CYTOLOGICAL AND INTERFERTILITY RELATIONSHIPS OF ARACHIS SECTION ARACHIS

Twenty-nine recently introduced diploid (2n = 2x = 20) accessions of section Arachis plus an A. correntina (Burk) Krap. et Greg. nom. nud. control were hybridized to the diploid A-genome species A. duranensis Krap. et Greg. nom. nud. (ace. 7988), the diploid B-genome species A. batizocoi Krap. et Greg. (acc. 9484), and with two subspecies of the A-B genome (2n = 4x = 40) A. hypogaea cultivars NC 4 and Argentine. Most attempted crosses were successful and the resulting plants were vigorous. However, A. batizocoi × accession 30008 hybrids died as seedlings and A. batizocoi × accession 30017 produced only dwarf plants. The 710 diploid F₁s from A. batizocoi were generally sterile, while those from A. duranensis had fertility ranges from 5% to 84%. Meiotic chromosome relationships in diploid crosses were cytologically evaluated in 185 plants plus tester accessions. Most taxa in section Arachis have an A genome, only A. batizocoi accessions have a B genome, a D genome is represented by accessions 30091 and 30099, and two other genomic groups, represented by accessions 30011 and 30033, may be present in the section. Most cytological differentiation was found among species originally collected in southern and eastern Bolivia. On the other hand, species collected at the extremes of the distribution of section Arachis species (northern Argentina to north-central Brazil) were cytologically very similar. Evidence is presented for speciation in Arachis being associated with both genetic differentiation and with translocated chromosomes. All taxa in the section except the D-genome species are believed to be cross-compatible with A. hypogaea, so germplasm introgression from most Arachis species should be possible.     

Restriction fragment length polymorphism evaluation of six peanut species within the Avachis section

Summary Restriction fragment length polymorphisms (RFLP) were assessed among accessions within six peanut species of the Arachis section: tetraploid cultivated species, A. hypogaea; tetraploid wild species, A. monticola; and four diploid wild species, A. batizocoi,A. cardenasii, A. duranensis and A. glandulifera. While the two tetraploid species did not show polymorphism with 16 PstI-generated random genomic probes, two of seven seed cDNA probes detected polymorphisms. The RFLP variation detected by two seed cDNA probes appeared to be related to structural changes occurring within tetraploid species. The botanical var. fastigiata (Valencia market type) of A. hypogaea subspecies fastigiata was shown to be the most variable. Arachis monticola was found to be more closely related to A. hypogaea subspecies hypogaea than to subspecies fastigiata. Diploid species A. cardenasii, A. duranensis, and A. glandulifera showed considerable intraspecific genetic diversity, but A. batizocoi showed little polymorphism. The genetic distance between the cultivated peanut and wild diploid species was found to be closest for A. duranensis.Florida Agricultural Experiment Station, Journal Series No. R-01493     

Genetic relationships between peanut and wild species ofArachis sect.Arachis (Fabaceae): Evidence from RAPDs

Twenty-six accessions of wildArachis species and domesticated peanuts,A. hypogaea, introduced from South America were analyzed for random amplified polymorphic DNA (RAPD). The objective of the study was to investigate inter- and intraspecific variation and affinities among species of sect.Arachis which have been proposed as possible progenitors for the domesticated peanut. Ten primers resolved 132 DNA bands which were useful for separating species and accessions. The most variation was observed among accessions ofA. cardenasii andA. glandulifera whereas the least amount of variation was observed inA. hypogaea andA. monticola. The two tetraploid species could not be separated by using RAPDs.Arachis duranensis was most closely related to the domesticated peanut and is believed to be the donor of the A genome. The data indicated thatA. batizocoi, a species previously hypothesized to contribute the B genome toA. hypogaea, was not involved in its evolution. The investigation showed that RAPDs can be used to analyze both inter- and intraspecific variation in peanut species. Southern hybridization of RAPD probes to blots containing RAPD of theArachis species provided information on genomic relationships and revealed the repetitive nature of the amplified DNA.     

Identification of resistance to Peanut bud necrosis virus (PBNV) in wild Arachis germplasm

Eighty three wild Arachis germplasm accessions, belonging to 24 species of five sections and one natural hybrid derivative of a cross between the cultivated and a wild Arachis species, were evaluated along with a susceptible groundnut cultivar for resistance to Peanut bud necrosis virus (PBNV) in a replicated field trial at ICRISAT, Patancheru, India. Thirty days after sowing, the percentage of infected plants were recorded for all the accessions and subsequently young leaflets from all these accessions were tested for the presence of the virus by enzyme linked immunosorbent assay (ELISA). One accession each of A. benensis and A. cardenasii, and two accessions of A. villosa, in the section Arachis, two accessions of A. appressipila in the section Procumbentes, and one accession of A. triseminata under section Triseminatae were not infected by PBNV. These seven field‐resistant accessions were tested under glasshouse conditions for virus resistance by mechanical sap inoculations. One accession of A. cardenasii and two accessions of A. villosa did not show systemic infection. Similarly, in another glasshouse test, where 13 A. cardenasii accessions of section Arachis were evaluated, two accessions did not show systemic infection. In all these resistant accessions, the inoculated leaves showed infection, but the systemic leaves did not show the presence of virus in spite of repeated mechanical sap inoculations. So, the resistance in these accessions appears to be due to a block in systemic movement of the virus. To our knowledge this is the first report on the identification of resistance to PBNV in wild Arachis species. Since both A. cardenasii and A. villosa are the progenitors of cultivated groundnut and can be hybridised with the latter, the resistant accessions are being utilised in conventional breeding programmes to transfer PBNV resistance to widely adapted groundnut cultivars.     

RFLP variability in peanut (Arachis hypogaea L.) cultivars and wild species

Summary RFLP variability was studied in eight U.S. peanut cultivars, representing the four market types, and in 14 wild Arachis species accessions, using random genomic clones from a PstI library. Very low levels of RFLP variability were found among the allotetraploids, which included the U.S. cultivars and Arachis monticola, a wild species. The diploid wild species were very diverse, however. RFLP patterns of the allotetraploids were more complex than the diploids, and the two constituent genomes could usually be distinguished. On the basis of RFLP band sharing, A. ipaensis, A. duranensis, and A. spegazzinii appeared most closely related to the diploid progenitor species of the allotetraploids. A dendrogram of relationships among the diploid wild species was constructed based on band sharing.     

Genetic relationships among seven sections of genus <Emphasis Type="Italic">Arachis</Emphasis>studied by using SSR markers

Background  

The 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.     

Variation in chromosomal DNA associated with the evolution of Arachis species.

The 2C nuclear DNA amounts were determined for 99 accessions, representing 23 Arachis species from 8 of 9 taxonomic sections, and two synthetic amphidiploids. Mean 2C DNA amounts varied by 15.20%, ranging from 10.26 to 11.82 pg, between accessions of Arachis hypogaea (2n = 4x = 40). Nuclear DNA content variation (5.33-5.91 pg) was also detected among Arachis duranensis (2n = 2x = 20) accessions. The intraspecific variation in the two species may have resulted from indirect selection for favourable genome sizes in particular environmental conditions. The accessions belonging to A. hypogaea ssp. hypogaea (mean value 11.27 pg) with longer life cycle had significantly larger mean DNA content than the accessions of A. hypogaea ssp. fastigiata (mean value 10.97 pg). For 20 diploid (2n = 2x = 20) species of the genus, 2C nuclear DNA amounts ranged from approximately 3 to 7 pg. The diploid perennial species of section Arachis have about 12% more DNA than the annual species. Comparisons of DNA amounts show that evolutionary rating is not a reliable guide to DNA amounts in generic sections of the genus; lower DNA values with evolutionary advancement were found in sections Heteranthae and Triseminatae, but the same was not true for sections Arachis and Caulorrhizae. Similarly, there is evidence of significant differences in DNA content between 4 ancient sections (Procumbentes, Erectoides, Rhizomatosae, and Extranervosae) of the genus. The occurrence of genome size plasticity in both A. duranensis and A. hypogaea provides evidence that A. duranensis could be one of the diploid progenitors of A. hypogaea. The DNA content in the two synthetic amphidiploids corresponded to the sum value estimated for parental species. Key words : Arachis species, genome size, Arachis hypogaea, Arachis duranensis, intraspecific variation.     

Abundant Microsatellite Diversity and Oil Content in Wild Arachis Species

The peanut (Arachis hypogaea) is an important oil crop. Breeding for high oil content is becoming increasingly important. Wild Arachis species have been reported to harbor genes for many valuable traits that may enable the improvement of cultivated Arachis hypogaea, such as resistance to pests and disease. However, only limited information is available on variation in oil content. In the present study, a collection of 72 wild Arachis accessions representing 19 species and 3 cultivated peanut accessions were genotyped using 136 genome-wide SSR markers and phenotyped for oil content over three growing seasons. The wild Arachis accessions showed abundant diversity across the 19 species. A. duranensis exhibited the highest diversity, with a Shannon-Weaver diversity index of 0.35. A total of 129 unique alleles were detected in the species studied. A. rigonii exhibited the largest number of unique alleles (75), indicating that this species is highly differentiated. AMOVA and genetic distance analyses confirmed the genetic differentiation between the wild Arachis species. The majority of SSR alleles were detected exclusively in the wild species and not in A. hypogaea, indicating that directional selection or the hitchhiking effect has played an important role in the domestication of the cultivated peanut. The 75 accessions were grouped into three clusters based on population structure and phylogenic analysis, consistent with their taxonomic sections, species and genome types. A. villosa and A. batizocoi were grouped with A. hypogaea, suggesting the close relationship between these two diploid wild species and the cultivated peanut. Considerable phenotypic variation in oil content was observed among different sections and species. Nine alleles were identified as associated with oil content based on association analysis, of these, three alleles were associated with higher oil content but were absent in the cultivated peanut. The results demonstrated that there is great potential to increase the oil content in A. hypogaea by using the wild Arachis germplasm.     

Taxonomic relationships among Arachis sect. Arachis species as revealed by AFLP markers.

Cultivated peanut, Arachis hypogaea L., is a tetraploid (2n = 4x = 40) species thought to be of allopolyploid origin. Its closest relatives are the diploid (2n = 2x = 20) annual and perennial species included with it in Arachis sect. Arachis. Species in section Arachis represent an important source of novel alleles for improvement of cultivated peanut. A better understanding of the level of speciation and taxonomic relationships between taxa within section Arachis is a prerequisite to the effective use of this secondary gene pool in peanut breeding programs. The AFLP technique was used to determine intra- and interspecific relationships among and within 108 accessions of 26 species of this section. A total of 1328 fragments were generated with 8 primer combinations. From those, 239 bands ranging in size from 65 to 760 bp were scored as binary data. Genetic distances among accessions ranged from 0 to 0.50. Average distances among diploid species (0.30) were much higher than that detected between tetraploid species (0.05). Cluster analysis using different methods and principal component analysis were performed. The resulting grouping of accessions and species supports previous taxonomic classifications and genome designations. Based on genetic distances and cluster analysis, A-genome accessions KG 30029 (Arachis helodes) and KSSc 36009 (Arachis simpsonii) and B-genome accession KGBSPSc 30076 (A. ipaensis) were the most closely related to both Arachis hypogaea and Arachis monticola. This finding suggests their involvement in the evolution of the tetraploid peanut species.     

Karyological features and banding patterns in Arachis species belonging to the Heteranthae section

The section Heteranthae of Arachis is endemic to Brazil, occurring mainly in the semi-arid northeastern region. The section is considered derived within the genus and includes only annual herbs. Most previous cytological evaluations were restricted to chromosome numbers and morphology. The present approach comprised karyomorphological evaluation in 10 accessions from five species of this section, including standard staining and fluorochrome banding [chromomycin A3 (CMA)/4′,6-diamidino-2-phenylindole (DAPI)]. All accessions presented diploid chromosome numbers (2n = 20) with a prevalence of metacentric to submetacentric chromosome morphology. Arachis dardani, Arachis pusilla, and Arachis interrupta presented karyotypic formula 18m + 4sm and satellite type 2, while Arachis sylvestris and Arachis giacomettii presented 16m + 4sm and satellite type 10. Despite the conserved morphological features, higher diversity was detected in terms of size and number of GC-rich (CMA⁺) heterochromatic blocks among the species; however, all of them were located in the pericentromeric regions. The species A. pusilla presented the highest number of GC-rich blocks, present in all chromosomes of the complement. Based on the data obtained and considering literature data, we suggest that A. dardani and A. interrupta occupy a basal position in the group due to their moderate asymmetry and satellite type. At least in A. pusilla, the constitutive heterochromatin seems to have suffered recent modifications of its constitution, in contrast to other species that present pericentromeric CMA⁺ blocks in all chromosomes. A. giacomettii and A. sylvestris are closely related to each other and also similar to the previously studied Arachis seridoensis, revealing two clear-cut subgroups within the section from the karyological point of view.     

A single dominant gene for Fusarium wilt resistance in protoplast-derived tomato plants

Summary Autotetraploids were established from 8 diploid wild species of section Arachis. In all the autotetraploids the chromosomes paired largely as bivalents even though they possess the ability to pair as multivalents. Pollen and pod fertility in the C₁ generation were not directly associated with chromosome pairing. The C₂ generation autotetraploids showed a gradual increase in bivalent associations and pollen and pod fertility. The identification of two genomes, A and B, in the diploid species and in the tetraploid, A. hypogaea, of the section Arachis, a fairly good crossability, and the type of chromosome associations observed in hybrids between A. hypogaea and the autotetraploids of wild Arachis species indicated good prospects of utilizing autotetraploids as genetic bridges in transferring desired traits from these taxa into groundnut.Submitted as Journal Article No. 516 by International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)     

Isozyme variation and species relationships in peanut and its wild relatives (Arachis L. — Leguminosae)

Summary Arachis hypogaea (peanut or groundnut) is an AABB allotetraploid whose precise ancestry is not yet clear. Its closest diploid relatives are the annual and perennial wild species included with it in the section Arachis. Variation in these species for 11 different enzymes was studied by starch-gel electrophoresis. Differences attributed to at least 13 genetic loci were found among eight enzymes, while three enzymes appeared uniform throughout the section. Values for Nei's genetic distance were calculated for all pairs of species and were used to estimate relationships. All diploid species, apart from two whose validity had previously been questioned, could be distinguished by their overall zymotypes, but few contained unique alleles. When species were grouped by their mean genetic distances, they formed two clusters, which agreed reasonably well with the division of the section into annual versus perennial species. The single B-genome species was an outlier within the annual group. A. hypogaea showed fixed heterozygosity at four loci (in ssp. hypogaea) or six loci (in ssp. fastigiata), which agrees with previous conclusions that the peanut is an allotetraploid. None of the diploids included in this survey could be conclusively identified as donors of either the A or the B genome to the tetraploids. The two subspecies of A. hypogaea differed consistently in two of the thirteen putative loci studied. This may call into question the simple hypothesis that A. hypogaea originated from just two diploid species.     

Utilisation of wild relatives in the genetic improvement of Arachis hypogaea L.

Summary Cross-compatibility of species in section Arachis Krap. et Greg. nom. nud., and chromosome pairing and pollen fertility in their interspecific F₁ hybrids were studied to further understand the phylogenetic relationships among these species. Except those with A. batizocoi Krap. et Greg. nom. nud., hybrids between diploid species have near normal bivalent frequency (9.1–9.8) and moderate to high pollen fertility (60–91%). Hybrids between A. batizocoi and other species have low bivalent frequency (5.2–6.9) and very low pollen fertility (3–7%). These results confirm the earlier separation of these species into two groups based on karyomorphology and Mahalanobis D² calculated on arm ratios. These studies also provide a picture of relative affinities between A. batizocoi, the lone member of one cluster, and the other species, and among the rest of the species. They also indicate that the basic chromosome complement in the two groups of species is the same. Chromosome pairing in triploid hybrids, (A. hypogaea L. X diploid wild species), suggests that A. batizocoi is the closest diploid relative of A. hypogaea. It is closer to A. hypogaea subspecies fastigiata Waldron than to A. hypogaea subspecies hypogaea Krap. et. Rig. Other diploid species of the section Arachis are equidistant from A. hypogaea, and have the same genome which has strong homology to one of the genomes of A. hypogaea. Based on the present results, the two tetraploid species, A. monticola Krap. et Rig. and A. hypogaea can be recognised as two forms of the same species. Breeding implications have been discussed in the light of chromosome behaviour observed in hybrids of A. hypogaea X diploid species, and on the presumptions that A. hypogaea has an AABB genomic constitution, and that among the diploid species, the B genome is present in A. batizocoi while the A genome is common to the other diploid species of section Arachis.Submitted as Journal Article No. 328 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)     

CYTOPHOTOMETRIC DETERMINATION OF THE AMOUNT OF DNA IN ARACHIS L. SECT. ARACHIS (LEGUMINOSAE)

The 2C amounts of DNA for 12 taxa of the section Arachis nom. nud. of the genus Arachis L. were determined using cytophotometric techniques. The diploid taxa ranged from 4.92 to 5.98 pg of DNA per cell. The species of the diploid series Annuae Krap. & Greg. nom. nud. averaged ca. 1 pg less DNA per cell than the taxa of the diploid series Perennes Krap. & Greg. nom. nud. No significant differences were found between taxa within these two series. The tetraploid taxa ranged from 10.36 to 11.35 pg of DNA per cell. Within the tetraploid series Amphiploides Krap. & Greg. nom. nud. differences were found between A. monticola Krap. & Rig. and A. hypogaea L. The two subspecies of A. hypogaea, ssp. hypogaea and ssp. fastigiata Waldron, were found to differ significantly in their 2C amounts of DNA. The implications of the cytophotometric data on the chromosomal evolution of this section are discussed.     

Putative genome donors ofArachis hypogaea (Fabaceae), evidence from crosses with synthetic amphidiploids

Chromosome pairing, pollen and pod fertility in hybrids between cultivated tetraploidArachis hypogaea and 15 synthetic amphidiploids from 8 diploid species (7 of the A genome and 1 of the B genome) of sect.Arachis have been utilized for the identification of putative genome donors in the evolution of cultivatedA. hypogaea. These results, in conjunction with evidence from morphological similarities, phytogeographical distribution and some phytochemical features, confirm the segmental amphidiploid origin ofA. hypogaea. A. batizocoi andA. duranensis are suggested as the donors of the B genome and the A genome respectively.     

Phylogenetic relations in section Arachis based on seed protein profile

Summary Seed protein profiles of nine diploid species (2n = 20), ten tetraploid accessions, two synthetic amphidiploids and two autotetraploids (2n = 40) were studied using SDS-polyacrylamide gel electrophoresis. While the general profiles suggested considerable homology among these taxa in spite of speciation and ploidy differences, appreciable genetic differences were present to support the existing genomic divisions and sub-divisions in the section Arachis. A high degree of relationship was indicated between the two diploid species (A. duranensis containing the A genome and A. batizocoi (ICG 8210) containing the B genome) and tetraploids A. monticola/ A. hypogaea (2n = 40) containing AABB genome. Similar relationships were recorded between the AABB synthetic amphidiploid and the profile obtained from the mixture of protein of A. duranensis and A. batizocoi, suggesting that these two diploid species were the donors of the A and B genome, respectively, to tetraploid A. monticola/A. hypogaea.Submitted as Journal Article No. 1114 by International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)     

Genomic in situ hybridization inArachis (Fabaceae) identifies the diploid wild progenitors of cultivated (A. hypogaea) and related wild (A. monticola) peanut species

Genomic in situ hybridization offers a powerful tool for investigating genome organisation and evolution of taxa known, or suspected, to be allopolyploids. The question of the diploid progenitors of cultivated peanut (Arachis hypogaea, 2n=4x=40) has been the subject of numerous studies at cytogenetical, cytochemical, biochemical and molecular levels, but no definitive conclusions have been reached. The biotinylated total genomic DNA from potential diploidArachis species were separately hybridized in situ to root tip chromosomes ofA. hypogaea and wild speciesA. monticola (2n=4x=40) without or mixed with an excess of unlabelled DNA from the species not used as a probe. Among the range of different species combinations used, the strong and uniform signals given by labelledA. ipaensis DNA when hybridized toA. hypogaea andA. monticola in combination with unlabelledA. villosa DNA indicates that overall molecular composition of twenty chromosomes ofA. hypogaea andA. monticola is very similar toA. ipaensis chromosomes. ProbingA. hypogaea andA. monticola chromosomes with labelled genomic DNA fromA. villosa mixed with unlabelled DNA fromA. ipaensis likewise labelled strongly and uniformly the other twenty chromosomes. BarringA. ipaensis, all the diploidArachis species presently investigated had characteristic centromeric bands in the twenty chromosomes within the complement indicating a clear division ofA. ipaensis from other species. InA. hypogaea andA. monticola only twenty chromosomes showed centromeric bands. These results (i) confirm the allopolyploid nature ofA. hypogaea andA. monticola, (ii) strongly support the view that wildA. monticola and cultivatedA. hypogaea are very closely related, and (iii) indicate thatA. villosa andA. ipaensis are the diploid wild progenitors of the tetraploid species studied. The present results also reveal that the nucleolus organizing region (NOR) originating fromA. villosa alone is expressed in the two tetraploid species.     

Use of single-primer DNA amplifications in genetic studies of peanut (Arachis hypogaea L.)

A recent approach to detecting genetic polymorphism involves the amplification of genomic DNA using single primers of arbitrary sequence. When separated electrophoretically in agarose gels, the amplification products give banding patterns that can be scored for genetic variation. The objective of this research was to apply these techniques to cultivated peanut (Arachis hypogaea L.) and related wild species to determine whether such an approach would be feasible for the construction of a genetic linkage map in peanut or for systematic studies of the genus. Two peanut cultivars, 25 unadapted germplasm lines of A. hypogaea, the wild allotetraploid progenitor of cultivated peanut (A. monticola), A. glabrata (a tetraploid species from section Rhizomatosae), and 29 diploid wild species of Arachis were evaluated for variability using primers of arbitrary sequence to amplify segments of genomic DNA. No variation in banding pattern was observed among the cultivars and germplasm lines of A. hypogaea, whereas the wild Arachis species were uniquely identified with most primers tested. Bands were scored (+/–) in the wild species and the PAUP computer program for phylogenetic analysis and the HyperRFLP program for genetic distance analysis were used to generate dendrograms showing genetic relationships among the diploid Arachis species evaluated. The two analyses produced nearly identical dendrograms of species relationships. In addition, approximately 100 F₂ progeny from each of two interspecific crosses were evaluated for segregation of banding patterns. Although normal segregation was observed among the F₂ progeny from both crosses, banding patterns were quite complex and undesirable for use in genetic mapping. The dominant behavior of the markers prevented the differentiation of heterozygotes from homozygotes with certainty, limiting the usefulness of arbitrary primer amplification products as markers in the construction of a genetic linkage map in peanut.     

Characterization and transferability of microsatellite markers of the cultivated peanut (<Emphasis Type="Italic">Arachis hypogaea</Emphasis>)

Background  

The genus Arachis includes Arachis hypogaea (cultivated peanut) and wild species that are used in peanut breeding or as forage. Molecular markers have been employed in several studies of this genus, but microsatellite markers have only been used in few investigations. Microsatellites are very informative and are useful to assess genetic variability, analyze mating systems and in genetic mapping. The objectives of this study were to develop A. hypogaea microsatellite loci and to evaluate the transferability of these markers to other Arachis species.     

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.