Meiotic chromosome behavior of the male-fertile allotriploid lily cultivar 'Cocossa'.

KEY MESSAGE: Cytological observations of microsporogenesis in the allotriploid lily cultivar 'Cocossa' showed that viable pollen production could be attributed mainly to disoriented spindles, abnormal cytokinesis, and cytomixis during male meiosis. To identify the reasons why the allotriploid lily cultivar 'Cocossa' can produce aneuploid and euploid functional male gametes and can be used as the paternal parent in lily introgression breeding, we performed a detailed investigation of microsporogenesis using the conventional cytological methods. The allotriploid not only produced single pollen grains with variable sizes but also produced adherent pollen grains. Pollen viability was estimated at 50.1% based on staining and 30.8% based on germination. Based on the chromosomal analysis of BC2 plants derived from Oriental cultivars (♀) crossed with the OOT cultivar 'Cocossa' (♂), it was concluded that the objective allotriploid contributed haploid (x), diploid (2x), and aneuploid chromosome complements. Common meiotic abnormalities were observed, indicating the high genetic imbalance of this allotriploid. In addition to normally oriented metaphase II spindles (linear and perpendicular), abnormal spindles, such as parallel, tripolar, fused, and multiple spindles, accounted for 6.21, 6.41, 14.27, and 1.17%, respectively. Tripolar and fused spindles resulted in the production of triads and dyads, which contributed to unreduced pollen production. Some microsporocytes exhibited complete or partial absence of cytokinesis, which led to relatively high frequencies of monads, dyads, and triads. Furthermore, the phenomenon of cytomixis during microsporogenesis occurred mainly in the first meiotic prophase and early development of pollen grains, which we assume is a possible cause of unreduced gamete generation. Our study offers a new resource for lily introgression breeding.