Nonreduction via meiotic restitution and pollen heterogeneity may explain residual male fertility in triploid marine halophyte Limonium algarvense (Plumbaginaceae)

The cosmopolitan halophylic genus Limonium (Plumbaginaceae) presents high cytogenetic interest because of the natural occurrence of diploid and polyploid variants. Natural triploids are very rare in nature but common in this genus, including the widespread triploid Limonium algarvense found in the Iberian Peninsula and in Morocco. This study describes male sporogenesis and gametogenesis, pollen formation and germination, and seed production in triploid L. algarvense and diploid Limonium ovalifolium using various cytological approaches. The diploid species presented regular meiosis. The triploid species was defective in male meiosis due to unpaired chromosomes, trivalent and tetravalent pairing, unbalanced chromosome segregation in meiosis I, and meiotic restitution in both meiosis I and II. These results may be explained by indeterminate and broad first meiotic restitution. Dyads and restitution nuclei at meiosis I were the most frequent meiotic products in the triploid species. Cytomixis was observed in both species, and callose deposition did not differ among them. In the diploid species, regular, tricolpate pollen grains, which germinated in vitro were found. Contrastingly, the triploid species produced heterogeneous pollen in morphology and size, with moderate to no viability that poorly germinated in vitro. We conclude that even if most triploids male gametes are non-functional, they seem to generate small numbers of viable gametes via nonreduction of chromosomes. Flow cytometric seed screening demonstrated that the diploid species presented a diploid progeny whereas triploids only showed triploid progenies. In the triploids low pollen fertility coupled with viable seed production may assure their persistence in natural populations.