Evaluation of European-developed hemp cultivars (Cannabis sativa L.) in response to water regimes

Aim of study: The present study aimed to evaluate the effect of water deficit on the growth and yield of hemp (Cannabis sativa L.) cultivars under semi-arid Mediterranean conditions. Area of study: Southern Greece, Athens. Material and methods: Three different irrigation regimes (well-watered; IRR100, mild water-stressed; IRR75, and severe water-stressed; IRR50) were supplied to determine their effect on five hemp cultivars' growth, seed and cannabidiol (CBD) yield, and water productivity by a three-year field experiment. Main results: Water deficit (IRR50) decreased plant height by 38.7%, 15.8%, and 18.7%, and above-ground biomass by 71.9%, 74.6%, and 27.7% during 2019, 2020, and 2021 years respectively, compared to IRR100. The IRR50 treatment reduced inflorescence length, seed weight per inflorescence, and seed yield by 19%, 27.6%, and 29.9% respectively. The longest inflorescences with the most seeds were performed by Cannabis sativa ʻFedora 17ʼ with mean values ranging from 35.1 cm to 36.8 cm, and 223 to 247 seeds per inflorescence across growing seasons. By increasing drought stress to IRR50, the cannabidiolic acid concentration increased thrice, and CBD and total cannabidiol (CBD total) concentrations were almost duplicated with Cannabis sativa ʻFerimonʼ recording the highest total CBD yield. All cultivars showed sensitivity to water deficit, reducing their water productivity and Normalized Difference Vegetation Index values. Cannabis sativa ʻFutura 75ʼ recorded the highest water productivity under all water regimes. Research highlights: Water stress (IRR50) limited hemp biomass and seed yield, whereas enhanced CBD yield of inflorescences. ʻFutura 75ʼ cultivar is the most suitable for biomass production, ʻFerimonʼ cultivar for CBD production, and ʻFedora 17ʼ cultivar is appropriate for the dual-purpose production of both biomass and seed.