Ranking 26 European hemp (Cannabis sativa L.) cultivars for osmotic stress tolerance and transpiration efficiency

•European hemp cultivars display a genetic variability of osmotic stress tolerance.•European hemp cultivars display a genetic variability of transpiration efficiency.•Cultivars 'Codimono', 'Carmaleonte', 'Futura 75' and 'Santhica 70' ranked the highest.•The observed variability also exists within cultivars sharing a common origin.