Photoperiod Modulates Phenotypic Traits in Cyclamen Under Drought: Insights from High-Throughput Imaging

Background: Drought and heat stress increasingly limit ornamental crop yield, increasing demand for rapid phenotyping tools to breed resistant cultivars. Infrared thermography estimates plant water status from canopy temperature, as well-watered plants transpire more and remain cooler than stressed plants. Pressure chamber measurement of leaf water potential (Ψleaf) is accurate but labor-intensive and destructive.

Methods: Three Cyclamen genotypes, ‘Origami’, 'Victoria,' and ‘Violet F,' were sown in September 2024, and drought stress was applied at the adult vegetative stage in June-July 2025. A dual experiment compared well-watered controls with drought stress by withholding irrigation. Canopy temperature and leaf relative water content were extracted from thermal-RGB images after plant segmentation. Total, wilted, and dead leaves were counted. ANOVA tested treatment and genotype effects, and Pearson correlation assessed the relationship between canopy temperature and leaf water status.

Results: Drought increased mean canopy temperature by ∼10°C across genotypes: ‘Origami’ 28.58°C vs 18.05°C control; ‘Victoria’ 29.05°C vs 18.98°C; ‘Violet F’ 29.00°C vs. 20.70°C. Leaf relative water content declined from 72-75% in controls to 55-61% under drought. Drought accelerated senescence: dead leaves rose from 1.5 to 3.5 in controls to 6.0 to 9.0 in stressed plants and wilted leaves from 1.0 to 3.5 to 4.75. Controls showed senescence only in older leaves, while drought induced canopy-wide chlorosis. Canopy temperature was inversely related to leaf water content, reflecting stomatal closure and reduced evaporative cooling.

Conclusion: Thermal-RGB imaging reliably detected drought stress and genotypic variation in Cyclamen at canopy level. The ∼10°C thermal difference provides a robust signature for irrigation scheduling and drought phenotyping. Future studies should integrate advanced data processing to improve thermal sensing accuracy for precision horticulture.