Cytology of Some Apomictic Paspalum Species 1

Paspalum almum Chase had a chromosome number of 2n=4x=24. The number for P. brunneum Trin., P. coryphaeum Trin., P. haumanii Parodi, and P. rufum Nees. was 2n−4x−40; P. proliferum Arech. was 2n=6x−60. This is the first report of the chromosome number and cytological behavior for P. brunneum . The chromosome numbers found in P. coryphaeum , P. haumanii , P. rufum , and P. proliferum were different from any previously reported for these species. During metaphase I, the chromosomes in P. almum , P. brunneum , P. coryphaeum , P. haumanii , and P. rufum paired primarily as bivalents with occasional quadrivalents and a limited number of univalents were observed. P. almum , previously considered a diploid, had as many as five quadrivalents, which indicates it is an autotetraploid. Meiosis in P. proliferum was irregular with pairing primarily as 50 univalents and 5 bivalents at metaphase I and numerous laggards and micronuclei were observed. Megasporogenesis and embryo sac development of all six species showed aposporous apomixis followed by pseudogamy. This limits their use in an interspecific hybridization program. The possible origin of the new chromosome races, their relationships to other reported chromosome races of the same species, the role of apomixis in their evolution, and changes in the basic chromosome number of the genus were discussed.