Supplemental red light more than other wavebands activates antioxidant defenses in greenhouse-cultivated Fragaria × ananassa var. Elsanta plants

This work offers new insights into the physiological and biochemical responses of strawberry plants to red (R), green (G), blue (B) and white (W- R:G:B; 1:1:1) LED light supplementation (250 µmol m −2 s −1; 5 h d −1). Gas exchange and chlorophyll a fluorescence parameters, pigment content, antioxidant enzyme activities and oxidative stress markers (i.e., H2O2 and malondialdehyde by-products - MDA) were measured in plants grown for 60 days with light supplementation. Supplementation with R light induced a reduction of net CO2 assimilation rates (–13% on average with respect to the other treatments) which is not dependent to R-triggered stomatal closure, but rather to the biochemical activity of the photosynthetic apparatus. Despite that, biometric parameters (leaf biomass/area) were not significantly affected by these physiological changes, suggesting that those alterations were not the result of a distress, but rather an efficient eustress to stimulate plant antioxidant defenses. Indeed, R light promoted the activity of antioxidant enzymes and R-enriched plants showed the highest level of H2O2 and MDA, which could explain the higher tolerance to Botrytis cinerea observed in a previous experiment. The above is supporting for the role of R light enrichment as a priming eustress which could be useful in strawberry indoor cultivation as a way to promote fruit enhancement in terms of antioxidant compounds and fruit tolerance to pathogens thus reducing agrochemical inputs.