RESUMO
This is the first report on chromosome numbers and the reproductive behaviour in Stenodrepanum Harms, a rare endemic and monotypic legume genus from the arid and salty areas of central-western Argentina. Sixty individuals belonging to two populations from two salty areas ("salinas") were surveyed and included mostly triploid (2n = 3x = 36) and only two diploid (2n = 2x = 24) plants. Meiosis in diploids is regular, with bivalent pairing and uniform and viable pollen. In contrast, meiosis in triploids is characterized by high trivalent pairing, with irregularly shaped pollen and variation in cytoplasm content and stainability, which is in agreement with an unbalanced segregation occurring in anaphases I and II. However, different triploid plants/individuals showed various degrees of pollen fertility, which may be attributed to particular genotypes. Research on reproductive biology events indicates sexual cross-pollinated reproduction enhanced by protogyny in both cytotypes. All plants produced seeds, but seedlings were only recovered from diploid plants pollinated with triploids, and even those eventually perished. Chromosome counts in these seedlings revealed aneuploid chromosome numbers owing to the combination of unbalanced gametes.
Assuntos
Cromossomos de Plantas/genética , Fabaceae/crescimento & desenvolvimento , Fabaceae/genética , Ploidias , Argentina , Diploide , Fertilidade/genética , Variação Genética , MeioseRESUMO
Mitotic chromosome number of 14 taxa of Bothriochloa native to Argentina, Brazil and Uruguay were surveyed. Chromosome numbers of B. eurylemma, B. meridionalis and B. velutina are reported for the first time, with 2n = 6x = 60, and this ploidy level is the most common among the studied taxa. In addition, new cytotypes were found for B. alta (2n = 60), B. barbinodis (2n = 60), B. exaristata (2n = 80), B. laguroides var. torreyana (2n = 80), B. longipaniculata (2n = 60 and 80), B. perforata (2n = 60) and B. springfieldii (2n = 60). These numbers differ from those reported in the literature.
Assuntos
Cromossomos de Plantas , Cariotipagem , Ploidias , Poaceae/genética , Argentina , Evolução Biológica , Brasil , DNA de Plantas/genética , UruguaiRESUMO
Andropogon is a pantropical grass genus comprising 100-120 species and found mainly in the grasslands of Africa and the Americas. While the genomic relationships between many Andropogon species have been resolved by studying chromosome behavior in interspecific hybrids, relationships between the North and South American diploids have remained elusive. Further, the genome composition of two hexaploid species (including the important forage grass Andropogon lateralis Nees) has been unclear because of the strong hybridization barriers that exist between species. Consequently, genomic in situ hybridization was applied to shed light on these issues. The results confirmed that (i) both the South American (Andropogon selloanus (Hack.) Hack., Andropogon macrothrix Trin.) and North American (Andropogon gyrans Michx.) diploid species shared a common S genome and (ii) the S genome comprises just one of the three genomes in the hexaploids A. lateralis Nees and Andropogon bicornis L. The evolutionary and taxonomic implications of these findings are discussed.