Apomixis and sexuality in some Paspalum species

Paspalum is a large genus that contains several important forage and turf grasses. Little or no information is available concerning the cytology and reproductive behavior of many of these species. The objectives of this study were to determine the cytology, method of reproduction, and fertility of accessions of eight different Paspalum species. Paspalum modestum Mez., P. monostachyum Vasey, P. repens Bergius, and one P. alcalinum Mez. accession were sexual diploids with 2n = 2x = 20 chromosomes. Meiosis was regular with primarily bivalent pairing. Even though P. modestum was sexual, the female gametophyte deteriorated in 43% of the ovules. Two P. alcalinum, one P. falcatum Nees, two P. paucifolium Swallen, three P. polyphyllum Nees, and one P. unispicatum (Scribn. et Merr.) Nash accessions were tetraploids with 2n = 4x = 40 chromosomes. During meiosis their chromosomes associated primarily as bivalents, quadrivalents, and univalents. Regardless of the species, all tetraploids were facultative aposporous apomicts. One P. alcalinum accession was a pentaploid with 50 chromosomes. Meiosis was irregular with the chromosomes associating as univalents, bivalents, trivalents, and quadrivalents. This accession reproduced as an obligate aposporous apomict. Seed set in P. modestum and P. monostachyum was very low but was high enough in the other species that they could be propagated by seed. These findings demonstrate the cytological and reproductive diversity within this large complex genus.