Autogamy and hybridization as evolutionary mechanisms in Panicum subgenus Dicanthelium (Gramineae)

A predominantly autogamous breeding system is described forP. occidentale Scribn.,P. pacificum Hitchc. & Chase, andP. thermale Boland. Five synthetic hybrids and three generations of progeny are also described for crosses among these three species. All parents haven = 9 chromosomes and normal meiosis. Hybrids exhibit various irregularities during meiosis, but nine bivalents are usually formed. One population ofP. occidentale and one ofP. thermale were found to have chromosomes with interchanges larger than those of other populations. The F₂ and F₃ generations had markedly increased fertility, as determined by pollen stainability. It is proposed that autogamy and hybridization are a common means of maintaining and stabilizing genetic variability in these grasses and that these means account for much of the taxonomic difficulty posed by the subgenus. The possibility of a low rate of introgression between populations is also proposed.