Aneuploidy-Induced Floral and Fertility Defects in <i>Hibiscus syriacus</i> Revealed by Cytogenetics and Integrative Trait Analysis: Implications for Chromosome Engineering in Ornamental Breeding

Artificial polyploidy induction is widely used in ornamental breeding but can yield aneuploidy derivatives that vary in developmental stability and breeding utility. In Hibiscus syriacus ‘Blue Bird’, in vivo colchicine and oryzalin treatments generated regenerated shoots in which genome-size shifts were detected by flow cytometry; among the candidate lines, a subset reached flowering maturity and was characterized in detail. These flowering aneuploids displayed diverse floral alterations, including reduced corolla size, altered pigmentation, and partial conversion of stamens into petaloid organs. Flow cytometry and somatic chromosome counts indicated aneuploid status (150–182 chromosomes). Pollen morphology was highly variable, with frequent malformations and broad size distributions, and Alexander staining and in vitro germination assays showed markedly reduced viability and germination relative to the control. Cytological observations of microsporogenesis revealed abnormal products such as polyads and unequal tetrads, indicating disruption during late meiotic and/or post-meiotic stages. Targeted expression analysis of two anthocyanin-pathway genes showed uniform downregulation of DFR, whereas F3′5′H responses varied among lines, providing a limited but consistent signal in line with the observed pigmentation changes. For downstream analyses, lines were grouped a priori by explicit reproductive and developmental criteria into intermediate and severe classes, with severe lines failing to reach full anthesis and showing complete male sterility. Multivariate analyses were used in an exploratory manner and described severity-associated patterns and coordinated co-variation among pigmentation, floral organ composition, and male fertility traits within the analysed lines. Collectively, these results are consistent with induced aneuploidy in H. syriacus being accompanied by coordinated floral and reproductive changes in the material examined here, and they support the use of early ploidy screening and targeted cytogenetic triage to guide selection in ornamental breeding programmes.