Distant Hybridization of Kazakh Wheat Varieties with Wild Aegilops Species: Cytogenetic Compatibility, Fertilization Dynamics, and Breeding Implications

Distant hybridization between bread wheat (Triticum aestivum L.) and wild Aegilops species is a valuable approach to take to broaden genetic diversity, but it is frequently impeded by reproductive barriers. This study evaluated crossability, pollen tube dynamics, meiotic behavior, somatic chromosome numbers, and pollen fertility in twelve Kazakh wheat cultivars crossed with Ae. triaristata Willd., Ae. cylindrica Host, Ae. triuncialis L., and Ae. squarrosa L. under field-based controlled pollination. Hybridization success varied significantly among combinations, with Ae. triaristata showing the highest compatibility (26.0% in Bezostaya 1 × Ae. triaristata), while Ae. squarrosa produced the lowest seed set. In compatible crosses, pollen tubes reached the ovary within 20–30 min, whereas delayed elongation (>60 min) was associated with fertilization failure. Meiotic analysis revealed incomplete homologous pairing (3–7 bivalents per PMC) and high abnormality rates (>90%). Somatic chromosome counts (2n) of selected F1 hybrids confirmed extensive aneuploidy and partial chromosome elimination. Pollen fertility was generally below 20%. These results identify Ae. triaristata as a promising donor species for pre-breeding in Kazakhstan and underscores the importance of integrating classical cytology with molecular approaches to overcome hybridization barriers.