Abstract
As an emerging cash crop, industrial hemp (Cannabis sativa L.) grown for cannabidiol (CBD) has spurred a surge of interest in the United States. Cultivar selection and harvest timing are important to produce CBD hemp profitably and avoid economic loss resulting from the tetrahydrocannabinol (THC) concentration in the crop exceeding regulatory limits. Hence there is a need for differentiating CBD hemp cultivars and growth stages to aid in cultivar and genotype selection and optimization of harvest timing. Current methods that rely on visual assessment of plant phenotypes and chemical procedures are limited because of its subjective and destructive nature. In this study, hyperspectral imaging was proposed as a novel, objective, and non-destructive method for differentiating hemp cultivars, growth stages as well as plant organs (leaves and flowers). Five cultivars of CBD hemp were grown greenhouse conditions and leaves and flowers were sampled at five growth stages 2–10 weeks in 2-week intervals after flower initiation and scanned by a benchtop hyperspectral imaging system in the spectral range of 400–1000 nm. The acquired images were subjected to image processing procedures to extract the spectra of hemp samples. The spectral profiles and scatter plots of principal component analysis of the spectral data revealed a certain degree of separation between hemp cultivars, growth stages, and plant organs. Machine learning based on regularized linear discriminant analysis achieved the accuracy of up to 99.6% in differentiating the five hemp cultivars. Plant organ and growth stage need to be factored into model development for hemp cultivar classification. The classification models achieved 100% accuracy in differentiating the five growth stages and two plant organs. This study demonstrates the effectiveness of hyperspectral imaging for differentiating cultivars, growth stages and plant organs of CBD hemp, which is a potentially useful tool for growers and breeders of CBD hemp.
Highlights
Industrial hemp, or briefly known as hemp, is a crop cultivated for producing a wide range of industrial and consumer products (Renée, 2018)
This study demonstrates the efficacy of hyperspectral imaging technology as a tool to differentiate cultivars, growth stages and plant parts of CBD hemp, which will be beneficial for hemp cultivation and breeding programs
Five CBD hemp cultivars were used in this study, including Cherry Wine (CW), BaOx (BX), First Light 58 (FL58), First Light 70 (FL70), and TJ’s (TJ)
Summary
Industrial hemp, or briefly known as hemp, is a crop cultivated for producing a wide range of industrial and consumer products (Renée, 2018). In the United States, hemp is legally defined as Cannabis sativa L. that contains no more than 0.3% total tetrahydrocannabinol (THC), the compound that is responsible for getting a person high and more abundant in marijuana. Because of its association with marijuana, commercial production of hemp in the United States has been long restricted until the passage of the 2018 Farm Bill (Schluttenhofer and Yuan, 2019). As of 2021, all the states in the United States have legalized hemp production for commercial or research purposes. While the medicinal uses of CBD are still being researched, market opportunities for CBD hemp are expected to be significant, with CBD sales in the United States projected to reach $23.7 billion by 2023 (Brightfield Group, 2019)
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