Comparative analysis of QTLs affecting domestication traits between two domesticated x wild pearl millet ( Pennisetum glaucum L., Poaceae) crosses

Comparative mapping of Quantitative trait loci (QTLs) involved in domestication of adaptative syndrome traits of pearl millet was realized at the intra-specific level using two F(2) populations derived from domesticated ( Pennisetum glaucum ssp. glaucum) x wild ( Pennisetum glaucum ssp. monodii) crosses. The two domesticated parents analyzed differ in their geographical origins, agronomic characteristics and life cycles. In both populations, two regions of the genome were identified on linkage groups 6 and 7, that controlled most of the key morphological differences. The importance of these two linkage groups reveals their central role both in the developmental control of spikelet structure and in the domestication process of this crop. In contrast, QTLs involved in traits that are components of yield and measure differences in resource allocation (such as the shape of the spike, the number of spikes per plant and plant height) show a low level of correspondence among our two crosses. The results of the comparative mapping between cereals, although preliminary, reveal that genes involved in seed-shattering could correspond in maize, rice and sorghum. The evolutionary significance of our results, and especially the relationships between genome organization and cereal domestication, are discussed. The potential use of these results in pearl millet genetic-resources enhancement are presented.     

Identification of genetic factors controlling domestication-related traits of rice using an F2 population of a cross between Oryza sativa and O. rufipogon

 Domesticated rice differs from the wild progenitor in large arrays of morphological and physiological traits. The present study was conducted to identify the genetic factors controlling the differences between cultivated rice and its wild progenitor, with the intention to assess the genetic basis of the changes associated with the processes of rice domestication. A total of 19 traits, including seven qualitative and 12 quantitative traits, that are related to domestication were scored in an F₂ population from a cross between a variety of the Asian cultivated rice (Oryza sativa) and an accession of the common wild rice (O. rufipogon). Loci controlling the inheritance of these traits were determined by making use of a molecular linkage map consisting of 348 molecular-marker loci (313 RFLPs, 12 SSRs and 23 AFLPs) based on this F₂ population. All seven qualitative traits were each controlled by a single Mendelian locus. Analysis of the 12 quantitative traits resolved a total of 44 putative QTLs with an average of 3.7 QTLs per trait. The amount of variation explained by individual QTLs ranged from a low of 6.9% to a high of 59.8%, and many of the QTLs accounted for more than 20% of the variation. Thus, genes of both major and minor effect were involved in the differences between wild and cultivated rice. The results also showed that most of the genetic factors (qualitative or QTLs) controlling the domestication-related traits were concentrated in a few chromosomal blocks. Such a clustered distribution of the genes may provide explanations for the genetic basis of the “domestication syndrome” observed in evolutionary studies and also for the “linkage drag” that occurs in many breeding programs. The information on the genetic basis of some desirable traits possessed by the wild parent may also be useful for facilitating the utilization of these traits in rice-breeding programs. Received: 1 June 1998 / Accepted: 28 July 1998     

Inference of domestication history and differentiation between early‐ and late‐flowering varieties in pearl millet

Pearl millet (Pennisetum glaucum) is a staple crop in Sahelian Africa. Farmers usually grow varieties with different cycle lengths and complementary functions in Sahelian agrosystems. Both the level of genetic differentiation of these varieties and the domestication history of pearl millet have been poorly studied. We investigated the neutral genetic diversity and population genetic structure of early‐ and late‐flowering domesticated and wild pearl millet populations using 18 microsatellite loci and 8 nucleotide sequences. Strikingly, early‐ and late‐flowering domesticated varieties were not differentiated over their whole distribution area, despite a clear difference in their isolation‐by‐distance pattern. Conversely, our data brought evidence for two well‐differentiated genetic pools in wild pearl millet, allowing us to test scenarios with different numbers and origins of domestication using approximate Bayesian computation (ABC). The ABC analysis showed the likely existence of asymmetric migration between wild and domesticated populations. The model choice procedure indicated that a single domestication from the eastern wild populations was the more likely scenario to explain the polymorphism patterns observed in cultivated pearl millet.     

A intervarietal genetic map and QTL analysis for yield traits in wheat

A new genetic linkage map was constructed based on recombinant inbred lines (RILs) derived from the cross between the Chinese winter wheat (Triticum aestivum L.) varieties, Chuang 35050 and Shannong 483 (ChSh). The map included 381 loci on all the wheat chromosomes, which were composed of 167 SSR, 94 EST-SSR, 76 ISSR, 26 SRAP, 15 TRAP, and 3 Glu loci. This map covered 3636.7 cM with 1327.7 cM (36.5%), 1485.5 cM (40.9%), and 823.5 cM (22.6%) for A, B, and D genome, respectively, and contained 13 linkage gaps. Using the RILs and the map, we detected 46 putative QTLs on 12 chromosomes for grain yield (GY) per m², thousand-kernel weight (TKW), spike number (SN) per m², kernel number per spike (KNS), sterile spikelet number per spike (SSS), fertile spikelet number per spike (FSS), and total spikelet number per spike (TSS) in four environments. Each QTL explained 4.42–70.25% phenotypic variation. Four QTL cluster regions were detected on chromosomes 1D, 2A, 6B, and 7D. The most important QTL cluster was located on chromosome 7D near the markers of Xwmc31, Xgdm67, and Xgwm428, in which 8 QTLs for TKW, SN, SSS and FSS were observed with very high contributions (27.53–67.63%).     

The effect of genome and sex on recombination rates in Pennisetum species

The effects of homoeology and sex on recombination frequency were studied in crosses between cultivated pearl millet, Pennisetum glaucum, and two wild subspecies, P. violaceum and P. mollissimum. For the two wild x cultivated crosses, reciprocal three-way crosses were made between the F₁ hybrid and an inbred line (Tift 23DB₁). The three-way cross populations were mapped to produce a female map of each wide cross (where the F₁ was the female) and a male map (where the F₁ was the male). Total genetic map lengths of the two inter-subspecies crosses were broadly similar and around 85 % of a comparable intervarietal map. In the P. glaucumxP. mollissimum crosses, the map was further shortened by a large (40 cM) inversion in linkage group 1. Comparison of the recovered recombinants from male and female meiocytes showed an overall trend for the genetic maps to be longer in the male (10%) in both inter-subspecific crosses; however, analysis of individual linkage intervals showed no significant differences. Gametophytic selection was prevalent, and sometimes extreme, for example 121 in favour of wild alleles in the P. glaucumxP. mollissimum male recombinant population. One of the loci which determines panicle type in cultivated pearl millet and wild relatives, H, was mapped 9 cM from Xpsm812 on linkage group 7 in the P. violaceum cross.     

Genetic analysis of wheat domestication and evolution under domestication

Wheat is undoubtedly one of the world's major food sources since the dawn of Near Eastern agriculture and up to the present day. Morphological, physiological, and genetic modifications involved in domestication and subsequent evolution under domestication were investigated in a tetraploid recombinant inbred line population, derived from a cross between durum wheat and its immediate progenitor wild emmer wheat. Experimental data were used to test previous assumptions regarding a protracted domestication process. The brittle rachis (Br) spike, thought to be a primary characteristic of domestication, was mapped to chromosome 2A as a single gene, suggesting, in light of previously reported Br loci (homoeologous group 3), a complex genetic model involved in spike brittleness. Twenty-seven quantitative trait loci (QTLs) conferring threshability and yield components (kernel size and number of kernels per spike) were mapped. The large number of QTLs detected in this and other studies suggests that following domestication, wheat evolutionary processes involved many genomic changes. The Br gene did not show either genetic (co-localization with QTLs) or phenotypic association with threshability or yield components, suggesting independence of the respective loci. It is argued here that changes in spike threshability and agronomic traits (e.g. yield and its components) are the outcome of plant evolution under domestication, rather than the result of a protracted domestication process. Revealing the genomic basis of wheat domestication and evolution under domestication, and clarifying their inter-relationships, will improve our understanding of wheat biology and contribute to further crop improvement.     

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.     

The genetics of domestication of yardlong bean, Vigna unguiculata (L.) Walp. ssp. unguiculata cv.-gr. sesquipedalis

Background and Aims

The genetics of domestication of yardlong bean [Vigna unguiculata (L.) Walp. ssp. unguiculata cv.-gr. sesquipedalis] is of particular interest because the genome of this legume has experienced divergent domestication. Initially, cowpea was domesticated from wild cowpea in Africa; in Asia a vegetable form of cowpea, yardlong bean, subsequently evolved from cowpea. Information on the genetics of domestication-related traits would be useful for yardlong bean and cowpea breeding programmes, as well as comparative genome study among members of the genus Vigna. The objectives of this study were to identify quantitative trait loci (QTLs) for domestication-related traits in yardlong bean and compare them with previously reported QTLs in closely related Vigna.

Methods

Two linkage maps were developed from BC₁F₁ and F₂ populations from the cross between yardlong bean (V. unguiculata ssp. unguiculata cv.-gr. sesquipedalis) accession JP81610 and wild cowpea (V. unguiculata ssp. unguiculata var. spontanea) accession TVnu457. Using these linkage maps, QTLs for 24 domestication-related traits were analysed and mapped. QTLs were detected for traits related to seed, pod, stem and leaf.

Key Results

Most traits were controlled by between one and 11 QTLs. QTLs for domestication-related traits show co-location on several narrow genomic regions on almost all linkage groups (LGs), but especially on LGs 3, 7, 8 and 11. Major QTLs for sizes of seed, pod, stem and leaf were principally located on LG7. Pleiotropy or close linkage of genes for the traits is suggested in these chromosome regions.

Conclusions

This is the first report of QTLs for domestication-related traits in yardlong bean. The results provide a foundation for marker-assisted selection of domestication-related QTLs in yardlong bean and enhance understanding of domestication in the genus Vigna.     

QTL mapping of domestication-related traits in soybean (Glycine max)

BACKGROUND AND AIMS: Understanding the genetic basis underlying domestication-related traits (DRTs) is important in order to use wild germplasm efficiently for improving yield, stress tolerance and quality of crops. This study was conducted to characterize the genetic basis of DRTs in soybean (Glycine max) using quantitative trait locus (QTL) mapping. METHODS: A population of 96 recombinant inbred lines derived from a cultivated (ssp. max) x wild (ssp. soja) cross was used for mapping and QTL analysis. Nine DRTs were examined in 2004 and 2005. A linkage map was constructed with 282 markers by the Kosambi function, and the QTL was detected by composite interval mapping. KEY RESULTS: The early flowering and determinate habit derived from the max parent were each controlled by one major QTL, corresponding to the major genes for maturity (e1) and determinate habit (dt1), respectively. There were only one or two significant QTLs for twinning habit, pod dehiscence, seed weight and hard seededness, which each accounted for approx. 20-50 % of the total variance. A comparison with the QTLs detected previously indicated that in pod dehiscence and hard seededness, at least one major QTL was common across different crosses, whereas no such consistent QTL existed for seed weight. CONCLUSIONS: Most of the DRTs in soybeans were conditioned by one or two major QTLs and a number of genotype-dependent minor QTLs. The common major QTLs identified in pod dehiscence and hard seededness may have been key loci in the domestication of soybean. The evolutionary changes toward larger seed may have occurred through the accumulation of minor changes at many QTLs. Since the major QTLs for DRTs were scattered across only six of the 20 linkage groups, and since the QTLs were not clustered, introgression of useful genes from wild to cultivated soybeans can be carried out without large obstacles.     

Polymorphic microsatellite markers for inferring diversity in wild and domesticated sugar beet (Beta vulgaris)

Eight microsatellite loci were characterized within two cultivated beet (Beta vulgaris ssp. vulgaris) accessions and one accession of the wild progenitor of domesticated sugar beet, Beta vulgaris ssp. maritima. Allele diversity was high, yielding two to 11 alleles per locus. Polymorphism information content (PIC) values obtained for these eight loci where also high and indicate the highly informative nature of the microsatellites presented here. These described markers add to a small set of publicly available microsatellite markers for beet and will be instrumental in identifying patterns of genetic diversity and origins of domestication.     

Genetic dissection of embryo sac fertility, pollen fertility, and their contributions to spikelet fertility of intersubspecific hybrids in rice

The partial sterility of hybrids has been a major barrier for utilization of the strong heterosis expressed in hybrids between Oryza sativa ssp. indica and O. sativa ssp. japonica. Wide-compatibility varieties, comprising a special class of germplasm, are able to produce fertile hybrids when crossed to both indica and japonica varieties. However, all the work on wide compatibility and majority of studies on indica/japonica hybrid sterility reported so far were based only on spikelet fertility; thus, it is not known to what extent male and female gamete abortions influence hybrid sterility. In this study, we investigated pollen fertility, embryo sac fertility, and spikelet fertility in an F₁ population of 202 true hybrid plants derived from a three-way cross (02428/Nanjing 11//Balilla). A partial regression analysis showed that the pollen and embryo sac fertility contributed almost equally to spikelet fertility. QTL analysis based on a linkage map of 191 polymorphic marker loci identified two QTLs for pollen fertility, one QTL for embryo sac fertility, and three QTLs for spikelet fertility. The S5 locus, previously identified as a locus for wide compatibility by spikelet fertility analysis, is a major locus for embryo sac fertility, and a QTL on chromosome 5 had a major effect on pollen fertility. These two loci coincided with the two major QTLs for spikelet fertility. The study also detected a QTL on chromosome 8, showing a large effect on spikelet fertility but no effect on either pollen or embryo sac fertility. Very little interaction among the QTLs was detected. The implications of the findings in rice breeding programs are discussed.     

Construction of a Genetic Linkage Map and Genetic Analysis of Domestication Related Traits in Mungbean (Vigna radiata)

The genetic differences between mungbean and its presumed wild ancestor were analyzed for domestication related traits by QTL mapping. A genetic linkage map of mungbean was constructed using 430 SSR and EST-SSR markers from mungbean and its related species, and all these markers were mapped onto 11 linkage groups spanning a total of 727.6 cM. The present mungbean map is the first map where the number of linkage groups coincided with the haploid chromosome number of mungbean. In total 105 QTLs and genes for 38 domestication related traits were identified. Compared with the situation in other Vigna crops, many linkage groups have played an important role in the domestication of mungbean. In particular the QTLs with high contribution were distributed on seven out of 11 linkage groups. In addition, a large number of QTLs with small contribution were found. The accumulation of many mutations with large and/or small contribution has contributed to the differentiation between wild and cultivated mungbean. The useful QTLs for seed size, pod dehiscence and pod maturity that have not been found in other Asian Vigna species were identified in mungbean, and these QTLs may play the important role as new gene resources for other Asian Vigna species. The results provide the foundation that will be useful for improvement of mungbean and related legumes.     

Analysis of agronomic and domestication traits in a durum × cultivated emmer wheat population using a high-density single nucleotide polymorphism-based linkage map

Key message

Development of a high-density SNP map and evaluation of QTL shed light on domestication events in tetraploid wheat and the potential utility of cultivated emmer wheat for durum wheat improvement.

Abstract

Cultivated emmer wheat (Triticum turgidum ssp. dicoccum) is tetraploid and considered as one of the eight founder crops that spawned the Agricultural Revolution about 10,000 years ago. Cultivated emmer has non-free-threshing seed and a somewhat fragile rachis, but mutations in genes governing these and other agronomic traits occurred that led to the formation of today’s fully domesticated durum wheat (T. turgidum ssp. durum). Here, we evaluated a population of recombinant inbred lines (RILs) derived from a cross between a cultivated emmer accession and a durum wheat variety. A high-density single nucleotide polymorphism (SNP)-based genetic linkage map consisting of 2,593 markers was developed for the identification of quantitative trait loci. The major domestication gene Q had profound effects on spike length and compactness, rachis fragility, and threshability as expected. The cultivated emmer parent contributed increased spikelets per spike, and the durum parent contributed higher kernel weight, which led to the identification of some RILs that had significantly higher grain weight per spike than either parent. Threshability was governed not only by the Q locus, but other loci as well including Tg-B1 on chromosome 2B and a putative Tg-A1 locus on chromosome 2A indicating that mutations in the Tg loci occurred during the transition of cultivated emmer to the fully domesticated tetraploid. These results not only shed light on the events that shaped wheat domestication, but also demonstrate that cultivated emmer is a useful source of genetic variation for the enhancement of durum varieties.     

Mapping quantitative trait loci for yield,yield components and morphological traits in an advanced backcross population between <Emphasis Type="Italic">Oryza rufipogon</Emphasis> and the <Emphasis Type="Italic">Oryza sativa</Emphasis> cultivar Jefferson

An advanced backcross population between an accession of Oryza rufipogon (IRGC 105491) and the U.S. cultivar Jefferson (Oryza sativa ssp. japonica) was developed to identify quantitative trait loci (QTLs) for yield, yield components and morphological traits. The genetic linkage map generated for this population consisted of 153 SSR and RFLP markers with an average interval size of 10.3 cM. Thirteen traits were examined, nine of which were measured in multiple environments. Seventy-six QTLs above an experiment-wise significance threshold of P<0.01 (corresponding to an interval mapping LOD>3.6 or a composite interval mapping LOD>3.9) were identified. For the traits measured in multiple environments, 47% of the QTLs were detected in at least two environments. The O. rufipogon allele was favorable for 53% of the yield and yield component QTLs, including loci for yield, grains per panicle, panicle length, and grain weight. Morphological traits related to the domestication process and/or weedy characteristics, including plant height, shattering, tiller type and awns, were found clustered on chromosomes 1 and 4. Comparisons to previous studies involving wild x cultivated crosses revealed O. rufipogon alleles with stable effects in multiple genetic backgrounds and environments, several of which have not been detected in studies between Oryza sativa cultivars, indicating potentially novel alleles from O. rufipogon. Some O. rufipogon-derived QTLs, however, were in similar regions as previously reported QTLs from Oryza sativa cultivars, providing evidence for conservation of these QTLs across the Oryza genus. In addition, several QTLs for grain weight, plant height, and flowering time were localized to putative homeologous regions in maize where QTLs for these traits have been previously reported, supporting the hypothesis of functional conservation of QTLs across the grasses.     

QTL Analysis in Recombinant Chromosome Substitution Lines and Doubled Haploid Lines Derived from a Cross between Hordeum vulgare ssp. vulgare and Hordeum vulgare ssp. spontaneum

Recombinant chromosome substitution lines (RCSLs) were developed in BC₃ generation to introduce segments of a wild barley strain ‘H602’ (Hordeum vulgare ssp. spontaneum) into a barley cultivar ‘Haruna Nijo’ (H. vulgare ssp. vulgare) genetic background. One hundred thirty four RCSLs were genotyped by 25 SSR and 60 EST markers, which were localized on a linkage map of doubled haploid lines (DHLs) derived from the same cross combination. Graphical genotyping revealed that the observed average substitution ratio of H602 segment (12.9%) agreed with the expected substitution ratio (12.5%), and a minimum set of 19 RCSLs represented the entire H602 genome. Phenotypes of five qualitative and nine quantitative traits were scored in both the RCSLs and DHLs. Five qualitative traits were localized as morphological markers on the linkage map of the DHLs, and these molecular markers were aligned on the respective chromosomal regions in the RCSLs. Simple and composite interval mapping procedures detected a total of 18 and 24 QTLs for nine qualitative traits on the RCSLs and DHLs, respectively. Several QTLs were localized at coincident or very close regions on both linkage maps. In spite of general inferior agronomic performances in wild barley, several H602 QTL alleles showed agronomically positive effects. These RCSLs should contribute to substitution of favorable alleles from wild barley into cultivated barley. These RCSLs are also available as sources of near isogenic lines, with which we can apply advanced genetic analysis methods such as isolation of QTLs and detection of epistatic interactions among QTLs.     

Quantitative trait loci and candidate gene mapping of aluminum tolerance in diploid alfalfa

Aluminum (Al) toxicity in acid soils is a major limitation to the production of alfalfa (Medicago sativa subsp. sativa L.) in the USA. Developing Al-tolerant alfalfa cultivars is one approach to overcome this constraint. Accessions of wild diploid alfalfa (M. sativa subsp. coerulea) have been found to be a source of useful genes for Al tolerance. Previously, two genomic regions associated with Al tolerance were identified in this diploid species using restriction fragment length polymorphism (RFLP) markers and single marker analysis. This study was conducted to identify additional Al-tolerance quantitative trait loci (QTLs); to identify simple sequence repeat (SSR) markers that flank the previously identified QTLs; to map candidate genes associated with Al tolerance from other plant species; and to test for co-localization with mapped QTLs. A genetic linkage map was constructed using EST-SSR markers in a population of 130 BC₁F₁ plants derived from the cross between Al-sensitive and Al-tolerant genotypes. Three putative QTLs on linkage groups LG I, LG II and LG III, explaining 38, 16 and 27% of the phenotypic variation, respectively, were identified. Six candidate gene markers designed from Medicago truncatula ESTs that showed homology to known Al-tolerance genes identified in other plant species were placed on the QTL map. A marker designed from a candidate gene involved in malic acid release mapped near a marginally significant QTL (LOD 2.83) on LG I. The SSR markers flanking these QTLs will be useful for transferring them to cultivated alfalfa via marker-assisted selection and for pyramiding Al tolerance QTLs.     

QTL clusters reflect character associations in wild and cultivated rice

The genetic basis of character association related to differentiation found in the primary gene pool of rice was investigated based on the genomic distribution of quantitative trait loci (QTLs). Major evolutionary trends in cultivated rice of Asiatic origin (Oryza sativa) and its wild progenitor (O. rufipogon) are: (1) differentiation from wild to domesticated types (domestication), (2) ecotype differentiation between the perennial and annual types in wild races, and (3) the Indica versus Japonica type differentiation in cultivated races. Using 125 recombinant inbred lines (RILs) derived from a cross between an Indica cultivar of O. sativa and a strain of O. rufipogon carrying some Japonica-like characteristics, we mapped 147 markers, mostly RFLPs, on 12 chromosomes. Thirty-seven morphological and physiological quantitative traits were evaluated, and QTLs for 24 traits were detected. The mapped loci showed a tendency to form clusters that are composed of QTLs of the domestication-related traits as well as Indica/Japonica diagnostic traits. QTLs for perennial/annual type differences did not cluster. This cluster phenomenon could be considered "multifactorial linkages" followed by natural selection favoring co-adapted traits. Further, it is possible that the clustering phenomenon is partly due to pleiotropy of some unknown key factor(s) controlling various traits through diverse metabolic pathways. Chromosomal regions where QTL clusters were found coincided with the regions harboring genes or gene blocks where the frequency of cultivar-derived alleles in RILs is higher than expected. This distortion may be partly due to unconscious selection favoring cultivated plant type during the establishment of RILs.     

The genetics of domestication of rice bean, Vigna umbellata

Background and Aims

The Asian genus Vigna, to which four cultivated species (rice bean, azuki bean, mung bean and black gram) belong, is suitable for comparative genomics. The aims were to construct a genetic linkage map of rice bean, to identify the genomic regions associated with domestication in rice bean, and to compare these regions with those in azuki bean.

Methods

A genetic linkage map was constructed by using simple sequence repeat and amplified fragment length polymorphism markers in the BC₁F₁ population derived from a cross between cultivated and wild rice bean. Using this map, 31 domestication-related traits were dissected into quantitative trait loci (QTLs). The genetic linkage map and QTLs of rice bean were compared with those of azuki bean.

Key Results

A total of 326 markers converged into 11 linkage groups (LGs), corresponding to the haploid number of rice bean chromosomes. The domestication-related traits in rice bean associated with a few major QTLs distributed as clusters on LGs 2, 4 and 7. A high level of co-linearity in marker order between the rice bean and azuki bean linkage maps was observed. Major QTLs in rice bean were found on LG4, whereas major QTLs in azuki bean were found on LG9.

Conclusions

This is the first report of a genetic linkage map and QTLs for domestication-related traits in rice bean. The inheritance of domestication-related traits was so simple that a few major QTLs explained the phenotypic variation between cultivated and wild rice bean. The high level of genomic synteny between rice bean and azuki bean facilitates QTL comparison between species. These results provide a genetic foundation for improvement of rice bean; interchange of major QTLs between rice bean and azuki bean might be useful for broadening the genetic variation of both species.     

Analysis of recombination rate in female and male gametogenesis in pearl millet (Pennisetum glaucum) using RFLP markers

Sex as a factor affecting recovered recombination in plant gametes was investigated in pearl millet, Pennisetum glaucum, by using reciprocal three-way crosses [(AxB)xCvCx(A x B)]. The two populations were mapped at 42 loci pre-selected to cover the majority of the genome. No differences in recombination distances were observed at the whole-genome level and only a few individual linkage intervals were found to differ, all in favour of increased recombination through the male. Distorted segregations found in the three-way crosses provide evidence of post-gametic selection for particular gene(s) or chromosome regions. The significance of these results for the design of pearl millet breeding programmes and inheritance experiments, as well as for other experimental strategies, is discussed.     

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.