Effects of deficit irrigation during flower initiation of two blackcurrant (Ribes nigrum L.) cultivars

• Drought stress reduced evapotranspiration, RWC, ψl, ψπ, ψp, gs, and leaf area.
• Recovery of gs was faster in ‘Titania’ than in ‘Ben Hope’ upon rewatering.
• Root growth remained more inhibited in ‘Titania’ than ‘Ben Hope’ during recovery.
• The cultivar ‘Ben Hope’ responded to less severe drought stress than ‘Titania’.
• Drought stress reduced the number of strigs and flowers per node in ‘Ben Hope’.

The tolerance to water deficit and ability to recover was studied during flower initiation in two blackcurrant cultivars (Ribes nigrum L., ‘Titania’ and ‘Ben Hope’). 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 deficit irrigated (DI) for 3, 4, 5, 7 or 10 days. Deficit-irrigated plants received a volume of nutrient solution corresponding to 50% of the volume supplied to FI plants. Here after full irrigation was continued (FI) or resumed (DI) to allow for 2 and 10 days of recovery for stomatal conductance and leaf area increment, and 7 and 14 days of recovery for root intensity. Full irrigation was continued until the spring when the numbers of strigs and flowers per node were recorded.Deficit irrigation reduced the accumulated evapotranspiration (ETc), relative water content (RWC), leaf water potential (ψl), osmotic potential (ψπ) and turgor (ψp) in both cultivars. Stomatal conductance (gs) was reduced due to deficit irrigation, but more so in ‘Ben Hope’ than in ‘Titania’, indicating that ‘Ben Hope’ is more affected by drought stress than ‘Titania’. In both cultivars, deficit irrigation led to a significant decrease in the area of developing leaves, implying that leaf development of blackcurrant is sensitive to drought stress. Following deficit irrigation the speed of recovery of gs was faster in ‘Titania’ than in ‘Ben Hope’, whereas root growth remained more inhibited in ‘Titania’ than ‘Ben Hope’ during recovery. This supports the proposition that ‘Ben Hope’ is more affected by drought stress than ‘Titania’. In the long term, deficit irrigation reduced the number of strigs and flowers per node in ‘Ben Hope’, whereas in ‘Titania’ high temperature during flower initiation seemed more important for the formation of flower initials than water availability.Overall, the results of this study stress the importance of postharvest irrigation and breeding for cultivars that are tolerant to drought stress and high temperatures during flower initiation in order to meet future climate changes.