Cytology of Intra- and Interspecific Hybrids between two Cytotypes of Paspalum notatum and P. cromyorrhizon

Abstract

Intra- and interspecific hybrids were made between diploid and tetraploid cytotypes of Paspalum notatum Flugge and P. cromyorrhizon Trin, to study their phylogenetic relationships. Two P. notatum (2n = 4x = 40) x P. notatum var. saurae Parodi (2n = 2x = 20) hybrids had 2n = 3x = 30. At metaphase I of meiosis, the mean chromosome associations were 1.93 I, 1.93 II, and 8.07 III, confirming that tetraploid P. notatum is an autotetraploid. Because P. notatum var. saurae has the genome formula NN, P. notatum can be given the formula NNNN. Two hybrids were recovered from the P. cromyorrhizon (2n = 2x = 20) x P. cromyorrhizon (2n = 4x = 40) cross: one had 30, and the other 40, chromosomes. Meiosis was irregular in both hybrids. The mean meiotic chromosome associations for the triploid were 4.81 I, 4.73 II, 4.92 III, 0.1 IV, 0.03 V, and 0.07 VI, and for the tetraploid, 0.84 I, 10.56 II, 0.21 III, 4.15 IV, 0.11 VI, and 0.03 VIII. Of seven P. notatum var. saurae x P. cromyorrhizon (2n = 2x = 20) hybrids, six had 20 chromosomes and a mean chromosome association of 9.04 I, 5.42 II, and 0.04 III, and one had 40 chromosomes and a mean association of 1.2 I, 6.33 II, 0.4 III, 6.13 IV, and 0.07 VI. The frequency of bivalents in the 20-chromosome hybrids and tetravalents in the 40-chromosome hybrid indicates that the genomes of these two species are partially homologous and that both species have forms of the N genome. Two hybrids from the P. notatum x P. cromyorrhizon (2n = 2x = 20) cross had 2n = 3x = 30. The mean pairing behavior was 9.38 I, 9.09 II, 0.78 III, and 0.02 IV, and some cells had as many as 5 III. These findings support the traditional taxonomic treatment that P. notatum and P. cromyorrhizon are separate species.