Comparative UV-B Stress Responses in Maize and Sorghum Based on Biophoton Emission Measurements and Morphophysiological Traits

Ultraviolet-B (UV-B, 280–315 nm) radiation is an increasingly relevant abiotic stressor under climate-change scenarios, yet crop-specific tolerance mechanisms remain insufficiently understood. We compared maize (Zea mays L.) and grain sorghum (Sorghum bicolor L.) seedlings exposed to eight UV-B durations (1–12 h), applied every second day over 14 days of juvenile growth. Highly sensitive, non-invasive biophoton emission imaging (NightShade® LB 985), chlorophyll content measurements (SPAD-502), and morphophysiological traits (shoot/root lengths, biomass, root collar diameter) were assessed. Biophoton emission kinetics measured immediately and 24 h after exposure suggested differing temporal defense dynamics: maize showed an early modest increase, a mid-exposure reduction, and a later pronounced peak around 6 h. Sorghum tended to reach a dominant peak earlier (≈3 h) and maintain relatively steady emissions thereafter, potentially reflecting more uniform antioxidant activation. SPAD patterns aligned with these trends: maize retained higher chlorophyll at lower exposures (0–6 h; p < 0.05), whereas sorghum surpassed maize at extreme exposures (10–12 h; p = 0.036). Morphophysiological traits showed no significant treatment effects, though minor low-dose peaks suggested possible ROS-mediated stimulation. These results indicate species-specific UV-B acclimation patterns and demonstrate the utility of biophoton imaging as a rapid screening tool for assessing crop resilience.