Leaf lettuce is a very important greenhouse crop in the wintertime. Tipburn is a major limitation to production and quality of lettuce. The unpredictability of tipburn occurrence and the absence of totally effective control procedures make the problem very serious.
In experiments with lettuce, losses to the grower from tipburn may reach up to 50 % of production. Tipburn is caused by physiological calcium deficiency.
This investigation showed that lettuce is a crop, which responds to change in R/FR ratio. Plants grown under a far-red filter were light green whereas control plants were a yellowish, darker green. Plants grown under the far-red filter tasted less bitter than control plants. Scattered radiation penetrated deeper inside the lettuce than direct beam. Spectral filter also affected leaf orientation. Leaves on control plants were more upright than those on plants grown under a far-red absorbing film. This means that a far-red filter could be used to control the height of lettuce. The incidence of tipburn injury on leaves reduced under the far-red absorbing film in greenhouses. The calcium content of young leaves was higher under the far-red filter. A far-red filter could be used for plants, which are susceptible to calcium deficiency.
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