S23 - Session P1 - Impact of preharvest modified photoperiod on postharvest physiology of lettuces

Authors: Florence Charles , Cedric Dresch *, Justine Gricourt, Huguette Sallanon, Vincent Truffault

Postharvest storage duration is one of the key parameters to reduce food waste. Links between plants preharvest and postharvest parameters variations are today poorly studied. Furthermore, preharvest culture conditions are drivers for plants quality, including antioxidant capacity, phenolic compounds, and vitamins content, and might, as a result, have a major role on shelf life. The standard preharvest photoperiod condition (16 hours of light and 8 hours of obscurity, 16/8) allows plants to express their circadian rhythm, an endogenous rhythm naturally based on 24 hours that regulates metabolic processes of living organisms. Circadian rhythm perturbations have already been studied due to the changes of plants competitiveness and growth. In controlled environment agriculture that allows photoperiods changes, circadian rhythm has proven to be a new tool to optimize plants yield and quality while reducing energy cost. In this work, we studied two preharvest light modalities and their effect on postharvest: one control, with a standard photoperiod, and another under circadian rhythm perturbations by changing photoperiods duration throughout the culture. A butterhead lettuce variety were harvested, packaged in macroperforated film and stored at 4°C during 14 days. Visual aspect, browning and gas exchange were analysed after 7 and 14 days, respiratory intensity were carried out after 14 days only. No differences were observed on visual aspect, browning or fresh weight loss. Otherwise, significant differences were observed on gas exchange. Lettuces grown under circadian rhythm perturbations released significantly more CO 2 than control,. Furthermore, the respiratory quotient of the variety studied was significantly higher than standard one, illustrating that the respirated molecules are preferentially organic acid for lettuces under circadian rhythm perturbations compared to sugars for control ones. Our data suggest that preharvest conditions have a major impact on postharvest lettuces respiration metabolism and, consequently on freshness duration .