Cytological relationship between Paspalum dilatatum and diploid cytotypes of P. brunneum and P. rufum

Abstract

Tetraploid Paspalum dilatatum Poir. (2n = 4x = 40, genome formula IIJJ) was crossed with diploid cytotypes of P. brunneum Mez (2n = 2x = 20) and P. rufum Nees (2n = 2x = 20), both of which have the genome formula II. The objectives of this investigation were to determine the relationship of these two diploid species to P. dilatatum and to ascertain if they are more closely related to P. dilatatum than diploid P. intermedium Munro. ex Morong, which also has the genome formula II. Crossability for both crosses was in excess of 11%, which is very high for this genus. Twelve P. dilatatum × P. brunneum and 15 P. dilatatum × P. rufum hybrids studied cytologically had 30 chromosomes. The mean meiotic chromosome associations were 14.061, 7.91 II, and 0.04 III for the P. dilatatum × P. brunneum hybrids and 15.81 I, 7.04 II, and 0.03 III for the P. dilatatum × P. rufum hybrids. These data indicate that both P. brunneum and P. rufum are related to P. dilatatum, but the I genome in P. dilatatum differs from the I genome in these species. Thus, P. intermedium is more closely related to P. dilatatum than either P. brunneum or P. rufum and remains the most probable source for the I genome in P. dilatatum.Key words: meiosis, genomes, interspecific hybrids, chromosome pairing, dallisgrass.