Essential oil yield, composition, and fiber cell wall components in dual-purpose industrial hemp

Dual-purpose hemp crops have seen a resurgence of interest in recent years, driven by their diverse and growing market applications. One prominent application of hemp is the extraction of its essential oil (EO), which is rich in bioactive phytochemicals and has diverse uses. In addition, hemp has been extensively studied in recent years for the production of innovative substances and is gaining popularity as a sustainable alternative to synthetic fibers. The hypothesis of this study was that cultivar, row spacing, growing stage, and their interactions would affect industrial hemp EO content, composition, and fiber cell wall components. Field trials were conducted in Bački Petrovac, Serbia (45.3568° N, 19.6173° E) using cultivars Helena, Bob-1, and Marina, at two row spacings: 12.5 cm and 50 cm. The fresh samples from the top 50 cm of female plants were sampled at two times: (1) just before flowering, and (2) at harvest time for fiber. The results from the field study indicated that cv. Bob-1 consistently exhibited the highest content of EO in both years. Cannabidiol and four types of sesquiterpenes (E-caryophyllene, α-humulene, caryophyllene oxide, allo-aromadendrene) were identified as the primary compounds in all the EOs from both stages of sampling and year. Row spacing significantly impacted fiber cell wall composition, however, effects varied by cultivar. The content of neutral detergent fiber and acid detergent fiber was maintained or increased for Helena on wider spacing. Bob-1 exhibited reduced neutral detergent fiber and acid detergent fiber; however, it increased acid detergent lignin at wider spacing. Marina showed increased neutral detergent fiber and stable acid detergent fiber content with a low decrease in lignin content at wider spacing. A strong positive correlation between E-caryophyllene and acid detergent lignin was detected only in early sampling (S1) (r = 0.724, p = 0.008), along with a similarly significant acid detergent lignin–α-humulene relationship (r = 0.698, p = 0.012), whereas no correlations were observed at later sampling stages, suggesting seasonal variation in the association between terpene production and lignin accumulation. In the second sampling, α-humulene showed opposing correlations with acid detergent fiber (negative) and acid detergent lignin (positive), while caryophyllene oxide exhibited no significant relationships with any fiber component across sampling times, and overall acid detergent lignin consistently displayed the strongest associations with EO constituents. Implementing this dual-purpose approach, producing high-value EO from the upper plant portions and fiber from the lower stems, could enhance the economic viability and environmental sustainability of industrial hemp, providing a more resource-efficient model for the industry.