Lettuce (Lactuca sativa L.) is a popular salad vegetable and consumption of lettuce has many health benefits. The objective of this study was to select lettuce varieties grown in a closed hydroponic system based on their morphological parameters, phytochemical and mineral content for mixed fresh cut salads or as whole product. Principal component analysis illustrated three separate groups based on the bioactive compounds, color values and fresh leaf mass for the 16 lettuce varieties. Group 1; Multired 4 contained the highest concentrations of total phenols, flavonoids (isohamnetin, quercetin, kaempferol, epicatechin, mycertin, anthocyanin), β‐carotene, ascorbic acid and higher antioxidant property and lower leaf fresh mass. Group 2; included the green lettuce varieties (Multigreen 3 and Multigreen 1) and the red varieties (Cantarix, Lunix, Soltero, Veneza Roxa, Feska) revealed moderately higher in bioactive compounds and fresh leaf mass. Group 3 contained the green lettuce varieties (Smile, Palmir, Hardy, Nasir, Monary, Atlantis and Vera Green Frilly) and showed lower bioactive compounds with leaf higher fresh mass. Red lettuce varieties are rich in bioactive compounds and antioxidant property mainly due to higher total phenols and flavonoid compounds. Multired 4 (red), Multigreen 3 (green) and Multigreen 1 (green) and other red lettuce varieties can be recommended for mixed lettuce salads or as whole product. Practical Applications Lettuce consumption is determined by color, size, texture, taste and nutritional properties. Choice of lettuce varieties is important for lettuce mixed fresh cuts or as a whole product. Therefore, it is important to profile the phytochemical composition in different lettuce varieties to improve the antioxidant and nutrient intake in the diet.

The objective of this study was to determine the effect of nitrogen fertilization rate on growth and quality of leafy lettuce grown during the winter season in non-circulating hydroponic system. Plants were subjected to seven nitrogen (N) concentrations, i.e. 0, 30, 60, 90, 120, 150 and 180 mg L -1 N using ammonium nitrate. Nitrogen treatments did not have a significant effect on leaf fresh and dry mass, root fresh and dry mass, number leaves and leaf area. Leaf ascorbic Downloaded by [University of California Santa Barbara] at 00:59 15 June 2016 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 acid and total phenolic content, and antioxidant capacity peaked at 100 and 120 mg L -1 N,whereas leaf chlorophyll concentration linearly increased with increasing N application. The results indicate that a solution N concentration of 100 and 120 mg L -1 may be sufficient to improve growth, yield and quality parameters of leafy lettuce grown in non-circulating hydroponic system.

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To cite this article: M.M. Maboko & C.P. Du Plooy (2009) Effect of plant spacing on growth and yield of lettuce (Lactucasativa L.) in a soilless production system, South African Journal of Plant and Soil, 26:3,[195][196][197][198]