Closest Wild Relatives Research Articles

Origin Matters: Lessons from the Search for the Wild Ancestor of Maize

The wild ancestry of maize has long been a puzzle. Maize shows extraordinary phenotypic and genetic diversity with no obvious morphological similarity to any of its wild relatives. Beadle's teosinte hypothesis, which regards teosinte as the sole wild ancestor of maize, has become widely accepted as the most probable model of maize evolution based on taxonomic, genetic, and other types of evidence. Molecular studies have refined the teosinte hypothesis by identifying a particular form of teosinte, Zea mays ssp. parviglumis, as the direct ancestor of maize. Maize and teosinte therefore provide a typical case in which modem molecular genetic analyses, in the absence of obvious morphological similarity, have been critical for distinguishing the exact ancestor of a crop from other close wild relatives. Furthermore, a recent microsatellite-based study shows that all extant pre-Columbian maize landraces arose from Z. mays ssp. parviglumis roughly 9,000 years ago through a single domestication event in the central Balsas River drainage (southern Mexico). That model, showing that maize is a domesticated form of Z. mays ssp. parviglumis, provides a logical, practical framework for investigations of the genetic mechanisms that drove maize domestication and diversification. This points up the importance of knowing exact origins in studies that use crops and their wild relatives as models. An overview of the progress in genetic and evolutionary studies is presented herein to clarify the identity of the wild progenitor of maize. Implications of recent findings on the origin of maize diversity are discussed.

Molecular-genetic differentiation of the dairy yeast and its closest wild relatives

The currently accepted formal division of the species Kluyveromyces lactis into two taxonomic varieties, Kl. lactis var. lactis and Kl. lactis var. drosophilarum, is based arbitrarily on phenotypic and ecological characters. On the other hand, the genetic hybridisation analysis and molecular karyotyping of its synonyms allowed us [FEMS Yeast Res. 2 (2002) 39] to reinstate them in the genus Zygofabospora Kudriavzev emend G. Naumov (=Kluyveromyces Kurtzman et al., 2001) as the varieties Zf. lactis var. lactis, Zf. lactis var. krassilnikovii, Zf. lactis var. drosophilarum, Zf. lactis var. phaseolospora and Zf. lactis var. vanudenii. In the present work, we studied forty Kl. lactis strains of different geographic and ecological origins by means of restriction analysis of the PCR-amplified non-coding nrDNA regions encompassing the intergenic spacer 2 (IGS2) and the internal transcribed spacers (ITS1 and ITS2). The results confirmed the complex structure of Kl. lactis. Moreover, four additional genetic populations were identified: three in North America ('aquatic', 'pseudovanudenii' and 'new') and one in Far-East Asia ('oriental'). Comparative sequence analysis of the 5.8S-rRNA gene and the two internal transcribed spacers revealed that the populations 'aquatic' and 'oriental' formed distinct taxa which are phylogenetically separate from the five known populations. However, some discrepancies were observed between the restriction and sequencing data. Genetic hybridisation analysis needs to be done to further elucidate the genetic relationships between the populations of Kl. lactis.

The Genetics of Maize Evolution

Maize and its closest wild relatives, the teosintes, differ strikingly in the morphology of their female inflorescences or ears. Despite their divergent morphologies, several studies indicate that some varieties of teosinte are cytologically indistinguishable from maize and capable of forming fully fertile hybrids with maize. Molecular analyses identified one form of teosinte (Zea mays ssp. parviglumis) as the progenitor of maize. Analyses of the inheritance of the morphological traits that distinguish maize and teosinte indicates that they are under the control of multiple genes and exhibit quantitative inheritance. Nevertheless, these analyses have also identified a few loci of large effect that appear to represent key innovations during maize domestication. Remaining challenges are to identify additional major and minor effect genes, the polymorphisms within these genes that control the phenotypes, and how the combination of the individual and epistatic effects of these genes transformed teosinte into maize.

Slimy Leaves and Oily Seeds: Distribution and Use of Wild Relatives of Sesame in Africa

This is a cultural, ecological, economic, geographical and historical study of the close wild relatives of sesame in Africa. Medical, culinary, cosmetic and industrial use of each species is assembled along with ethnographic and linguistic data. Collectively, it presents a summary of the genetic resources of Sesamum. The relative importance of each species varies by location, however most of these taxa are used in strikingly similar ways by subsistence farmers. Comparison of usage by ethnic group reveals the social role these valuable leaf vegetables play in daily life, particularly during times of shortage and famine. Fieldwork provides firsthand data, supplementing herbarium specimens and the published literature about the distribution, uses and environmental adaptations of wild Sesamum species and their close relative, Ceratotheca sesamoides Endl.

Conserving biodiversity of soybean gene pool in the biotechnology era

AbstractCultivated soybean, Glycine max (L) Merrill, is a world's important food crop domesticated about 4000 years ago in China. It is a member of the genus Glycine in the legume family (Fabaceae). The genus Glycine includes about 20 annual and perennial species distributed primarily in Australia and Asia. The annual wild soybean, Glycine soja, is considered as the immediate ancestor of the cultivated soybean, with its diversification center in China, Korea, Japan and the Far East region of Russia. The weedy form, G. gracilis, is the interspecific hybrid and offspring between G. max and G. soja, indicating the close genetic relationships of the three species. The fast development of transgenic biotechnology and the extensive release of genetically modified (GM) soybean varieties into environment have caused a great biosafety concern of transgene escape and its ecologic consequences, particularly its impact on the origin and diversity center of the cultivated and wild soybeans. Therefore, safeguarding and maintenance of the world's heritage of soybean biodiversity under the circumstances of commercial production of GM soybeans has become a very important issue. This paper presents a general knowledge of the origin and diversification, taxonomic background and geographic distribution of soybeans, as well as the biosystematic and evolutionary relationships of species in the Glycine genus, in addition to the possible gene flow between the cultivated soybean and its closest wild relatives (G. soja and G. gracilis). It also considers how to conserve soybean biodiversity in its origin and diversity centers when GM soybean varieties are released into these areas.

The circumscription and concept of Hordeum (Poaceae) based on some leaf epidermal characteristics

The leaf epidermises of 15 taxa of Hordeum, Psathyrostachys, and Hordelymus were examined under the light microscope. It was found that these taxa are not identical in the lower epidermal characteristics. Their greatest difference is shown in the intercostal zones of the lower epidermis between the group constituted by the cultivated barley and its close wild relatives and the group constituted by the wild species of Hordeum and the taxa of Psathyrostachys and Hordelymus. The former has conspicuously elongated long-cells, large and usually 2-banded stomata, and has nearly no short-cells and prickle-hairs; whereas the latter has none or slightly elongated long-cells, relatively small and 2- to many-banded stomata, and the presence of short-cells and prickle-hairs. Moreover, the wild species of Hordeum, which belong to the latter group, differ from the taxa of Psathyrostachys and Hordelymus by the number of rows of long-cells in the intercostal zones and the quantity of short-cells. It was demonstrated that the wild species of Hordeum must be independent as Critesion, and the circumscription of Hordeum only includes the cultivated barley and its close wild relatives. This study therefore redefined the circumscription and concept of Hordeum.

Can transgenic rice cause ecological risks through transgene escape?*

Abstract Alien transgene escape from genetically engineered rice to non-transgenic varieties or close wild relatives (including weedy rice) may lead to unpredictable ecological risks. However, for transgene escape to occur three conditions need to be met: (i) spatially, transgenic rice and its non-transgenic counterparts or wild relatives should have sympatric distributions; (ii) temporally, the flowering time of transgenic rice and the non-transgenic varieties or wild relatives should overlap; and (iii) biologically, transgenic rice and its wild relative species should have such a sufficiently close relationship that their interspecific hybrids can have normal generative reproduction. This paper presents research data on the geographic distribution, flowering habits, interspecific hybridization, and gene flow of cultivated rice (Oryza sativa.) and its closely related wild relatives containing the AA genome. The objective is to estimate the possibility of transgene escape to non-transgenic rice varieties ...

Investigations of pod characters in the Vivieae

A study of the fruits of modern members of the Vicieae (vetch tribe) has been undertaken to seek morphological, micromorphological and anatomical criteria which may assist in the identification of the archaeological remains of pods and in particular ones that may be useful for the diagnosis of their wild or domesticated status. The study included wild and domesticated Pisum (peas), Lens (lentils) and Vicia (common vetch) and some of their wild relatives found in the Old World. The results show that the micromorphological features of the pod surface tend to be highly variable, and do not distinguish the taxa. Most importantly, the pods of less-developed domesticated taxa show no reduction in the number of fibrous layers in the pod wall compared with those of their closest wild relatives, and no morphological or anatomical evidence has been found to indicate the dehiscent or indehiscent status of a pod. This appears to challenge some of our accepted wisdom on the mechanics of legume dehiscence.

Epicuticular Wax Columns in CultivatedBrassicaSpecies and in their Close Wild Relatives

Three different types of epicuticular wax columns were found inBrassicaspecies with a chromosome number (n)=9: long columns (LC), short columns (SC) and netted columns (NC). LC were found inB. incanaandB. rupestris.SC were found inB. villosa, B. macrocarpa, B. cretica, B. hilarionisand also inB. montana. B. insulariscolumns were intermediate. NC waxes were found inB. oleraceaand its close alliesB. alboglabraandB. bourgeaui.Samples ofB. rapa (n=10)andB. nigra (n=8)examined did not show any wax columns but their amphidiploids withB. oleracea (B. napusandB. carinata,respectively) seemed to inherit the NC type of wax present inB. oleracea.

Sex differences in meiosis betweenVicia fabaL. and its close wild relatives

Comparison of chiasma frequency was made in male and female meiocytes of the widely cultivatedVicia fabaL. and its close wild allies in theVicia narbonensisspecies complex. Contrary to most of the earlier reports of higher chiasma frequency in female sex cells, a higher chiasma frequency was observed in male sex cells. This pattern is restricted to the species representing the Narbonensis complex, sinceVicia fabashows identical chiasma frequency in male and female sex cells. The genetic significance of these findings is that chiasma formation in the sex cells of the putative allies is governed and regulated by similar controlling systems of genes, but that ofV. fabaindicates a different kind of system.

Sex differences in meiosis between Vicia faba L. and its close wild relatives

Comparison of chiasma frequency was made in male and female meiocytes of the widely cultivated Vicia faba L. and its close wild allies in the Vwia narbonensis species complex. Contrary to most of the earlier reports of higher chiasma frequency in female sex cells, a higher chiasma frequency was observed in male sex cells. This pattern is restricted to the species representing the Narbonensis complex, since Vicia faba shows identical chiasma frequency in male and female sex cells. The genetic significance of these findings is that chiasma formation in the sex cells of the putative allies is governed and regulated by similar controlling systems of genes, but that of V. faba indicates a different kind of system.

The closest wild relatives of cassava (Manihot esculenta Crantz)

The origin of cassava has long eluded researchers. The botanical origin, the geographical origin, the area of domestication, all are disputed matters. The argument advanced here is that, once the wild ancestor is identified, speculation about the taxonomy and the geographical cradle of the root crop will narrow considerably, as a number of species and geographical areas will automatically become excluded from consideration in matters of classification, domestication and evolution. Current knowledge about the three subjects shows that discoveries on the botanical origin of manioc have progressed a great deal, discoveries on the geographical origin are in progress, and discoveries on the area where the beginning of cultivation happened are incipient. In this paper, five Brazilian Manihot species are suggested as the closest wild relatives of cassava. One of them (M. esculenta ssp. flabellifolia) is regarded as the wild progenitor of modern cultivars and thus part of the primary genepool of the root crop. Another species (M. pruinosa) is regarded as the nearest species to the GP1 of cassava and can hardly be separated from the wild strain M. esculenta ssp. flabellifolia on morphological grounds.

Isoenzyme diversity and phylogenetic affinities in Vicia subgenus Vicia (Fabaceae)

Isoenzyme composition of ten enzymes and variability of their genetically heterologous isoenzymes (heterozymes) encoded by 17 loci has been studied with the use of polyacrylamide gel electrophoresis in 21 vetch species of the type subgenus of the genus Vicia in comparison with V. pisiformis of the subgenus Vicilla. In total, 118 electromorphs (putative allozymes) of different frequency and variability pattern within and between species were recorded. Cladistic analysis of the allozyme data revealed in the subgenus two basic monophyletic groups with two monophyletic subclades in both. One subclade of the first group includes species related to sections Vicia, Sepium, Pseudolathyrus and Lathyroides. The second subclade of the first group consists of species of the section Peregrinae. The species of the section Narbonensis, which are considered to be closest wild relatives of the cultivated faba bean by morphological similarities, form a subclade in a second monophyletic group, with V. hybrida, V. pannonica, V. anatolica, and V. melanops of the section Hyperchusa as a sister subclade. Vicia hyrcanica and V. lutea of the same section are placed on the cladogram as basally paraphyletic in the second monophyletic group. Vicia faba is placed either as basally paraphyletic to both monophyletic groups or in the Peregrinae subclade, depending on the use of evolutionarily less variable isoenzymes alone or together with polymorphic ones in the data matrixes. The placement of cultivated V. faba and its morphologically closest wild relatives of the section Narbonensis in different monophyletic clades on the allozyme phylograms shows that they belong to different phylogenetic branches within the subgenus and indicates more remote relationship between them than previously assumed from morphological similarity. UPGMA phenograms of Manhattan distances characterizing the extent of allozymic divergence between species are presented.

Assessment of genome organization among diploid species (2n = 2x = 14) belonging to primary and tertiary gene pools of pearl millet using fluorescent in situ hybridization with rDNA probes

Two contrasting forms of Pennisetum belonging to the primary and tertiary gene pools were assessed for genomic organization using in situ hybridization with rDNA probes (18S-5.8S-25S and 5S) on metaphase and interphase cell nuclei. The primary gene pool is represented by diploid (2n = 2x = 14) cultivated pearl millet (Pennisetum glaucum) and its close wild relatives (Pennisetum violaceum and Pennisetum mollissimum). Pennisetum schweinfurthii (2n = 2x = 14) was taken as representative of the tertiary gene pool, owing to its diploid status and its similarity to the accessions of the primary gene pool in chromosome number. Using the 18S-5.8S-25S probe, we observed two sites of distribution in the four species but at different locations. Within the primary gene pool, signals were detected on the telomeric part of the short arm of chromosome pair VI and at the nucleolar organizing region (NOR) of the satellited chromosome pair (VII). Signals were observed at the NOR of the two satellited chromosome pairs (I and IV) of P. schweinfurthii. The 5S probe was detected at the telomeric part of the short arm of metacentric chromosome pair IV of the three species of the primary gene pool, while it occured in an intercalary position on the short arm of chromosome pair II of P. schweinfurthii. These results showed a chromosomal similarity of rDNA sequence locations within the primary gene pool and are in agreement with the high genetic identity between wild and cultivated forms of pearl millet previously revealed by allozyme studies. Implications of genomic organization for genetic resource enhancement are discussed. Key words : Pennisetum, in situ hybridization, rDNA probes, genomic organization.

Zea systematics: ribosomal ITS evidence.

Ribosomal internal transcribed spacer (ITS) sequences were used to evaluate the phylogenetics of Zea and Tripsacum. Maximum likelihood and polymorphism parsimony were used for phylogenetic reconstructions. Zea ITS nucleotide diversity was high compared to other plant species, but approximately equivalent to other maize loci. Coalescence of ITS alleles was rapid relative to other nuclear loci; however, there was still much diversity within populations. Zea and Tripsacum form a clade clearly differentiated from all other Poaceae. Four Zea ITS pseudogenes were identified by phylogenetic position and nucleotide composition. The phylogenetic position of Z. mays ssp. huehuetenangensis was clearly established as basal to the other Z. mays. The ITS phylogeny disfavored a Z. luxurians and Z. diploperennis clade, which conflicted with some previous studies. The introgression of Z. mays alleles into Z. perennis and Z. diploperennis was also established. The ITS data indicated a near contemporary divergence of domesticated maize and its two closest wild relatives.

The 5S rRNA gene units in ancestral two-rowed barley (Hordeum spontaneum C. Koch) and bulbous barley (H. bulbosum L.): sequence analysis and phylogenetic relationships with the 5S rDNA units of cultivated barley (H. vulgare L.).

5S rRNA genes from several accessions of Hordeum spontaneum and Hordeum bulbosum, wild relatives of cultivated barley, Hordeum vulgare, have been amplified by the polymerase chain reaction, cloned, and sequenced. Evaluation of aligned sequences along with principal coordinate analysis demonstrates that the two classes of 5S rDNA sequences found in cultivated barley, and subclasses (groups) of these sequences, can also be found in its closest wild relatives. The two classes of units, formerly categorized as containing short or long 5S rDNA repeats, are distinguishable by the presence or absence of a TAG repeating unit. Sequence comparisons of individual clones (units) isolated from different species have allowed us to confirm that orthology exists for several groups. This demonstration of orthologous groups suggests that the 5S rDNA sequence may be useful for further phylogenetic analysis in the genus Hordeum and possibly in the Triticeae.

Ribosomal DNA repeat unit polymorphism in 49 Vicia species

DNA restriction endonuclease fragment analysis was used to obtain new information on the genomic organization of Vicia ribosomal DNA (rDNA), more particularly among V. faba and its close relatives and the taxa within three (Narbonensis, Villosa, Sativa) species' complexes. Total genomic DNA of 90 accessions representing 49 Vicia species was restricted with 11 enzymes, and the restriction fragments were probed with three ribosomal clones. Twenty-eight repeat unit length classes were identified. The number of length classes (1-2) per accession did not correspond to the number of nucleolar organizing regions (NORs). The number of rRNA genes was independent of the 2C nuclear DNA amount present in the taxon. Each of the 90 accessions had 2 (rarely 1)-4 DraI sites. Those taxa with the same number of DraI sites generally could be distinguished from each other by different configurations. Probing of the DNA samples digested with tetranucleotide recognition restriction endonucleases emphasized differences between divergent spacer regions and enabled relative homologies between the coding regions to be established. Overall, rDNA restriction site variation among the species showed a good correlation with taxonomic classification. The rDNA analysis indicated evolutionary relatedness of the various taxa within the Narbonensis species complex. rDNA diversity within two other species complexes (Villosa, Sativa), on the other hand, was more extensive than expected. With few exceptions, data on the two complexes give evidence of taxon-specific divergences not seen with other approaches. The restriction site variability and repeat length heterogeneity in the rDNA repeat exhibited startling differences between V.faba and its close wild relatives included in the Narbonensis species complex. This analysis provides new evidence that none of the species within the complex can be considered to be putative allies of broad bean.

Chloroplast DNA diversity in Vicia faba and its close wild relatives: implications for reassessment

To obtain new information on phylogenetic relationships between wild and cultivated broad bean, restriction fragment length polymorphism (RFLP) analysis of chloroplast (cp) DNAs from Vicia faba and eight subspecies/species of its close wild relatives grouped together in the Narbonensis complex was carried out using 14 restriction endonucleases. The molecular sizes of the cpDNAs obtained were similar (122.6-123.4 kbp), indicating that they had all lost one of inverted repeats. Among the more than 300 sites surveyed, the three subspecies within V. narbonensis, which exhibit just as many types of karyotypes, were shown to have identical cp fragment patterns. Genetic distances between all of the pairs of species were calculated from RFLP data. The cpDNA diversity within the Narbonensis complex was found to be more extensive than expected, except for the genetic relationship between V. hyaeniscyamus and V. johannis in which a total of three mutations were detected among the 300 sites sampled, thereby showing their close relatedness. The cpDNA of V. faba vis-a-vis its wild relatives also exhibited startling differences, indicating a clear division of Vicia species into two distinct lineages. This analysis unambiguously provides new evidence that the wild species grouped in the complex did not contribute their plastomes to the evolution of V. faba, and hence none of the species can be considered to be putative allies of broad bean. The present study also demonstrates profound cpDNA diversity among closely related species that have lost one of inverted repeats.

Conservation of crop germplasm: an overview of the FAO/IBPGR regional programme for South West Asia

SynopsisThe International Board for Plant Genetic Resources (IBPGR) has paid particular emphasis to SW Asia in its endeavour to collect, conserve and promote utilisation of the world's plant germplasm. This is in view of the region's rich genetic diversity in many crop plants and their weedy/wild relatives, coupled with its alarming rate of genetic erosion. Action during the past decade has focused on collecting mainly cereal and grain legume crops and their closest wild relatives within the framework of a regional programme encompassing six countries. Gene banks were also set up in these member countries to handle a full range of operations including seed storage, characterisation/preliminary evaluation and documentation. In future, emphasis will be placed on ecogeographical surveys prior to mounting collecting missions and on more characterisation/preliminary evaluation work.

Species concepts and systematics of domesticated cereals

Cultivated cereals are domesticated grasses. Wild progenitors of domestic cereals are aggressive natural colonizers and often become weedy in man disturbed habitats. Hybridization between cultivated cereals and their close wild relatives gives rise to mimetic cereal weeds that often accompany the domestic species well beyond its natural range. Similar weeds may also evolve from abandoned cultivars as a result of mutations that restore their ability for natural seed dispersal. Cultivated complexes of domestic species are typically variable. Man selects and isolates phenotypes to suit his fancies, with the result that different phenotypes of a cereal are often grown for different uses in the same village, and adjacent villages often grow different phenotypes for similar uses. Conventional species concepts do not hold for domestic species. It is proposed that wild, weed and cultivated complexes of individual domestic species be recognized respectively as subspecies. Major discontinuities in variation within the weed or cultivated subspecies are then identified as races without formal taxonomic recognition.