CYTOEMBRYOLOGY OF PASPALUM-CHASEANUM AND SEXUAL DIPLOID BIOTYPES OF 2APOMICTIC PASPALUM SPECIES

This study was undertaken to determine the cytology, method of reprodu ction, and flowering behaviour of three Paspalum species. Paspalum pli catulum has long been considered a segmental allotetraploid that repro duces by obligate apomixis with the type being apospory followed by ps eudogamy. Paspalum simplex is an apomictic autotetraploid species, whi le P. chaseanum is a rare species for which no information regarding c ytology and reproduction is available. This investigation concerns dip loid cytotypes (2n = 2x = 20) of P. plicatulum and P. simplex that wer e recently collected in subtropical South America. In addition, two ac cessions of P. chaseanum were also recorded and both had 2n = 2x = 20 chromosomes. Meiosis showed regular bivalent chromosome pairing. Embry ological observations indicated that the three species reproduce sexua lly at the diploid level. Pollen-pistil interaction following self-pol lination suggested the presence of a self-incompatibility system respo nsible for allogamy. The results indicate that P. plicatulum and P. si mplex complexes consist of diploid sexual allogamous cytotypes in addi tion to the known tetraploid apomictic cytotypes. Diploid strains cons titute a source of sexuality for plant improvement. Chromosome doublin g will likely produce sexual tetraploids to be used as females in cros ses with natural apomictic tetraploid biotypes. Since diploid self-inc ompatible sexual Paspalum plants usually have apomictic tetraploid co- specific counterparts, the self-incompatible diploid P. chaseanum desc ribed in this study warrants further exploration for its apomictic cou nterpart.