Phylogenetic Relationships among Paspalum Species with Different Base Chromosome Numbers

Abstract

The genus Paspalum has two base chromosome numbers: x = 6 and x = 10. One P. jurgensii (2n = 20) x P. hexastachyum (2n = 12) hybrid had 2n = 16 and a mean meiotic chromosome pairing of 12.78I and 1.61II. Five hybrids were obtained from the P. intermedium (2n = 20) x P. hexastachyum; two hybrids had 2n = 16; the other three, 2n = 26. The mean meiotic chromosome association in the 2n = 16 hybrids was 9.08I and 3.46II and in the 2n = 26 hybrids, 6.07I and 9.96II. The 2n = 26 hybrids may have originated from the fertilization of an unreduced egg of P. intermedium. The crosses of P. dilatatum (2n = 40) x P. hexastachyum produced five hybrids with 2n = 26, with a mean meiotic association of 22.2I and 1.9II. Except for pairing between the P. intermedium chromosomes in the 2n = 26 P. intermedium x P. hexastachyum hybrids, the bivalents in all of the above hybrids were loosely synapsed and did not demonstrate strong homologies. Two hybrids were recovered from P. dilatatum x autotetraploid P. almum (2n = 24). One hybrid had 2n = 32, with 11.13I and 10.44II of which 6II were from autosyndetic pairing of the P. almum chromosomes, and the remaining bivalents, from intra- or intergenomic pairing of the P. dilatatum chromosomes. This study indicates that the x = 6 and x = 10 species are not closely related.