LIGHT EMITTING DIODES WITH A HIGH PROPORTION OF BLUE LIGHT AFFECTS EXTERNAL AND INTERNAL QUALITY PARAMETERS OF POT ROSES DIFFERENTLY THAN THE TRADITIONAL HIGH PRESSURE SODIUM LAMP

Abstract

Alterations in light quality affect plant quality but the effects vary significantly between species. In this study, we analyzed internal and external quality parameters of pot roses (Rosa × hybrid ‘Toril’) grown under different light qualities provided by light emitting diodes (LED, 80% red and 20% blue) and the traditional high pressure sodium (HPS) lamps. The experiments were conducted in closed growth chambers and in greenhouse during winter with supplemental lighting (100 µmol m-2 s-1). LED-grown plants showed higher chlorophyll and anthocyanin content and more thorns than HPS-grown plants. The stem and pedicle length were significantly shorter in LED-grown plant compared to HPS although the total production period was not affected. There was no significant difference in the storability of dark stored plants at high temperature (24°C) between the two light qualities. However, at 4°C a better storability was found in LED-grown plants and the flowers were more vital and a lower pH and osmolarity was found in petals 4 weeks after storage indicating delayed senescence compared to HPS-grown plants. Further, desiccation tests were performed on detached leaves to study the drought stress tolerance. When growing the pot roses under high relative air humidity (90%), LED-grown leaves had significantly higher water content (WC) after 3 h of desiccation compared to leaves from HPS.