EFFECT OF COOLING THE NUTRIENT SOLUTION, LIGHTING AND ETHREL SPRAYING ON PURPLE COLOURING IN NFT- LOLLO ROSSA LETTUCE

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.

International Symposium on Growing Media and Hydroponics

F. Benoit, N. Ceustermans

https://doi.org/10.17660/ActaHortic.1999.481.37