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.

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 Krapov. & W.C. Greg. and A. ipaënsis Krapov. & W.C. Greg—and subsequent binding of the unreduced gametes in the hybrid. Therefore, aiming to contribute to 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 regularity of 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.

ABSTRACT. 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 17574-17586 (2015) 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.

Arachis stenosperma is a wild relative of the groundnut, with a peculiar disjunct distribution in Central Brazil and along the Atlantic coast. Arachis species show one pair of satellited chromosomes (SAT) and some species have a distinct, smaller pair (A pair). The SAT chromosomes are classified according to 10 types. Previous literature information on A. stenosperma documents the presence of SAT type 3 only in the coastal populations, while type 5 was restricted to accessions from Central Brazil. This work sampled a broader area of geographic distribution, represented by an increased number of accessions, and provides further information on karyotypic characteristics. All 23 accessions analyzed present 2nϭ20. SAT type 5 was found in 10 accessions, irrespective to their area of occurrence. So, type 5 occurs also in the Atlantic coast. Type 3, so far exclusive to the Litoral, is not the most frequent type in the area. With the present data, the potential cytogenetic distinction between coastal and continental populations has vanished. The formula 18mϩ2sm clearly predominates, both in the Litoral and in Central Brazilian populations. Also irrespective to the area of origin, both idiogram positions A9/SAT10 and SAT9/A10 were identified. As the SAT of type 3 is considered more primitive than type 5, and the coastal area of distribution of A. stenosperma is secondary, it's future detection in continental populations is expected. In the meantime, a unique cytogenetic feature, the presence of SAT type 3 persists as an exclusive attribute of the populations of the secondary area of occurrence.

Se describe una nueva especie de Arachis, con hojas trifolioladas, A. sesquijuga. Esta se diferencia de las otras especies trifolioladas, ambas con folíolos ternados, por la presencia de un raquis evidente, lo que caracteriza a la hoja como pinnada. Datos históricos sobre la acumulación de conocimiento referente a las raras especies trifolioladas son comentados en secuencia cronológica.

Polyploidy is considered a driving force in plant evolution and domestication. Although in the genus Arachis, several diploid species were traditionally cultivated for their seeds, only the allotetraploid peanut Arachis hypogaea became the successful, widely spread legume crop. This suggests that polyploidy has given selective advantage for domestication of peanut. Here we study induced allotetraploid (neopolyploid) lineages obtained from crosses between the peanut’s progenitor species, A. ipaënsis and A. duranensis, at earlier and later generations. We observed plant morphology, seed dimensions, and genome structure using cytogenetics (FISH and GISH) and SNP genotyping. The neopolyploid lineages show more variable fertility and seed morphology than their progenitors and cultivated peanut. They also showed sexual and somatic genome instability, evidenced by changes of number of detectable 45S rDNA sites, and extensive homoeologous recombination indicated by mosaic patterns of chromosomes and changes in dosage of SNP alleles derived from the diploid species. Genome instability was not randomly distributed across the genome: the more syntenic chromosomes, the higher homoeologous recombination. Instability levels are higher than observed on peanut lines, therefore it is likely that more unstable lines tend to perish. We conclude that early stages of the origin and domestication of the allotetraploid peanut involved two genetic bottlenecks: the first, common to most allotetraploids, is composed of the rare hybridization and polyploidization events, followed by sexual reproductive isolation from its wild diploid relatives. Here we suggest a second bottleneck: the survival of the only very few lineages that had stronger mechanisms for limiting genomic instability.

A produtividade de amendoim pode ser reduzida devido a ocorrência de doenças foliares, necessitando, portanto, de controle químico com fungicidas para evitar perdas. Algumas espécies silvestres do gênero Arachis apresentam resistências às doenças foliares, sendo fontes de genes de resistências para introgressão no amendoim cultivado. O trabalho teve como objetivos avaliar a resistência às cercosporioses de progênies derivadas de espécies silvestres em combinação com linhagens e acompanhar os segmentos genômicos oriundos de espécies silvestres, possivelmente com genes de resistência às doenças foliares nas progênies. As progênies foram testadas em condição de alta pressão de inóculo das cercosporioses, sem controle com fungicidas e tiveram desenvolvimento vegetativo normal, porte predominantemente rasteiro e, plantas com sintomas de mancha anelar em diversas parcelas. Nenhuma progênie apresentou resistência completa às cercosporioses. A linhagem 19-2673 obteve o menor valor de severidade (2,94) apresentando dois segmentos com genes de resistência de A. cardenasii com locos em homozigose. Como referência, a cultivar IAC OL3 obteve valores médios de 8,88. As progênies 19-2675, 19-2674 e 19-2671 não tiveram desfolha completa do terço inferior, com todos os locos em heterozigose. As progênies 19-2688, 19-2687, 19-2680 e 19-2679 não apresentaram os segmentos de A. cardenasii e tiveram maior severidade intermediária e desfolha mais intensa dos terços inferior e médio das plantas. As progênies com alta severidade e maior desfolha também não apresentaram os segmentos de A. cardenasii. Foram identificadas quatro progênies interespecíficas, com maiores níveis de resistência às cercosporioses, provenientes das espécies A. magna, A. batizocoi e A. cardenasii.

<p>Estudios de compatibilidad cruzada en Arachis L. han sacado a la luz posibles nuevas fuentes de genes para introgresión en el maní cultivado. Se hicieron un total de 32 cruzamientos distintos, utilizando A. gregoryi C.E. Simpson, Krapov. &amp; Valls accesión V14957 como progenitor femenino y especies de Arachis que contienen siete genomas distintos como progenitores masculinos. Las 3167 polinizaciones resultaron en 153 híbridos inter e intraespecíficos confirmados. Estimaciones de viabilidad del polen paternal por tinción (PVS) variaron de 46.75 a 99.17%, mientras que el recuento de polen de los híbridos varió de 0.30 a 43.60 %, ese PVS más alto resultando de una combinación intraespecífica, lo que sugiere variabilidad apreciable entre accesiones de A. gregoryi. Las estimaciones de viabilidad del polen paterno por germinación (PVG) resultaron en valores consistentemente más bajos para todos los materiales, que van desde 41.91% a los 88.00%. Arachis gregoryi es importante para expandir la diversidad disponible de especies asociadas con el genoma B del maní; tiene el potencial de incorporarse como progenitor en cruzamientos que apuntan a la expansión de la base genética del maní y puede ser útil para concentrar genes importantes en líneas de premejoramento asociadas al genoma B.</p>