Meiotic irregularities in Alstroemeria andina var. Venustula (Alstroemeriaceae)

Alstroemeria andina Phil. var. venustula (Phil.) M. Muñoz (sub nom. A. andina Phil. subsp. venustula (Phil.) Ehr. Bayer) is a perennial, small herb, 5-16 cm tall, that occurs mainly at 2,800-3,700 meters above sea level, in populations of limited distribution from Argentina and Chile. The course of the meiosis was analyzed in a population of this taxon (2n = 2x = 16), and it proved to be highly irregular. It was characterized by presenting bridge and fragment configurations both at anaphases I and II. The highest number of bridges at anaphase I found in one cell was two, suggesting heterozygosity for as many as two paracentric inversions. Typical chiasmata were almost not detectable, even though they actually existed. The chiasma-like structures observed may be regarded as concealed chiasmata as it has been described in cryptochiasmate meiosis. A high frequency of tetrads with micronuclei was observed, implying significant levels of unbalanced gametes. Pollen stainability ranged between 28 and 30%. In Alstroemeria species the meiotic behaviour is highly regular, and the presence of rearrangements is very uncommon. The whole situation led us to suggest that some environmental factors have drastically affected the chromosome structure and the control of the meiotic process. The present study constitutes the first report of remarkable meiotic irregularities found in a wild population of this genus.Fil: Sanso, Andrea Mariel. Universidad Nacional del Centro de la Provincia de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Wulff, Arturo Federico. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Senecio ser. Chilenses, a New Name for Senecio ser. Suffruticosi (Asteraceae, Senecioneae) from Southern South America

The name Senecio L. ser. Chilenses DC. ex M. G. Lopez, A. F. Wulff & Xifreda is here validated to replace Senecio ser. Suffruticosi Cabrera, non Senecio sect. Suffruticosi Greenm. Although the epithet Suffruticosi was published at different infrageneric ranks within Senecio (Asteraceae, Senecioneae) for two different taxa from South and North America, respectively, the two epithets are considered homonyms. Series Chilenses was previously published by de Candolle, but without a description.El nombre Senecio L. ser. Chilenses DC. ex M. G. López, A. F. Wulff & Xifreda se valida aquí para reemplazar a Senecio ser. Suffruticosi Cabrera, non Senecio sect. Suffruticosi Greenm. A pesar de que el epíteto Suffruticosi fue publicado para definir rangos subgenéricos diferentes dentro Senecio (Asteraceae, Senecioneae) para dos taxa diferentes de América del Sur y del Norte, respectivamente, ambos epítetos son considerados homónimos. Series Chilenses fue publicado previamente por de Candolle pero sin una descripción.Laboratorio de Etnobotánica y Botánica Aplicad

Chromosome contribution to andean polyploid species of Senecio (Asteraceae), from Argentina

Fil: López, Mariana G.. Lab. de Citogenética y Evol.; Depto. de Ciencias Biológicas; Universidad de Buenos AiresFil: Wulff, Arturo F.. Lab. de Citogenética y Evol.; Depto. de Ciencias Biológicas; Universidad de Buenos AiresFil: Xifreda, Cecilia Carmen. Laboratorio de Etnobotánica y Botánica Aplicada (LEBA); Facultad de Ciencias Naturales y Museo; Universidad Nacional de La Plat

Karyotype studies in Mimosa (Mimosoideae, Leguminosae) from Southern South America and ecological and taxonomic relationships

In this work we studied the chromosome number and karyotype formula of seven species of Mimosa L. (Mimosoideae, Leguminosae). The chromosome number 2n = 2x = 26 for M. detinens Benth., M. hex- andra M. Micheli, M. ostenii Speg. ex Burkart and M. xanthocentra Mart. var. mansii (Benth.) Barneby are new records, while the chromosome number 2n = 2x = 26 for M. debilis var. debilis, M. urugüensis Hook. and Arn. and M. uliginosa Chodat and Hassl. confirm previous records. Karyotype formulae revealed the existence of metacentric and submetacentric chromosomes, and the chromosomal asymmetry indexes did not show significant differences between taxa. The chromosome length of xerophilous and endemic M. detinens and M. ostenii differed from the rest of species, indicating that this parameter could have taxonomic value. In addition, the relationship between total chromosome length and climatic parameters showed that diploid species of marginal areas of distribution have a larger chromosome size, and that this could be related with mechanisms of ecologi- cal adaptation.Instituto de Recursos BiológicosFil: Morales, Matias. Universidad de Moron. Facultad de Agronomia y Ciencias Agroalimentarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Wulff, Arturo Federico. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Fortunato, Renee Hersilia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Recursos Biológicos; Argentina. Universidad de Morón. Facultad de Agronomía y Ciencias Agroalimentarias; ArgentinaFil: Poggio, Lidia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Deep cytogenetics analysis reveals meiotic recombination depletion in species of Senecio (Asteraceae)

Background: Senecio is the largest genus in the Asteraceae family growing in all environments around the world. It displays taxonomic and systematical difficulties. Cytogenetic knowledge of this genus is ancient, scarce and mainly restricted to chromosome number records. Results: In this study we analyzed chromosome number, meiotic configuration, bivalent morphology, meiotic behavior and pollen grain stainability on 100 accessions of 27 different polyploid Senecio L. sect Senecio entities. Median, standard deviation and mode were calculated for number and position of chiasmata and meiotic recombination was statistically evaluated. Although high frequency of multivalents and associated meiotic irregularities are expected in high polyploids, bivalents predominance and, consequently, regular meiosis were observed, with normal sporogenesis and high pollen grain stainability. Conclusion: Depletion in the total chiasmata was significant only in some species but the terminal position was preferential in all the entities analyzed, indicating significant reduction in recombination. The regular meiosis observed suggest that intra and intergenomic reorganization process occur quickly and efficiently in this genus. Mechanisms of diploidization, common to all polyploids, are reinforced by the strong reduction in crossing-over rushing polyploids stabilization.Facultad de Ciencias Naturales y Muse

South African fireweed Senecio madagascariensis (Asteraceae) in Argentina: Relevance of chromosome studies to its systematics

The systematic identity of Senecio madagascariensis is ratified against the opinion that it is conspecific with Senecio inaequidens. Both species are native to South Africa and have been merged in the 'Senecio inaequidens complex', a group of entities difficult to distinguish from each other. Senecio madagascariensis is widespread in South America and Australia, where it is an invasive weed. Mitotic and meiotic studies were conducted on Argentinian material; chromosome counts solved the chromosome number controversy, validating 2n = 20. The karyotype was symmetrical, composed of ten pairs of metacentric chromosomes varying from 1.62 to 2.38 μm in length. The most frequent number of satellited chromosomes was three, but their position was difficult to assign. Meiosis was regular, with a configuration of ten predominantly open bivalents. Univalents and quadrivalents were rarely observed. High frequencies of secondary associations of bivalents, chromosome asynchrony and bivalent grouping were documented, reinforcing the hypothesis that x = 5 is the basic chromosome number. Pollen stainability ranged from 94 to 99%. The relevance of chromosomal studies in the circumscription of S. madagascariensis is discussed. Hybridization and polyploidy, as principal evolutionary forces in this genus, explain the systematic difficulties.Facultad de Ciencias Naturales y Muse

South African fireweed Senecio madagascariensis (Asteraceae) in Argentina: Relevance of chromosome studies to its systematics

The systematic identity of Senecio madagascariensis is ratified against the opinion that it is conspecific with Senecio inaequidens. Both species are native to South Africa and have been merged in the 'Senecio inaequidens complex', a group of entities difficult to distinguish from each other. Senecio madagascariensis is widespread in South America and Australia, where it is an invasive weed. Mitotic and meiotic studies were conducted on Argentinian material; chromosome counts solved the chromosome number controversy, validating 2n = 20. The karyotype was symmetrical, composed of ten pairs of metacentric chromosomes varying from 1.62 to 2.38 μm in length. The most frequent number of satellited chromosomes was three, but their position was difficult to assign. Meiosis was regular, with a configuration of ten predominantly open bivalents. Univalents and quadrivalents were rarely observed. High frequencies of secondary associations of bivalents, chromosome asynchrony and bivalent grouping were documented, reinforcing the hypothesis that x = 5 is the basic chromosome number. Pollen stainability ranged from 94 to 99%. The relevance of chromosomal studies in the circumscription of S. madagascariensis is discussed. Hybridization and polyploidy, as principal evolutionary forces in this genus, explain the systematic difficulties.Facultad de Ciencias Naturales y Muse

Chromosome numbers and meiotic studies in species of Senecio (Asteraceae) from Argentina

Meiotic chromosome counts, chromosomal behaviour and meiotic configurations of ten taxa of Senecio from Argentina were examined. Most counts are original: S. crepidifolius DC., S. francisci Phil. and S. octolepis Griseb. var. saltensis (Hicken) Cabrera & Zardini have 2n = 40, and S. chrysolepis Phil., 2n = 80 + 8B. We confirmed previous reports for S. deferens Griseb. (2n = 40 + 4B), S. filaginoides DC. var. filaginoides (2n = 40), S. hieronymi Griseb. (2n = 40 + 7B), S. pampeanus Cabrera (2n = 40) and S. rudbeckiifolius Meyen & Walp. (2n = 40 + 7B). In S. bracteolatus Hook. & Arn. var. bracteolatus, we found a new number (2n = 40) that differs from the one cited previously. In four species, numerical polymorphisms for B-chromosomes were observed. Several of the analysed species presented secondary bivalent association. This phenomenon, together with other evidence, supports x = 5 as the basic chromosome number. The number of chiasmata and their positions were also surveyed, with the finding that open bivalents were the most frequent meiotic figures and terminal chiasmata the preferential position. These features are related to recombination rate, and the success and persistence of these polyploids. We discuss some systematic and evolutionary aspects in the light of cytogenetic data and conclude that polyploidy is the major force modelling the chromosome evolution within this genus. Laboratorio de Etnobotánica y Botánica Aplicad

Chromosome contribution to Andean Polyploid Species of Senecio (Asteraceae), from Argentina

Meiotic chromosome numbers were determined and observations of meiotic behavior were made in six species and two hybrid specimens of Senecio L. (Asteraceae). Two different numbers were found: 2n=4x=40 in S. pogonias Cabr., S. ragonesei Cabr., S. sectilis Griseb. and S. viridis Phil. var. radiatus R. E. Fr. and 2n=8x=80 in S. subulatus D. Don. var. subulatus and in S. uspallatensis Hook. et Arn.; the latter showed the same chromosome number previously reported. The chromosome number of the hybrid individuals was 2n=4x=40, being their putative parents S. ragonesei and S. sectilis. B chromosomes were found in some individuals of S. pogonias, S. sectilis, S. subulatus var. subulatus and S. uspallatensis. Many meiotic irregularities such as bridges, fragments, laggard chromosomes, micronuclei and cellular fusion were observed. The results are analyzed in relation to the persistence and success of these polyploids, and the speciation mechanisms operating within this group are discussed.Facultad de Ciencias Naturales y Muse

Senecio ser. Chilenses, a New Name for Senecio ser. Suffruticosi (Asteraceae, Senecioneae) from Southern South America

The name Senecio L. ser. Chilenses DC. ex M. G. Lopez, A. F. Wulff & Xifreda is here validated to replace Senecio ser. Suffruticosi Cabrera, non Senecio sect. Suffruticosi Greenm. Although the epithet Suffruticosi was published at different infrageneric ranks within Senecio (Asteraceae, Senecioneae) for two different taxa from South and North America, respectively, the two epithets are considered homonyms. Series Chilenses was previously published by de Candolle, but without a description.El nombre Senecio L. ser. Chilenses DC. ex M. G. López, A. F. Wulff & Xifreda se valida aquí para reemplazar a Senecio ser. Suffruticosi Cabrera, non Senecio sect. Suffruticosi Greenm. A pesar de que el epíteto Suffruticosi fue publicado para definir rangos subgenéricos diferentes dentro Senecio (Asteraceae, Senecioneae) para dos taxa diferentes de América del Sur y del Norte, respectivamente, ambos epítetos son considerados homónimos. Series Chilenses fue publicado previamente por de Candolle pero sin una descripción.Laboratorio de Etnobotánica y Botánica Aplicad