Occurrence Of Polyploidy Research Articles

Complete chloroplast genomes of two mint species (Lamiaceae) from Al-Madinah, Saudi Arabia: phylogenetic and genomic comparative analyses

The genus Mentha encompasses mint species cultivated for their essential oils, which are formulated into a vast array of consumer products. However, the systematics of the genus Mentha is very complicated and still uncertain. This is largely because of the presence of frequent interspecific hybridization, variation in chromosome number, cytomixis, polymorphism in morphology and essential oil composition under different environmental conditions, colonial mutant propagation, as well as the occurrence of polyploidy, aneuploidy, and nothomorphs. Here, we present the plastome assemblies for a wilt-resistant Saudi Arabian accession of Mentha longifolia (L.) Huds and an alien hybrid Mentha × verticillata L. which are 152,078 bp and 152,026 bp in length, respectively, and exhibited large single-copy (LSC) and small single-copy (SSC) regions separated by a pair of inverted repeat regions. The chloroplast genome of M. longifolia has 133 annotated genes, including 88 protein-coding genes and 37 tRNAs while M. × verticillata has 133 annotated genes, including 87 protein-coding genes and 38 tRNAs. Both cp genomes have eight rRNA genes. Phylogenetic analysis using a total chloroplast genome DNA sequence of 17 species revealed that M. longifolia sequenced in this study did not form a sister relationship with M. longifolia from another study. This opens a window for further investigations.

Chromosome Pairing in Polyploid Grasses.

Polyploids are species in which three or more sets of chromosomes coexist. Polyploidy frequently occurs in plants and plays a major role in their evolution. Based on their origin, polyploid species can be divided into two groups: autopolyploids and allopolyploids. The autopolyploids arise by multiplication of the chromosome sets from a single species, whereas allopolyploids emerge from the hybridization between distinct species followed or preceded by whole genome duplication, leading to the combination of divergent genomes. Having a polyploid constitution offers some fitness advantages, which could become evolutionarily successful. Nevertheless, polyploid species must develop mechanism(s) that control proper segregation of genetic material during meiosis, and hence, genome stability. Otherwise, the coexistence of more than two copies of the same or similar chromosome sets may lead to multivalent formation during the first meiotic division and subsequent production of aneuploid gametes. In this review, we aim to discuss the pathways leading to the formation of polyploids, the occurrence of polyploidy in the grass family (Poaceae), and mechanisms controlling chromosome associations during meiosis, with special emphasis on wheat.

Cyanobacterial multi-copy chromosomes and their replication.

NGS: next-generation sequencing; Repli-seq: replication sequencing; BrdU: 5-bromo-2'-deoxyuridine; TK: thymidine kinase; GCSI: GC skew index; PET: photosynthetic electron transport; RET: respiration electron transport; Cyt b6f complex: cytochrome b6f complex; PQ: plastoquinone; PC: plastocyanin.

Dysploidy and polyploidy trigger strong variation of chromosome numbers in the prayer-plant family (Marantaceae)

Karyotype analyses in species of the family Marantaceae (550 species, 31 genera) were conducted to shed light on the reported strong variation of chromosome number and size and the occurrence of polyploidy. Special attention was paid to the alterations in basic chromosome numbers, karyotypes and ploidy levels. Taxon sampling covered the whole distribution area of Marantaceae in Africa, Asia and America. We applied mitotic chromosome counting using conventional rapid squash techniques in 43 accessions (39 species, 16 genera), evaluated literature records for 51 species and conducted karyotype analyses. Eleven different somatic chromosome numbers were found (2n = 20, 22, 24, 26, 28, 33, 44, 36, 52, 65, 72). Based on the presumed basic chromosome numbers of x = 9, 10, 11, 12, 13, 14, this may correspond to diploid, triploid, tetraploid, pentaploid and octoploid levels, respectively. Dysploid variation, polyploidy and, to a lesser extend, hybridization may be the main factors in chromosome number evolution of the family. Our results also point to a certain degree of association with species diversification and geographical patterns.

An inter-comparison study of three stomatal-proxy methods for CO2 reconstruction applied to early Jurassic Ginkgoales plants

The inverse relationship between concentrations of CO2 in the atmosphere (pCO2) and the stomatal index of vascular plant has been widely used to estimate ancient levels of atmospheric CO2. However, some atmospheric concentration of CO2 in the geological past (paleo-CO2) estimates show little congruence because they are derived using different correlative methods, or from different fossil plant species with different calibration approaches. Here we apply three methods, including (1) the empirical method of McElwain (1998), (2) the empirical method of Barclay and Wing (2016) and (3) the mechanistic method of Franks et al., (2014) to a single fossil Ginkgo species (Ginkgoites marginatus) to track and assess their consistency of pCO2 estimates for the Early Jurassic. By using an inter-comparison of three methods, a high degree of consistency in pCO2 estimates and trends has been observed in two empirical proxy methods. In addition, the mechanistic method and both the empirical methods also show generally good consistent paleo-CO2 estimates at the bed-level. To test the congruence of paleo-CO2 estimates, we also apply all three methods to one additional Ginkgoalean fossil species (Sphenobaiera huangii). All three methods show species-dependent uncertainty in paleo-CO2 estimates when applied to different Ginkgalean fossil species collected from the same fossiliferous bed. Moreover, considering the potential effect of guard cell size to the mechanistic method, the genome size of fossil and living Ginkgo taxa was analyzed based on the significant positive relationship between genome size and guard cell size. The result demonstrates that a likely occurrence of polyploidy in Sphenobaiera huangii may result in underestimated paleo-CO2 when applying mechanistic method due to an increase in the size of the stomatal complex.

Leaf micromorphology of 19 Mentha taxa

Mentha (mint) is a genus in the Lamiaceae with a worldwide distribution. It has a complex classification due to frequent hybridisation at the interspecific level, variation in basic chromosome number and the occurrence of polyploidy (diploid to nonaploid). Although there have been many studies of Mentha leaf micromorphology, usually only a few taxa were described. The aim of this study was to characterise the micromorphology of Mentha leaves. Nineteen Mentha taxa, covering all four sections of the genus, were grown under controlled conditions and adaxial and abaxial leaf surfaces were examined using stereo and scanning electron microscopes. This study included examination of the previously uninvestigated Australian species, M. australis and M. diemenica. The study revealed that average lamina length varied from 3 mm (M. requienii) to 34 mm (M. × niliaca) and leaves were sessile (M. spicata) to where petiole length was 50% of total leaf length (M. requienii). Peltate and capitate glandular trichomes were found on the adaxial and abaxial leaf surfaces of almost all taxa. Most taxa were hypostomatous. A few taxa had amphistomatous leaves which was interesting given that Mentha is a mesophytic genus naturally found in moist environments beside streambanks and lake shores. Average guard cell length varied from 14 µm (M. suaveolens) to 27 µm (M. × piperita f. citrata ‘Basil’) with larger guard cell length correlated with larger DNA content and chromosome number. Two species in section Pulegium (M. requienii and M. pulegium) had small laminas, relatively long petioles and high adaxial stomatal density which distinguished them from taxa in the other three sections. Larger DNA content in plants can be associated with larger cell size. Most studies of Mentha leaf micromorphology make no mention of ploidy. The present study indicates this should be considered when comparing relative cell size between species.

Genome size and ISSR markers for Mentha L. (Lamiaceae) genetic diversity assessment and species identification

The systematics of the Mentha genus is very complicated and still unclear. This is mainly due to the existence of variation in basic chromosome number, frequent interspecific hybridization, cytomixis, polymorphism in morphology and essential oil composition under different environmental conditions, colonial mutant propagation, as well as the occurrence of polyploidy, aneuploidy and nothomorphs. Morphological traits, chemical composition, and even caryological analysis failed in discrimination of Mentha species. Therefore, the aim of this study was to combine genome size estimation with ISSR markers for quick and precise species identification, determination the inter- and intraspecific variation within this genus, as well as description of relationships between genotypes. Genome size estimation revealed, that investigated Mentha species possessed very small and small genomes. Additionally, for 13 Mentha species, this is the first report on genome size. Within one species different values of genome size occurred, which indicated polyploidy and aneuploidy. The smallest genome (0.63 pg/2C) was detected in M. gattefossei, while the largest in M. × verticillata (4.15 pg/2C). Flow cytometric measurements of genome size allowed to distinguish some species and cytotypes, and thus it can be used as a first step in species identification. More precise and detailed characterisation were provided by ISSR markers. All the primers used in ISSR-PCR, revealed to be useful in species identification, while primers (GACA)4, (GTG)6T, (CTC)4RC, (GA)6CC enabled to distinguish M. aquatica, M. canadensis, M. longifolia, M. pulegium and M. spicata cytotypes, and primers (GACA)4, (GA)6CC and (GA)8YC to identify M. × gracilis and M. × piperita cultivars. The phylogenetic analysis revealed the existence of seven main clusters and two species (M. requienii and M. × smithiana) being not clustered to any of the created groups within the Mentha genus. This analysis mostly confirms the latest taxonomical classification of the Mentha genus, however some exceptions are discussed. The identification system of combined genome size estimation, and ISSR markers proved to be useful for species in Mentha genus.

Stability of DNA content and molecular cytogenetic markers in the genus Stylosanthes (Fabaceae)

Stylosanthes (Leguminosae) comprises about 50 species being some of them with great economic importance. Some species are widely used as forages, to recover degraded areas due to its adaptability to low fertility soils and nitrogen fixing capacity as well as a green fertilizer. The genus is distributed in tropical and subtropicals areas. Brazil is considered the larger diversity center, with great inter and intraspecific variation. Breeding studies have increased, however, the taxonomic situation of the group remains unsettled and controversial. The occurrence of polyploidy, hybrids and many additional synonyms reinforce the importance to add new information about the genus. Cytogenetic data are scarce, even considering as an important tool to give relevant information about the genome. Here we describe, for the first time, karyotypic aspects and the DNA content of diploid species (S. grandifolia, S. gracilis, S. hipocampoides, S. acuminata and four varieties of S. guianensis) by using molecular cytogenetic techniques (CMA/DAPI banding and in situ hybridization) and flow cytometry. Seeds germination was induced by temperature variation (18° to 40°C) and growth hormones (CEPA 0.1mM) in a germination chamber. Meristematic roots were used to slides preparation. Chromosomes were stained with CMA/DAPI for banding patterns analysis and ribosomal 5S, 45S rDNA sites were mapped by in situ hybridization technique. To estimate the DNA content, Pisum sativum were used as a reference standard. The chromosomal morphometry showed a symmetrical karyotype with few variations among the species. The number of CG rich regions ranged from 2 to 4. Regarding 5S and 45S rDNA, two sites were observed in most species, excepting in S. acuminata, in which four 45S markers were identified. DNA content estimation was about 2.50pg in all species. These new data constitutes an important contribution in the study of evolutionary history of the group, opening new possibilities for future comparisons among genomes of different Stylosanthes species and also being of great value for breeding programs of species with economic importance.

Occurrence of polyploidy in populations of Acacia dealbata in south-eastern Tasmania and cytotypic variation in reproductive traits

The frequency of polyploid trees in 10 populations of the predominantly diploid species Acacia dealbata subsp. dealbata Link in south-eastern Tasmania was determined using flow cytometry. At seven of the sites, all trees were diploid. At two sites, single triploid genets were found and, at a third, two tetraploids. Microsatellite markers were used to confirm that triploid trees distributed over an area of at least 930 m2 at the major study site were all ramets of a single genet. Three diploid clones were also confirmed at this site. The 16-grain polyads from the triploid genet were significantly larger than those from diploids, but only the diploid pollen showed any viability in vitro. At three months the green pods on diploids averaged 36 mm and contained four developing seeds per pod. Pods on the triploid were only 13 mm long, with no developing seeds. In spite of maturing pods, two of the diploids did not yield full seed, whereas two other diploids averaged only 0.1 seeds per pod. Seeds were not produced on triploid trees. The low reproductive output is discussed with reference to the breeding system and the impact of clonality on effective cross-pollination.

Ecological range shift in the polyploid members of the South American genus Fosterella (Bromeliaceae).

The distribution of polyploidy along a relatively steep Andean elevation and climatic gradient is studied using the genus Fosterella L.B. Sm. (Bromeliaceae) as a model system. Ecological differentiation of cytotypes and the link of polyploidy with historical biogeographic processes such as dispersal events and range shift are assessed. 4',6-Diamidino-2-phenylindole (DAPI) staining of nuclei and flow cytometry were used to estimate the ploidy levels of 159 plants from 22 species sampled throughout the distribution range of the genus. Ecological differentiation among ploidy levels was tested by comparing the sets of climatic variables. Ancestral chromosome number reconstruction was carried out on the basis of a previously generated phylogeographic framework. This study represents the first assessment of intrageneric, intraspecific and partially intrapopulational cytotype diversity in a genus of the Bromeliaceae family. In Fosterella , the occurrence of polyploidy was limited to the phylogenetically isolated penduliflora and rusbyi groups. Cytotypes were found to be ecologically differentiated, showing that polyploids preferentially occupy colder habitats with high annual temperature variability (seasonality). The combined effects of biogeographic history and adaptive processes are presumed to have shaped the current cytotype distribution in the genus. The results provide indirect evidence for both adaptive ecological and non-adaptive historical processes that jointly influenced the cytotype distribution in the predominantly Andean genus Fosterella (Bromeliaceae). The results also exemplify the role of polyploidy as an important driver of speciation in a topographically highly structured and thus climatically diverse landscape.

Clues to the evolution of genome size and chromosome number in Tabebuia alliance (Bignoniaceae)

The 82 genera recognized for Bignoniaceae are organized in eight major tribes, Jacarandeae, Tourrettieae, Tecomeae, Coleeae, Crescentiae, Oroxyleae, Catalpeae and Bignonieae. In addition, a monophyletic group, Crescentiina, including the Tabebuia alliance and the Paleotropical clade is recognized. The Tabebuia alliance, endemic to the Neotropics, includes c. 14 genera of trees and shrubs and is comprised of c. 147 species mainly of the genera Tabebuia and Handroanthus. We measured the nuclear DNA contents of 19 Bignoniaceae species to address genome size and chromosome number evolution of the Tabebuia alliance. Nuclear DNA content was estimated using flow cytometry and chromosome counts were performed using propidium iodide-stained metaphase cells. We also obtained data for three different Bignoniaceae species from the Royal Botanical Garden, Kew Plant DNA C-values database. We obtained the phylogenetic tree of analysed species from published data and used independent phylogenetic contrast to correlate chromosome number and 1C DNA content. An almost threefold range of variation in nuclear DNA content was observed among the 22 Bignoniaceae species that could only partially be explained by the occurrence of polyploidy. We found no significant correlation between chromosome number and DNA content among the analysed species. Our results suggest that both increases and decreases of genome size occurred in the evolution of the analysed Bignoniaceae Juss. species, with a large variation among Tabebuia alliance species.

Is post-polyploidization diploidization the key to the evolutionary success of angiosperms?

Advances in recent years have revolutionized our understanding of both the context and occurrence of polyploidy in plants. Molecular phylogenetics has vastly improved our understanding of plant relationships, enabling us to better understand trait and character evolution, including chromosome number changes. This, in turn, has allowed us to appreciate better the frequent occurrence and extent of polyploidy throughout the history of angiosperms, despite the occurrence of low chromosome numbers in some groups, such as in Arabidopsis (A. thaliana was the first plant genome to be sequenced and assembled). In tandem with an enhanced appreciation of phylogenetic relationships, the accumulation of genomic data has led to the conclusion that all angiosperms are palaeopolyploids, together with better estimates of the frequency and type of polyploidy in different angiosperm lineages. The focus therefore becomes when a lineage last underwent polyploidization, rather than simply whether a plant is ‘diploid’ or ‘polyploid’. This legacy of past polyploidization in plants is masked by large-scale genome reorganization involving repetitive DNA loss, chromosome rearrangements (including fusions and fissions) and complex patterns of gene loss, a set of processes that are collectively termed ‘diploidization’. We argue here that it is the diploidization process that is responsible for the ‘lag phase’ between polyploidization events and lineage diversification. If so, diploidization is important in determining chromosome structure and gene content, and has therefore made a significant contribution to the evolutionary success of flowering plants. © 2015 The Authors. Botanical Journal of the Linnean Society published by John Wiley & Sons Ltd on behalf of The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, ●●, ●●–●●.

Dynamics of sex expression and chromosome diversity in Cucurbitaceae: a story in the making.

The family Cucurbitaceae showcases a wide range of sexual phenotypes being variedly regulated by biological and environmental factors. In the present context, we have tried to assemble reports of cytogenetic investigations carried out in cucurbits accompanied by information on sex expression diversities and chromosomal or molecular basis of sex determination in dioecious (or other sexual types, if reported) taxa known so far. Most of the Cucurbitaceae tribes have mixed sexual phenotypes with varying range of chromosome numbers and hence, ancestral conditions become difficult to probe. Occurrence of polyploidy is rare in the family and has no influence on sexual traits. The sex determination mechanisms have been elucidated in some well-studied taxa like Bryonia,Coccinia and Cucumis showing interplay of genic, biochemical, developmental and sometimes chromosomal determinants. Substantial knowledge about genic and molecular sex differentiation has been obtained for genera like Momordica, Cucurbita and Trichosanthes. The detailed information on sex determination schemes, genomic sequences and molecular phylogenetic relationships facilitate further comprehensive investigations in the tribe Bryonieae. The discovery of organ identity genes and sex-specific sequences regulating sexual behaviour in Coccinia,Cucumis and Cucurbita opens up opportunities of relevant investigations to answer yet unaddressed questions pertaining to floral unisexuality, dioecy and chromosome evolution in the family. The present discussion brings the genera in light, previously recognized under subfamily Nhandiroboideae, where the study of chromosome cytology and sex determination mechanisms can simplify our understanding of sex expression pathways and its phylogenetic impacts.

Extensive variation in chromosome number and genome size in sexual and parthenogenetic species of the jumping-bristletail genus Machilis (Archaeognatha).

Parthenogenesis in animals is often associated with polyploidy and restriction to extreme habitats or recently deglaciated areas. It has been hypothesized that benefits conferred by asexual reproduction and polyploidy are essential for colonizing these habitats. However, while evolutionary routes to parthenogenesis are manifold, study systems including polyploids are scarce in arthropods. The jumping-bristletail genus Machilis (Insecta: Archaeognatha) includes both sexual and parthenogenetic species, and recently, the occurrence of polyploidy has been postulated. Here, we applied flow cytometry, karyotyping, and mitochondrial DNA sequencing to three sexual and five putatively parthenogenetic Eastern-Alpine Machilis species to investigate whether (1) parthenogenesis originated once or multiply and (2) whether parthenogenesis is strictly associated with polyploidy. The mitochondrial phylogeny revealed that parthenogenesis evolved at least five times independently among Eastern-Alpine representatives of this genus. One parthenogenetic species was exclusively triploid, while a second consisted of both diploid and triploid populations. The three other parthenogenetic species and all sexual species were diploid. Our results thus indicate that polyploidy can co-occur with parthenogenesis, but that it was not mandatory for the emergence of parthenogenesis in Machilis. Overall, we found a weak negative correlation of monoploid genome size (Cx) and chromosome base number (x), and this connection is stronger among parthenogenetic species alone. Likewise, monoploid genome size decreased with elevation, and we therefore hypothesize that genome downsizing could have been crucial for the persistence of alpine Machilis species. Finally, we discuss the evolutionary consequences of intraspecific chromosomal rearrangements and the presence of B chromosomes. In doing so, we highlight the potential of Alpine Machilis species for research on chromosomal and genome-size alterations during speciation.

Karyomorphological study and report of B chromosome in Allium griffithianum Boiss. from India

The chromosomal characteristics of Allium L. have intrigued scientists on account of variation in basic chromosome number (x) ranging from 8 to 11, occurrence of polyploidy and presence of B chromosomes. The present study provides karyotypic details Allium griffithianum and presence of B chromosome in the species, the being a first report. The root-tip mitosis in this species showed presence 16 chromosomes, but 30 % of cells also showed occurrence of an additional B chromosome. The chromosome size ranged from 8.45 μm to 18.46 μm. The B chromosome size ranged between 2.4 and 2.7 μm in the mitotic metaphase plates. The mean karyotype formula was deduced to be 4.5 M + 7.5 m + 1sm + 1st +2 m (SAT) + 1B.

Polyploidy-associated genome modifications during land plant evolution.

The occurrence of polyploidy in land plant evolution has led to an acceleration of genome modifications relative to other crown eukaryotes and is correlated with key innovations in plant evolution. Extensive genome resources provide for relating genomic changes to the origins of novel morphological and physiological features of plants. Ancestral gene contents for key nodes of the plant family tree are inferred. Pervasive polyploidy in angiosperms appears likely to be the major factor generating novel angiosperm genes and expanding some gene families. However, most gene families lose most duplicated copies in a quasi-neutral process, and a few families are actively selected for single-copy status. One of the great challenges of evolutionary genomics is to link genome modifications to speciation, diversification and the morphological and/or physiological innovations that collectively compose biodiversity. Rapid accumulation of genomic data and its ongoing investigation may greatly improve the resolution at which evolutionary approaches can contribute to the identification of specific genes responsible for particular innovations. The resulting, more 'particulate' understanding of plant evolution, may elevate to a new level fundamental knowledge of botanical diversity, including economically important traits in the crop plants that sustain humanity.

Phylogenetic relationships of Artemisia subg. Dracunculus (Asteraceae) based on ribosomal and chloroplast DNA sequences

AbstractMolecular‐phylogenetic analyses of a large sampling of Artemisia subg. Dracunculus were carried out under Bayesian and maximum parsimony criteria to circumscribe the subgenus and explore the relationships between the species in the core of the subgenus. The Dracunculus complex was resolved into two main clades: one core clade including most of the Eurasian representatives plus a few closely related North American endemic species, and a second, small clade including A. salsoloides and A. tanaitica. Segregation of the latter two species is proposed in order to keep the subgenus monophyletic. Within the core clade, the existence of different lineages such as the A. dracunculus or A. campestris complexes, as well as the relationships of Mausolea, Neopallasia and Turaniphytum, are scrutinized. Discordances between the molecular data and previous morphological taxonomic treatments are noted. The occurrence of polyploidy in the subgenus is explored using previously published and newly generated genome size data.

Chromosome number and ploidy level of some South American species of Schizachyrium (Poaceae, Andropogoneae)

Chromosome numbers are reported here for 53 accessions belonging to 13 taxa of the genus Schizachyrium. The chromosome counts for the following seven species are recorded here for the first time: S. bimucronatum (2n = 20), S. gracilipes (2n = 20), S. hatschbachii (2n = 20), S. lactiflorum (2n = 20), S. plumigerum (2n = 20), S. salzmannii (2n = 20; 2n = 40) and S. spicatum (2n = 20). Counts differing from those previously reported are given for two species: S. scabriflorum (2n = 20 and 80) and S. tenerum (2n = 40). Most of the analyzed species of this genus are diploids. The occurrence of polyploidy in S. glaziovii, S. lactiflorum, S. salzmanni, S. scabriflorum and S. tenerum is reported here for the first time. Data on chromosome numbers and ploidy levels are discussed in relation to the taxonomy and evolution of the genus.

Polyploidization and epigenetics

The occurrence of polyploidy, or whole genome duplication, can result in instantaneous speciation. Because new polyploids are immediately reproductively isolated from their non-polyploid congeners, polyploidization has played an important role in the diversification of flowering plants and some vertebrates. Newly formed polyploids must respond to this instantaneous genomic change, which resembles “genome shock” syndrome to survive and reproduce successfully. Epigenetic changes, which do not cause changes to the sequence of DNA, can significantly contribute to the survival of and ultimately to the evolutionary success of new polyploids. Epigenetic regulation, both transcriptional and post-transcriptional, entails changes in DNA methylation, gene status and/or nucleolus dominance. These changes provide effective and flexible ways for a new polyploid to respond quickly to the enormous change in genetic material, to survive and potentially reproduce. We examine and assess certain epigenetic phenomena and possible pathways that may facilitate the evolutionary success of polyploid organisms.

ON THE STATUS OF CHROMOSOMES OF THE DATE PALM (PHOENIX DACTYLIFERA L.)

The present article summarizes the status of the existing data on the issue of chromosome number and karyotype studies of the date palm, Phoenix dactylifera L. The literature on this subject is rather heterogeneous and confusing, and the number of chromosomes reported ranged from 2n=26 to 2n=36, in addition to the possible occurrence of polyploidy and aneuploidy. As early as 1910 Nemec examined young embryos of P. dactylifera and reported the presence of 2n=28 chromosomes. Beal (1937), however, observed 18 pairs of chromosomes (18 bivalents) as seen in M1 in the microsporocytes of 5 male cultivars of date palm; and 2n=36 chromosomes in root tips of 6 varieties of both male and female plants. Beal also observed in 2 other species of the genus Phoenix 1n=18 in P. canariensis and P. sylvastris; and 2n=36 chromosomes in 3 other species of the genus. Selbi (1988) in his analysis of the chromosome karyotypes of both male and female date palms, indicated an identical chromosome number for both; and he reported 2n=36. Loutfi (1989) in his study on tissue culture-derived date palm plants obtained from inflorescence culture, found that the plants produced were morphologically identical to plants produced via organogenesis, and the chromosome number for these plants were strictly diploid. Ibrahim et al. (1998) also reported 2n=36 in some cultivars of date palm. Surprisingly, however, a chromosome number of 2n=26 was observed in two Moroccan date palm cultivars in the in vitro generated plantlets (Loutfi, 1999). The establishment of a date palm genomic map is important; and cytogenetic studies to firmly establish the chromosome number, and to detect chromosomal aberrations; expansion of date palm Gene Bank and biodiversity management using molecular tools, also represent important goals. The application of in situ hybridization, fluorescent in situ hybridization (FISH), spectral karyotyping (SKY) and other techniques to identify the chromosomes and karyotype, and to detect chromosomal aberrations and clonal variations; and early detection of gender in seedlings resulting from seed germination, should also not be ruled out. Although Sijak-Yakovlov et al. (1996) have detected the presence of sex chromosomes carrying distinctive nucleolar heterochromatins, based on chromomycin staining, nevertheless, a rather simpler tool for early detection of gender in date palm is of great importance. As early as the 1980's we have recognized an early disjunction of one pair of the 18 bivalents in some male cultivars of date palm during microsporogenesis at early A1 of the first meiotic division (Al-Ani and Nawal Abdullah, 1987); and through personal communication (Al-Mayiah et al., 2009) counted 2n=36 in some date palm cultivars, and detected the presence of sex chromosomes. Furthermore, they have detected some polyploidy and aneuploidy during their cytological investigation. Finally, the date palm whose seeds stand tolerant and totipotent; and maintained its true-to-typeness over a period of more than 2000 years, deserves more effort from biologists and other scientists to solve some cytogenetical problems associated with this socio-economically important crop, the 'blessed tree'. It is suggested that some of these investigations may be a partial fulfillment of getting a higher degree at UAEU.