Aveliano Fernández

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.

Karyotype analysis and chromosome evolution in South American species of Lathyrus (Leguminosae)

The karyotypes of 10 species and one variety of South American Lathyrus were determined and compared with those obtained of five entities from the Northern Hemisphere. Although all the species have a chromosome number of 2n = 14, they could be differentiated by their karyotype formula and quantitative parameters of the karyotypes. Phenetic distance and principal component analysis showed that in spite of the differences observed among entities, they can be grouped in clusters that coincide with the taxonomic sections established by F. K. Kupicha and with the life cycle of the species. South American species form a homogeneous group and can be distinguished by the presence of a subtelocentric pair, which has a macrosatellite in the long arm, and the lack of a short metacentric pair characteristic of most species of the Northern Hemisphere. From an evolutionary point of view, variation in total chromosome length without major changes in the karyotype formula suggests that changes in the amounts of genomic DNA are proportional to the relative length of each chromosome arm and that species of Notolathyrus evolved in a concerted fashion. Variation in genome size, however, is congruent with morphological variation of some reproductive organs as well as with the life cycle and minimum generation time, as predicted by the nucleotype hypothesis.

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 Feulgeńs 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.

Karyotypic studies in Turnera sidoides complex (Turneraceae, Leiocarpae).

Turnera sidoides, with the most southerly distribution of all Turnera species in America, is a complex of obligately outcrossing perennial herbs. Karyotypes of the five subspecies of T. sidoides (x = 7) are described for the first time utilizing root-tip mitotic metaphases. Different ploidy levels were found for all of the subspecies, ranging from diploid to octoploid. The results obtained, coupled with available meiotic and preliminary biosystematic data, support the hypothesis of autopolyploidy within this species complex. Although detailed karyotype analysis shows a high degree of intraspecific uniformity, subspecies may be differentiated by the number, type, and position of satellites, suggesting that chromosome rearrangements may also be involved in the karyotypic evolution of T. sidoides. Karyotype data, coupled with morphological and anatomical features, suggest the removal of T. sidoides from series Leiocarpae.

Genomic Relationships between Turnera krapovickasii (2x, 4x) and T. ulmifolia (6x) (Turneraceae, Turnera)

Abstract Interspecific crosses between two species of the Turnera ulmifolia complex with yellow flowers have been carried out. As a result, two hybrids were obtained: T. krapovickasii (K4) x T. ulmifolia (U), 2n = 4x=20 and T. ulmifolia (U) x T. krapovickasii (K5), 2n = 5x=25. The hybrids were cytologically studied in order to determine their genomic relationships. The chromosome pairing data of hybrids indicates that T. ulmifolia is a segmental allopolyploid and, on the basis of the results obtained, the genomic constitution AuAuBaBaBuBu is proposed for this species. The cytological analysis of the tetraploid hybrid has also revealed the presence of PMCs with 2n = 40 that should have been formed by pre-meiotic chromosome doublings and would give rise to the formation of fertile 2n gametes. From this finding, it is suggested that, in the genus Turnera, unreduced gametes may result from at least two mechanisms: (1) premeiotic doubling and (2) meiotic nuclear restitution.

Karyotypic studies in Arachis hypogaea L. varieties

Abstract The karyotypes of nine Arachis hypogaea accessions, including two botanical varieties of subspecies hypogaea and four of subspecies fastigiata, were analyzed. Varieties aequatoriana and peruviana were studied for the first time. The mean chromosome length showed that variety hirsuta is distinctive when compared with the others because it is the shortest; besides, significant intravarietal differences exist within variety hypogaea, but not between subspecies. The karyotypes are highly symmetric since metacentric chromosomes are the most frequent. A pair of satellites was observed in all the accessions in mitotic metaphases, this feature was useful to differentiate groups. These data suggest that all Arachis accessions present a very similar chromosomal complement and support the hypothesis of a monophyletic origin.

Heterochromatin variation in Oziroë argentinensis (Hyacinthaceae) revealed by florescent banding

Abstract Previous studies in Oziroë argentinensis (Lillo et Hauman) Speta, have showed variation of heterochromatic regions between and within different populations of the species. In this study, were examined the heterochromatic regions of nine individuals obtained by vegetative propagation from a single plant in an attempt to determine possible modifications of the heterochromatin distribution after 14 years. The analyzed individuals have not showed differences in chromosome number and karyotype formulae respect to the parental plant. However, the Q-banding technique revealed a wide variation in number, position and size of the heterochromatic regions. The number of heterochromatic regions ranged between 11 and 15, differing from the parental plant that presented 14. The total amount of heterochromatin ranged between 6.25 μm and 13.5 μm, which represent approximately 5.34 % and 8.99 of the total karyotype length. Likewise, the distribution of the heterochromatic regions was considerably different in all the studied specimens, due to which has been not found two or more individuals with the same Q-banding pattern. The wide variation of the heterochromatic regions observed in this species could be explained through different mechanisms, such as tandem duplications, saltatory amplification and somatic cross-over.