Sexuality, apomixis, ploidy levels, and genomic relationships among four Paspalum species of the subgenus Anachyris (Poaceae)

The subgenus Anachyris of the genus Paspalum comprises six species, all native to the New World. Cytology, embryology, Fertility, and hybridization experiments were examined in four of the six species and different chromosome races. Meiotic chromosome behavior supported autoploid origin for tetraploid P. procurrens and tetraploid P. usterii, and also corroborates autoploidy for P. malacophyllum. Meiosis of the three species was compared with the meiotic chromosome behavior of a tetraploid P. simplex strain acquired by artificial autopolyploidization. Moreover, chromosome associations observed in tetraploid interspecific hybrids of P. simplex x procurrens and P. simplex x usterii, in triploid hybrids of P. simplex x malacophyllum, and in diploid hybrids of P. simplex x malacophyllum, indicate that the four species share the same basic genome, and that the polyploid races are autoploids. Facultative apomixis of the aposporous type is reported for the first time in tetraploid strains of P. procurrens and P. usterii. It is also confirmed for tetraploid P. malacophyllum, a species whose diploid representative is here reported to reproduce sexually, though embryological analyses demonstrated some potential for apospory. Our results suggest that the whole subgenus Anachyris of Paspalum is basically an agamic complex. At least three species: P. simplex, P. procurrens, and P. malacophyllum involve sexual self-incompatible diploid races as well as apomietic polyploid (mainly tetraploid) representatives. (c) 2008 Elsevier GmbH. All rights reserved.