Presence of resveratrol in wild Arachis species adds new value to this overlooked genetic resource.

Genus Arachis comprises 82 species distributed into nine taxonomic sections. Most Arachis species are wild and those from Arachis section have been evaluated for many traits, since they can be used in peanut breeding. Most of the remaining species have been neglected and understudied. Recently, resveratrol content and expression of a resveratrol synthase gene were analyzed in wild Arachis species. Our aim was to expand the knowledge about resveratrol in Arachis, analyzing species from five sections and evaluating the expression of a resveratrol synthase (RS) gene responsive to ultraviolet light (UV) along the time. In a first experiment, the resveratrol content after UV induction was analyzed on detached leaves of 12 species from five sections. Variation was observed among species and accessions of the same species. The highest contents were found in A. lignosa (843.9 µg/g) and A. triseminata (745.4 µg/g). In a second experiment, RS expression and resveratrol content in four species and one synthetic amphidiploid were analyzed at 0, 7, 15 and 24 h pos induction (hpi) with UV. In most genotypes, the highest RS expression level was at 0 hpi, whereas the highest resveratrol content was at 15 hpi. Our results suggested that resveratrol is ubiquitously present in the genus Arachis with different capacities of synthesis among species and accessions in response to ultraviolet treatment. Presence of resveratrol in wild Arachis species adds new value to these genetic resources.

The genome sequence of segmental allotetraploid peanut Arachis hypogaea.

Like many other crops, the cultivated peanut (Arachis hypogaea L.) is of hybrid origin and has a polyploid genome that contains essentially complete sets of chromosomes from two ancestral species. Here we report the genome sequence of peanut and show that after its polyploid origin, the genome has evolved through mobile-element activity, deletions and by the flow of genetic information between corresponding ancestral chromosomes (that is, homeologous recombination). Uniformity of patterns of homeologous recombination at the ends of chromosomes favors a single origin for cultivated peanut and its wild counterpart A. monticola. However, through much of the genome, homeologous recombination has created diversity. Using new polyploid hybrids made from the ancestral species, we show how this can generate phenotypic changes such as spontaneous changes in the color of the flowers. We suggest that diversity generated by these genetic mechanisms helped to favor the domestication of the polyploid A. hypogaea over other diploid Arachis species cultivated by humans.

Selected nutrients and antinutrients in peanut cultivars harvested in Brazil.

BACKGROUND: There are more than 30 peanut cultivars registered in Brazil. However, there are no published data about the content of nutrients and antinutrients even in the most commercially important ones. Therefore, our objective was to characterize commercial peanut cultivars harvested in Brazil by determining proximate and fatty acid composition and content of selected minerals and phytates, saponins and condensed tannins. RESULTS: Significant variations were found among the cultivars for almost all studied nutrients, except Mg. Granoleico and IAC 505 were identified as high oleic. Results were compared with data from the Brazilian Food Composition Table (TACO) and, for this, percentage differences (D%) were calculated. Appreciable D% were found for proteins, lipids, ash, dietary fiber, almost all fatty acids (except 20:0) and almost all studied minerals (except zinc). Moreover, remarkable variations in content of antinutrients were observed. IAC Red Tatu had the highest content of saponins; IAC OL3 and IAC 886 had the highest amounts of phytates; and IAC 886 had the highest amounts of condensed tannins. CONCLUSION: Results confirm the relevance of differentiating cultivars in the market and in national food composition tables and databases. Furthermore, some of these cultivars may be indicated for new use trends. © 2019 Society of Chemical Industry.

Morphological, cytogenetic, and molecular characterization of Arachis kuhlmannii Krapov. & W.C. Greg. (Leguminosae).

Arachis kuhlmannii occurs in Mato Grosso and Mato Grosso do Sul States, Brazil. Its area of occurrence partially overlaps with that of other species in the Arachis section. Because of their morphological similarities, these species are often mistaken one for another. This study aimed the correct classification of available accessions as Arachis kuhlmannii, or other species, and the characterization of similarities among accessions and Arachis hypogaea by morphological, cytogenetic, and molecular marker analyses. Thirty-eight accessions were used. Principal component analysis was used for morphological characterization, root tips for mitotic metaphase analysis, and RAPD markers for molecular characterization. Cluster analysis discriminated accessions with the A genome from the B genome. Cluster analysis based on molecular markers discriminated natural populations in a manner that correlated with geographical areas of the collection. Arachis cardenasii and A. hypogaea were isolated from other A-genome accessions. Cytogenetic analyses confirmed the existence of diagnostic characteristics that distinguish species with the A genome from those with the B genome. Results suggest the need for a taxonomic review of some species in the Arachis section, as we could not discriminate as distinct species all of the accessions identified as A. kuhlmannii, A. helodes, and A. simpsonii by using morphological, molecular, and cytogenetic markers.

Genetic diversity of the forage peanut in the Jequitinhonha, São Francisco, and Paranã River valleys of Brazil.

Arachis pintoi and A. repens are legumes with a high forage value that are used to feed ruminants in consortium systems. Not only do they increase the persistence and quality of pastures, they are also used for ornamental and green cover. The objective of this study was to analyze microsatellite markers in order to access the genetic diversity of 65 forage peanut germplasm accessions in the section Caulorrhizae of the genus Arachis in the Jequitinhonha, São Francisco and Paranã River valleys of Brazil. Fifty-seven accessions of A. pintoi and eight of A. repens were analyzed using 17 microsatellites, and the observed heterozygosity (HO), expected heterozygosity (HE), number of alleles per locus, discriminatory power, and polymorphism information content were all estimated. Ten loci (58.8%) were polymorphic, and 125 alleles were found in total. The HE ranged from 0.30 to 0.94, and HO values ranged from 0.03 to 0.88. By using Bayesian analysis, the accessions were genetically differentiated into three gene pools. Neither the unweighted pair group method with arithmetic mean nor a neighbor-joining analysis clustered samples into species, origin, or collection area. These results reveal a very weak genetic structure that does not form defined clusters, and that there is a high degree of similarity between the two species.

Identification of Fungus Resistant Wild Accessions and Interspecific Hybrids of the Genus Arachis.

Peanut, Arachis hypogaea L., is a protein-rich species consumed worldwide. A key improvement to peanut culture involves the development of cultivars that resist fungal diseases such as rust, leaf spot and scab. Over three years, we evaluated fungal resistance under field conditions of 43 wild accessions and three interspecific hybrids of the genus Arachis, as well as six A. hypogaea genotypes. In the first year, we evaluated resistance to early and late leaf spot, rust and scab. In the second and third years, we evaluated the 18 wild species with the best resistance scores and control cultivar IAC Caiapó for resistance to leaf spot and rust. All wild accessions displayed greater resistance than A. hypogaea but differed in their degree of resistance, even within the same species. We found accessions with as good as or better resistance than A. cardenasii, including: A. stenosperma (V15076 and Sv 3712), A. kuhlmannii (V 6413), A. kempff-mercadoi (V 13250), A. hoehnei (KG 30006), and A. helodes (V 6325). Amphidiploids and hybrids of A. hypogaea behaved similarly to wild species. An additional four accessions deserve further evaluation: A. magna (V 13751 and KG 30097) and A. gregoryi (V 14767 and V 14957). Although they did not display as strong resistance as the accessions cited above, they belong to the B genome type that is crucial to resistance gene introgression and pyramidization in A. hypogaea.

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

BACKGROUND AND AIMS: 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. METHODS: Intron sequences and microsatellite markers were used to reconstruct phylogenetic relationships in section Arachis through maximum parsimony and genetic distance analyses. KEY RESULTS: 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. CONCLUSIONS: 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.

Determinação do nível de controle econômico de Enneothrips flavens moulton, 1941 (Thysanoptera: Thropidae) em cultivar de amendoim de porto ereto / Determination of the level of economic control of Enneothrips flavens moulton, 1941 (Thysanoptera: Thripidae) in the upright peanut crop

O objetivo do presente trabalho foi avaliar diferentes níveis de controle econômico de Enneothrips flavens, na cultura do amendoim ereto, nas épocas de cultivo “das águas” e “da seca ”. O estudo foi realizado na área experimental do Departamento de Fitossanidade da FCAV/UNESP - Campus de Jaboticabal, SP, em 2007/2008. Para a avaliação, foram realizadas amostragens a partir dos 17 dias após a emergência das plantas (DAE), coletando-se dez folíolos fechados por parcela. Determinaram-se a produção de grãos em casca e a massa seca de 100 sementes. Determinadas a produção e o número de aplicações de thiametoxam + lambda-cialotrina, foram obtidos o ganho de produção e a variação no rendimento líquido. Concluiu-se no estudo que as plantas de amendoim foram mais infestadas dos 17 aos 30 e dos 47 aos 74 (DAE) para o plantio na época “da seca” e dos 32 aos 53 (DAE) na época “das águas”; o tratamento controle total obteve as maiores produções e variação no rendimento líquido em relação à testemunha com 26,43 sacas. ha-1 e R$ 585,66 para o plantio realizado na época “da seca”, e com 53,88 sacas. ha-1 e R$ 1354,26 para o plantio realizado na época “das águas”. O controle de E. flavens com 20% dos folíolos atacados para os cultivos rea-lizados foi o mais próximo do controle total na produção (sacas.ha-1) e variação do rendimento líquido; o inseticida thiametoxam + lambda-cialotrina mostrou-se eficiente no controle da praga resultando em acréscimo na produção de amendoim nas duas épocas de cultivo.(AU)

The present work was aimed to evaluate different economic control levels of Enneothrips flavens in upright peanut plants, during the “dry” and “wet” seasons. The experiments were carried out at the Departamento de Fitossanidade, FCAV/UNESP Jaboticabal, SP, Brazil, in 2007/2008. To evaluate the different E. flavens infestation levels, samplings were carried out at 17 days after plant emergence (DAE), collecting 10 closed leaflets per parcel. Peeled grain production (kg ha-1), and 100-seed dry mass (g) were also determined. Once the production and thiamethoxam + lambda-cyhalothrin spraying times were determined, the production gain (25 kg bags and kg.ha-1) and net profit variation were obtained. It was concluded that the peanut plants were more infested from 17 to 30 DAE and from 47 to 74 DAE for the “dry” cultivation and 32 to 53 DAE for the “wet” cultivation; the total-control treatment presented higher production and net profit variation as compared to the control plot with 26.43 bags.ha-1 and R$ 585.66 for the planting season held in “drought,” and 53.88 bags.ha-1 and R$ 1,354.26 for the planting done during the “wet” time; E. flavens control with 20% of leaflets attacked in both seasons was the closest to total control in the production (bags.ha-1) and net profit variation; the insecticide thiamethoxam + lambda-cyhalothrin was effective to control the pest, resulting in increased the peanut production in both cultivation seasons.(AU)

Avaliação de resistência de cultivares de amendoim de hábito de crescimento rasteiro a Enneothrips flavens Moulton (Thysanoptera: Thripidae) / Evaluation of peanut cultivars with runner growing habit for resistance to Enneothrips flavens, Moulton (Thysanoptera: Thripidae)

Devido a sua ampla distribuição e aos danos acarretados, Enneothripsflavens Moulton destacase como a principal praga do amendoim no Brasil. O objetivo do presente trabalho foi avaliar, em condições de campo, o comportamento de quatro cultivares de amendoim de hábito de crescimento rasteiro sob infestação natural de E. flavens. Os experimentos foram desenvolvidos na área experimental do Departamento de Fitossanidade da FCAV/UNESP - Campus de Jaboticabal, SP. O delineamento experimental utilizado foi em blocos ao acaso, com quatro tratamentos em seis repetições. Foram utilizadas os cultivares IAC Caiapó, IAC 125, IAC 147 e IAC Runner-886. Foram avaliados o número de ninfas e adultos de E. flavens, porcentagem de folíolos atacados, sintomas de intensidade de ataque, número de brotos apicais por planta, massa seca das plantas, produção de grãos em casca (kg ha-1) e a massa seca de 100 sementes (g). Os cultivares não diferiram quanto ao nível de infestação de ninfas e adultos de E. flavens. O período de maior infestação de ninfas ocorreu entre 15 e 41 DAE, e de adultos entre 15 e 48 DAE. Analisando-se a produção, o cultivar IAC Caiapó comportou-se como portador de resistência do tipo tolerância ao ataque de E. flavens. (AU)

EVALUATION OF PEANUT CULTIVARS WITH RUNNER GROWING HABIT FOR RESISTANCE TO ENNEOTHRIPS FLAVENS, MOULTON (THYSANOPTERA: THRIPIDAE). Due to its widespread distribution and known damages, Enneothrips flavens Moulton is considered the major pest of the peanut crop in Brazil. The objective of the present study was to evaluate the behavior of four runner peanut cultivars under natural field infestation of this insect. The experiments were carried out in the experimental area of FCAV/UNESP, Jaboticabal, state of São Paulo, Brazil, using a completely randomized block design with 4 treatments and 6 replications. The cultivars studied were IAC Caiapó, IAC 125, IAC 147 and Runner IAC 886. Insect infestation and damage, as well as plant behavior were evaluated as to the number of nymphae and adults, percentage of attacked leaflets, symptoms of attack intensity, number of apical buds/plant, plant dry weight, yield of unshelled pods/plant and 100 kernel weight. No significant difference was noted between cultivars regarding the level of E. flavens (adult and nymphae) infestation. The largest nymphae infestation was recorded at the 15-41 DAE (days after emergency) period. As for the adults, the largest infestation occurred between 15 and 48 days after emergence. The evaluation of yield performance under thrips (E. flavens) infestation suggested that the cultivar IAC Caiapó behaved as tolerant to the attack of this insect. (AU)

Determinação do nível de controle econômico de Enneothrips flavens moulton, 1941 (Thysanoptera: Thropidae) em cultivar de amendoim de porto ereto / Determination of the level of economic control of Enneothrips flavens moulton, 1941 (Thysanoptera: Thripidae) in the upright peanut crop

O objetivo do presente trabalho foi avaliar diferentes níveis de controle econômico de Enneothrips flavens, na cultura do amendoim ereto, nas épocas de cultivo “das águas” e “da seca ”. O estudo foi realizado na área experimental do Departamento de Fitossanidade da FCAV/UNESP - Campus de Jaboticabal, SP, em 2007/2008. Para a avaliação, foram realizadas amostragens a partir dos 17 dias após a emergência das plantas (DAE), coletando-se dez folíolos fechados por parcela. Determinaram-se a produção de grãos em casca e a massa seca de 100 sementes. Determinadas a produção e o número de aplicações de thiametoxam + lambda-cialotrina, foram obtidos o ganho de produção e a variação no rendimento líquido. Concluiu-se no estudo que as plantas de amendoim foram mais infestadas dos 17 aos 30 e dos 47 aos 74 (DAE) para o plantio na época “da seca” e dos 32 aos 53 (DAE) na época “das águas”; o tratamento controle total obteve as maiores produções e variação no rendimento líquido em relação à testemunha com 26,43 sacas. ha-1 e R$ 585,66 para o plantio realizado na época “da seca”, e com 53,88 sacas. ha-1 e R$ 1354,26 para o plantio realizado na época “das águas”. O controle de E. flavens com 20% dos folíolos atacados para os cultivos rea-lizados foi o mais próximo do controle total na produção (sacas.ha-1) e variação do rendimento líquido; o inseticida thiametoxam + lambda-cialotrina mostrou-se eficiente no controle da praga resultando em acréscimo na produção de amendoim nas duas épocas de cultivo.

The present work was aimed to evaluate different economic control levels of Enneothrips flavens in upright peanut plants, during the “dry” and “wet” seasons. The experiments were carried out at the Departamento de Fitossanidade, FCAV/UNESP – Jaboticabal, SP, Brazil, in 2007/2008. To evaluate the different E. flavens infestation levels, samplings were carried out at 17 days after plant emergence (DAE), collecting 10 closed leaflets per parcel. Peeled grain production (kg ha-1), and 100-seed dry mass (g) were also determined. Once the production and thiamethoxam + lambda-cyhalothrin spraying times were determined, the production gain (25 kg bags and kg.ha-1) and net profit variation were obtained. It was concluded that the peanut plants were more infested from 17 to 30 DAE and from 47 to 74 DAE for the “dry” cultivation and 32 to 53 DAE for the “wet” cultivation; the total-control treatment presented higher production and net profit variation as compared to the control plot with 26.43 bags.ha-1 and R$ 585.66 for the planting season held in “drought,” and 53.88 bags.ha-1 and R$ 1,354.26 for the planting done during the “wet” time; E. flavens control with 20% of leaflets attacked in both seasons was the closest to total control in the production (bags.ha-1) and net profit variation; the insecticide thiamethoxam + lambda-cyhalothrin was effective to control the pest, resulting in increased the peanut production in both cultivation seasons.

Avaliação de resistência de cultivares de amendoim de hábito de crescimento rasteiro a Enneothrips flavens Moulton (Thysanoptera: Thripidae) / Evaluation of peanut cultivars with runner growing habit for resistance to Enneothrips flavens, Moulton (Thysanoptera: Thripidae)

Devido a sua ampla distribuição e aos danos acarretados, Enneothripsflavens Moulton destacase como a principal praga do amendoim no Brasil. O objetivo do presente trabalho foi avaliar, em condições de campo, o comportamento de quatro cultivares de amendoim de hábito de crescimento rasteiro sob infestação natural de E. flavens. Os experimentos foram desenvolvidos na área experimental do Departamento de Fitossanidade da FCAV/UNESP - Campus de Jaboticabal, SP. O delineamento experimental utilizado foi em blocos ao acaso, com quatro tratamentos em seis repetições. Foram utilizadas os cultivares IAC Caiapó, IAC 125, IAC 147 e IAC Runner-886. Foram avaliados o número de ninfas e adultos de E. flavens, porcentagem de folíolos atacados, sintomas de intensidade de ataque, número de brotos apicais por planta, massa seca das plantas, produção de grãos em casca (kg ha-1) e a massa seca de 100 sementes (g). Os cultivares não diferiram quanto ao nível de infestação de ninfas e adultos de E. flavens. O período de maior infestação de ninfas ocorreu entre 15 e 41 DAE, e de adultos entre 15 e 48 DAE. Analisando-se a produção, o cultivar IAC Caiapó comportou-se como portador de resistência do tipo tolerância ao ataque de E. flavens.

EVALUATION OF PEANUT CULTIVARS WITH RUNNER GROWING HABIT FOR RESISTANCE TO ENNEOTHRIPS FLAVENS, MOULTON (THYSANOPTERA: THRIPIDAE). Due to its widespread distribution and known damages, Enneothrips flavens Moulton is considered the major pest of the peanut crop in Brazil. The objective of the present study was to evaluate the behavior of four runner peanut cultivars under natural field infestation of this insect. The experiments were carried out in the experimental area of FCAV/UNESP, Jaboticabal, state of São Paulo, Brazil, using a completely randomized block design with 4 treatments and 6 replications. The cultivars studied were IAC Caiapó, IAC 125, IAC 147 and Runner IAC 886. Insect infestation and damage, as well as plant behavior were evaluated as to the number of nymphae and adults, percentage of attacked leaflets, symptoms of attack intensity, number of apical buds/plant, plant dry weight, yield of unshelled pods/plant and 100 kernel weight. No significant difference was noted between cultivars regarding the level of E. flavens (adult and nymphae) infestation. The largest nymphae infestation was recorded at the 15-41 DAE (days after emergency) period. As for the adults, the largest infestation occurred between 15 and 48 days after emergence. The evaluation of yield performance under thrips (E. flavens) infestation suggested that the cultivar IAC Caiapó behaved as tolerant to the attack of this insect.

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

BACKGROUND: The 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. RESULTS: Intraspecific 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. CONCLUSION: The 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 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.

Genetic diversity of peanut (Arachis hypogaea L.) and its wild relatives based on the analysis of hypervariable regions of the genome.

BACKGROUND: The genus Arachis is native to a region that includes Central Brazil and neighboring countries. Little is known about the genetic variability of the Brazilian cultivated peanut (Arachis hypogaea, genome AABB) germplasm collection at the DNA level. The understanding of the genetic diversity of cultivated and wild species of peanut (Arachis spp.) is essential to develop strategies of collection, conservation and use of the germplasm in variety development. The identity of the ancestor progenitor species of cultivated peanut has also been of great interest. Several species have been suggested as putative AA and BB genome donors to allotetraploid A. hypogaea. Microsatellite or SSR (Simple Sequence Repeat) markers are co-dominant, multiallelic, and highly polymorphic genetic markers, appropriate for genetic diversity studies. Microsatellite markers may also, to some extent, support phylogenetic inferences. Here we report the use of a set of microsatellite markers, including newly developed ones, for phylogenetic inferences and the analysis of genetic variation of accessions of A. hypogea and its wild relatives. RESULTS: A total of 67 new microsatellite markers (mainly TTG motif) were developed for Arachis. Only three of these markers, however, were polymorphic in cultivated peanut. These three new markers plus five other markers characterized previously were evaluated for number of alleles per locus and gene diversity using 60 accessions of A. hypogaea. Genetic relationships among these 60 accessions and a sample of 36 wild accessions representative of section Arachis were estimated using allelic variation observed in a selected set of 12 SSR markers. Results showed that the Brazilian peanut germplasm collection has considerable levels of genetic diversity detected by SSR markers. Similarity groups for A. hypogaea accessions were established, which is a useful criteria for selecting parental plants for crop improvement. Microsatellite marker transferability was up to 76% for species of the section Arachis, but only 45% for species from the other eight Arachis sections tested. A new marker (Ah-041) presented a 100% transferability and could be used to classify the peanut accessions in AA and non-AA genome carriers. CONCLUSION: The level of polymorphism observed among accessions of A. hypogaea analyzed with newly developed microsatellite markers was low, corroborating the accumulated data which show that cultivated peanut presents a relatively reduced variation at the DNA level. A selected panel of SSR markers allowed the classification of A. hypogaea accessions into two major groups. The identification of similarity groups will be useful for the selection of parental plants to be used in breeding programs. Marker transferability is relatively high between accessions of section Arachis. The possibility of using microsatellite markers developed for one species in genetic evaluation of other species greatly reduces the cost of the analysis, since the development of microsatellite markers is still expensive and time consuming. The SSR markers developed in this study could be very useful for genetic analysis of wild species of Arachis, including comparative genome mapping, population genetic structure and phylogenetic inferences among species.

A large scale analysis of resistance gene homologues in Arachis.

Arachis hypogaea L., commonly known as the peanut or groundnut, is an important and widespread food legume. Because the crop has a narrow genetic base, genetic diversity in A. hypogaea is low and it lacks sources of resistance to many pests and diseases. In contrast, wild diploid Arachis species are genetically diverse and are rich sources of disease resistance genes. The majority of known plant disease resistance genes encode proteins with a nucleotide binding site domain (NBS). In this study, degenerate PCR primers designed to bind to DNA regions encoding conserved motifs within this domain were used to amplify NBS-encoding regions from Arachis spp. The Arachis spp. used were A. hypogaea var. Tatu and wild species that are known to be sources of disease resistance: A. cardenasii, A. duranensis, A. stenosperma and A. simpsonii. A total of 78 complete NBS-encoding regions were isolated, of which 63 had uninterrupted ORFs. Phylogenetic analysis of the Arachis NBS sequences derived in this study and other NBS sequences from Arabidopsis thaliana, Medicago trunculata, Glycine max, Lotus japonicus and Phaseolus vulgaris that are available in public databases This analysis indicates that most Arachis NBS sequences fall within legume-specific clades, some of which appear to have undergone extensive copy number expansions in the legumes. In addition, NBS motifs from A. thaliana and legumes were characterized. Differences in the TIR and non-TIR motifs were identified. The likely effect of these differences on the amplification of NBS-encoding sequences by PCR is discussed.