Variety, Shading, and Growth Stage Effects on Pigment Concentrations in Lettuce Grown under Contrasting Temperature Regimens

Abstract

Shading effects on chlorophyll a (ChlA), chlorophyll b (ChlB) and anthocyanin (Antho) concentrations were examined at three developmental stages in four varieties of lettuce (Lactuca sativa) grown under contrasting temperature regimens in the greenhouse. Seedlings were transplanted to pots and grown at 30 °C (86.0 °F) day/night (D/N) (Study 1) or 30/18 °C (86.0/64.4 °F) D/N (Study 2). One-half of all plants in each study were positioned under bottomless shade boxes which reduced incoming light intensity by 50%. Pigment concentrations were measured in leaf tissue 9, 16, and 23 days after transplanting. Each study was repeated twice. Regardless of temperature regimen, variety influenced all pigment concentrations, while shading affected, primarily, Antho concentrations. ChlA and ChlB concentrations were influenced by growth stage. In Study 1, chlorophyll concentrations were significantly greater in `Green Vision' than `New Red Fire' or `Rolina', but not `Galactic'. Also, Antho concentrations were significantly greater in `Galactic' than the other varieties. In Study 2, chlorophyll concentrations were greatest in `Green Vision', with similar concentrations among the remaining varieties. Antho concentrations were greatest in `Galactic', intermediate in `New Red Fire' and `Rolina', and lowest in `Green Vision'. Shading significantly reduced Antho concentrations in `Galactic' and `Rolina' under both temperature regimens and `New Red Fire' at 30/18 °C D/N, but increased Antho concentrations in `Green Vision'. Chlorophyll concentrations tended to decrease with plant age. Pigment concentration data clarified what was apparent to the unaided eye—namely, that the amount and intensity of green and red color varied among plants subjected to different shading and temperature treatments. Therefore, these data may aid in developing strategies to achieve targeted levels of pigmentation (especially red) in lettuce, an important criterion of crop quality and potential market value.