Effects of drought stress during flowering of two pot-grownblackcurrant (Ribes nigrum L.) cultivarsN

The drought stress tolerance of two blackcurrant cultivars (Ribes nigrum L., 'Narve Viking' and 'Ben Gairn') during the flowering period and their ability to recover following drought stress were studied by examining the effects of drought stress on growth and various physiological traits. The experiment was conducted under greenhouse conditions, and plants were either fully irrigated (FI), with a volume of water replacing the previous day's evapotranspiration, or non-irrigated (NI) for 12 days. Hereafter irrigation was continued (FI) or resumed (NI) to allow for 17 days of recovery.Drought stress reduced the accumulated evapotranspiration of both cultivars mainly due to stomatal closure and a reduced leaf area. Stomata were more open in the morning than at midday, which could be attributed to an increase in vapour pressure deficit (VPD) at midday. Moreover, stomatal conductance (g) varied between days of treatment, possibly due to differences in air temperature and VPD. Drought stress reduced the leaf water potential (ψ), osmotic potential (ψ) and turgor potential (ψ) of both cultivars, but more so in 'Narve Viking' than in 'Ben Gairn', indicating that 'Narve Viking' was most affected by drought stress. In both cultivars osmotic adjustment only slightly contributed to turgor maintenance.In both cultivars, the drought stress significantly reduced leaf and flower dry weight and there was no regrowth of flowers after 17 days of recovery. In 'Ben Gairn' the aerial biomass accumulation after 12 days of drought stress was less reduced and regrowth of roots during the recovery phase was faster than in 'Narve Viking'. This indicates that 'Ben Gairn' was more tolerant of drought stress and recovered better than 'Narve Viking' but may also to some extent reflect differences in plant size. However, a slow regrowth of roots and high N uptake activity of drought stressed 'Narve Viking' at the end of the recovery phase indicated that this cultivar was slowly recovering too.The presented results stress the importance of installing irrigation systems in blackcurrant orchards during flowering and can assist the selection of drought stress tolerant cultivars in blackcurrant breeding programs.