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Unreduced (2n) gametes are the driving force that leads to polyploidization of plants in nature and an important tool for ploidy breeding. Peanut (Arachis hypogaea L., Leguminosae) seems most likely to have originated by sexual polyploidization through interspecific hybridization between the wild diploid relatives -A. duranensis and A. ipaënsis-, and subsequent binding of the unreduced gametes in the hybrid. Therefore, aiming to contribute to the understanding the event of polyploid origin of this important crop, we made diploid hybrids between A. duranensis and A. ipaënsis, and then investigated the production of unreduced gametes in the hybrids by analyzing the size range of pollen, the constitution of the sporads, and the microsporogenesis process. The meiotic abnormalities found, such as persistent bridges, tripolar spindles and cytomixis processes, would lead to the formation of restitution nuclei in both the first and second meiotic division. These failures in the regularityof meiosis lead to the formation of dyads and triads, and consequently to 2n pollen grains. These findings constitute the first evidence of the formation of unreduced gametes in intergenomic hybrids obtained between the wild progenitors of A. hypogaea and enable us to propose a model of origin of the crop through sexual polyploidization. Fil: García, Alejandra Vanina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina Fil: Ortiz, Alejandra Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina Fil: Silvestri, María Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina Fil: Custódio Alves, Raquel. Ministerio da Agricultura Pecuaria e Abastecimento de Brasil. Empresa Brasileira de Pesquisa Agropecuaria; Brasil Fil: Moretzsohn, M. C.. Ministerio da Agricultura Pecuaria e Abastecimento de Brasil. Empresa Brasileira de Pesquisa Agropecuaria; Brasil Fil: Lavia, Graciela Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina

Fil: Silvestri, Maria Celeste. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Nordeste. Instituto de Botanica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botanica del Nordeste; Argentina

Peanut (Arachis hypogaea L.) is an important oilseed crop and food legume that is highly susceptible to biotic and abiotic factors. Wild Arachis species represent useful genetic resources because of their resistance to pests and diseases. In particular, understanding the affinity between B-genome species is important for broadening the genetic base of A. hypogaea (AABB genome), since only one population of A. ipaensis is known, and relatively few other species have been described. Therefore, we aimed to determine the genomic affinity between A. ipaensis and A. williamsii by developing hybrids. Microsatellite markers verified the hybrid status, and chromosome pairing and pollen viability results revealed that the species share high genomic affinity. Additionally, the presence of dyads detected in sporad and pollen analyses indicated the production of 2n gametes. These results will be useful for performing evolutionary studies and developing strategies for introgression programs to improve the B genome of A. hypogaea.

The species of the genus Arachis (Leguminosae) are ordered into nine sections. The assignment of genome types in this genus has been based on cross-compatibility analysis and molecular cytogenetic studies. The latter has also allowed karyotypically establishing well-defined genomes and reassigning the genome of several species. However, most of these studies have been focused mainly on the sections Arachis and Rhizomatosae. To increase the knowledge about the chromosome diversity of the whole genus, here we performed a detailed karyotype characterization of representative species of most of the sections and genomes of Arachis. This characterization included chromosome morphology, CMA/DAPI chromosome banding, and chromosome marker localization (rDNAloci and one satDNA sequence) by fluorescent in situ hybridization (FISH). Based on the data obtained and other previously published data, we established the karyotype similarities by cluster analysis and defined eleven karyotype groups. The grouping was partly coincident with the traditional genome assignment, except for some groups and some individual species. Karyotype similarities among some genomes were also found. The main characteristics of each karyotype group of Arachis were summarized. Together, our results provide information that may be beneficial for future cytogenetic and evolutionary studies, and also contribute to the identification of interspecific hybrids. Fil: Silvestri, María Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina Fil: Ortiz, Alejandra Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina Fil: Robledo Dobladez, Germán Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina Fil: Lavia, Graciela Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina

The genus Arachis is composed of 82 species (Krapovickas and Gregory 1994; Valls and Simpson 2005; Valls et al 2013; Santana and Valls 2015) mainly distributed within a large region of South America, which extends from the eastern foothills of the Andes Mountains in Bolivia and northern Argentina to the Atlantic coast in Brazil, and from the southern limit of the Amazonian rainforest towards the northern coast of La Plata River in Uruguay. Based on morphology, cross-compatibility, viability of the hybrids, geographic distribution and cytogenetics, the Arachis species have been arranged in nine taxonomic sections: Trierectoides, Erectoides, Procumbentes, Rhizomatosae, Heteranthae, Caulorrhizae, Extranervosae, Triseminatae and Arachis (Krapovickas and Gregory 1994; Fernández and Krapovickas 1994; Lavia 1996; Valls and Simpson 2005). Cross compatibility, karyotypic and meiotic analysis also allowed the identification and description of six different genomes within the section Arachis: namely A, B, D, F, K and G (Smartt et al 1978; Stalker 1991; Robledo and Seijo 2008, 2010; Robledo et al 2009; Silvestri et al 2015). The genomic constitution of the remaining species of the genus, in the absence of comprehensive cytogenetic and molecular analysis, is less precise and have been traditionally assigned on the basis of the subgeneric divisions, that is: Am (Heteranthae), C (Caulorrhizae), E (Trierectoides, Erectoides and Procumbentes), Ex (Extranervosae), T (Triseminatae) and R (Rhizomatosae) (Smartt and Stalker 1982). Classical and modern molecular cytogenetics revealed a huge variability within and among species of different sections. These studies provided important information about the complexity of the peanut genome, and were very useful to unravel the taxonomy of the genus and to establish relationships among the wild species with the cultivated peanut. Here we present an update of the cytological information on Arachis species, and some examples in which the use of chromosome markers were decisive to understand critical and long lasting problems in the genus. Fil: Seijo, José Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina Fil: Samoluk, Sergio Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina Fil: Ortiz, Alejandra Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina Fil: Silvestri, María Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina Fil: Chalup, Laura María Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina Fil: Robledo Dobladez, Germán Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina Fil: Lavia, Graciela Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina

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. Fil: Silvestri, María Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura; Argentina Fil: Ortiz, Alejandra Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura; Argentina Fil: Lavia, Graciela Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura; Argentina

Summary: Karyotypes of three diploid species belonging to sections Erectoides (Arachis hermannii), Procumbentes (A. rigonii) and Rhizomatosae (A. burkartii) were analyzed by Feulgen’s technique. The karyotype formula was different in each of the taxa analyzed: 2n=2x=16m+4sm in A. hermannii, 2n=2x=18m+2sm in A. rigonii, and 2n=2x=20m in A. burkartii. All species had a pair of satellited chromosomes, which corresponded to type 2 in A. hermannii, type 9 in A. rigonii, and type 8 in A. burkartii. Arachis hermannii and A. rigonii presented chromosomal features similar to those of the other species included in their respective sections. However, A. burkartii showed chromosome characteristics different from those found in the rest of the species of section Rhizomatosae.Key words: Arachis hermannii, A. rigonii, A. burkartii, chromosomes, phylogenetic relationships.Resumen: Estudios cariotípicos en especies silvestres de Arachis (Leguminosae) pertenecientes a las secciones Erectoides, Procumbentes y Rhizomatosae. Los cariotipos de tres especies diploides pertenecientes a las secciones Erectoides (A. hermannii), Procumbentes (A. rigonii) y Rhizomatosae (A. burkartii) fueron analizados mediante la técnica de Feulgen. Las fórmulas cariotípicas obtenidas son diferentes en los taxones analizados, 2n=2x=16m+4sm en A. hermannii, 2n=2x=18m+2sm en A. rigonii, y 2n=2x=20m en A. burkartii. Las tres especies presentaron un par de cromosomas con satélite, en A. hermannii tipo 2, en A. rigonii tipo 9 y en A. burkartii tipo 8. Arachis hermannii y A. rigonii presentaron características cromosómicas similares a las especies incluidas en sus respectivas secciones. Sin embargo, A. burkartii no comparte características cromosómicas con el resto de las especies de la sección Rhizomatosae.Palabras clave: Arachis hermannii, A. rigonii, A. burkartii, cromosomas, relaciones filogenéticas.