Greenhouse vapour pressure deficit and lighting conditions during growth can influence postharvest quality through the functioning of stomata

There is a tendency in horticulture to grow plants in greenhouses with high humidity and prolonged light periods, especially in winter. Although plants grow well in greenhouses with high relative humidity (RH) (low vapour pressure deficit; VPD), the plants produced under such greenhouse climates have limited control over water loss after harvest, leading to uncontrolled transpiration and decreased water content in the postharvest stage. This results in shortened vase-life of cut flowers and decreased quality of leafy vegetables. When plants had been produced in greenhouses with moderate humidity and natural day length, their stomata close when they are exposed to stomata closure-promoting environments (low RH, desiccation and darkness), as usually happens during the postharvest stage. However, in greenhouses with low VPD conditions and long photoperiods, stomata will not fully close during the postharvest stage; even decreased leaf water content will not result in full stomatal closure (stomatal malfunctioning) in products coming from those greenhouses. In this paper, greenhouse climate factors during the growth of plants that induce stomatal malfunctioning in the postharvest stage will be characterised. Approaches will be discussed to improve stomatal functionality under such greenhouse conditions in order to increase vase- and shelf-lives of products.