# Yield and Quality of Essential Oils in Hemp Varieties in Different Environments
## 1 Introduction  
_Cannabis sativa_ L. is one of the oldest plant sources for food, textile fibers and medicine [1]. Hemp, namely industrial hemp or fiber hemp, is an annual and dioecious plant. However, breeders have developed several monoecious cultivars, considered particularly suitable for dual-proposal cultivation (seeds and fiber). There has also recently been growing interest in the utilization of hemp secondary metabolites, extracted from inflorescences of low-THC types cultivated by farmers without restrictions, namely non-psychotropic cannabinoids, terpenoids and flavonoids [2; 3; 4]. Unlike phytocannabinoids, which are specific to the genus _Cannabis_, terpenes are common in many plant families [5] and in _Cannabis sativa_ essential oils (EOs) are the largest group of chemical compounds, with more than 100 molecules identified. Terpenes are classified in different families depending on the degree of polymerization of isoprene units (C5); monoterenes and sesquiterpenes, which include terpenes with 10 and 15 carbon atoms, respectively, are the most common in nature and are also the main constituents of the EOs in hemp [6; 7]. Terpenes are responsible for the smell and flavor typical of the different varieties of _C. sativa_, whereas phytocannabinoids are odorless [7]; thus, anti-drug dogs are trained to recognize the \(\beta\)-cariofilene-epoxides, a sesquiterpene [8]. Biosynthesis and bioaccumulation of these substances take place mainly in the pedunculated glandular trichomes, which are abundant on the perigon bracts at the beginning of flowering, while the sessile glandular trichomes are in all the aerial plant parts from the earliest growth stages [9]. Two pathways areinvolved in the biosynthesis of terpenes: the plasidial methylerythritol phosphate (MEP) pathway and the cytosolic mevalonate (MEV) pathway. The former, through eight steps, leads to the synthesis of geranyl diphosphate (GPP) the precursor of monoterpenes. Instead, farnesyl disphosphate (FPP), synthetized through the MEV pathway, is the precursor of sesquiterpenes [7; 10]. Ternepenes are lipophilic compounds that pass easily through membranes, particularly the blood-brain barrier, and therefore have a wide range of pharmacological properties; among these, the most important are: anticancer, anxiolytic, immune stimulating, anti-inflammatory, analgesic, memory skills improving and gastro protective [7]. Hemp EOs can be used in cosmetics for the production of soaps, shampoos, perfumes, creams and even in food as flavoring for alcoholic and non-alcoholic beverages, or as additives in bakery and catering [11]. Thanks to their antimicrobial properties [12; 13; 14] they are used in topical treatments of wounds and skin infections, against pathogens involved in nosocomial infections, in food spoilage and poisoning, intestinal syndromes and against bacterial strains resistant to antibiotics [13]. Hemp essential oil has also proven to be effective as an insecticide [15; 16; 17], nematicide [18], fungicide [19], allelopathic [20; 21; 22] and anti leishmaniasis [23], justifying its use in crop protection [15] as an alternative to petrochemical-derived products. The quantitative and qualitative composition of _C. sativa_ essential oil varies substantially in relation to variety, pedo-climate conditions, harvest time and extraction method [24; 25] and for this reason, their terpene profile is often unpredictable and not easily standardized [5; 26]. An increase in essential oil yields is possible by preventing pollination: indeed _C. sativa_ continues to produce new flowers until it is pollinated, but as documented in studies by [PERSON] and [PERSON] [11], this is feasible only in a greenhouse, utilizing diocious varieties. In the field, low humidity conditions increase the amount of trichomes in infloreserences [22], as well as the terpene concentration of essential oil [11].