Abstract
To detect possible reproductive barriers isolating the two subspecies of Aegilops geniculata, ssp. gibberosa was crossed with ssp. geniculata. The two subspecies differ significantly in shape of spikes, spikelet density on spikes, and number of awns on empty glumes. The F hybrids were intermediate in morphology and almost completely sterile. A chromatid bridge with a fragment was observed at first anaphase (AI) of meiosis in some pollen mother cells (PMCs) of the F1 hybrids. Though multivalents were formed at first metaphase (MI) in all the PMCs of the F1 hybrids, the frequency was not higher than that in the intra-subspecific hybrids of ssp. geniculata. These results suggest that the intraspecific sterility is not caused by a gross chromosome differentiation. The hybrid sterility, which is an effective reproductive barrier isolating the two subspecies, might be caused by negative interaction(s) between genes of the two subspecies, or by small chromosomal rearrangements not detectable from chromosome pairing configuration at MI. It is strongly proposed that the delineation of species and infraspecific taxa in the polyploid species of the genus Aegilops is worthy of reassessment from a biosystematic viewpoint.
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