Leafy greens are a rich dietary source of nutrients including calcium, magnesium, potassium, and iron (Kopsell et al., 2004). In addition, many leafy greens, particularly those of the Brassicaceae family, contain high levels of plant secondary metabolites such as S-methyl cysteine sulfoxide, carotenoids, flavonoids, and anthocyanins (Manchali et al., 2012). Compounds such as sulforaphane, a phytochemical evolved from hydrolysis of glucoraphanin by the enzyme myrosinase, have been reported to have chemopreventive properties (Liang and Yuan, 2012). Consumption of kale and collard greens, which are rich in carotenoids, has been shown to increase macular pigment optic density in humans, which has been associated with improved eye health (Kopsell et al., 2009).
Leafy greens may be attractive to consumers wanting a nutrient-rich diet. It is noteworthy that those consumers concerned with health and diet may also be regular purchasers of organically grown fruits and vegetables (Zanoli and Naspetti, 2002). In a review of consumer behavior toward organic foods, Hughner et al. (2007) reported that a majority of previously published studies noted perceived positive effects on health as the primary reason for choosing organic food. Thus, it is not surprising that the authors have observed that leafy greens are frequently grown by organic farmers in Kentucky.
Organic fruit and vegetable production has risen steadily in the past decade, reaching more than 156,000 acres in 2008, a nearly 100% increase from 2002 levels [U.S. Department of Agriculture (USDA), 2010]. Organically certified production represented ≈11% of total U.S. fruit and vegetable sales in 2010 (Organic Trade Association, 2011). Despite rapid growth of organic farming nationwide, variety recommendations specifically for organic growers are lacking. Recently, partnerships such as the Northern Organic Vegetable Improvement Cooperative (NOVIC) have initiated variety trials for a number of organically grown vegetables including broccoli (Brassica oleracea italica group), sweet corn (Zea mays), tomato [Solanum lycopersicum (synonym Lycopersicon esculentum)], bell pepper (Capsicum annuum), winter squash (Cucurbita sp.), and snap pea (Pisum sativum var. macrocarpon) (NOVIC, 2012). Continued field evaluation of varieties for suitability in organic farming systems is necessary. It has been estimated that more than 95% of varieties grown organically were originally developed for conventional farming systems (van Bueren et al., 2011). However, it has been reported that there can be significant genotype by farming system interaction when evaluating varieties grown conventionally and organically (Murphy et al., 2007). It is often suggested varieties that yield highest in conventional systems would likely perform equally as well when grown organically. However, in a trial evaluating conventionally bred varieties in organic farming systems, Murphy et al. (2007) reported that this was not necessarily correct. This suggests the long-term need for breeding programs focused on developing such varieties. Varieties developed specifically for organic production may differ from their conventional counterparts in terms of nutrient use efficiency and the ability to form symbiotic relationships with soil microorganisms, as well as have a greater tolerance to mechanical cultivation and disease resistance (van Bueren et al., 2011). Until breeding for organic production systems becomes more common, we must rely on trials of organically grown varieties previously bred for conventional production.
In addition to genotypic variability, phytonutrients—an essential quality attribute of edible greens, particularly those in the Brassicaceae family—have been shown to be significantly affected by environmental conditions (Farnham and Kopsell, 2009). Air temperature, fertility, and light levels have been reported to affect secondary phytonutrient content of Brassicaceae (Kopsell and Randle, 2001; Lefsrud et al., 2005, 2006). Because of the impact of environmental conditions on growth and quality attributes of leafy greens, regional variety trials are necessary to make informed decisions regarding the best performing varieties for a particular area. Olson and Freeman (2008) reported results from four years of conventionally managed collard trials in northern Florida, with several hybrid varieties performing well. However, published information regarding the performance of leafy greens in organic production systems for the midsouth region of the United States is not widely available. Therefore, the objective of this research was to evaluate several types of organically grown leafy greens over multiple seasons and years to determine the most suitable varieties for organic growers in the midsouth growing region. Because many organic farmers grow a diverse array of crops in a given season (van Bueren et al., 2011), multiple types of leafy greens were evaluated. In addition, only varieties for which organically certified or untreated seeds were available were examined. Many of the varieties that are available as untreated or organically certified seeds are open-pollinated, with relatively few hybrids. Although there are numerous additional hybrid varieties marketed with treated seed for several of the crops tested, these varieties were not included because of their inability to be used on certified organic farms.
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