Identifying physiological traits related with drought tolerance and water‐use efficiency in floral hemp (Cannabis sativa L.)

Abstract Hemp ( Cannabis sativa L.) is a reemerging crop that was once deeply rooted in many global civilizations. Due to climate change and the increasing risk of water‐deficit situations, it is important to use water judiciously. Hemp production has interested many producers; however, due to its past illegal status, there is a lack of research‐based knowledge about the physiological parameters that are affected by drought and which parameters could be responsible for drought tolerance. Therefore, our objective was to study and understand the effects of different drought intensities and timings on physiological parameters such as water‐use efficiency (WUE), photosynthesis, stomatal conductance, and fluorescence parameters and determine if cultivar variation exists as this could mean the possibility of selection for drought‐tolerant cultivars. In addition, we tested if carbon isotope discrimination can be used to predict whole plant WUE as this technique is quick and allows moderate throughput for selection. Hemp cultivars BaOx and Cherry Mom were grown in a greenhouse from July to October during 2021 and 2022 under different water stress intensities and timings. During the water stress period, WUE was determined by the gravimetric method and photosynthetic traits were measured using two portable gas analyzers (LI‐6800). Moderate water stress (30%–50% field capacity) was found to have the least effect on physiological parameters studied, while intense water stresses significantly reduced many physiological parameters such as photosynthesis, stomatal conductance ( g s ), and electron transport rate (ETR). It was found that the cultivar BaOx had a greater WUE than Cherry Mom. This was confirmed with carbon isotope discrimination measurements, which were demonstrated to estimate WUE accurately, and therefore, this technique could be used for germplasm screening. Drought first decreased g s , which caused the reduction in photosynthesis, although cultivar variation in these traits was not observed. Twenty days after drought, negative effects on fluoresce parameters such as ETR were observed with the cultivar Cherry Mon being more affected. This study states that hemp is negatively affected by different timings and intensities of drought; however, there is physiological variation in the response between cultivars. More research is needed to investigate the sources of genotypic variation in physiological parameters to find the sources of drought tolerance.