Metabolism and Yield of Grape–Tomato Hybrids Under Heat Stress in an Innovative Protected Environment Using Twin-Walled Polycarbonates with Laminar Water Flow

Background/Objectives: The high temperatures associated with climate change represent an important constraint for tomato production in tropical regions, affecting plant growth, reproductive development, and fruit metabolic composition. In this context, protected cultivation systems capable of modifying greenhouse microclimates may help reduce thermal stress and maintain crop productivity. Methods: This study evaluated the effects of two protective environments, diffuse agricultural film (AF) and twin-walled polycarbonate panels with laminar water flow (P), on the agronomic performance and fruit metabolic traits of five grape–tomato hybrids grown under tropical conditions. Microclimatic variables, vegetative growth, yield components, postharvest behavior, and fruit quality attributes were evaluated, with emphasis on carotenoid accumulation. Results: Compared with the agricultural film environment, the polycarbonate system reduced global radiation and photosynthetically active radiation (PAR) and was associated with an increase in yield of approximately 25%, an increase in fruit number of approximately 13%, and an 8% increase in fruit diameter. In addition, some hybrids cultivated under the polycarbonate system showed greater lycopene and β-carotene accumulation, indicating that microclimate moderation may favor carotenoid-related fruit quality depending on genotype. Principal component analysis revealed a clear separation between cultivation environments, with the polycarbonate system more closely associated with yield-related and canopy development traits, whereas the agricultural film environment was linked to biomass accumulation and selected physicochemical attributes. Among the evaluated hybrids, BS IGR0104, Jacy, and GI7545 showed the most favorable combination of agronomic performance and fruit quality traits. Conclusions: These results demonstrate the importance of climate-adaptive protected cultivation systems and hybrid selection for improving tomato productivity under tropical heat conditions.