Evidence of the domestication history of flax (Linum usitatissimum L.) from genetic diversity of the sad2 locus

A phylogenetic analysis was conducted on 34 alleles of 2.5 kb sized stearoyl-ACP desaturase II (sad2), obtained from 30 accessions of cultivated and pale flax (Linum spp.), to elucidate the history of flax domestication. The analysis supports a single domestication origin for extant cultivated flax. The phylogenetic evidence indicates that flax was first domesticated for oil, rather than fibre. The genetic diversity of the sad2 locus in cultivated flax is low when compared to that of the pale flax assayed. An absolute archaeological date could be applied to the synonymous substitution rate of sad2 in cultivated flax, yielding a high estimate of 1.60–1.71×10⁻⁷ substitutions/site/year. The occurrence of nonsynonymous substitutions at conserved positions of the third exon in alleles from cultivated flax suggests that the locus may have been subjected to an artificial selection pressure. The elevated synonymous substitution rate is also compatible with a population expansion of flax since domestication, followed by a population decline in historic times. These findings provide new insight into flax domestication and are significant for the continuous exploration of the flax germplasm for utilization.     

From the cradle of agriculture a handful of lentils: History of domestication

Literature on lentil domestication is reviewed, particularly considering archeobotanical, phylogenetic, and molecular evidence. Lentils are one of the oldest crops cultivated and domesticated by man. Carbonized small lentil seeds have been found in several archaeological remains starting from the Neolithic. It is probable, however, that the most ancient remains refer to wild lentils; this is difficult to ascertain since seed size was probably selected after the establishment of a domesticated lentil. It is general opinion that cultivation occurred before domestication, but for how long is still an open question. It is now well accepted that the domestication of lentils was accomplished in the Near East, in an area called “the cradle of agriculture”. The genus Lens is very small, containing only 6 taxa. A wide range of morphological and molecular evidence supports the idea that the lentil wild progenitor is Lens culinaris ssp. orientalis. On the other hand, the most distantly related species within the genus appears to be L. nigricans, whose domestication was also attempted without success. The first characters involved in lentil domestication were pod dehiscence and seed dormancy. These traits are under a simple genetic control, and therefore mutants must have been fixed in a relatively short time. These and other morphological traits possibly involved in lentil domestication have been mapped in several linkage maps. However, generally these maps are not easily integrated since they are based on a limited number of markers. Newer maps, mainly built on different kinds of molecular markers, have been more recently produced. A consensus map is needed to fill the gap in lentil breeding and, at the same time, endow with deeper information on the genetics of lentil domestication, giving new insight into the origins of this crop, which present fragmented knowledge is unable.      

First report on the presence of fire blight resistance in linkage group 11 ofPyrus ussuriensis Maxim

Fire blight, caused by the gram-negative bacteriumErwinia amylovora (Burrill) Winslow et al., is a dangerous disease of pome fruits, including pear. A pear breeding program for fire blight resistance was initiated in 2003 at the Department of Pomology, Warsaw University of Life Sciences, Poland. Since several Asian species are considered to be potential sources of resistance to fire blight, the susceptiblePyrus communis ‘Doyenne du Comice’ was crossed with the resistantP. ussuriensis. The F₁ full-sib progeny composed of 155 seedlings was tested for susceptibility to fire blight by artificial shoot inoculation. A framework linkage map of both parents was constructed based on 48 AFLP and 32 SSR markers and covered a length of 595 cM and 680 cM in ‘Doyenne du Comice’ andP. ussuriensis, respectively. For the first time a putative QTL for fire blight resistance inP. ussuriensis linkage group 11 was identified. Another putative QTL in linkage group 4 of ‘Doyenne du Comice’ seems to indicate that sources of fire blight resistance can be identified also in the susceptible cultivars.     

The Horn of Africa as a centre of barley diversification and a potential domestication site

According to a widely accepted theory on barley domestication, wild barley (Hordeum vulgare ssp. spontaneum) from the Fertile Crescent is the progenitor of all cultivated barley (H. vulgare ssp. vulgare). To determine whether barley has undergone one or more domestication events, barley accessions from three continents have been studied (a) using 38 nuclear SSR (nuSSRs) markers, (b) using five chloroplast SSR (cpSSR) markers yielding 5 polymorphic loci and (c) by detecting the differences in a 468 bp fragment from the non-coding region of chloroplast DNA. A clear separation was found between Eritrean/Ethiopian barley and barley from West Asia and North Africa (WANA) as well as from Europe. The data from chloroplast DNA clearly indicate that the wild barley (H. vulgare ssp. spontaneum) as it is found today in the “Fertile Crescent” might not be the progenitor of the barley cultivated in Eritrea (and Ethiopia). Consequently, an independent domestication might have taken place at the Horn of Africa. Jihad Orabi and Gunter Backes have contributed equally to this work.     

Above-ground biomass and structure of pristine Siberian Scots pine forests as controlled by competition and fire

The study presents a data set of above-ground biomass (AGB), structure, spacing and fire regime, for 24 stands of pristine Siberian Scots pine (Pinus sylvestris) forests with lichens (n = 20) or Vaccinium/mosses (n = 4) as ground cover, along four chronosequences. The stands of the “lichen” site type (LT) were stratified into three chronosequences according to stand density and fire history. Allometric equations were established from 90 sample trees for stem, coarse branch, fine branch, twig and needle biomass. The LT stands exhibited a low but sustained biomass accumulation until a stand age of 383 years. AGB reached only 6–10 kg_dw m⁻² after 200 years depending on stand density and fire history compared to 20 kg_dw m⁻² in the “Vaccinium” type (VT) stands. Leaf area index (LAI) in the LT stands remained at 0.5–1.5 and crown cover was 30–60%, whereas LAI reached 2.5 and crown cover was >100% in the VT stands. Although nearest-neighbour analyses suggested the existence of density-dependent mortality, fire impact turned out to have a much stronger effect on density dynamics. Fire scar dating and calculation of mean and initial fire return intervals revealed that within the LT stands differences in structure and biomass were related to the severity of fire regimes, which in turn was related to the degree of landscape fragmentation by wetlands. Self-thinning analysis was used to define the local carrying capacity for biomass. A series of undisturbed LT stands was used to characterise the upper self-thinning boundary. Stands that had experienced a moderate fire regime were positioned well below the self-thinning boundary in a distinct fire-thinning band of reduced major axis regression slope −0.26. We discuss how this downward shift resulted from alternating phases of density reduction by fire and subsequent regrowth. We conclude that biomass in Siberian Scots pine forests is strongly influenced by fire and that climate change will affect ecosystem functions predominantly via changes in fire regimes. Received: 2 July 1998 / Accepted: 10 June 1999     

Seed bank dynamics of two obligate seeders, <Emphasis Type="Italic">Cistus monspeliensis</Emphasis> and <Emphasis Type="Italic">Rosmarinus officinalis</Emphasis>, in relation to time since fire

Many species in Mediterranean-type ecosystems regenerate after fire by seed germination from soil seed banks. Seed bank dynamics of two of those obligate seeders, Cistus monspeliensis and Rosmarinus officinalis, were investigated in relation to stand age since fire in southwestern Portugal. Soil seed density, annual seed input, annual seed losses through germination and seed persistence were compared between species at stands differing in age since fire (5, 10 and 35 years). Soil seed density and seed input increased over the first decade after fire and were lowest at 35-year-old stands for C. monspeliensis. In R. officinalis, few seeds were produced and found in the soil at early stages, and maximum seed input and soil seed density were attained at 35-year-old stands. Soil seed density was mostly driven by seed production in both species, which is largely dependent on plant traits and population dynamics related to fire. Overall, stand age since fire had a negligible effect on seed germination, seed persistence and viability. Ten to 39% of buried seeds were not recovered after 1 year, and viability of seeds recovered was 97–100% for C. monspeliensis and only 0–3% for R. officinalis. Variation in plant traits within the seeder syndrome was evidenced by this study. R. officinalis evidenced lower seed persistence, lower proportion of viable seed produced and lower density of viable soil seed than C. monspeliensis at any stage after fire. R. officinalis is expected to depend largely on previous year seed production for population replacement after fire.     

QTL mapping of fire blight resistance in apple

Fire blight caused by the bacterium Erwinia amylovora is a severe threat to apple and pear orchards worldwide. Apple varieties exhibit a wide range of relative susceptibility/tolerance to fire blight. Although, no monogenic resistance against fire blight has been identified yet, recent evidence indicates the existence of quantitative resistance. Potential sources of fire blight resistance include several wild Malus species and some apple cultivars. F1 progenies of ‘Fiesta’בDiscovery’ were inoculated with the Swiss strain Ea 610 and studied under controlled conditions to identify quantitative trait loci (QTLs) for fire blight resistance. Disease was evaluated at four time points after inoculation. Shoot lesion length and the area under disease progress curve (AUDPC) values were used for QTL analysis. One significant (LOD score of 7.5–8.1, p<0.001) QTL was identified on the linkage group 7 of ‘Fiesta’ (F7). The F7 QTL explained about 37.5–38.6% of the phenotypic variation.     

Succession after stand replacing disturbances by fire,wind throw,and insects in the dark Taiga of Central Siberia

The dark taiga of Siberia is a boreal vegetation dominated by Picea obovata, Abies sibirica, and Pinus sibirica during the late succession. This paper investigates the population and age structure of 18 stands representing different stages after fire, wind throw, and insect damage. To our knowledge, this is the first time that the forest dynamics of the Siberian dark taiga is described quantitatively in terms of succession, and age after disturbance, stand density, and basal area. The basis for the curve–linear age/diameter relation of trees is being analyzed. (1) After a stand-replacing fire Betula dominates (4,000 trees) for about 70 years. Although tree density of Betula decreases rapidly, basal area (BA) reached >30 m²/ha after 40 years. (2) After fire, Abies, Picea, and Pinus establish at the same time as Betula, but grow slower, continue to gain height and eventually replace Betula. Abies has the highest seedling number (about 1,000 trees/ha) and the highest mortality. Picea establishes with 100–400 trees/ha, it has less mortality, but reached the highest age (>350 years, DBH 51 cm). Picea is the most important indicator for successional age after disturbance. Pinus sibirica is an accompanying species. The widely distributed “mixed boreal forest” is a stage about 120 years after fire reaching a BA of >40 m²/ha. (3) Wind throw and insect damage occur in old conifer stands. Betula does not establish. Abies initially dominates (2,000–6,000 trees/ha), but Picea becomes dominant after 150–200 years since Abies is shorter lived. (4) Without disturbance the forest develops into a pure coniferous canopy (BA 40–50 m²/ha) with a self-regenerating density of 1,000 coniferous canopy trees/ha. There is no collapse of old-growth stands. The dark taiga may serve as an example in which a limited set to tree species may gain dominance under certain disturbance conditions without ever getting monotypic.     

T’ef (<Emphasis Type="Italic">Eragrostis tef</Emphasis>) in Ancient Agricultural Systems of Highland Ethiopia

T’ef ( Eragrostis tef ) in Ancient Agricultural Systems of Highland Ethiopia. T’ef (Eragrostis tef) has been cultivated in the Horn of Africa for at least 2,000 years. The earliest known agricultural systems in this region date to the Pre-Aksumite period (800–400 b.c.) and appear to have focused on Near Eastern crops, with indigenous African species increasing in importance during Aksumite times (400 b.c.–a.d. 700). While palaeoethnobotanical data are available from Pre-Aksumite and late Aksumite periods, macroscopic botanical remains from the site of Ona Nagast, northern Ethiopia, provide a first glimpse of agricultural systems dating to Proto-Aksumite (400–50 b.c.), Early to Classic (50 b.c.–a.d. 340), and Post-Aksumite (a.d. 700–900) times. Archaeological t’ef remains from Ona Nagast are examined in detail. Guidelines are developed for the identification of t’ef grains preserved on archaeological sites, with a focus on how to differentiate them from seeds of wild Eragrostis species. Charring experiments reveal that in some cases t’ef may not survive high temperatures tolerated by larger cereal grains, such as wheat and barley. The domestication history of t’ef appears to be different from some other cereals, a factor which may explain the preponderance of indeterminate Eragrostis seeds in archaeological samples. Selection of large seed size and intensified tillage were not key factors in t’ef domestication. Early cultivators were likely selecting for increased branching and higher percentage seed set under conditions of minimal tillage.     

Alternative fire resistance strategies in savanna trees

Bark properties (mainly thickness) are usually presented as the main explanation for tree survival in intense fires. Savanna fires are mild, frequent, and supposed to affect tree recruitment rather than adult survival: trunk profile and growth rate of young trees between two successive fires can also affect survival. These factors and fire severity were measured on a sample of 20 trees near the recruitment stage of two savanna species chosen for their contrasted fire resistance strategies (Crossopteryx febrifuga and Piliostigma thonningii). Crossopteryx has a higher intrinsic resistance to fire (bark properties) than Piliostigma: a 20-mm-diameter stem of Crossopteryx survives exposure to 650°C, while Piliostigma needs a diameter of at least 40 mm to survive. Crossopteryx has a thicker trunk than Piliostigma: for two trees of the same height, the basal diameter of Crossopteryx will be 1.6 times greater. Piliostigma grows 2.26 times faster than Crossopteryx between two successive fires. The two species have different fire resistance strategies: one relies on resistance of aboveground structures to fire, while the other relies on its ability to quickly re-build aboveground structures. Crossopteryx is able to recruit in almost any fire conditions while Piliostigma needs locally or temporarily milder fire conditions. In savannas, fire resistance is a complex property which cannot be assessed simply by measuring only one of its components, such as bark thickness. Bark properties, trunk profile and growth rate define strategies of fire resistance. Fire resistance may interact with competition: we suggest that differences in fire resistance strategies have important effects on the structure and dynamics of savanna ecosystems. Received: 16 August 1996 / Accepted: 4 January 1997     

Genetic diversity of globe artichoke landraces from Sicilian small-holdings: implications for evolution and domestication of the species

Globe artichoke (Cynara cardunculus var. scolymus) is native to the Mediterranean Basin, where it grows in close proximity with its ancestor wild cardoon (C. cardunculus var. sylvestris); its commercial production is mainly based on vegetatively propagated clones which guarantee high yields of marketable product (i.e. immature inflorescence or capitula). A collection of 24 landraces of globe artichoke was made from small-holdings in Sicily, which is assumed to be one of the possible centres of its domestication. These landraces have been cultivated for centuries by local farmers, mainly due to their culinary uniqueness. The collection was characterised for a combination of morphological traits and AFLP, gSSR and cpSSr markers. Molecular analyses included genotypes of wild cardoon collected from different sites in Sicily as well as accessions of the most widely grown Sicilian varietal types: the spiny ‘Spinoso di Palermo’ and the non-spiny ‘Violetto di Sicilia’. The landraces follow a gradient of ‘ennoblement’ towards either the domesticated spiny or the non-spiny types. ‘Cimiciusa di Mazzarino’ was an outlier, in that it resembled the cultivated forms with respect to its AFLP fingerprint, but was more closely related to the wild cardoon on the basis of SSR profile. This particular landrace presents an example of an intermediary form in the domestication process, although it could also have derived from introgression from sympatric wild cardoon, followed by farmer selection. The abundant genetic variation present demonstrates the key role of farmers’ practice in the maintenance of genetic diversity, which should be preserved because of its potential value for plant breeders.     

A suggestion for another statistical interpretation of the fundamental equations of the mathematical biophysics of the central nervous system

In a preceding paper an interpretation of the ε andj factors has been given in terms of an average effect of a large number of interneurons. In the present paper, a different interpretation is given in terms of the probability of a sufficient number of afferents to fire within the period of latent addition of the efferent. From this interpretation it follows that the old equations for ε andj are only first linear approximations to more complicated equations, the nature of which is suggested by this interpretation.     

Andropogon gayanus (Gamba Grass) Invasion Increases Fire-mediated Nitrogen Losses in the Tropical Savannas of Northern Australia

Invasive alien grasses can substantially alter fuel loads and fire regimes which could have significant consequences for fire-mediated nutrient losses. The effects of the alien grass Andropogon gayanus Kunth. (Gamba grass) on fire-mediated nutrient losses was evaluated in Australia’s tropical savannas. Losses of macronutrients during fire were determined by comparing the nutrient pools contained in the fine fuel before fire and in the ash after fire. Pre-fire grass nutrient pools were significantly higher in A. gayanus plots than in native grass plots for all nutrients measured (N, P, K, S, Ca, and Mg). Nutrient losses were substantially higher in A. gayanus plots, with 113% higher losses for N, 80% for P, 56% for K, 63 for S, 355% for Ca, and 345% for Mg. However, only losses of N and Mg varied significantly between grass types. A simplified savanna ecosystem nutrient budget estimated that A. gayanus fires led to the net N loss of 20 kg ha⁻¹ y⁻¹. This is a conservative estimate because total fuel loads were relatively low (7.85 t ha⁻¹) for A. gayanus invaded plots leading to a relatively moderate intensity fire (6,408 kW m⁻¹). Higher A. gayanus fuel loads and fire intensities could potentially lead to losses of up to 61.5 kg N ha⁻¹ from the grass fuel. Over the long term, this is likely to lead to depletion of soil nutrients, particularly N, in the already low-fertility tropical savanna soils.     

Animal evolution during domestication: the domesticated fox as a model

We review the evolution of domestic animals, emphasizing the effect of the earliest steps of domestication on its course. Using the first domesticated species, the dog (Canis familiaris), for illustration, we describe the evolutionary peculiarities during the historical domestication, such as the high level and wide range of diversity. We suggest that the process of earliest domestication via unconscious and later conscious selection of human‐defined behavioral traits may accelerate phenotypic variations. The review is based on the results of a long‐term experiment designed to reproduce early mammalian domestication in the silver fox (Vulpes vulpes) selected for tameability or amenability to domestication. We describe changes in behavior, morphology and physiology that appeared in the fox during its selection for tameability, which were similar to those observed in the domestic dog. Based on the data of the fox experiment and survey of relevant data, we discuss the developmental, genetic and possible molecular genetic mechanisms underlying these changes. We ascribe the causative role in evolutionary transformation of domestic animals to the selection for behavior and to the neurospecific regulatory genes it affects.     

Mimicry of lentil and the domestication of common vetch and grass pea

A hypothesis is proposed whereby weedy vetch (Vicia sativa L.) seed moved with seed of the cultivated lentil (Lens culinaris Medikus) as a tolerated weed during the spread of the lentil from the Fertile Crescent in the Near East to its current distribution. As a result, selection occurred in vetch weeds for a reduction in dormancy/hard-seededness, increased competitive ability and biomass, and phenological adaptation to new environments⇆redisposing the weed for domestication. The cropping of common vetch for forage in pure culture followed. Archaeological evidence of admixtures of grass pea (Lathyrus sativus L.) in Neolithic finds of lentil, pea (Pisum sativum L.) and bitter vetch (Vicia ervilia (L.) Wild.) suggests a similar process of selection in grass pea for a weedy habit from which domestication later occurred.     

Assessing Sustainability of Nontimber Forest Product Extractions: How Fire Affects Sustainability

Sustainable use of nontimber forest products (NTFPs) can be affected by levels of extractions as well as by other anthropogenic influences such as fire and grazing. We examined the effects of fire on the demography of Phyllanthus emblica, an important NTFP in the forests of Biligiri Rangan Hills, India. We then assessed demographic responses to the combined effects of fire and current fruit harvesting patterns. Fruits of Phyllanthus are commercially harvested by an indigenous forest dwelling people. Using matrix population models, we compared demographic indices across a chronosequence of time since last fire. Population growth rates (λ) ranged from 0.7692 to 1.1443 across the five times since last fire. λ was the lowest at times since last fire of 2 and 3 yr. Frequent fires increased time to maturity by altering growth and survival rates, thereby causing a demographic shift from growth to regressions or negative growth. Elasticity analysis revealed that stasis of adults makes the biggest contribution to λ. Simulations of periodic and stochastic fire regimes suggest that higher λ and population persistence can be achieved at fire-return intervals of ≥7 and ≥9 yr, respectively. These fire-return intervals became longer when the simulations included harvesting and fire. Extinction probabilities under the current fire regimes (every 2–3 yr) suggest that populations will decline to lower densities. Our findings provide critical information for developing guidelines for sustainable use and management of NTFPs in Biligiri Rangan Hills, and demonstrate the need to incorporate various human-generated physical regimes in assessing sustainability of NTFPs.     

Cultivation as slow evolutionary entanglement: comparative data on rate and sequence of domestication

Recent studies have suggested that domestication was a slower evolutionary process than was previously thought. We address this issue by quantifying rates of phenotypic change in crops undergoing domestication, including five crops from the Near East (Triticum monococcum, T. dicoccum, Hordeum vulgare, Pisum sativum, Lens culinaris) and six crops from other regions (Oryza sativa, Pennisetum glaucum, Vigna radiata, Cucumis melo, Helianthus annus, Iva annua). We calculate rates using the metrics of darwin units and haldane units, which have been used in evolutionary biology, and apply this to data on non-shattering cereal spikelets and seed size. Rates are calculated by considering data over a 4,000-year period from archaeological sites in the region of origin, although we discuss the likelihood that a shorter period of domestication (1,000–2,000) years may be more appropriate for some crops, such as pulses. We report broadly comparable rates of change across all the crops and traits considered, and find that these are close to the averages and median values reported in various evolutionary biological studies. Nevertheless, there is still variation in rates between domesticates, such as melon seeds increasing at twice the rate of cereals, and between traits, such as non-shattering evolving faster than grain size. Such comparisons underline the utility of a quantitative approach to domestication rates, and the need to develop larger datasets for comparisons between crops and across regions.     

Molecular domestication – more than a sporadic episode in evolution

Transposable elements are short but complex pieces of DNA or RNA containing a streamlined minimal-genome with the capacity for its selfish replication in a foreign genomic environment. Cis-regulatory sections within the elements orchestrate tempo and mode of TE expression. Proteins encoded by TEs mainly direct their own propagation within the genome by recruitment of host-encoded factors. On the other hand, TE-encoded proteins harbor a very attractive repertoire of functional abilities for a cell. These proteins mediate excision, replication and integration of defined DNA fragments. Furthermore, some of these proteins are able to manipulate important host factors by altering their original function. Thus, if the host genome succeeds in domesticating such TE-encoded proteins by taming their ‘anarchistic behavior,’ such an event can be considered as an important evolutionary innovation for its own benefit. In fact, the domestication of TE-derived cis-regulatory modules and protein coding sections took place repeatedly in the course of genome evolution. We will present prominent cases that impressively demonstrate the beneficial impact of TEs on host biology over evolutionary time. Furthermore, we will propose that molecular domestication might be considered as a resumption of the same evolutionary process that drove the transition from ‘primitive genomes’ to ‘modern’ ones at the early dawn of life, that is, the adaptive integration of a short piece of autonomous DNA into a complex regulatory network. This revised version was published online in July 2006 with corrections to the Cover Date.     

Geographical variation in population demography and life history traits of Tecate cypress (<Emphasis Type="Italic">Hesperocyparis forbesii</Emphasis>) suggests a fire regime gradient across the USA–Mexico border

Plant adaptations to fire often display spatial heterogeneity associated with geographical variation in fire regime. We examined whether populations of the Tecate cypress (Hesperocyparis forbesii Adams) in southern California and northern Baja, Mexico, exhibited spatial heterogeneity in cone serotiny, in other life history traits associated with fire-adaptation, and in population demographic structure, to assess a putative difference in fire regime across the USA–Mexico border. Demographic data, tree life history data, and tree ring series were used to compare the demographic structure and life history traits of three populations in southern California with three populations in northern Baja California. In Baja populations, a greater number of tree size classes were present (χ ² = 12,589; P < 0.05), cone serotiny was more facultative (Mann–Whitney U = 58, P < 0.05), and young adult trees had a higher reproductive output (Mann–Whitney U = 2.65, P < 0.05), suggesting that a difference in fire regime between southern California and northern Baja has existed long enough (ca 8000 years) to drive microevolutionary divergence between the two sets of populations, and is not solely the result of 20th century differences in fire management policies across the international border. The transitional area between the two different fire regimes does not appear to coincide with the border itself but may lie in a zone of ecological transition south of Ensenada. The range of phenotypic variation observed within the Tecate cypress metapopulation suggests this species has the capacity to adapt to future environmental changes.     

Genetic diversity and domestication history of African rice (<Emphasis Type="Italic">Oryza glaberrima</Emphasis>) as inferred from multiple gene sequences

Nucleotide variation in 14 unlinked nuclear genes was investigated in species-wide samples of African rice (Oryza glaberrima) and its wild progenitor (O. barthii). Average estimates of nucleotide diversity were extremely low in both species (θ _sil = 0.0007 for O. glaberrima; θ _sil = 0.0024 for O. barthii). About 70% less diversity was found in O. glaberrima than in its progenitor O. barthii. Coalescent simulation indicated that such dramatic reduction of nucleotide diversity in African rice could be explained mainly by a severe bottleneck during its domestication. The progenitor of African rice maintained also low genetic diversity, which may be attributed to small effective population size in O. barthii. Self-pollinating would be another factor leading to the unusually low diversity in both species. Genealogical analyses showed that all O. glaberrima accessions formed a strongly supported cluster with seven O. barthii individuals that were sampled exclusively from the proposed domestication centers of African rice. Population structure and principal component analyses found that the O. glaberrima group was homogeneous with no obvious genetic subdivision, in contrast to the heterogeneous O. barthii cluster. These findings support a single domestication origin of African rice in areas of the Upper Niger and Sahelian Rivers.