Growth and development of cucumber Cucumis sativus L. in the prereproductive period under long photoperiods

When plants are grown in a greenhouse or in controlled environment growth rooms, prolonging the photoperiod, including towards continuous light, is one of the ways to increase plant productivity and energy savings. However, exposing some plant species to long photoperiods causes leaf injuries and growth reductions. We studied the effect of the photoperiod (8, 12, 16, 20, and 24 h) and photosynthetic photon flux density (60, 120, and 160 μmol/m2 s PAR) on cucumber plants Cucumis sativus L. in a prereproductive period. It was shown that the response of the cucumber plants to a photoperiod over 20 h, including continuous light, depending on the plant age and light intensity, may include leaf movement or paraheliotropism, non-photochemical energy dissipation, and/or reversible photoinhibition of a reaction center of photosystem II, development of reversible chlorosis, reduction of a light-harvesting complex, and increase in the content of carotenoids. Reaction of immature and virginile plants to long photoperiods was different, which high-lights the need for experimental separation of the prereproductive period in terms of age states and consideration of this when developing crop production plan.