Maternal ontogeny modulates auxin-associated cutting mortality in Amentotaxus formosana, with genotype-specific responses revealed by Cox proportional hazards modelling.

Amentotaxus formosana (Taxaceae) is an endangered relict conifer for which stem-cutting propagation is essential for ex situ conservation. Seed-based regeneration is unreliable in its small, fragmented, dioecious populations. However, extreme and uncharacterized cutting mortality has severely bottlenecked these efforts. Because conventional static endpoint evaluations mask the critical temporal dynamics of rhizogenesis and failure, the underlying drivers of this attrition remain obscure. Here, we applied Kaplan-Meier estimation and Cox proportional hazards modelling to a two-stage factorial experiment involving 641 cuttings to identify factors associated with cutting mortality over time. Stage 1 revealed that substrate composition significantly influenced survival, with pure shredded shale approximately doubling the mortality hazard relative to peat-perlite. Among plant growth regulator (PGR) treatments, indole-3-butyric acid (IBA) significantly reduced mortality risk relative to the ABT-1 composite treatment. Stage 2 identified specific maternal-DBH- and genotype-dependent treatment responses within an analytical subset of five adequately sampled genotypes. The association between maternal DBH and mortality hazard was treatment-dependent, with a significant maternal DBH × IBA interaction. In analyses including all 12 genotypes, stratified log-rank tests detected significant among-genotype survival differences under IBA and NAA, but not under the untreated control. Within the five-genotype Cox model, DG-15-12 showed a significant genotype × NAA interaction. This study represents the first application of time-to-event survival analysis in Amentotaxus propagation. We demonstrate that cutting mortality is partially associated with interactions involving substrate type, auxin treatment, maternal DBH, and genotype. However, the magnitude and statistical detectability of these interactions varied across factor combinations. These findings provide a quantitative framework for genotype-resolved, risk-informed conservation propagation of recalcitrant relict species.