Cytotaxonomy of Australian Danthonia

Abstract

Cytological and cytogenetic studies of 29 Australian species of Danthonia revealed an extensive polyploid series ranging from 2n = 24 to 2n = 120. Meiosis was regular and fertility high in the species. Field hybrids were detected by aberrant chromosome number, meiotic behaviour, and reduced fertility.

An extensive series of interspecific crosses resulted in some viable hybrids but many combinations failed or gave F₁ plants which failed to flower. Most viable F₁ plants were highly sterile. Diploid hybrids were completely sterile, but in higher polyploids crossing was more often successful and hybrids had increased fertility.

Meiotic pairing and chiasma frequency were drastically reduced in all F₁s. Multivalent associations indicated gross structural rearrangements. The restoration of fertility by chromosome doubling indicated cryptic structural changes.

Neither cross compatibility nor meiotic behaviour showed any strong relationship with taxonomic grouping.

These results together with the intermediate morphology of F₁s and the increased morphological variation in polyploid forms of D. caespitosa and D. linkii strongly suggest alloploidy as the main mechanism of evolution of the polyploid species.

Twenty-three of the species had Panicoid type of epidermis and Festucoid chloroplast arrangement. The exceptions were D. pallida, D. procera, D. frigicla, D. nivicola, D. nudiflora, and D. sp. indescr.

These studies throw light on the relationship of the arid form, D. bipartita, the alpine forms D. frigida, D. nivicola, and D. nuclifiora, and the highly variable forms such as D. caespitosa and D. linkii with the rest of the genus.

Plant improvement by conventional methods would be virtually impossible unless restricted to high polyploids and intraspecific crossing, but true-breeding, highly fertile amphidiploids could be produced.