Increases in fresh spinach consumption during the past decade have been attributed to spinach salad products and a growing public awareness of the health benefits of the crop (Silva, 2002; U.S. Dept. of Agriculture, 2006). Spinach provides dietary fiber and supplies high levels of vitamins, minerals, and antioxidants (Leskovar et al., 2000; McCord and McVeigh, 2000).
Numerous aspects of spinach production have been evaluated in field cultivar trials, including yield, color intensity, and bolting resistance. Yield has been included in a majority of studies and is considered to be a key component of cultivar selection (Dainello et al., 1987; Djurovka et al., 1988). The presence of dark green color in spinach is an important aspect of evaluation (Brandenberger et al., 2004; Dainello et al., 1984). Murphy and Morelock (1999, 2000) indicated that dark green vegetables contain high levels of carotenoids such as lutein, which may be visually selected because of a strong correlation between carotenoids and chlorophyll-a. Flower stalk formation (bolting) in spinach is controlled by daylength (Chun et al., 2001) and renders the crop unsalable when it occurs (Knott, 1939).
Fruiting vegetables, leafy greens, and herbs have been produced in the greenhouse (Hood, 2000). Tomatoes (Lycopersicon esculentum) are perhaps the most popular, but Snyder (2001) noted that greenhouse tomatoes are difficult because of the processes and time (2 to 5 months) needed to produce the crop. Greenhouse spinach production is an alternative to traditional tomato production because it allows for multiple short-duration production cycles during the same time period as one tomato crop.
Production cycles of 30 to 48 d for spinach are possible year round in a soilless culture with appropriate cultivars and manipulation of the nutrient solution temperature (Ikeda et al., 1995). Frantz and Welbaum (1998) used hydroponic float beds for growing several horticultural crops in the greenhouse, including basil (Ocimum basilicum) and water spinach (Ipomoea aquatica). Other investigators (Thompson et al., 1998) demonstrated the use of float beds for greenhouse lettuce (Lactuca sativa) production. There are few reports of spinach cultivar trials in the greenhouse; Joshi et al. (1992) evaluated six cultivars and found differences in yield and leaf area.
The objective of this work was to determine the suitability of spinach cultivars for greenhouse production in Oklahoma. Production attributes included in the studies were fresh leaf yield, quality including color intensity and foliage mass, and bolting resistance.
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Thompson, H.C., Langhans, R.W., Both, A.J. & Albright, L.D. 1998 Shoot and root temperature effects on lettuce growth in a floating hydroponic system J. Amer. Soc. Hort. Sci. 123 361 364
U.S. Dept. of Agriculture 2006 Vegetables 2005 summary. Jan. 2006 8 June 2006<http://usda.mannlib.cornell.edu/reports/nassr/fruit/pvg-bban/vgan0106.pdf>