The United States has experienced an abrupt increase in commercial industrial hemp production following the Agricultural Improvement Act of 2018. However, the historical prohibition has resulted in a lack of basic research on the physiology of this crop and its response to stresses such as those produced by local climatic conditions and pests that feed on hemp, which are needed to guide development of effective management practices. For example, abiotic stress can stimulate plants to increase production of secondary metabolites such as phytocannabinoids. This is of particularly high importance to growers of hemp crops that are oriented to the production of phytocannabinoids concentrated in flowers, balancing optimization of CBD yield (crop value) with regulatory requirements (total THC < 0.3% by mass) that could lead to 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 vegetative and late flowering yielded no significant change in total % phytocannabinoid concentration at harvest. However, defoliation stress during early flowering yielded a significant increase in phytocannabinoids, including total % CBD and THC, at harvest as compared to untreated controls.

中文翻译：

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落叶胁迫对工业大麻植物大麻素含量的影响

自 2018 年《农业改进法案》颁布以来，美国商业工业大麻产量急剧增加。然而，历史上的禁令导致缺乏对这种作物的生理学及其对压力（例如由植物产生的压力）的响应的基础研究。当地气候条件和以大麻为食的害虫，需要这些信息来指导制定有效的管理实践。例如，非生物胁迫可以刺激植物增加次生代谢物（例如植物大麻素）的产量。这对于以生产集中在花卉中的植物大麻素为导向的大麻作物种植者来说尤其重要，平衡 CBD 产量（作物价值）的优化与监管要求（总 THC < 0.3% 按质量计），这可能导致强制销毁。在这项研究中，我们评估了三个不同生长阶段的落叶应激（模拟冰雹损害）的影响。我们的结果表明，营养和晚花期间的落叶胁迫对收获时植物大麻素总浓度百分比没有显着变化。然而，与未经处理的对照相比，开花早期的落叶胁迫导致收获时植物大麻素的含量显着增加，包括 CBD 和 THC 的总百分比。