Structural defects in male meiotic cell division lead to reproductive genome instability and disturbed microsporogenesis in banana (Musa spp.)

Reduced fertility in banana poses issues towards the genetic improvement of the crop. This study investigates male meiotic instability in banana, taking into account how it is shaped by genomic determinants, like ploidy, structural heterozygosity, and multiple ancestor contributions, and how it relates to decreased male fertility. In addition, the prevalence of meiotic restitution and related 2n gamete formation will be assessed due to its pivotal role in the emergence of current triploid landraces and its relevance for current triploid breeding. Wild diploid Musa species are generally expected to undergo regular meiosis, yet several displayed significant polyad formation, particularly M. acuminata ‘Banksii’ and M. balbisiana ‘Eti Kehel’, due to univalents and lagging chromosomes in meiosis I. Polyad formation was more pronounced in cultivated diploids; for instance, ‘Pisang Jari Buaya’ exhibited extensive lagging chromosomes in both anaphase I and II, suggesting spindle attachment defects. A baseline of ~10% polyads was observed in triploid and tetraploid genotypes, while the triploid ‘Williams Bell’ showed elevated polyad formation linked to high levels of asynapsis and persistent univalents. Only a few genotypes across ploidy levels showed evidence of meiotic restitution, indicating that 2n pollen formation may be driven more by mutations in meiotic genes than by structural genome variation. Notably, the diploid ‘Pisang Lilin’ consistently produced 2n pollen, potentially through both premeiotic doubling and restitution. Although the influence of hybrid genome composition on meiotic behavior was inconclusive, increased hybridity correlated with reduced pollen production. Meiotic stability in banana could be related to mature pollen size. Pollen larger than 120 µm was associated with meiotic restitution in cultivated diploids, while pollen smaller than 60 µm correlated with polyad formation in wild diploids. This study contributes to our understanding of how genomic determinants affect meiotic stability and male fertility in banana and can aid in high-throughput assessment of meiotic stability in banana on the mature pollen level.