CYTOLOGY OF PASPALUM-CHACOENCE AND PASPALUM-DURIFOLIUM AND THEIR RELATIONSHIP TO P-DILATATUM

P. chacoence Parodi is a sexual diploid with 20 chromosomes that pair as 10 II at meiosis, P. durifolium Mez. has 60 chromosomes with essentially 30 II during meiosis and reproduces by aposporous apomixis. A yellow-anthered sexual biotype of P. dilatatum, 2n = 4x = 40, was crossed with both species. Meiosis for 6 P. dilatatum .times. P. chacoence hybrids, 2n = 3x = 30, was irregular, a mean association of 27.32 I and 1.34 II per cell indicated that these species do not have homologous genomes. Two P. dilatatum .times. P. durifolium hybrids, 2n = 5x = 50, had irregular meiosis and mean chromosome associations of 20.4 I, 14.61 II, 0.1 III, and 0.01 IV, indicating 1 homologous genome and a partially homologous genome. On the basis of chromosome pairing in the species and the hybrids, P. durifolium was given the genome formula II J2J2 XX. This is the 1st indication that a form of the J genome is present in a species of the Quadrifaria group. Implications that P. durifolium may be the hexaploid progenitor of the common apomictic P. dilatatum biotype, 2n = 5x = 50, are discussed.