Genotype-Specific Photosynthetic Plasticity and Leaf Yield of Stevia rebaudiana Under Contrasting Radiation Across Caribbean Environments

Light availability drives <i>Stevia rebaudiana</i> productivity, yet how incident radiation interacts with genotype and site under tropical field conditions remains unclear. We evaluated four genotypes (L020, L102, L082, and 'Morita II') across three Caribbean locations in Colombia under two contrasting light levels (600 vs. 1800 μmol photons m^-2 s^-1) using a split-plot randomised complete block design with four replicates. Incident photosynthetic photon flux density (PPFD) was logged and, at 85 days after transplanting (DAT), net CO₂ assimilation, stomatal conductance, transpiration, and intercellular CO₂ concentration were measured alongside light-adapted chlorophyll fluorescence parameters, including the effective quantum yield of photosystem II (ΦPSII), the maximum efficiency of PSII in the light (Fv'/Fm'), photochemical quenching (<i>qP</i>), and electron transport rate (ETR); biomass and leaf yield were quantified at harvest. Data were analysed using factorial analysis of variance (ANOVA) and complementary multivariate approaches, including Pearson correlation analysis and principal component analysis (PCA). Radiation responses were strongly site-dependent: under 1800 μmol photons m^-2 s^-1, net CO₂ assimilation increased by 90.2% at El Carmen de Bolívar and 21.5% at Polonuevo but decreased by 36.4% at Montería. Leaf yield was highest in El Carmen de Bolívar (1951.46 ± 182.03 kg ha^-1), followed by Montería (1510.94 ± 173.75 kg ha^-1) and Polonuevo (576.31 ± 42.36 kg ha^-1). Genotype rankings shifted with environment and radiation, with L102 reaching 3256.25 ± 126.39 kg ha^-1 under direct radiation in El Carmen de Bolívar and 'Morita II' showing strong responsiveness in Montería. These results demonstrate that photosynthetic plasticity and leaf yield in <i>S. rebaudiana</i> depend on genotype × radiation × environment interactions, supporting location-tailored radiation management combined with targeted genotype deployment.