Photoperiodic Stress in Eggplant and Tomato: Growth Retardation and Leaf Disorders

In controlled-environment agriculture systems, such as vertical farms, plants can be cultivated under artificial light-dark (L/D) cycles that deviate substantially from the natural 24 h photoperiod. While these regimes may enhance the growth and quality of certain crops, the physiological response is highly species-specific, and long-term implications for many crop species remain insufficiently characterized. This study aimed to evaluate the effects of a shortened L/D cycle (8/4 h, repeated twice daily) on the morphology, photosynthetic activity, and redox status of eggplant (Solanum melongena L., cv. 'Almaz') and tomato (Solanum lycopersicum L., cv. 'Verlioka Plus') seedlings, compared to a standard 16/8 h photoperiod. Plants were grown in chambers equipped with light-emitting diode (LED) and fluorescent (FLU) lamps under an equivalent daily light integral (DLI: 11.5 mol m^-2 day^-1). The shortened 8/4 h L/D cycle induced significant growth suppression, reduced leaf area, and decreased the maximum quantum yield of photosystem II (Fv/Fm), as well as chlorophyll and carotenoid content in both species. Under this regime, eggplants exhibited leaf chlorosis accompanied by necrotic lesions, whereas tomato plants displayed interveinal chlorosis. Notably, significant accumulation of oxidative stress markers-a 37% increase in malondialdehyde (MDA) and a 30% elevation in H₂O₂ levels-occurred exclusively in eggplant. These findings demonstrate that redistributing the same 16 h daily illumination into two 8/4 h L/D cycles induces stress in both eggplant and tomato plants, with eggplant exhibiting greater injury than tomato. The underlying circadian mechanisms and the apparent differences between LED and FLU lighting require further controlled validation.