Cytogenetic evidence for cryptic structural hybridity causing intraspecific hybrid sterility in Aegilops caudata L..

To elucidate the mechanism causing the intraspecific hybrid sterility in Aegilops caudata, chromosome pairing and segregation at meiosis and fertility were examined in sterile F1 hybrids, a tetraploid derivative induced from one of the sterile hybrids, and their parental lines. The F1 hybrids showed a normal configuration and frequency of chromosome pairing at MI but was completely sterile. At AI, chromosomes consisting of two sister chromatids different in length were observed. The induced tetraploid was shown to be an autotetraploid based on the configuration and frequency of chromosome pairing at MI, and it showed incomplete but obvious restoration of fertility. From the results, it was strongly suggested that the intraspecific hybrid sterility observed in this species is a chromosomal sterility caused by cryptic structural hybridity defined by Stebbins (1945, 1950). However, the differences in chromosomal structure between parental lines are presumably not great enough to cause preferential pairing in the induced tetraploid. Ae. caudata, thus, most probably is considered to be just on the way to speciation due to cryptic chromosomal rearrangements.