Evaluation of response of lettuce (Lactuca sativa L.) to temperature and light stress

The aim of the study was to assess the effect of irrigation water temperature and shading on the rate of photosynthesis and transpiration in four varieties of lettuce (Lactuca sativa L.) – green foliage (‘Salakis’ and ‘Estony’) and red foliage (‘Lollo Rossa’ and ‘Nika’). During the production of seedlings in the greenhouse, two irrigation water temperature regimes (12 and 20°C) were applied. After transplanting in the field plants were grown under three lighting systems (100, 70, and 50% of lighting in the open). The rates of photosynthesis and transpiration were measured at the end of the greenhouse period and 14 days after shading in the field using a Li 6400 infrared gas analyzer. In most varieties, cooling of the irrigation water was not found to have an effect on the rate of photosynthesis. Plants of all the varieties responded to the decrease in irrigation water temperature and to strong shading by reducing transpiration and increasing the water use efficiency. The ‘Salakis’ and ‘Estony’ plants have shown the best adaptability to the changing conditions and therefore they could be used successfully in the practice of extending vegetative growth