EFFECTS OF SUPPLEMENTAL LIGHT DURATION ON GREENHOUSE SWEET-PEPPER PLANTS AND FRUIT YIELDS

Sweet pepper (Capsicum annuum L.) plants were grown under natural or s upplemental lighting that extended the photoperiods to 16, 20, or 24 h ours. Increasing the photoperiod to 16 and 20 hours increased pepper p lant yields, but continuous light (24 hours) decreased yields compared to the 20-hour photoperiod. In a second experiment, plants were expos ed to a photoperiod of 14 or 24 hours and either pruned to one fruit e very four nodes or not pruned. During the first weeks of treatments, p lants grown under continuous light had higher shoot mass (fresh and dr y) and yields. After 7 to 8 weeks of treatments, plants under continuo us 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 treatme nt. Leaf mineral composition was not affected by photoperiod treatment , indicating that reduced growth and yields under continuous light wer e not due to unbalanced mineral nutrition. Leaf starch and sugar conte nts were increased under continuous light. However, fruit pruning trea tments did not modify the pattern of starch and sugar accumulation und er the different photoperiod treatments, Reduced growth and yields mea sured under a 24-hour photoperiod are probably explained by starch and sugar accumulation in leaves as a result of leaf limitations rather t han a sink limitation.