Unreduced gamete formation in wheat x Aegilops spp. hybrids is genotype specific and prevented by shared homologous subgenomes

The presence of homologous subgenomes inhibited unreduced gamete formation in wheat x Aegilops interspecific hybrids. Unreduced gamete rates were under the control of the wheat nuclear genome. Production of unreduced gametes is common among interspecific hybrids, and may be affected by parental genotypes and genomic similarity. In the present study, five cultivars of Triticum aestivum and two tetraploid Aegilops species (i.e. Ae. triuncialis and Ae. cylindrica) were reciprocally crossed to produce 20 interspecific hybrid combinations. These hybrids comprised two different types: T. aestivum x Aegilops triuncialis; 2n = ABDU(t)C(t) (which lack a common subgenome) and T. aestivum x Ae. cylindrica; 2n = ABDD(c)C(c) (which share a common subgenome). The frequency of unreduced gametes in F-1 hybrids was estimated in sporads from the frequency of dyads, and the frequency of viable pollen, germinated pollen and seed set were recorded. Different meiotic abnormalities recorded in the hybrids included precocious chromosome migration to the poles at metaphase I and II, laggards in anaphase I and II, micronuclei and chromosome stickiness, failure in cell wall formation, premature cytokinesis and microspore fusion. The mean frequency of restitution meiosis was 10.1 %, and the mean frequency of unreduced viable pollen was 4.84 % in T. aestivum x Ae. triuncialis hybrids. By contrast, in T. aestivum x Ae. cylindrica hybrids no meiotic restitution was observed, and a low rate of viable gametes (0.3 %) was recorded. This study present evidence that high levels of homologous pairing between the D and D-c subgenomes may interfere with meiotic restitution and the formation of unreduced gametes. Variation in unreduced gamete production was also observed between T. aestivum x Ae. triuncialis hybrid plants, suggesting genetic control of this trait.