Genome Relationship and Reproductive Behavior of Intraspecific Paspalum dilatatum Hybrids: Yellow-Anthered x Uruguaiana

Abstract

Sexual, tetraploid (2n = 4x = 40) yellow-anthered dallisgrass, Paspalum dilatatum Poir., was crossed with apomictic, hexaploid (2n = 6x = 60) Uruguaiana dallisgrass from Brazil for the purpose of determining their cytological relationship, the genome composition of the Uruguaiana biotype, and the reproductive behavior of their hybrids. Five hybrids were recovered; two had a chromosome number of 50 and the others had 45, 55, and 70 chromosomes. Meiotic chromosome pairing in these hybrids indicated that the biotypes have two homologous genomes, I and J, which comprise the yellow-anthered biotype (IIJJ). The identity and source of the third genome in the hexaploid biotype is unknown, and it was designated as X. The 55-chromosome hybrid had five extra chromosomes belonging to the X genome. Limited pairing involving these duplicated homologues indicates that the Uruguaiana biotype has modified versions of the X genome. The meiotic irregularities in this biotype support these findings. Consequently, this biotype was assigned the genome formula IIJJXX2, where X and X2 represent different forms of the X genome. All hybrids, except for the one with 45 chromosomes, were facultative apomicts in that both sexual and aposporous embryo sacs were produced in their ovules. The 45-chromosome plant was sexual, which indicates that the gene(s) controlling apomixis are on one of the missing X chromosomes. There was a high degree of ovule abortion in all hybrids, and seed set was low.