Effects of supplemental light duration on greenhouse sweet pepper plants and fruit yields

Abstract

Sweet pepper (Capsicum annuum L.) plants were grown under natural or supplemental lighting that extended the photoperiods to 16, 20, or 24 hours. Increasing the photoperiod to 16 and 20 hours increased pepper plant yields, but continuous light (24 hours) decreased yields compared to the 20-hour photoperiod. In a second experiment, plants were exposed to a photoperiod of 14 or 24 hours and either pruned to one fruit every four nodes or not pruned. During the first weeks of treatments, plants grown under continuous light had higher shoot mass (fresh and dry) and yields. After 7 to 8 weeks of treatments, plants under continuous light grew more slowly than plants exposed to a 14-hour photoperiod. At the end of the experiment, shoot mass and yields of plants grown under a 14-hour photoperiod were equal to or higher than plants under continuous light. So, it seems possible to provide continuous lighting for a few weeks to improve growth and yields. Limiting the number of fruit per plant increased shoot mass and decreased yields, but had no effect on the general response of pepper plants to photoperiod treatment. Leaf mineral composition was not affected by photoperiod treatment, indicating that reduced growth and yields under continuous light were not due to unbalanced mineral nutrition. Leaf starch and sugar contents were increased under continuous light. However, fruit pruning treatments did not modify the pattern of starch and sugar accumulation under the different photoperiod treatments. Reduced growth and yields measured under a 24-hour photoperiod are probably explained by starch and sugar accumulation in leaves as a result of leaf limitations rather than a sink limitation.