Genomic relationships of the polyploid rhizoma peanut (Arachis glabrata Benth.) inferred by genomic in situ hybridization (GISH).

The rhizoma peanut (Arachis glabrata Benth., section Rhizomatosae) is a tetraploid perennial legume. Although several A. glabrata cultivars have been developed as forage and ornamental turf, the origin and genomic constitution of this species are still unknown. In this study, we evaluated the affinity between the genomes of A. glabrata and the probable diploid donors of the sections Rhizomatosae, Arachis, Erectoides and Procumbentes by genomic in situ hybridization (GISH). Single GISH analyses detected that species of the sections Erectoides (E2 subgenome) and Procumbentes (E3 subgenome) were the diploid species with the highest degree of genomic affinity with A. glabrata. Based on single GISH experiments and DNA sequence similarity, three species -A. duranensis, A. paraguariensis subsp. capibarensis, and A. rigonii-, which showed the most uniform and brightest hybridization patterns and lowest genetic distance, were selected as probes for double GISH experiments. Double GISH experiments showed that A. glabrata is constituted by four identical or very similar chromosome complements. In these assays, A. paraguariensis subsp. capibarensis showed the highest brightness onto A. glabrata chromosomes. Thus, our results support the autopolyploid origin of A. glabrata and show that the species with E2 subgenome are the most probable ancestors of this polyploid legume forage.

Chromosome diversity in species of the genus Arachis, revealed by FISH and CMA/DAPI banding, and inferences about their karyotype differentiation.

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.

Producción de frutos de Gleditsia amorphoides (Fabaceae) y abundancia de Bruchidius endotubercularis Arora (Coleoptera: Chrysomelidae) en Formosa, Argentina / Production of fruits of Gleditsia amorphoides (Fabaceae) and abundance of Bruchidius endotubercularis Arora (Coleoptera: Chrysomelidae) during three consecutive years in the Southeast of the Formosa Province (Argentina)

Resumen Gleditsia amorphoides (Griseb.) Taub. es una especie arbórea nativa de Sudamérica, conocida por su madera de buena calidad y por los frutos que contienen una goma de utilización industrial. Una de las causas de la disminución de la producción de semillas viables en árboles forestales es el daño ocasionado por depredadores de frutos y semillas. La relación entre producción de frutos y depredadores no es conocida para G. amorphoides. Por lo tanto, en este trabajo se evaluó la producción de frutos en árboles de esta especie y la abundancia de ejemplares pertenecientes a la Subfamilia Bruchinae asociada a la misma. El estudio se efectuó en tres localidades ubicadas en la provincia de Formosa en el noreste de Argentina durante tres años consecutivos. Se halló una especie de Bruchinae, identificada como Bruchidius endotubercularis Arora. Los resultados mostraron la existencia de variabilidad en la producción de frutos entre los años, no así entre localidades, mientras que la abundancia de insectos se mantuvo constante, no respondiendo a la variación en la producción de frutos entre años. En este trabajo se reporta por primera vez la presencia de B. endotubercularis asociado a G. amorphoides en Argentina.

Abstract Gleditsia amorphoides (Griseb.) Taub. is a tree species native to South America. It is known for its good quality wood and for its fruits that contain a rubber for industrial uses. One of the causes for the reduction of the production of viable seeds in forest trees is the damage caused by predators of fruits and seeds. The relationship between fruit production and predators is not known for G. amorphoides. Therefore, in this study, we evaluated the fruit production in this three species and the abundance of specimens of the Subfamily Bruchinae associated to G. amorphoides. The study was carried out in three localities of the Formosa Province in the Northeast of Argentina for three consecutive years. We found a single species of Bruchinae, identified as Bruchidius endotubercularis Arora. The results showed the existence of variability in the production of G. amorphoidesfruits between years, but not between locations. The abundance of insects remained constant, not responding to the variation in the production of fruits between years. In this study, we report for the first time, the occurrence of B. endotubercularis associated with G. amorphoides in Argentina. Rev. Biol. Trop. 66(3): 1046-1054. Epub 2018 September 01.

Genomic characterisation of Arachis porphyrocalyx (Valls & C.E. Simpson, 2005) (Leguminosae): multiple origin of Arachis species with x = 9.

The genus Arachis Linnaeus, 1753 comprises four species with x = 9, three belong to the section Arachis: Arachis praecox (Krapov. W.C. Greg. & Valls, 1994), Arachis palustris (Krapov. W.C. Greg. & Valls, 1994) and Arachis decora (Krapov. W.C. Greg. & Valls, 1994) and only one belongs to the section Erectoides: Arachis porphyrocalyx (Valls & C.E. Simpson, 2005). Recently, the x = 9 species of section Arachis have been assigned to G genome, the latest described so far. The genomic relationship of Arachis porphyrocalyx with these species is controversial. In the present work, we carried out a karyotypic characterisation of Arachis porphyrocalyx to evaluate its genomic structure and analyse the origin of all x = 9 Arachis species. Arachis porphyrocalyx showed a karyotype formula of 14m+4st, one pair of A chromosomes, satellited chromosomes type 8, one pair of 45S rDNA sites in the SAT chromosomes, one pair of 5S rDNA sites and pericentromeric C-DAPI+ bands in all chromosomes. Karyotype structure indicates that Arachis porphyrocalyx does not share the same genome type with the other three x = 9 species and neither with the remaining Erectoides species. Taking into account the geographic distribution, morphological and cytogenetic features, the origin of species with x = 9 of the genus Arachis cannot be unique; instead, they originated at least twice in the evolutionary history of the genus.

Cytogenetic evidences on the evolutionary relationships between the tetraploids of the section Rhizomatosae and related diploid species (Arachis, Leguminosae).

Rhizomatosae is a taxonomic section of the South American genus Arachis, whose diagnostic character is the presence of rhizomes in all its species. This section is of particular evolutionary interest because it has three polyploid (A. pseudovillosa, A. nitida and A. glabrata, 2n = 4x = 40) and only one diploid (A. burkartii, 2n = 2x = 20) species. The phylogenetic relationships of these species as well as the polyploidy nature and the origin of the tetraploids are still controversial. The present study provides an exhaustive analysis of the karyotypes of all rhizomatous species and six closely related diploid species of the sections Erectoides and Procumbentes by cytogenetic mapping of DAPI/CMA heterochromatin bands and 5S and 18-26S rDNA loci. Chromosome banding showed variation in the DAPI heterochromatin distribution pattern, which, together with the number and distribution of rDNA loci, allowed the characterization of all species studied here. The bulk of chromosomal markers suggest that the three rhizomatous tetraploid species constitute a natural group and may have at least one common diploid ancestor. The cytogenetic data of the diploid species analyzed evidenced that the only rhizomatous diploid species-A. burkartii-has a karyotype pattern different from those of the rhizomatous tetraploids, showing that it is not likely the genome donor of the tetraploids and the non-monophyletic nature of the section Rhizomatosae. Thus, the tetraploid species should be excluded from the R genome, which should remain exclusively for A. burkartii. Instead, the karyotype features of these tetraploids are compatible with those of different species of the sections Erectoides and Procumbentes (E genome species), suggesting the hypothesis of multiple origins of these tetraploids. In addition, the polyploid nature and the group of diploid species closer to the tetraploids are discussed.

Corrigenda: Genomic characterisation of Arachis porphyrocalyx (Valls & C.E. Simpson, 2005) (Leguminosae): multiple origin of Arachis species with x = 9. Comparative Cytogenetics 11(1): 29-43. doi: 10.3897/CompCytogen.v11i1.10339.

[This corrects the article DOI: 10.3897/CompCytogen.v11i1.10339.].

Origin of triploid Arachis pintoi (Leguminosae) by autopolyploidy evidenced by FISH and meiotic behaviour.

BACKGROUND AND AIMS: Polyploidy is a dominant feature of flowering-plant genomes, including those of many important crop species. Arachis is a largely diploid genus with just four polyploid species. Two of them are economically important: the cultivated peanut and A. glabrata, a tropical forage crop. Even though it is usually accepted that polyploids within papilionoid legumes have arisen via hybridization and further chromosome doubling, it has been recently suggested that peanut arose through bilateral sexual polyploidization. In this paper, the polyploid nature of the recent, spontaneously originated triploid cytotype of the tropical lucerne, A. pintoi, was analysed, and thereby the mechanism by which polyploids may arise in the genus. METHODS: Chromosome morphology of 2x and 3x A. pintoi was determined by the Feulgens technique and the rDNA sites were mapped by FISH. To investigate whether polyploidization occurred by means of unreduced gametes, a detailed analysis of the microsporogenesis and pollen grains was made. KEY RESULTS: The 2x and 3x plants presented 9m + 1sm and a satellited chromosome type 2 in each haploid genome. Physical mapping revealed a cluster of 18S-26S rDNA, proximally located on chromosome 6, and two 5S rDNA loci on chromosomes 3 and 5. Diploid plants presented 10II in meiosis while trivalents were observed in all triploids, with a maximum of 10III by cell. Diploid A. pintoi produced normal tetrads, but also triads, dyads and monads. Two types of pollen grains were detected: (1) normal-sized with a prolate shape and (2) large ones with a tetrahedral morphology. CONCLUSIONS: Karyotype and meiotic analysis demonstrate that the 3x clone of A. pintoi arose by autopolyploidy. The occurrence of unreduced gametes strongly supports unilateral sexual polyploidization as the most probable mechanism that could have led to the origin of the triploid cytotype. This mechanism of polyploidization would probably be one of the most important mechanisms involved in the origin of economically important species of Arachis, either by triploid bridge or bilateral sexual polyploidization.

Genome re-assignment of Arachis trinitensis (Sect. Arachis, Leguminosae) and its implications for the genetic origin of cultivated peanut.

The karyotype structure of Arachis trinitensis was studied by conventional Feulgen staining, CMA/DAPI banding and rDNA loci detection by fluorescence in situ hybridization (FISH) in order to establish its genome status and test the hypothesis that this species is a genome donor of cultivated peanut. Conventional staining revealed that the karyotype lacked the small "A chromosomes" characteristic of the A genome. In agreement with this, chromosomal banding showed that none of the chromosomes had the large centromeric bands expected for A chromosomes. FISH revealed one pair each of 5S and 45S rDNA loci, located in different medium-sized metacentric chromosomes. Collectively, these results suggest that A. trinitensis should be removed from the A genome and be considered as a B or non-A genome species. The pattern of heterochromatic bands and rDNA loci of A. trinitensis differ markedly from any of the complements of A. hypogaea, suggesting that the former species is unlikely to be one of the wild diploid progenitors of the latter.

Genome re-assignment of Arachis trinitensis (Sect. Arachis, Leguminosae) and its implications for the genetic origin of cultivated peanut

The karyotype structure of Arachis trinitensis was studied by conventional Feulgen staining, CMA/DAPI banding and rDNA loci detection by fluorescence in situ hybridization (FISH) in order to establish its genome status and test the hypothesis that this species is a genome donor of cultivated peanut. Conventional staining revealed that the karyotype lacked the small "A chromosomes" characteristic of the A genome. In agreement with this, chromosomal banding showed that none of the chromosomes had the large centromeric bands expected for A chromosomes. FISH revealed one pair each of 5S and 45S rDNA loci, located in different medium-sized metacentric chromosomes. Collectively, these results suggest that A. trinitensis should be removed from the A genome and be considered as a B or non-A genome species. The pattern of heterochromatic bands and rDNA loci of A. trinitensis differ markedly from any of the complements of A. hypogaea, suggesting that the former species is unlikely to be one of the wild diploid progenitors of the latter.

Genomic relationships between the cultivated peanut (Arachis hypogaea, Leguminosae) and its close relatives revealed by double GISH.

Arachis hypogaea is a natural, well-established allotetraploid (AABB) with 2n = 40. However, researchers disagree on the diploid genome donor species and on whether peanut originated by a single or multiple events of polyploidization. Here we provide evidence on the genetic origin of peanut and on the involved wild relatives using double GISH (genomic in situ hybridization). Seven wild diploid species (2n = 20), harboring either the A or B genome, were tested. Of all genomic DNA probe combinations assayed, A. duranensis (A genome) and A. ipaensis (B genome) appeared to be the best candidates for the genome donors because they yielded the most intense and uniform hybridization pattern when tested against the corresponding chromosome subsets of A. hypogaea. A similar GISH pattern was observed for all varieties of the cultigen and also for A. monticola. These results suggest that all presently known subspecies and varieties of A. hypogaea have arisen from a unique allotetraploid plant population, or alternatively, from different allotetraploid populations that originated from the same two diploid species. Furthermore, the bulk of the data demonstrated a close genomic relationship between both tetraploids and strongly supports the hypothesis that A. monticola is the immediate wild antecessor of A. hypogaea.

Physical mapping of the 5S and 18S-25S rRNA genes by FISH as evidence that Arachis duranensis and A. ipaensis are the wild diploid progenitors of A. hypogaea (Leguminosae).

The 5S and the 18S-25S rRNA genes were physically mapped by fluorescent in situ hybridization (FISH) in all botanical varieties of cultivated peanut Arachis hypogaea (2n = 4x = 40), in the wild tetraploid A. monticola, and in seven wild diploid species considered as putative ancestors of the tetraploids. A detailed karyotype analysis including the FISH signals and the heterochromatic bands was carried out. Molecular cytogenetic landmarks are provided for the construction of a FISH-based karyotype in Arachis species. The size, number, and chromosome position of FISH signals and heterochromatic bands are similar in all A. hypogaea varieties and A. monticola, but vary among the diploid species. Genome constitution of the species is discussed and several chromosome homeologies are established. The bulk of the chromosome markers mapped, together with data on geographical distribution of the taxa, suggest that peanut originated upon domestication of A. monticola and evidence that the diploids A. duranensis and A. ipaensis are the most probable ancestors of both tetraploid species. Allopolyploidy could have arisen by a single event or, if by multiple events, always from the same diploid species.