Medicinal herbs represent an emerging market with many opportunities for innovative research because they are generally safe, effective, economical, and easily accessible by consumers looking for health-promoting products (Prakash and Gupta, 2005). Ocimum tenuiflorum L. syn. Ocimum sanctum, and O. gratissimum L., known as tulsi or holy basil (Winston and Maimes, 2007), is a medicinal herb native to India with a wide distribution over the subcontinent. It is best known for its stress-reducing adaptogenic properties, i.e., it has the capability to help the body adapt to stress, normalize physiological function, and restore balance regardless of the origin of the stressor (Kuhn and Winston, 2000; Pattanayak et al., 2010; Singh et al., 2012).
Holy basil has been broadly researched and widely cultivated in India (Aggarwal and Mali, 2015; Raina et al., 2013; Sharma et al., 2011). With a growing demand for natural alternatives for managing stress (Esch et al., 2002), it is likely that the popularity and demand for holy basil will continue to increase in the coming years (Pattanayak et al., 2010). According to Roy Upton, Executive Director of the American Herbal Pharmacopeia, with the implementation of good manufacturing practices, fewer overseas suppliers can meet the requirements for quality and product verification (Smith, 2011). With the promising therapeutic potential of holy basil, it shows capacity as a high-value cash crop that can be grown in the United States, using production methods that meet quality and traceability standards. According to a recent publication by the American Botanical Council, tea sales for the United States exceeded 15 billion USD in 2013, and tea drinking is predicted to increase in future years (Keating et al., 2014).
To increase cultivation of holy basil in the southeastern United States, the first step is to evaluate available holy basil varieties to determine which are most suited for commercial production. At present, growers typically select varieties based on seed availability, market demand, and harvestable weight, and not necessarily on the presence or concentration of biologically active compounds (Zhang et al., 2012). With medicinal herbs, an important consideration is the measurable difference in therapeutic constituents, such as essential oils, that are indicators of quality and efficacy. For example, a notable phenolic compound found in holy basil essential oil is eugenol. It is a versatile molecule with application in many industries (Kamatou et al., 2012). It has a spicy clove-like scent and has been shown to be therapeutically effective for neurological, inflammatory, allergic, and immunological disorders (Bakkali et al., 2008; Kamatou et al., 2012; Sen, 1993). Eugenol is largely extracted from natural sources, most commonly clove essential oil (Eugenia caryophyllata), which has a gross market value of US$30–70 million annually for use in food and cosmetics (Bohnert et al., 2008). However, clove production is labor-intensive and not easily grown in the United States. Holy basil has lower production costs, can be grown easily in the southeast, and is a less-expensive option for extracting eugenol commercially (Saran et al., 2017).
For this study, varieties of holy basil consisted of five commercially available cultivars and nine USDA germplasm accessions. Presently, there is considerable confusion regarding labeling: many U.S. seed companies list only the genus and species name, with no mention of a cultivar. Thus, it is difficult to differentiate between available seed stock or know which ones should be grown to achieve maximum yield and quality. Furthermore, details concerning yield, essential oil content, and eugenol concentration are lacking for many of the USDA accessions. This investigation is unique in that it provides a comparison of a large selection of holy basil varieties grown in the southeastern United States and offers important information for growers seeking diversification and alternative crop options. Moreover, such details provide important baseline information to be used in future studies evaluating the effect of specific horticulture practices on yield and essential oils and can potentially help identify future breeding goals.
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