Cytogenetic and Evolutionary Relationships in the Genus Axonopus (Gramineae)

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Chromosome number, meiotic behavior, pollen stainability and other morphologic and ecologic data from 35 strains belonging to 29 natural and cultivated entities of the genus Axonopus collected in Rio Grande do Sul, other Brazilian States and Uruguay are reported. In the series Axonopus n varied from 10 to 50 (2x-10x); the series Suffulti shows diploid and tetraploid entities, while in Barbigeri only diploids were observed. In a general way our results agree with those obtained by other authors in those taxa where previous cytological studies were made; some ploidy levels observed in A. compressus and A. affinis, however, were not encountered by us. Meiotic abnormalities were most frequent in the Suffulti series, occurring in six of the seven tetraploid entities studied; in the Axonopus series about half of the polyploid forms had a regular meiotic behavior, while the five Barbigeri strains studied showed an essentially regular pattern. Subspecific hybridization may be involved in the origin of the taxa of the first series, while in the second allopolyploidy may have played an important role. Peculiar non-chromosomic structures were observed in the pollen mother cells of two strains of the series Suffulti, resembling the round and nuclear bodies described previously in Zea and Bromus.