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Characterizing smoke taint in hops (Humulus lupulus) and investigating the impact of defoliation stress on phytocannabinoid content in industrial hemp (Cannabis sativa)


The family Cannabaceae contains at least 10 genera, with Cannabis (hemp) and Humulus (hop) being two of the most economically important. Both genera have long been valued by humans for their chemical constituents and are used today for both medicinal and recreational purposes. However, adverse environmental factors may impact the chemical profile of these important crops, leading them away from a true-to-type quality. This thesis will explore the effects of an abiotic stress on the chemical profile of each crop: smoke-taint in hops and defoliative hail damage of hemp. The Pacific Northwest contains 97.5% of U.S. commercial hop acreage and has also seen an increase in the number and severity of wildfire events in recent years. While there is extensive research from the wine industry on the impact of smoke taint in grapes, our knowledge of smoke taint in hops is limited. Here, we aimed to characterize smoke taint in hops using laboratory simulated wildfires with distinct fuel types and non-targeted gas chromatography-mass spectrometry. Our results reveal an overall variation in the chemical profiles between smoked and control hops and across fuel types and the detection of known and novel smoke taint markers including guaiacol, 4-methylguaiacol, and xylopyranose. This research provides evidence to support the use of established smoke taint markers for hop analysis and lays the groundwork for future studies to investigate various fuel types and their impact on hop quality. The United States has seen an abrupt increase in commercial industrial hemp production since the Agricultural Improvement Act of 2018. However, the historical prohibition of this crop has resulted in a lack of basic physiological research to guide management practices. For example, abiotic stress can stimulate plants to increase production of secondary metabolites such as phytocannabinoids and this is of high importance to farmers as they as they must balance optimization of CBD yield (crop value) with regulatory requirements (THC < 0.3% by mass) that could lead to crop loss (mandated destruction). In this study we evaluated the impact of defoliation stress (to simulate hail damage) at three different growth stages. Our results indicate that defoliation stress during late flowering yielded no significant change in phytocannabinoid production. However, defoliation stress during vegetative and early flowering yielded a significant increase in phytocannabinoids, including total CBD and THC, at harvest.


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