploids. Transmission of the parental chromosomes into microspores was also evaluated by GISH analysis of androgenic plants produced by direct embryogenesis from the amphidiploid somatic hybrids. Of the four androgenic regenerants, three were diploids (2n=2x=24 or 2n=2x+1=25) derived from reduced male gametes of the somatic hybrids, and one plant was a hypertetraploid (2n=4x+4=52). GISH revealed that each anther-derived plant had a unique chromosome composition. The prospects for introgression of desirable traits from S. etuberosum into the gene pool of cultivated tomato are discussed. Received: 2 August 2000 / Accepted: 4 December 2000     

Chromosome numbers and karyotype evolution in holoparasitic Orobanche (Orobanchaceae) and related genera

Chromosome numbers and karyotypes of species of Orobanche, Cistanche, and Diphelypaea (Orobanchaceae) were investigated, and 108 chromosome counts of 53 taxa, 19 counted for the first time, are presented with a thorough compilation of previously published data. Additionally, karyotypes of representatives of these genera, including Orobanche sects. Orobanche and Trionychon, are reported. Cistanche (x = 20) has large meta- to submetacentric chromosomes, while those of Diphelypaea (x = 19) are medium-sized submeta- to acrocentrics. Within three analyzed sections of Orobanche, sects. Myzorrhiza (x = 24) and Trionychon (x = 12) possess medium-sized submeta- to acrocentrics, while sect. Orobanche (x = 19) has small, mostly meta- to submetacentric, chromosomes. Polyploidy is unevenly distributed in Orobanche and restricted to a few lineages, e.g., O. sect. Myzorrhiza or Orobanche gracilis and its relatives (sect. Orobanche). The distribution of basic chromosome numbers supports the groups found by molecular phylogenetic analyses: Cistanche has x = 20, the Orobanche-group (Orobanche sect. Orobanche, Diphelypaea) has x = 19, and the Phelipanche-group (Orobanche sects. Gymnocaulis, Myzorrhiza, Trionychon) has x = 12, 24. A model of chromosome number evolution in Orobanche and related genera is presented: from two ancestral base numbers, x(h) = 5 and x(h) = 6, independent polyploidizations led to x = 20 (Cistanche) and (after dysploidization) x = 19 (Orobanche-group) and to x = 12 and x = 24 (Phelipanche-group), respectively.     

Some naturally occurring chromosome anomalies in Tulipa clusiana DC

Tulipa clusiana is characterized by a highly variable phenotype. The species comprises var. chrysantha Sealy (2n=2x=24), var. stellata Regel (2n=3x=36; 2n=4x=48) and var. typica Regel (2n=2x=24; 2n=4x=48; 2n=5x=60). Several populations of these varieties were all found to exhibit remarkable uniformity in basic karyotype. A few plants had some structurally altered chromosomes otherwise unknown within the species and its allies. These chromosomes are suspected to be products of translocations. They are very long with almost median centromere. Occasional aneusomaty and polysomaty have also been observed in some plants. The evolutionary significance of these aberrations is discussed.     

Chromosome markers and alterations in mitotic cells from interspecific Citrus somatic hybrids analysed by fluorochrome staining

Mitotic cells from Rough lemon (Citrus jambhiri Lush.), Ohta ponkan (C. reticulata Blanco) and two somatic hybrid plants obtained from protoplast fusion were analysed by double staining with chromomycin A₃ (CMA) and 4′-6-diamidino-2-phenylindole. Only CMA-positive bands were observed in metaphasic chromosomes. The two parental karyotypes (2n=2x=18) were heteromorphic, yielding some marker chromosomes that could be identified in the somatic hybrids. One of the somatic hybrids had 2n=37 chromosomes, and the possible extra chromosome was distinguishable. The second somatic hybrid was tetraploid (2n=4x=36), with one of the chromosomes bearing a putative structural alteration. Furthermore, aneusomaty and some mitotic abnormalities were also observed in this latter plant. Such irregularities are reported for the first time for citrus somatic hybrids, and their possible causes and implications are discussed. Received: 23 December 1996 / Revision received: 21 May 1997 / Accepted: 16 June 1997     

First report of chromosome numbers and karyotypes of two monotypic genera endemic to eastern Asia: Brachystemma (Caryophyllaceae) and Craspedolobium (Fabaceae)

The chromosome numbers and karyotypes of Brachystemma and Craspedolobium, two monotypic genera endemic to eastern Asia, are reported here for the first time. The somatic chromosome numbers are 2n=40 for Brachystemma calycinum and 2n=22 for Craspedolobium unijugum. A karyotype of 2n=2x=40=28m+12sm was found in B. calycinum and that of 2n=2x=22=12m+10sm in C. unijugum, both of them have a moderately symmetrical karyotype type 2B and small‐sized chromosomes. Brachystemma has a unique basic chromosome number in Alsinoideae, which may support its isolated taxonomic position. As do some morphological characters, the basic chromosome number x=11 suggests that Craspedolobium belongs in the Millettioid clade.     

Chromosomal instability in lemon grass,Cymbopogon flexuosus (Steudel) Wats

Somatic mitoses in C. flexuosus exhibit a significant degree of chromosomal instability leading to nearly 33% cells with chromosome elimination. A range of chromosome numbers between 20-8 (most common being 2n=20, the somatic number for this species) was encountered from root tip cells. The course of variation suggests a gradual elimination of somatic chromosomes. The larger chromosomes are less stable and are eliminated earlier. The variation in chromosome number in somatic cells within individual plants is possibly controlled by genetic factors, which result from weaker spindle operation and minute chromosomes.CIMAP Publication No. 571 (1984)     

栓皮栎核型及体胚发生的细胞学特性研究

采用常规制片方法对栓皮栎核型、体胚发生过程中胚性愈伤组织细胞染色体进行了分析。结果表明,栓皮栎体细胞染色体数目2n＝24,核型公式K(2n)＝2x=24=20m十4sm,属于“2B”型,染色体组总长18.55 μm。继代8个月的胚性愈伤组织细胞的染色体数目和结构相对稳定,其中二倍体细胞占 97.20%,四倍体细胞占1.87%,单倍体细胞占0.93%。未发现有非整倍体细胞和染色体形态结构变异。子叶期体胚胚轴亚表层起源的分生组织团中有些细胞核呈片状或椭圆形。个别成熟体胚中偶见有3核细胞。     

The origin ofMentha X gracilis (Lamiaceae). I. Chromosome numbers,Fertility, and three morphological characters

Employing nine clones ofMentha arvensis and four clones ofM. spicata, 932 F, hybrids were synthesized and compared to 20 clones ofM. x gracilis. Two clones ofM. x gracilis with 60 somatic chromosomes were matched to a selected F₁ hybrid. The other 18 clones ofM. x gracilis had somatic chromosome numbers of 60, 72, 84, and 96, and while these chromosome numbers appeared in the F₁ progeny, morphological matches correlated with their correct chromosome numbers were not synthesized. The range of pollen and seed fertility, as well as the inheritance of male-sterility, leaf pubescence, and crispness, indicates that no one character can be used to identifyM. x gracilis, but all characters can be explained fromM. arvensis x M. spicata.     

Somatic hybridization between birdsfoot trefoil (Lotus corniculatus L.) and L. conimbricensis Willd

Summary Somatic hybrid plants were produced by fusion of birdsfoot trefoil (Lotus corniculatus) cv Leo and L. conimbricensis Willd. protoplasts. Birdsfoot trefoil etiolated hypocotyl protoplasts were inactivated with iodoacetate to inhibit cell division prior to fusion with L. conimbricensis suspension culture protoplasts. L. conimbricensis protoplasts divided to form callus which did not regenerate plants. Thus, plant regeneration from protoplast-derived callus was used to tentatively identify somatic hybrid cell lines. Plants regenerated from three cell lines exhibited additive combinations of parental isozymes of phosphoglucomutase, and L. conimbricensis-specific esterases indicating that they were somatic hybrids. The somatic chromosome number of one somatic hybrid was 36. The other somatic hybrid exhibited variable chromosome numbers ranging from 33 to 40. These observations approximate the expected combination of the birdsfoot trefoil (2n=4x=24) and L. conimbricensis (2n=2x=12) genomes. Somatic hybrid flowers were less yellow than birdsfoot trefoil flowers and had purple keel tips, a trait inherited from the white flowered L. conimbricensis. Somatic hybrids also had inflorescence structure that was intermediate to the parents. Fifteen somatic hybrid plants regenerated from the three callus lines were male sterile. Successul fertilization in backcrosses with birdsfoot trefoil pollen has not yet been obtained suggesting that the hybrids are also female sterile. This is the first example of somatic hybridization between these two sexually incompatible Lotus species.Formerly USDA-ARS, St. Paul, Minn, USA     

Differential transmission of extra genome chromosomes in pentaploid blueberry

Summary Transmission of extra genome chromosomes by three Vaccinium ashei (2n=6x=72)/V. corymbosum (2n=4x=48) pentaploid hybrids backcrossed to the hexaploid species V. ashei was examined. Chromosome numbers were determined for 36 and 31 progeny representing 5x × 6x and 6x × 5x type crosses, respectively. Chromosome numbers ranged from hypopentaploid (2n=4x+11=59) to hexaploid with means of 2n=66.2 for 5x × 6x progeny and 2n=68.0 for 6x × 5x progeny, representing overall extra genome chromosome gains of 3.3% and 33.3%, respectively. Extra chromosome number distributions for both the 5x × 6x and x × 5x progeny deviated significantly from the theoretical distribution assuming random chromosome transmission and were also found to be heterogeneous. The 2n=5x+9=69 class predominated in 6x × 5x progeny, while a predominate class was lacking in the 5x × 6x progeny. Higher than expected frequencies of plants with chromosome numbers near the pentaploid and hexaploid levels were found in the 5x × 6x progeny, whereas the frequency was only greater at the hexaploid number in 6x × 5x progeny. Present and previous results (Vorsa et al. 1986) indicate that extra genome chromosome transmission in oddploids can be influenced by selection at both gametophytic (pollen) and post-zygotic stages. However, post-zygotic selection may involve two different mechanisms acting concurrently: 1) chromosome imbalance due to aneuploidy and/or 2) endosperm imbalance referring to maternal: paternal genome ratios deviating from 21. Such a mechanism could result in differential transmission rates of extra genome chromosomes in oddploids when crosses are made to differing ploidy levels, and to reciprocal differences as well.     

Genetic instability in somatic hybrids of Nicotiana tabacum and Nicotiana knightiana

Summary Somatic hybrids of Nicotiana knightiana (2n=2X=24) and an albino mutant of Nicotiana tabacum (2n=4X=48) were selected after polyethylene glycol induced protoplast fusion. Three lines were selected on the basis of the simultaneous expression of shoot inducibility and green pigmentation, traits originally separated in the parental species.The hybrid nature of the lines was confirmed by their characteristic isoenzyme patterns, the morphology of the regenerated plants, and by the appearance of heterochromatic blocks in the interphase nuclei.Chromosome numbers in the somatic hybrids varied greatly within individual plants. Variegation in leaf and flower colour and segregation for morphological traits in vegetatively multiplied plants are attributed to segregation of chromosomes in the somatic cells, a consequence of the numerical instability. Hybridity, caryotypic changes induced by tissue culture, and high chromosome numbers, are discussed as possible reasons for the observed genetic instability.     

Gametogenesis and Reproduction of Seven Species of Pratylenchus

Three bisexual Pratylenchus species, P. penetrans, P. vulnus and P. coffeae have n = 5, 6 and 7 chromosomes, respectively, and reproduce by cross-fertilization. The monosexual P. scribneri comprises two chromosomal and reproductive forms. One has n = 6 chromosomes and reproduces by meiotic parthenogenesis, the other has a somatic chromosome number of approximately 25 and reproduces by mitotic parthenogenesis. The monosexual species P. zeae, P. brachyurus and P. neglectus have somatic chromosome numbers of approximately 21 to 26, 30 to 32, and 20, respectively, and reproduce by mitotic parthenogenesis. All mitotic parthenogenetic forms probably are polyploid. The phyletic relationships of some species are discussed briefly.     

Chromosome relationships between Lolium and Festuca (Gramineae)

With a view to eclucidating chromosome relationships between Lolium perenne (Lp), L. multiflorum (Lm) and Festuca pratensis (Fp), chromosome pairing in different diploid (2n=14), auto-allotriploid (2n=3x=21), trispecific (2n=3x=21), amphidiploid (2n=4x=28) and auto-allohexaploid (2n=6x=42) hybrids between them was analysed. At all these levels of ploidy there was very good chiasmate pairing between the chromosomes of the three species and, on the whole, there was little evidence of preferential pairing of the chromosomes of a particular species in the triploid, tetraploid and hexaploid hybrids. A critical test for this also came from the synaptic ability of the chromosomes of the single genome with those of the duplicated genome in the auto-allotriploids which formed predominantly trivalents with 2, 3 or even 4 chiasmata. Moreover, the homology between the Lp and Lm chromosomes seems strong enough to pass the discrimination limits of the B-chromosomes which do not suppress homoeologous pairing in the Lp LmLm triploid and LpLm diploid hybrids. — The triploids having two genomes of a Lolium species and one of F. pratensis had some male and female fertility which suggested genetic compatibility of the parental chromosomes resulting, presumably, in compensation at the gametic level. Also, the occurrence of comparable chiasma frequencies in the auto-allotriploids and trispecific hybrids showed that they were not markedly affected whether two doses of one genome and one of the other or all the three different genomes from the three species were present. From the trend of chromosome pairing in all these hybrids it is concluded that there is little structural differentiation between the chromosomes of the three species, no effective isolation barrier to gene-flow between them, and that they are closely related phylogenetically, having possibly evolved from a common progenitor. Taxonomic revision of the two Lolium species is suggested.     

Chromosome evolution by robertsonian translocation in Gibasis (Commelinaceae)

The plant species Gibasis schiedeana (Kunth) D. R. Hunt sens. lat. contains two cytotypes viz. a self-sterile diploid with 2n=10 (x=5) and a selffertile cytological autotetraploid with 2n=16 (x=4). Single chromosome sets of these plants consist of 2 metacentrics +3 acrocentrics, and 3 metacentrics +1 acrocentric chromosomes respectively suggesting a Robertsonian relationship between them. Their artificial F₁ hybrids show the pairing of acrocentrics with metacentric arms confirming the supposed nature of the chromosome affinities. Both breeding systems and ploidy levels show that the direction of the change has been from x=5 to x=4 by a translocation of the Robertsonian type.     

Comparative karyomorphology and interrelationships ofSelaginella in Japan

Karyomorphological comparisons were made of 16 native and cultivated species ofSelaginella in Japan. The somatic chromosome numbers are 2n=16 inS. boninensis; 2n=18 inS. doederleinii, S. helvetica, S. limbata, S. lutchuensis, S. nipponica, S. selaginoides, S. tama-montana, andS. uncinata; 2n=20 inS. biformis, S. involvens, S. moellendorffii, S. remotifolia, andS. tamariscina; 2n=30 inS. rossii; and 2n=32 inS. heterostachys. The interphase nuclei of all species examined are uniformly assigned to the simple chromocenter type. The metaphase karyotype of 2n=16 (x=8) is 8 m (=median centromeric chromosomes)+8(st+t)(=subterminal and terminal). The group of the species having 2n=18 (x=9) is heterogeneous karyomorphologically: The karyotype ofS. nipponica is 2n=18=6 m+12(st+t),S. tama-montana 10 m+2 sm(=submedian)+6(st+t), andS. uncinata 6 m+7 sm+5(st+t). Although the remaining five species have the common karyotype 8 m+4 sm+6(st+t), the values of mean chromosome length are variable. Another group of the specles having 2n=20 (x=10) is homogeneous, since all species have the same karyotypes 8 m+4 sm+8(st+t) and have similar chromosome size. The karyotype of 2n=30 is 12 m+6 sm+12(st+t) and is suggested to be a triploid of x=10, and 2n=32=16m+16(st+t), a tetraploid of x=8. Thus, three kinds of basic chromosome numbers, x=8, 9, 10 are present in JapaneseSelaginella examined, and their karyomorphological relationships are discussed.     

A cytological study ofPelargonium sect.Eumorpha (Geraniaceae)

The chromosome numbers of seven species ofPelargonium sect.Eumorpha have been determined from material of known wild origin, and karyotypic comparisons have been made. Within the section there is variation in basic chromosome number (x = 4, 8, 9, 11), variation in chromosome size, and two species have polyploid races. The three species with chromosome numbers based on x = 11 have the smallest chromosomes (1.0–1.5 µm); chromosomes are larger (1.0–3.0 µm) in the other species.P. elongatum has the lowest chromosome number in the genus (2n = 8).P. alchemilloides is exceptional in that it has four cytotypes, 2n = 16, 18, 34 and 36, and the form with 2n = 36 has large chromosomes (2.0–5.0 µm). Evidence from a synthesized hybrid suggests thatP. alchemilloides with 2n = 16 may be of polyploid origin. The three species based on x = 11 appear to be more closely related to species from other sections ofPelargonium that have the same basic chromosome number and small chromosome size, rather than to other species of sect.Eumorpha.     

Oogenesis and the Chromosomes of the Parthenogenic Root-knot Nematode Meloidogyne incognita

220 populations of Meloidogyne incognita and related forms from 46 countries reproduced by mitotic parthenogenesis (apomixis). Determination of somatic chromosome numbers from oogonia and oocytes revealed the existence of a predominant, possibly triploid race A with 3n = 40 to 46 and a rare, diploid race B with 2n = 32 to 36 chromosomes. There is no correlation between cytological races and the four recognized host races of this species. The characteristic behavior of prophase I chromosomes of maturing oocytes, which results in a prolonged prophase stage, is a unifying feature of all forms of M. incognita and supports monophyletic evolution, distinct from that of other Meloidogyne species. Extensive chromosomal polymorphism detected among populations can be helpful in elucidating the cytological pathway of evolution of the species.