Section Arachis Research Articles

Crossability of Arachis valida and B genome Arachis species.

The peanut (Arachis hypogaea) is an important food crop in much of the tropical and semi-tropical parts of the world. The peanut is an allotetraploid with an AABB genome formula derived from diploids A. duranensis (A genome) and A. ipaënsis (B genome). The success of an introgression program that aims to improve cultivated varieties of the peanut depends on whether the chosen B genome species is homologous with the B genome of the peanut. While not directly involved in the origin of the peanut to the best of our knowledge, Arachis valida is a B genome species that could potentially be a bridge species or a source of new and different alleles, because of its resistance to diseases and pests. In this study, we investigated the crossability of A. valida with five other B genome species of section Arachis. Eight cross-combinations were made with A. valida and A. gregoryi, A. ipaënsis, A. magna, A. valida, and A. williamsii. Two hundred and forty pollinations were made yielding 61 fruit segments, 61 seeds, one abortion, and 24 hybrid plants. An analysis of the morphological characteristics and pollen viability confirmed that the plants were hybrids. Our results indicated that higher pollen viability of hybrid plants corresponded with higher affinity between parent plants used in crossings. This conclusion corroborates much of previous research carried out by many other authors in the past.

Genome sizes in diploid and allopolyploid Arachis L. species (section Arachis)

Species of section Arachis with x = 10 are important for peanut breeding and have been organized in five different genomes (A, B, D, F and K). The few available estimates of the DNA content are inconsistent and hampered the understanding of the evolutionary trends and in decision making for genomic studies of the group. Considering that, the objectives of this research were to measure the DNA content for all available (26) species and to make evolutionary inferences at the diploid and tetraploid level for section Arachis. The 2C values obtained by flow cytometry ranged from 2.55 to 3.22 pg among the diploid species. The annual species belonging to different genomes tend to have different genome sizes. However, the 2C values of the perennial species of the A genome were distributed almost along the whole range of genome sizes here observed. The distribution of 2C values partially support the genome arrangement proposed for the section. The comparisons of 2C values with karyotype parameters suggests that changes in DNA content have been proportionally distributed among the chromosome arms, and that the heterochromatic fraction was not directly involved in that changes. Within the A genome, the annual species has lower DNA content than the perennial ones, according to the nucleotype hypothesis. However, the lack of significant relationships with geoclimatic variables suggests that there are many intrinsic factors determining particular ecological roles of the DNA content in the different lineages of section Arachis. The constancy of the Cx values observed in the polyploids compared to those of the parental species suggests that the allopolyploidization event that originated the cultivated peanut did not induce significant changes in the genome size.

RDNA loci and heterochromatin positions support a distinct genome type for ‘x = 9 species’ of section Arachis (Arachis, Leguminosae)

Most species of the genus Arachis (Leguminosae; 80 spp.) are diploid with x = 10 and only four species have x = 9 chromosomes. Three of these x = 9 species belong to section Arachis and are morphologically and chromosomally similar. To study the homeology of the genomes of x = 9 species and their relation to other genomes in section Arachis, we applied fluorescence in situ hybridization (FISH) of 18S–26S and 5S rDNA and 4′,6-diamidino-2-phenylindole (DAPI) banding. FISH revealed for these three species one pair of 5S rDNA sites interstitially within the short arm of the metacentric pair 6 and one pair of 18S–26S rDNA sites in the proximal region of the long arm of the SAT chromosomes. Conspicuous DAPI+ bands were detected pericentromerically in all nine chromosome pairs of A. decora and A. praecox and in all but one pair of A. palustris. Our results suggest that all three species with x = 9 of section Arachis share the same genome type and are different from the other genome types A, B, D, F, and K described for this section. Apparently, the x = 9 species of section Arachis form a monophyletic group characterized by a genome type, that we propose to call G genome.

Phylogenetic relationships of species of genus Arachis based on genic sequences.

The genus Arachis (Fabaceae), which originated in South America, consists of 80 species. Based on morphological traits and cross-compatibility among the species, the genus is divided into nine taxonomic sections. Arachis is the largest section including the economically valuable cultivated peanut (A. hypogaea). Seven genic sequences were utilized to better understand the phylogenetic relationships between species of genus Arachis. Our study displayed four clades of species of Arachis. Arachis triseminata was genetically isolated from all other species of Arachis studied, and it formed the basal clade with A. retusa and A. dardani from the most ancient sections Extranervosae and Heteranthae, respectively. Species of section Arachis formed a separated single clade from all other species, within which species having B and D genome clustered in one subgroup and three species characterized with an A genome grouped together in another subgroup. A divergent clade including species from five sections was sister to the clade of section Arachis. Between the sister clades and the basal clade there was a clade containing species from the more advanced sections. Phylogenetic relationships of all the species of Arachis using multiple genic sequences were similar to the phylogenies produced with single-copy genes.

Greenhouse Evaluation of Section Arachis Wild Species for Sclerotinia Blight and Cylindrocladium Black Rot Resistance

ABSTRACT Wild Arachis species from section Arachis have been promoted as sources of resistance to common peanut diseases and insect pests. The objective of our study was to identify wild Arachis species with resistance to Sclerotinia blight and Cylindrocladium black rot (CBR). One hundred and ten accessions/entries from 23 Arachis species including A. hypogaea were evaluated in the greenhouses at North Carolina State University between January and March of 2010 in a 11×10 rectangular lattice experimental design with 4 replications for Sclerotinia blight and 6 replications for CBR. For the Sclerotinia blight test, seeds were planted in 10 cm clay pots and 8-wk-old plants were inoculated in a mist chamber with BEEM capsules containing the fungus inserted on the petioles of the 4th leaf from the apex on the primary branch. Lesion lengths were measured 4, 5, 6, and 7 d after inoculation, and areas under the disease progress curves (AUDPC) were calculated. For the CBR test, seeds were planted in soil mixed with microsclerotia (25/g) in cone-tainers partly immersed in water. Root damage was recorded after 60 d on a 0–5 proportional scale (0 = no decay to 5 = completely decayed). Data analysis indicated significant (p<0.05) variation among and within Arachis species for both diseases. Arachis glandulifera exhibited the highest level of Sclerotinia blight resistance followed by A. correntina, A. herzogii, and A. helodes, although the last three species were not significantly different from A. hypogaea. Overall, low genetic variability for Sclerotinia blight resistance was observed among the wild species accessions. For CBR, A. valida, A. cruziana, A. microsperma, A. williamsii, A. kempff-mercadoi, A. kuhlmannii, A. helodes, A. cardenasii and A. correntina formed the most resistant group with A. hypogaea in the most susceptible group. Overall, significant genetic variability for CBR resistance was found among the different wild species accessions. However, not all accessions within a species were resistant to either disease, and most accessions that were resistant to one disease were susceptible to the other.

Characterization of resveratrol content in ten wild species of section Arachis, genus Arachis

Peanut is one of the few plants that synthesizes resveratrol, a phenolic compound of the stilbene class, which has been associated with reduced risk of developing chronic diseases, such as cancer, cardiovascular diseases, skin diseases, pulmonary diseases, diabetes and neurological diseases. Resveratrol was detected in different parts of the peanut plant, including roots, leaves, seeds and their derivatives. The wild species of the Arachis section are also strong candidates to synthesize resveratrol because they are phylogenetically closely related to cultivated peanut. Our objective was to characterize the resveratrol content in ten wild species of Arachis with three different genomes (A, B and K). The plant material was composed of leaves of the ten species treated (test) and not treated (control) with ultraviolet (UV) radiation. The test and control samples were extracted and the identification and quantification of resveratrol was performed using high performance liquid chromatography (HPLC). All species studied synthesized resveratrol and the concentrations ranged from 299.5 μg/g in A. kempff-mercadoi to 819.9 μg/g in A. cardenasii. DPPH antioxidant activity varied between 18.7 % for A. duranensis and 48.2 % in A. simpsonii. The results showed that wild Arachis species are a potential source of alleles for improvement of cultivated peanut, with the aim of achieving higher resveratrol content in leaves.

Characterization of Brazilian accessions of wild Arachis species of section Arachis (Fabaceae) using heterochromatin detection and fluorescence in situ hybridization (FISH)

The cytogenetic characterization of Arachis species is useful for assessing the genomes present in this genus, for establishing the relationship among their representatives and for understanding the variability in the available germplasm. In this study, we used fluorescence in situ hybridization (FISH) to examine the distribution patterns of heterochromatin and rDNA genes in 12 Brazilian accessions of five species of the taxonomic section Arachis. The heterochromatic pattern varied considerably among the species: complements with centromeric bands in all of the chromosomes (A. hoehnei) and complements completely devoid of heterochromatin (A. gregoryi, A. magna) were observed. The number of 45S rDNA loci ranged from two (A. gregoryi) to eight (A. glandulifera), while the number of 5S rDNA loci was more conserved and varied from two (in most species) to four (A. hoehnei). In some species one pair of 5S rDNA loci was observed adjacent to 45S rDNA loci. The chromosomal markers revealed polymorphism in the three species with more than one accession (A. gregoryi, A. magna and A. valida) that were tested. The previous genome assignment for each of the species studied was confirmed, except for A. hoehnei. The intraspecific variability observed here suggests that an exhaustive cytogenetic and taxonomic analysis is still needed for some Arachis species.

A study of the relationships of cultivated peanut (Arachis hypogaea) and its most closely related wild species using intron sequences and microsatellite markers

The genus Arachis contains 80 described species. Section Arachis is of particular interest because it includes cultivated peanut, an allotetraploid, and closely related wild species, most of which are diploids. This study aimed to analyse the genetic relationships of multiple accessions of section Arachis species using two complementary methods. Microsatellites allowed the analysis of inter- and intraspecific variability. Intron sequences from single-copy genes allowed phylogenetic analysis including the separation of the allotetraploid genome components. Intron sequences and microsatellite markers were used to reconstruct phylogenetic relationships in section Arachis through maximum parsimony and genetic distance analyses. Although high intraspecific variability was evident, there was good support for most species. However, some problems were revealed, notably a probable polyphyletic origin for A. kuhlmannii. The validity of the genome groups was well supported. The F, K and D genomes grouped close to the A genome group. The 2n = 18 species grouped closer to the B genome group. The phylogenetic tree based on the intron data strongly indicated that A. duranensis and A. ipaënsis are the ancestors of A. hypogaea and A. monticola. Intron nucleotide substitutions allowed the ages of divergences of the main genome groups to be estimated at a relatively recent 2·3-2·9 million years ago. This age and the number of species described indicate a much higher speciation rate for section Arachis than for legumes in general. The analyses revealed relationships between the species and genome groups and showed a generally high level of intraspecific genetic diversity. The improved knowledge of species relationships should facilitate the utilization of wild species for peanut improvement. The estimates of speciation rates in section Arachis are high, but not unprecedented. We suggest these high rates may be linked to the peculiar reproductive biology of Arachis.

Cloning and Characterization of Chromosomal Markers from a Cot-1 Library of Peanut (Arachis hypogaea L.)

The cultivated peanut, Arachis hypogaea (AABB, 2n = 40), is an allotetraploid which was probably originated from a hybridization event between 2 ancestors, A. duranensis (A genome) and A. ipaensis (B genome) followed by chromosome doubling. The wild species in the Arachis section are useful genetic resources for genes that confer biotic and abiotic stress resistance for peanut breeding. However, the resource is not well exploited because little information on the genetic, cytogenetic, and phylogenetic relationships between cultivated peanut and its wild relatives is known. Characterization of its chromosome components will benefit the understanding of these issues. But the paucity of information on the DNA sequence and the presence of morphologically similar chromosomes impede the construction of a detailed karyotype for peanut chromosome identification. In our study, a peanut Cot-1 library was constructed to isolate highly and moderately repetitive sequences from the cultivated peanut, and the chromosomal distributions of these repeats were investigated. Both genome and chromosome specific markers were identified that allowed the distinguishing of A and B genomes in tetraploid peanut and a possible karyotyping of peanut chromosomes by FISH. In particular, a 115-bp tandem repetitive sequence was identified to be a possible centromere repetitive DNA, mainly localized in the centromeres of B chromosomes, and a partial retrotransposable element was also identified in the centromeres of B chromosomes. The cloning and characterization of various chromosomal markers is a major step for FISH-based karyotyping of peanut. The FISH markers are expected to provide a reference tool for sequence assembly, phylogenetic studies of peanut and its wild species, and breeding.

Production of peanut hybrid seeds in an intersectional cross through post-pollination treatment of flower bases with plant growth regulators

To broaden the narrow gene base of the cultivated peanut and utilize sources of resistance to abiotic/biotic stresses, quality-related traits and high yielding factors, much attention has been paid to wild relatives of the oilseed crop since 1980s. Species outside section Arachis are cross-incompatible with A. hypogaea L.; even some of the species from section Arachis, which are supposed to be compatible, may also encounter obstacles when crossed with the peanut cultigen. The objective of the present communication is to study the effects of simple hormone treatment on production of true incompatible hybrids in peanut to replace the tedious and lengthy in vitro embryo rescue procedures currently in use. In the incompatible cross, A. hypogaea cv Qunyu 101 × A. paraguariensis, post-pollination application of a hormone aqueous solution (IAA 4 mg/L + GA 2 mg/L) at flower bases resulted in 42 seeds, of which 26 were identified as true hybrids by allele-specific PCR for FAD2A genotyping. As a desirable alternative to in vitro embryo/ovules/peg culture, the present method may facilitate the utilization of wild species in peanut breeding. The method described here for peanut may be of reference to other crop plants where embryo abortion is also a problem.

Phylogenetic relationships in genus Arachis based on ITS and 5.8S rDNA sequences

BackgroundThe genus Arachis comprises 80 species and it is subdivided into nine taxonomic sections (Arachis, Caulorrhizae, Erectoides, Extranervosae, Heteranthae, Procumbentes, Rhizomatosae, Trierectoides, and Triseminatae). This genus is naturally confined to South America and most of its species are native to Brazil. In order to provide a better understanding of the evolution of the genus, we reconstructed the phylogeny of 45 species using the variation observed on nucleotide sequences in internal transcribed spacer regions (ITS1 and ITS2) and 5.8 S of nuclear ribosomal DNA.ResultsIntraspecific variation was detected, but in general it was not enough to place accessions of the same species in different clades. Our data support the view that Arachis is a monophyletic group and suggested Heteranthae as the most primitive section of genus Arachis. The results confirmed the circumscriptions of some sections (Caulorrhizae, Extranervosae), but raised questions about others. Sections Erectoides, Trierectoides and Procumbentes were not well defined, while sections Arachis and Rhizomatosae seem to include species that could be moved to different sections. The division of section Arachis into A and B genome species was also observed in the phylogenetic tree and these two groups of species may not have a monophyletic origin. The 2n = 2x = 18 species of section Arachis (A. praecox, A. palustris and A. decora) were all placed in the same clade, indicating they are closely related to each other, and their genomes are more related to B genome than to the A genome. Data also allowed insights on the origin of tetraploid A. glabrata, suggesting rhizome appeared twice within the genus and raising questions about the placement of that species in section Rhizomatosae.ConclusionThe main clades established in this study in general agreed with many other studies that have used other types of evidences and sets of species, being some of them included in our study and some not. Thus, the relationships established can be a useful framework for future systematic reviews of genus Arachis and for the selection of species to pre-breeding programs.

Species, genomes, and section relationships in the genus Arachis (Fabaceae): a molecular phylogeny

The economically important genus Arachis (Fabaceae) comprises 80 species restricted to South America. One monograph on the genus divided it into nine sections and included an intuitive assessment of evolutionary relationships. There is no comprehensive phylogenetic study of the genus. To test the current systematic treatment of the genus, we reconstructed a phylogeny for Arachis using nuclear ITS and plastid trnT–trnF sequences from 46 species representing all nine sections. ITS cloning of the allotetraploid species of section Arachis indicated the presence of A and B genome alleles and chimeric sequences. Our study revealed that species from section Extranervosae were the first emerging lineage in the genus, followed by sections Triseminatae and Caulorrhizae, and two terminal major lineages, which we refer to as erectoides and arachis. The lineage erectoides comprises members of sections Erectoides, Heteranthae, Procumbentes, Rhizomatosae, and Trierectoides. Species in the arachis lineage form two major clades, arachis I (B and D genomes species and the aneuploids) and arachis II (A genome species). Our results substantiated the sectional treatment of Caulorrhizae, Extranervosae, and Triseminatae, but demonstrated that sections Erectoides, Procumbentes, and Trierectoides are not monophyletic. A detailed study of the genus Arachis with denser taxon sampling, additional genomic regions, plus information from morphology and cytogenetics is needed for comprehensive assessment of its systematics.

Species relationships among the wild B genome of Arachis species (section Arachis) based on FISH mapping of rDNA loci and heterochromatin detection: a new proposal for genome arrangement

Arachis hypogaea is an allotetraploid species with low genetic variability. Its closest relatives, all of the genus Arachis, are important sources of alleles for peanut breeding. However, a better understanding of the genome constitution of the species and of the relationships among taxa is needed for the effective use of the secondary gene pool of Arachis. In the present work, we focused on all 11 non-A genome (or B genome sensu lato) species of Arachis recognized so far. Detailed karyotypes were developed by heterochromatin detection and mapping of the 5S and the 18S-25S rRNA using FISH. On the basis of outstanding differences observed in the karyotype structures, we propose segregating the non-A genome taxa into three genomes: B sensu stricto (s.s.), F and K. The B genome s.s. is deprived of centromeric heterochromatin and is homologous to one of the A. hypogaea complements. The other two genomes have centromeric bands on most of the chromosomes, but differ in the amount and distribution of heterochromatin. This organization is supported by previously published data on molecular markers, cross compatibility assays and bivalent formation at meiosis in interspecific hybrids. The geographic structure of the karyotype variability observed also reflects that each genome group may constitute lineages that have evolved through independent evolutionary pathways. In the present study, we confirmed that Arachis ipaensis was the most probable B genome donor for A. hypogaea, and we identified a group of other closely related species. The data provided here will facilitate the identification of the most suitable species for the development of prebreeding materials for further improvement of cultivated peanut.

Phylogeny of Arachis based on internal transcribed spacer sequences

Phylogenetic analysis, based on nuclear rDNA internal transcribed spacers (ITS) of Arachis species, corroborated a broad sub-classification of the genus. Three clustering algorithms were used to generate dendrograms which showed that Arachis Sections Extranervosae, Heteranthae and Triseminata were most primitive, and Section Arachis was most advanced, with Sections Caulorrhizae, Erectoides, Procumbentes, Rhizomatosae, and Trierectoides intermediate in evolutionary terms, in relation to the genus Stylosanthes, when it was used as the outgroup.

Genetic relationships among seven sections of genus Arachisstudied by using SSR markers

BackgroundThe genus Arachis, originated in South America, is divided into nine taxonomical sections comprising of 80 species. Most of the Arachis species are diploids (2n = 2x = 20) and the tetraploid species (2n = 2x = 40) are found in sections Arachis, Extranervosae and Rhizomatosae. Diploid species have great potential to be used as resistance sources for agronomic traits like pests and diseases, drought related traits and different life cycle spans. Understanding of genetic relationships among wild species and between wild and cultivated species will be useful for enhanced utilization of wild species in improving cultivated germplasm. The present study was undertaken to evaluate genetic relationships among species (96 accessions) belonging to seven sections of Arachis by using simple sequence repeat (SSR) markers developed from Arachis hypogaea genomic library and gene sequences from related genera of Arachis.ResultsThe average transferability rate of 101 SSR markers tested to section Arachis and six other sections was 81% and 59% respectively. Five markers (IPAHM 164, IPAHM 165, IPAHM 407a, IPAHM 409, and IPAHM 659) showed 100% transferability. Cluster analysis of allelic data from a subset of 32 SSR markers on 85 wild and 11 cultivated accessions grouped accessions according to their genome composition, sections and species to which they belong. A total of 109 species specific alleles were detected in different wild species, Arachis pusilla exhibited largest number of species specific alleles (15). Based on genetic distance analysis, the A-genome accession ICG 8200 (A. duranensis) and the B-genome accession ICG 8206 (A. ipaënsis) were found most closely related to A. hypogaea.ConclusionA set of cross species and cross section transferable SSR markers has been identified that will be useful for genetic studies of wild species of Arachis, including comparative genome mapping, germplasm analysis, population genetic structure and phylogenetic inferences among species. The present study provides strong support based on both genomic and genic markers, probably for the first time, on relationships of A. monticola and A. hypogaea as well as on the most probable donor of A and B-genomes of cultivated groundnut.

Peanut improvement: production of fertile hybrids and backcross progeny between Arachis hypogaea and A. kretschmeri

There are only a few reports of successful crosses between cultivated peanut (Arachis hypogaea L., section Arachis) and wild species from sections other than section Arachis. Many of the wild Arachis species harbor important traits necessary for the improvement of peanut. For example, Arachis kretschmeri Krapov., W.C. Gregory & C.E. Simpson (section Procumbentes) can grow under water-logged conditions and has been identified as one of the few wild species of Arachis with resistance to late leaf spot (LLS) and peanut rosette disease. Peanut rosette, caused by a combination of viruses, is an economically important disease only in Africa, while LLS, caused by Cercosporidium personatum, is an important fungal disease in Asia and the Americas as well as Africa. Interspecific hybrids between A. hypogaea and A. kretschmeri were produced by applying growth regulators to pollinated pistils and hybrid plants were obtained by germinating embryos in vitro. A total of seven hybrids were produced and confirmed by Simple Sequence Repeat (SSR) analysis. All hybrids were fertile, although initially slow growing. F1 hybrids were backcrossed to A. hypogaea and all plants in the F1BC1 generation were single-seeded with a prominent beak, characteristic of A. kretschmeri, but many of the F1BC2 pods were double-seeded resembling A. hypogaea. F1BC2 plants were moderately resistant to LLS. When a large number of seeds are obtained, the progeny will be screened for resistance to both LLS and rosette disease. Thus crosses with species outside the section Arachis may not only confer disease resistance but will also broaden the genetic base of cultivated peanut.

Species relations among wild Arachis species with the A genome as revealed by FISH mapping of rDNA loci and heterochromatin detection

Section Arachis of the homonymous genus includes 29 wild diploid species and two allotetraploids (A. monticola and the domesticated peanut, A. hypogaea L.). Although, three different genomes (A, B and D) have been proposed for diploid species with x = 10, they are still not well characterized. Moreover, neither the relationships among species within each genome group nor between diploids and tetraploids (AABB) are completely resolved. To tackle these issues, particularly within the A genome, in this study the rRNA genes (5S and 18S-26S) and heterochromatic bands were physically mapped using fluorescent in situ hybridization (FISH) in 13 species of Arachis. These molecular cytogenetic landmarks have allowed individual identification of a set of chromosomes and were used to construct detailed FISH-based karyotypes for each species. The bulk of the chromosome markers mapped revealed that, although the A genome species have a common karyotype structure, the species can be arranged in three groups (La Plata River Basin, Chiquitano, and Pantanal) on the basis of the variability observed in the heterochromatin and 18S-26S rRNA loci. Notably, these groups are consistent with the geographical co-distribution of the species. This coincidence is discussed on the basis of the particular reproductive traits of the species such as autogamy and geocarpy. Combined with geographic distribution of the taxa, the cytogenetic data provide evidence that A. duranensis is the most probable A genome ancestor of tetraploid species. It is expected that the groups of diploid species established, and their relation with the cultigen, may aid to rationally select wild species with agronomic traits desirable for peanut breeding programs.

Characterization of rust, early and late leaf spot resistance in wild and cultivated peanut germplasm

Groundnut (Arachis hypogaea) has an AB genome and is one of the most important oil crops in the world. The main constraints of crop management in Brazil are fungal diseases. Several species of the genus Arachis are resistant to pests and diseases. The objective of our experiments was to identify wild species belonging to the taxonomic section Arachis with either A or B (or " non-A" ) genomes that are resistant to early leaf spot (Cercospora arachidicola), late leaf spot (Cercosporidium personatum) and rust (Puccinia arachidis). For the identification of genotypes resistant to fungal diseases, bioassays with detached leaves were done in laboratory conditions, with artificial inoculation, a controlled temperature of 25ºC and a photoperiod of 10 h light/14 h dark, for 20-42 days, depending on the fungi species. Most of the accessions of wild species were more resistant than accessions of A. hypogaea for one, two or all three fungi species studied. Arachis monticola, considered to be a possible tetraploid ancestor or a derivative of A. hypogaea, was also more susceptible to Cercosporidium personatum and Puccinia arachidis, as compared to most of the wild species. Therefore, wild germplasm accessions of both genome types are available to be used for the introgression of resistance genes against three fungal diseases of peanut.

Phylogenetic Relationships in Genus Arachis Based on SSR and AFLP Markers

Fourteen wild species of different sections in the genus Arachis and 24 accessions of the AABB allotetraploid A. hypogaea (cultivated peanut) from several countries which belong to different botanical varieties, were analyzed by SSR and AFLP marker systems. The assay-units per system needed to distinguish among all the tested accessions were at least five for SSR or two for AFLP. The genetic distance detected by the SSR markers ranged from 0.09 to 0.95, and the mean was 0.73; and the genetic distance detected by the AFLP markers ranged from 0.01 to 0.79 with an average of 0.42. All the tested peanut SSR primer pairs were multilocus ones, and the amplified fragments per SSR marker in each peanut genome ranged from 2 to 15 with the mean of 4.77. The peanut cultivars were closely related to each other, and shared a large numbers of SSR and AFLP fragments. In contrast, the species in the genus Arachis shared few fragments. The results indicated that the cultivated peanut ( A. hypogaea L.) varieties could be partitioned into two main groups and tour subgroups at the molecular level, and that A. duranensis is one of the wild ancestors of A. hypogaea . The lowest genetic variation was detected between A. cardenasii and A. batizocoi , and the highest was detected between A. pintoi and the species in the section Arachis . The relationships among the botanical varieties in the cultivated peanut ( A. hypogaea L.) and among wild species accessions in section Arachis and those in other sections in the genus Arachis were discussed.

Genetic diversity in section Rhizomatosae of the genus Arachis (Fabaceae) based on microsatellite markers

The genus Arachis (Fabaceae) native to South America, contains 80 species divided into nine sections, three of which contain species of special economic importance such as the cultivated peanut (Arachis hypogaea), belonging to the section Arachis, and some perennial forage species from sections Caulorrhizae and Rhizomatosae. We used microsatellite markers to assay genetic variability among 77 accessions of four species from section Rhizomatosae, the diploid Arachis burkartii (2n = 2x = 20) and the tetraploid Arachis glabrata, Arachis pseudovillosa and Arachis nitida (2n = 4x = 40). A total of 249 alleles were found in the fifteen loci analyzed and a high degree of intra and interspecific polymorphism was detected. The lowest intraspecific variation occurred in Arachis burkartii, while the smallest estimated interspecific value was between A. nitida and A. pseudovillosa and the largest was between A. burkartii and A. nitida. High observed heterozygosity was detected in A. glabrata. The diploid accessions grouped in one cluster and the tetraploid accessions in another. It was possible to distinguish all 77 accessions and the genetic distance between accessions could not be correlated with geographic origin.