Chromosomal and embryological analyses in sexual x apomictic hybrids ofPanicum maximum Jacq.

Summary Cytological analyses in series of crosses between 7 sexual pistillate and 8 apomictic staminate parents of speciesPanicum maximum (Gramineae) are reported. Although these 15 progenitors were tetraploid (2n = 32), 2 dihaploids (2n = 16), 45 hexaploids (2n = 48) and 5 octoploids (2n = 64) were observed among 333 progeny plants. The role of unreduced gametes as the originators of polyploidy is discussed in relation to the so-called elements of apomixis. The 2 dihaploids appeared to be sexual while the hexaploids and octoploids were all apomictic. At the tetraploid level sexual and apomictic hybrids segregated in a ratio close to 11. These results were then compared to those already obtained from studies on other tropical grasses and indicate a simple genetic determinism for gametophytic apomixis.