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| Authors: | F. Benoit, N. Ceustermans |
Abstract:
During the growing periods of the year that are poor in light (November to April) the purple colouring of Lollo Rossa under glass is slight and constitutes a marketing problem.
The leaves of this lettuce tend to remain paler as light intensity is lower.
In NFT we compared 4 different Lollo Rossa cultivars, of which Impuls (L. De Mos) showed a more intense purple colouring than Valeria (L. De Mos), Sesam (R. Zwaan), and Malibu (R. Zwaan). Cooling of the circulating NFT-nutrient solution to 6.5 °C caused a significant increase of the purple colouring, but reduced plant weight.
High pressure sodium lighting (SON-T-Agro 400 W Philips) at a rate of 35 W/m2 from 6 a.m. to 10 a.m. and again from 4 p.m. to 8 p.m. during the entire growing period increased purple colouring to the same degree as cooling, and in addition improved plant development.
A combination of cooling and lighting intensified the purple colouring.
Spraying with Ethrel (480 g ethephon/l) at a rate of 1 to 5 ml/l caused the purple colouring to increase proportionally, but higher doses were phytotoxic and caused marginal necrosis.
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