Chromosome number variation and polyploidy in the genus Echinocereus (Cactaceae)

Analyses of meiotic and mitotic chromosomes were undertaken in 16 taxa of Echinocereus belonging to 12 species and all seven taxonomic sections (sensu Taylor). Chromosome numbers are reported for the first time for eight taxa, and previously published chromosome counts are confirmed for the remaining eight. Both diploid and polyploid counts were obtained. Eleven (69%) of the taxa surveyed were diploid (2n = 22); the five varieties of E. engelmannii were polyploid (2n = 44). Overall, chromosome counts are available for 23 of the 48 proposed species (sensu Taylor). Of these, 19 (82%) are diploid, and four (18%) are polyploid. Polyploid cytotypes are most common in the primitive sections, e.g., sections Erecti and Triglochidiatus, which suggests that polyploidy is probably a derived condition in Echinocereus. Polyploid taxa range from medium to high latitudes and elevations relative to the overall distribution of the genus. Polyploidy, hybridization, and cryptic chromosomal rearrangements are thought to be the major causes of the speciation events of the genus.     

A chromosome-specific sequence common to the B genome of polyploid wheat and Aegilops searsii

A low-copy, non-coding chromosome-specific DNA sequence, isolated from common wheat, was physically mapped to the distal 19% region of the long arm of chromosome 3B (3BL) of common wheat. This sequence, designated WPG118, was then characterized by Southern hybridization, PCR amplification and sequence comparison using a large collection of polyploid wheats and diploid Triticum and Aegilops species. The data show that the sequence exists in all polyploid wheats containing the B genome and absent from those containing the G genome. At the diploid level, it exists only in Ae. searsii, a diploid species of section Sitopsis, and not in other diploids including Ae. speltoides, the closest extant relative to the donor of the B genome of polyploid wheat. This finding may support the hypothesis that the B-genome of polyploid wheat is of a polyphyletic origin, i.e. it is a recombined genome derived from two or more diploid Aegilops species.     

Plastid genomes reveal recurrent formation of allopolyploid Fragaria

Premise of the Study

Recurrent formation of polyploid taxa is a common observation in many plant groups. Haploid, cytoplasmic genomes like the plastid genome can be used to overcome the problem of homeologous genes and recombination in polyploid taxa. Fragaria (Rosaceae) contains several octo‐ and decaploid species. We use plastome sequences to infer the plastid ancestry of these taxa with special focus on the decaploid Fragaria cascadensis.

Methods

We used genome skimming of 96 polyploid Fragaria samples on a single Illumina HiSeq 3000 lane to obtain whole plastome sequences. These sequences were used for phylogenetic reconstructions and dating analyses. Ploidy of all samples was inferred with flow cytometry, and plastid inheritance was examined in a controlled cross of F. cascadensis.

Key Results

The plastid genome phylogeny shows that only the octoploid F. chiloensis is monophyletic, all other polyploid taxa were supported to be para‐ or polyphyletic. The decaploid Fragaria cascadensis has biparental plastid inheritance and four different plastid donors. Diversification of the F. cascadensis clades occurred in the last 230,000 years. The southern part of its distribution range harbors considerably higher genetic diversity, suggestive of a potential refugium.

Conclusions

Fragaria cascadensis had at least four independent origins from parents with different plastomes. In contrast, para‐ and polyphyletic taxa of the octoploid Fragaria species are best explained by incomplete lineage sorting and/or hybridization. Biogeographic patterns in F. cascadensis are probably a result of range shift during the last glacial maximum.     

Phylogenetic studies in Papaver section Oxytona: cytogenetics of the species and interspecific hybrids

Summary Chromosome behaviour at meiosis was studied in the F₁, F₂, and backcross generations, in the three species of Papaver section Oxytona, and in artificially induced autopolyploids of P. bracteatum. Close homology was found between the genome of P. bracteatum and that of the two polyploid species, P. orientale and P. pseudo-orientale, suggesting that the P. bracteatum genome is present in both polyploid species. A genetic mechanism controlling bivalent pairing in the polyploid species is suggested. Further study is needed for finding out the breeding potential of interspecific hybridization in section Oxytona.Contribution no. 1569-E, 1985 series from the Agricultural Research Organization, The Volcani Center, Bet Dagan 50 250. Israel     

长三角及邻近地区138种草本植物DNA C-值测定及其生物学意义

为了评估DNA C-值和基因组大小(genome size)在植物入侵性评估中的价值,应用流式细胞仪测定了长三角及邻近地区138种草本植物的核DNA含量,其中111种为首次报道。在此基础上比较了不同植物类群这两个值的差异,特别是入侵性与非入侵性植物这两个值的差异。结果表明:(1)138种草本植物平均DNA C-值为1.55 pg,最大者是最小者的37.17倍。127个类群平均基因组大小为1.08 pg,最大者是最小者的34.11倍;(2)统计了菊科(Asteraceae)、禾本科(Poaceae)、石竹科(Caryophyllaceae)、十字花科(Brassicaceae)、玄参科(Scrophulariaceae)、蓼科(Polygonaceae)、唇形科(Labiatae)和伞形科(Umbelliferae)的DNA C-值和基因组大小,发现禾本科植物的这两个值显著地大于其他7个科(P0.01)。单子叶的DNA C-值和基因组极显著地大于双子叶植物(P0.01);(3)杂草比非杂草具有更低的DNA C-值(P0.01)和基因组大小(P0.001);与DNA C-值相比,基因组大小在这两个类群之间的差异更为明显(P0.001),这种现象也体现在菊科植物中。随着基因组(X1)和DNA C-值(X2)由大变小,植物的杂草性(入侵性,Y)由弱变强,两者关系分别符合:Y=2.2334-1.2847 ln(X1)(r=0.4612,P0.01)和Y=2.4421-0.7234 ln(X2)(r=0.2522,P0.01),DNA C-值和基因组大小可以作为植物入侵性评估的一个指标;(4)多倍体杂草的基因组极明显地小于二倍体杂草(P0.01),前者为后者的0.63倍。在非杂草中,多倍体基因组比二倍体的略小,前者仅为后者的0.84倍,差异不显著(P0.5)。菊科植物中多倍体杂草的基因组也显著地小于二倍体杂草(P0.1)。基因组变小和多倍体化相结合,进一步增强了植物的入侵性。在多倍体植物入侵性评估中,基因组大小比DNA C-值更有价值。     

Phylogenetic relationships among Leymus and related diploid genera (Triticeae: Poaceae) based on chloroplast trnQ–rps16 sequences

To investigate the phylogenetic relationships among Leymus and related diploid genera, the genome donor of Leymus, and the evolutionary history of polyploid Leymus species, chloroplast trnQ–rps16 sequences were analyzed for 36 accessions of Leymus representing 25 species, together with 11 diploid taxa from six monogenomic genera. The phylogenetic analyses (Neighbor‐Joining and MJ network) supported three major clades (Ns, St and Xm). Sequence diversity and genealogical analysis suggested that 1) Leymus species from the same areas or neighboring geographic regions are closely related; 2) most of the Eurasian Leymus species are closely related to Psathyrostachys: P. juncea might serve as the Ns genome donor of polyploid Eurasian Leymus species; 3) the Xm genome may originate from ancestral lineages of Pseudoroegneria (St), Lophopyrum (E^e), Australopyrum (W) and Agropyron (P); 4) the trnQ–rps16 sequences of Leymus are evolutionarily distinct, and may clarify parental lineages and phylogenetic relationships in Leymus.     

Phylogenetic analysis of Carthamus species based on the nucleotide sequence of the nuclear SACPD gene and chloroplast trnL-trnF IGS region

To clarify the phylogenetic relationships of Carthamus species, we performed sequence analysis of the nuclear stearoyl acyl carrier protein desaturase (SACPD) gene and the chloroplast intergenic spacer region between leucine and phenylalanine tRNA genes (trnL-trnF IGS) in 13 taxa of Carthamus. The previous division of the genus into 4 taxonomic sections and allocation of particular genomes to various taxa on the basis of morphological, cytogenetic, and biosystematic analyses is not supported by the present study. Our results provide evidence of the occurrence of 5 nuclear genomes (A, B, C, X, and Y) and 3 cytoplasm types (A, B, and C) in the genus Carthamus. The cultivated safflower, C. tinctorius (2n = 24), has the B genome and type B cytoplasm. Both of these are not present in the polyploid taxa. This contradicts the earlier view that one of the genomes involved in the origin of the polyploid taxa of Carthamus is the B genome. Comparison with an outgroup species (Cirsium japonicum) indicated that C. arborescens is the most primitive species in the genus. Carthamus palaestinus is genetically closest to the cultivated safflower.     

Molecular phylogeny of the genus Triticum L

The genus Triticum L. includes the major cereal crop, common or bread wheat (hexaploid Triticum aestivum L.), and other important cultivated species. Here, we conducted a phylogenetic analysis of all known wheat species and the closely related Aegilops species. This analysis was based on chloroplast matK gene comparison along with trnL intron sequences of some species. Polyploid wheat species are successfully divided only into two groups – Emmer (sections Dicoccoides and Triticum) and Timopheevii (section Timopheevii). Results reveal strictly maternal plastid inheritance of synthetic wheat amphiploids included in the study. A concordance of chloroplast origin with the definite nuclear genomes of polyploid species that were inherited at the last hybridization events was found. Our analysis suggests that there were two ancestral representatives of Aegilops speltoides Tausch that participated in the speciation of polyploid wheats with B and G genome in their genome composition. However, G genome species are younger in evolution than ones with B genome. B genome-specific PCR primers were developed for amplification of Acc-1 gene.     

Transferable bread wheat EST-SSRs can be useful for phylogenetic studies among the Triticeae species

The genetic similarity between 150 accessions, representing 14 diploidand polyploid species of the Triticeae tribe, was investigated following the UPGMA clustering method. Seventy-three common wheat EST-derived SSR markers (EST-SSRs) that were demonstrated to be transferable across several wheat-related species were used. When diploid species only are concerned, all the accessions bearing the same genome were clustered together without ambiguity while the separation between the different sub-species of tetraploid as well as hexaploid wheats was less clear. Dendrograms reconstructed based on data of 16 EST-SSRs mapped on the A genome confirmed that Triticum aestivum and Triticum durum had closer relationships with Triticum urartu than with Triticum monococcum and Triticum boeoticum, supporting the evidence that T. urartu is the A-genome ancestor of polyploid wheats. Similarly, another tree reconstructed based on data of ten EST-SSRs mapped on the B genome showed that Aegilops speltoides had the closest relationship with T. aestivum and T. durum, suggesting that it was the main contributor of the B genome of polyploid wheats. All these results were expected and demonstrate thus that EST-SSR markers are powerful enough for phylogenetic analysis among the Triticeae tribe.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Molecular cytogenetics of <Emphasis Type="Italic">Bellevalia</Emphasis> (Hyacinthaceae) species occurring in Greece

Eight taxa of the genus Bellevalia (Hyacinthaceae) occurring in Greece, all with basic chromosome number x = 4, were cytologically studied using classical and molecular-cytogenetic techniques [fluorochrome banding with chromomycin A₃, fluorescence in situ hybridization (FISH) using probes of 18S–5.8S–26S and 5S ribosomal RNA genes]. Two of the examined taxa are endemic, i.e., B. brevipedicellata and B. sitiaca, both restricted to the Island of Kriti. B. hyacinthoides and B. edirnensis are Balkan endemics, and the four remaining taxa, i.e., B. dubia subsp. boissieri, B. trifoliata, B. romana, and B. ciliata, are more widely distributed Mediterranean elements. Genome size, estimated by flow cytometry, ranged from 18.59 to 53.38 pg. The results of fluorochrome banding and FISH are reported for the first time for the genus Bellevalia. Despite the morphological similarity of the chromosome complement, which is in accordance with the general “basic” Bellevalia karyotype formula, the karyotypes of the studied species are clearly distinguished by the number and position of GC-rich bands and ribosomal DNA (rDNA) loci, revealing clear interspecific differentiation among the taxa. Additionally, examination of the polyploid species B. sitiaca and B. edirnensis and populations of B. hyacinthoides and B. ciliata with different ploidy levels permits discussion about the origin of polyploids and the taxonomic relationships among the taxa.     

CHROMOSOME NUMBERS IN UMBELLIFERAE. III

Chromosome numbers are reported for 156 collections representing 100 taxa of Umbelliferae. Approximately two thirds of the collections are from Mexico, Central and South America and indicate a high percentage of polyploid species in certain genera found in this area. Chromosome numbers for plants belonging to 78 taxa are published here for the first time, previously published chromosome numbers are verified for 18 taxa and chromosome numbers differing from those previously published are reported in seven instances. No chromosome counts have been previously published for nine of the genera included here. Further aneuploidy and polyploidy were found in Eryngium, and Lomatium columbianum has been found to be a high polyploid with 2n = 14x. Every chromosome count is referable to a cited herbarium specimen.     

Phylogenetic inferences in Avena based on analysis of FL intron2 sequences

The development and application of molecular methods in oats has been relatively slow compared with other crops. Results from the previous analyses have left many questions concerning species evolutionary relationships unanswered, especially regarding the origins of the B and D genomes, which are only known to be present in polyploid oat species. To investigate the species and genome relationships in genus Avena, among 13 diploid (A and C genomes), we used the second intron of the nuclear gene FLORICAULA/LEAFY (FL int2) in seven tetraploid (AB and AC genomes), and five hexaploid (ACD genome) species. The Avena FL int2 is rather long, and high levels of variation in length and sequence composition were found. Evidence for more than one copy of the FL int2 sequence was obtained for both the A and C genome groups, and the degree of divergence of the A genome copies was greater than that observed within the C genome sequences. Phylogenetic analysis of the FL int2 sequences resulted in topologies that contained four major groups; these groups reemphasize the major genomic divergence between the A and C genomes, and the close relationship among the A, B, and D genomes. However, the D genome in hexaploids more likely originated from a C genome diploid rather than the generally believed A genome, and the C genome diploid A. clauda may have played an important role in the origination of both the C and D genome in polyploids.     

New chromosome counts and evidence of polyploidy in Haageocereus and related genera in tribe Trichocereeae and other tribes of Cactaceae

Chromosome numbers for a total of 54 individuals representing 13 genera and 40 species of Cactaceae, mostly in tribe Trichocereeae, are reported. Five additional taxa examined belong to subfamily Opuntioideae and other tribes of Cactoideae (Browningieae, Pachycereeae, Notocacteae, and Cereeae). Among Trichocereeae, counts for 35 taxa in eight genera are reported, with half of these (17 species) for the genus Haageocereus. These are the first chromosome numbers reported for 36 of the 40 taxa examined, as well as the first counts for the genus Haageocereus. Both diploid and polyploid counts were obtained. Twenty nine species were diploid with 2n=2x=22. Polyploid counts were obtained from the genera Espostoa, Cleistocactus, Haageocereus, and Weberbauerocereus; we detected one triploid (2n=3x=33), nine tetraploids (2n=4x=44), one hexaploid (2n=6x=66), and three octoploids (2n=8x=88). In two cases, different counts were recorded for different individuals of the same species (Espostoa lanata, with 2n=22, 44, and 66; and Weberbauerocereus rauhii, with 2n=44 and 88). These are the first reported polyploid counts for Haageocereus, Cleistocactus, and Espostoa. Our counts support the hypothesis that polyploidy and hybridization have played prominent roles in the evolution of Haageocereus, Weberbauerocereus, and other Trichocereeae.     

CHLOROPLAST DNA EVIDENCE FOR GENOME DIFFERENTIATION IN WILD POTATOES (SOLANUM SECT. PETOTA: SOLANACEAE)

Chloroplast DNA restriction site analysis has been used to test Hawkes's phylogenetic interpretations of the genomic data in Solanum sect. Petota. Hawkes hypothesized a diploid (2n = 24) origin of the tuber-bearing members of this group (subsection Potatoe) in Mexico and Central America (as a B genome) with later migrations and evolution to an A genome in South America, later followed by a return migration of the A genome to Mexico and Central America with A × B hybridizations and polyploidizations to produce ser. Longipedicellata (4x) and Demissa (6x). Our results provide partial support for this hypothesis by demonstrating the paraphyletic and primitive nature of the B genome species group, and the monophyletic and derived nature of all A genome and A × B genome species, including S. verrucosum, a hypothesized A genome progenitor of ser. Demissa. Thus, the Mexican and Central American polyploid species must have obtained their cytoplasm from the A genome. However, our results question the Stellata/Rotata hypothesis of Hawkes and the taxonomic placement of S. chomatophilum in ser. Conicibaccata.     

CHROMOSOME NUMBERS IN THE LEGUMINOSAE. III. SPECIES OF THE SOUTHWESTERN UNITED STATES AND MEXICO

Turner, B. L., and Olin S. Fearing. (U. Texas, Austin.) Chromosome numbers in the Leguminosae. III. Species of the Southwestern United States and Mexico. Amer. Jour. Bot. 47(7) : 603–608. Illus. 1960.—Chromosome counts for 43 species of the Leguminosae from the southwestern United States and Mexico have been reported. These include first reports for 42 taxa of which 16 are for the subfamily Mimosoideae. Olneya tesota (2n = 18) is the only new generic count listed. Chromosome reports of particular significance include a single polyploid count for a North American species of Acacia, as well as diploid and tetraploid counts for closely related taxa in this genus. Four species of the genus Schrankia were found to be diploid with In = 26, indicating a base of x = 13 instead of the x = 8 reported by some previous workers. Leucaena pulverulenta was found to have a diploid count of 2n = 56 indicating a base of x = 14.     

Investigations on the artificial synthesis of amphidiploids of Brassica tournefortii Gouan with the other elementary species of Brassica. I. Genomic relationships

With the object of studying the genomic relationships of Brassica tournefortii Gouan with the other elementary species of Brassica viz. B. campestris (2n=20, A genome), B. oleracea (2n=18, C genome) and B. nigra (2n=16, B genome), it has been hybridized with them. The percentage of F₁ hybrids formed, their morphology and meiotic behaviour have been described. Based upon crossability relationships and meiotic pairing in the F₁ hybrids, it is inferred that the D genome of B. tournefortii is more closely related to the A genome than to the B and C genomes. It may have been derived from the A genome which likewise shows a strong genetic isolation from B and C. The species has developed a strong genetic barrier in the course of its evolution and shows little crossability, high hybrid sterility and no gene flow with any of the other elementary species. The fact that it has not formed any natural amphidiploids with the elementary species which otherwise are formed in all combinations, is more evidence that it originated more recently than the A genome. It is presumed that B. tournefortii, being more distantly related to B. nigra than to other elementary species, may form stable artificial aphid resistant amphidiploids with the former.     

Electrophoretic survey of seedling esterases in wheats in relation to their phylogeny

Summary Evolutionary and ontogenetic variation of six seedling esterases of independent genetic control is studied in polyploid wheats and their diploid relatives by means of polyacrylamide gel electrophoresis. Four of them are shown to be controlled by homoeoallelic genes in chromosomes of third, sixth and seventh homoeologous groups.The isoesterase electrophoretic data are considered supporting a monophyletic origin of both the primitive tetraploid and the primitive hexaploid wheat from which contemporary taxa of polyploid wheats have emerged polyphyletically and polytopically through recurrent introgressive hybridization and accumulation of mutations. Ancestral diploids belonging or closely related to Triticum boeoticum, T. urartu, Aegilops speltoides and Ae. tauschii ssp. strangulata are genetically the most suitable genome donors of polyploid wheats. Diploids of the Emarginata subsection of the section Sitopsis, Aegilops longissima s.str., Ae. sharonensis, Ae. searsii and Ae. bicornis, are unsuitable for the role of the wheat B genome donors, being all fixed for the esterase B and D electromorphs different from those of tetraploid wheats.     

Phylogeny and molecular evolution of the DMC1 gene within the StH genome species in Triticeae (Poaceae)

To estimate the phylogeny and molecular evolution of a single-copy nuclear disrupted meiotic cDNA (DMC1) gene within the StH genome species, two DMC1 homoeologous sequences were isolated from nearly all the sampled StH genome species and were analyzed with those from seven diploid taxa representing the St and H genomes in Triticeae. Sequence diversity patterns and genealogical analysis suggested that (1) there is a close relationship among North American StH genome species; (2) the DMC1 gene sequences of the StH genome species from North America and Eurasia are evolutionarily distinct; (3) the StH genome polyploids have higher levels of sequence diversity in the St genome homoeolog than the H genome homoeolog; (4) the DMC1 sequence may evolve faster in the polyploid species than in the diploids; (5) high dN and dN/dS values in the St genome within polyploid species could be caused by low selective constraints or AT-biased mutation pressure. Our result provides some insight on evolutionary dynamics of duplicate DMC1 gene, the polyploidization events and phylogeny of the StH genome species.     

New 18S·26S ribosomal RNA gene loci: chromosomal landmarks for the evolution of polyploid wheats

Three new 18S·26S rRNA gene loci were identified in common wheat by sequential N-banding and in situ hybridization (ISH) analysis. Locus Nor-A7 is located at the terminal area of the long arm of 5A in both diploid and polyploid wheats. Locus Nor-B6 is located in N-band 1BL2.5 of the long arm of chromosome 1B in Triticum turgidum and Triticum aestivum. ISH sites, similar to Nor-B6, were also detected on the long arms of chromosomes 1G in Triticum timopheevii and 1S in Aegilops speltoides, but their locations on the chromosomes were different from that of Nor-B6, indicating possible chromosome rearrangements in 1GL and 1BL during evolution. The third new locus, Nor-D8, was only found on the short arm of chromosome 3D in the common wheat Wichita. The loss of rRNA gene locus Nor-A3 and gain of repetitive DNA sequence pSc119 on the terminal part of 5AS suggest a structural modification of 5AS. Comparative studies of the location of the 18S·26S rRNA gene loci in polyploid wheats and putative A and B (G) genome progenitor species support the idea that: (1) Triticum monococcum subsp. urartu is the donor of both the A and A^t genome of polyploid wheats. (2) Ae. speltoides is closer to the B and G genome of polyploid wheats than Aegilops longissima and is the most probable progenitor of these two genomes.     

CYTOLOGICAL AND INTERFERTILITY RELATIONSHIPS OF ARACHIS SECTION ARACHIS

Twenty-nine recently introduced diploid (2n = 2x = 20) accessions of section Arachis plus an A. correntina (Burk) Krap. et Greg. nom. nud. control were hybridized to the diploid A-genome species A. duranensis Krap. et Greg. nom. nud. (ace. 7988), the diploid B-genome species A. batizocoi Krap. et Greg. (acc. 9484), and with two subspecies of the A-B genome (2n = 4x = 40) A. hypogaea cultivars NC 4 and Argentine. Most attempted crosses were successful and the resulting plants were vigorous. However, A. batizocoi × accession 30008 hybrids died as seedlings and A. batizocoi × accession 30017 produced only dwarf plants. The 710 diploid F₁s from A. batizocoi were generally sterile, while those from A. duranensis had fertility ranges from 5% to 84%. Meiotic chromosome relationships in diploid crosses were cytologically evaluated in 185 plants plus tester accessions. Most taxa in section Arachis have an A genome, only A. batizocoi accessions have a B genome, a D genome is represented by accessions 30091 and 30099, and two other genomic groups, represented by accessions 30011 and 30033, may be present in the section. Most cytological differentiation was found among species originally collected in southern and eastern Bolivia. On the other hand, species collected at the extremes of the distribution of section Arachis species (northern Argentina to north-central Brazil) were cytologically very similar. Evidence is presented for speciation in Arachis being associated with both genetic differentiation and with translocated chromosomes. All taxa in the section except the D-genome species are believed to be cross-compatible with A. hypogaea, so germplasm introgression from most Arachis species should be possible.