Introduction
The oldest evidence of medicinal plant usage goes back to 60,000 years ago to Kurdistan in Shanidar cave (Lietava, 1992). Bitter fennel is one of the oldest medicinal plants that due to possessing certain metabolites, is used as flavoring agents in food and beverages, and as curative agents in pharmaceutical products (Hornok, 1992).
Bitter fennel (Foeniculum vulgare var. Vulgare ), hereafter just fennel, as the source subspecies for fennel-derived drugs, originated from Mediterranean regions, but now has been naturalized in many other regions (Hornok, 1992). Fennel produces several valuable phytochemicals in the seeds. One group of these compounds is fatty acids, also called fixed oils, or just oil (Hornok, 1992).
Plant-based oils are considered heathier than animal-based oils due to a lower ratio of omega-6 to omega-3 fatty acids, and a higher ratio of monounsaturated to polyunsaturated and saturated fatty acids (Vidrih, et al., 2009). Exploring new crops as complementary or substituting sources of fatty acids to the current main oil crops, including soybeans, sunflower, canola (FAO, 2018), is valuable for meeting market demand, and diversifying our oil production sources. Currently, species within the family Apiaceae are gaining a lot of attention as potential sources of fatty acids. Among Apiaceae species, fennel is a candidate as a new source of fatty acids, due to its suitability for mechanized mass production, high seed yield potential (400-3000 kg/ha), and high fatty acid content (12-20% of seed mass) (Matthaus and Ozcan, 2015; He and Huang, 2011; Cosge et al., 2008; Gupta et al., 1995; Reiter, et al., 1998).
Seeds are the main storage location of fatty acids in fennel, and they can contain from 3 to 20% oil with the major fatty acids being C18:1 isomers (25-83%), C18:2 or linoleic acid (1-17%), C16:0, or palmitic acid (0-13%), C14:0 or myristic acid (0-6.5%), C18:3(N3) or linolenic acid (0.3-4%), C18:0 or stearic (0.8-1.9%), and C20:0 or arachidic acid (0-0.4%) (Rezaei Chiyaneh et al., 2020; Hayat et al., 2019; Sayed Ahmad et al., 2018; Agarwal et al., 2018; Rebey et al., 2016; Nguyen et al., 2015; Acimovic et al., 2015; Bogdanov et al., 2015; Barros et al., 2010; Vidrih, et al., 2009; Cosge et al., 2008; Singh et al., 2006; Gupta et al., 1995; Reiter et al., 1998). Petroselinic acid (18:1-cis6), oleic acid (18:1-9cis), and vaccenic acid (18:1-11cis) are three positional isomers of C18:1, which can make separation and quantification cumbersome, but petroselinic acid is the major isomer (Reiter et al., 1998). Both oleic acid and linoleic acid are essential fatty acids with many health benefits in human nutrition, and numerous usages in various industries (Sales Campos et al., 2013; Simopoulos, 2008). The high concentration of oleic acid (77-83% of seed mass) in an Iranian fennel genotype in different intercropping systems was reported by Rezaei Chiyaneh et al. (2020).
According to our previous studies on Iranian fennel landraces, there is significant genetic diversity (Bahmani et al., 2012 and 2013) and agro-morphological variation among fennel landraces for maturity habit, seed yield, and essential oil yield composition (Bahmani et al, 2015 and 2016). In terms of maturity habit, Iranian fennel landraces are divided into early, medium, and late maturity landraces (120, 180, and 230 days to harvest time, respectively). Little is known about variation in fatty acid content or composition among Iranian fennel landraces. Therefore the objectives of the current study were to 1) evaluate potential oil production in Iranian fennel landraces, 2) evaluate their oil compositions, 3) identify high potential landraces.