Cultivated peanut (Arachis hypogaea) is an important crop, widely grown in tropical and subtropical regions of the world. It is highly susceptible to several biotic and abiotic stresses to which wild species are resistant. As a first step towards the introgression of these resistance genes into cultivated peanut, a linkage map based on microsatellite markers was constructed, using an F(2) population obtained from a cross between two diploid wild species with AA genome (A. duranensis and A. stenosperma). A total of 271 new microsatellite markers were developed in the present study from SSR-enriched genomic libraries, expressed sequence tags (ESTs), and by "data-mining" sequences available in GenBank. Of these, 66 were polymorphic for cultivated peanut. The 271 new markers plus another 162 published for peanut were screened against both progenitors and 204 of these (47.1%) were polymorphic, with 170 codominant and 34 dominant markers. The 80 codominant markers segregating 1:2:1 (P<0.05) were initially used to establish the linkage groups. Distorted and dominant markers were subsequently included in the map. The resulting linkage map consists of 11 linkage groups covering 1,230.89 cM of total map distance, with an average distance of 7.24 cM between markers. This is the first microsatellite-based map published for Arachis, and the first map based on sequences that are all currently publicly available. Because most markers used were derived from ESTs and genomic libraries made using methylation-sensitive restriction enzymes, about one-third of the mapped markers are genic. Linkage group ordering is being validated in other mapping populations, with the aim of constructing a transferable reference map for Arachis.

Nuclear restriction fragment length polymorphism (RFLP) analysis was used to determine the wild diploid Arachis species that hybridized to form tetraploid domesticated peanut. Results using 20 previously mapped cDNA clones strongly indicated A. duranensis as the progenitor of the A genome of domesticated peanut and A. ipaensis as the B genome parent. A large amount of RFLP variability was found among the various accessions of A. duranensis, and accessions most similar to the A genome of cultivated peanut were identified. Chloroplast DNA RFLP analysis determined that A. duranensis was the female parent of the original hybridization event. Domesticated peanut is known to have one genome with a distinctly smaller pair of chromosomes (“A”), and one genome that lacks this pair. Cytogenetic analysis demonstrated that A. duranensis has a pair of “A” chromosomes, and A. ipaensis does not. The cytogenetic evidence is thus consistent with the RFLP evidence concerning the identity of the progenitors. RFLP and cytogenetic evidence indicate a single origin for domesticated peanut in Northern Argentina or Southern Bolivia, followed by diversification under the influence of cultivation.

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Background: Arachis hypogaea (peanut) is an important crop worldwide, being mostly used for edible oil production, direct consumption and animal feed. Cultivated peanut is an allotetraploid species with two different genome components, A and B. Genetic linkage maps can greatly assist molecular breeding and genomic studies. However, the development of linkage maps for A. hypogaea is difficult because it has very low levels of polymorphism. This can be overcome by the utilization of wild species of Arachis, which present the A-and Bgenomes in the diploid state, and show high levels of genetic variability.

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.

Fifteen polymorphic microsatellite markers were isolated and characterized in two species of Bromeliaceae: Vriesea gigantea and Alcantarea imperialis. The number of alleles observed for each locus ranged from three to 16. The loci will be used for studies of the genetic structure of natural populations, reproductive biology, and evolutionary relationships among and within these genera. A cross‐amplification test in 22 taxa suggests that the markers will be useful for similar applications in numerous other bromeliad species.

RESUMO -Um dos principais mecanismos de sobrevivência das plantas daninhas em ambientes constantemente perturbados é a alta produção de sementes. Essas possuem geralmente algum mecanismo de dormência, o qual contribui para a perpetuação de espécies interferentes nos cultivos agrícolas. A dormência pode ser caracterizada pela ausência temporária da germinação, mesmo quando em condições adequadas de sua ocorrência. Isso permite que inúmeras espécies vegetais sobrevivam às adversidades, sobretudo aquelas que dificultam ou impeçam o seu crescimento vegetativo e reprodutivo. As causas da dormência são provenientes de dois mecanismos básicos, sendo o primeiro relacionado a eventos internos das sementes (embrião) e o segundo, às características externas (tegumento, endosperma ou as barreiras impostas pelo fruto). Conceitualmente, a dormência pode ser distinguida em dois tipos: dormência primária (quando os mecanismos de dormência ocorrem ainda na planta-mãe) e secundária (quando os mecanismos de estabelecimento da dormência ocorrem após a dispersão das sementes). A ocorrência desses dois tipos de dormência é comum em plantas daninhas. A sua alternância ou ciclagem garante o fluxo de germinação destas espécies, o qual depende das características iniciais durante a formação das sementes (dormência primária) e, posteriormente, das condições ambientais (dormência secundária). Todavia, muitos são os mecanismos que coordenam a dormência, sendo a distinção destes ainda controversos. Nesse sentido, este estudo tem por objetivo abordar alguns dos principais conceitos e mecanismos de dormência em plantas daninhas, com intuito de contribuir e estimular as pesquisas, ainda escassas, nessa área.Palavras-chave: germinação, banco de sementes, interferência.ABSTRACT -The high production of seeds in constantly disturbed environments is one of the main mechanisms of weeds survival. These seeds have usually some dormancy mechanism which constitutes weed species perpetuation in the crops. Seed dormancy can be characterized by temporally absence of the germination capacity, even though the seeds have satisfactorily conditions to germinate, thus allowing species survival under adversities, mainly those that make it difficult or hinder vegetative and reproductive growth. The causes of dormancy stem from two basic mechanisms: the first is related to inner seed events (embryo) and the second to outer characteristics in the seeds (tegument, endosperm or fruit barriers). Conceptually, dormancy can be classified as primary dormancy (when the mechanisms occur in plants-mother) and secondary dormancy (when the mechanisms causing dormancy occur after seed dispersion). These types of dormancy occur normally in weeds. Their alternation or cycling ensures germination flow these species, which depends on the characteristics occurring at the initial stages of seed formation (primary dormancy), and later, on the environmental conditions (secondary dormancy). However, many mechanisms coordinate dormancy, with the differences among them being still controve...

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.