LAUSR

In containerized (potted) annual nursery and greenhouse crops, set-point controlled irrigation allows adaptation to increasing water insecurity by precisely reducing water inputs. A key factor influencing adoption is lack of information on disease risk. To facilitate adaptive water use, effects of set-point substrate moisture (SM) control on disease risk and water savings in containerized annual production were evaluated using the Phytophthora capsici -tomato pathosystem (a model system for water-stress predisposition to pathogen infection), comparing outcomes of imposing mid-range SM [15% Volumetric Water Content (VWC)] and low-range SM (10% VWC) to well-watered (20% VWC) plants. Reducing soil moisture to 10% VWC differentially reduced stem water potential (P < 0.05) and enhanced rate of wilt progress (P = 0.006) and root rot severity (P = 0.03) in P. capsici inoculated plants compared to non-inoculated plants. Further, incidence of fine root infections in inoculated-asymptomatic plants was greater under reduced SM (10% VWC) compared to well-watered plants (P < 0.05). Mild reductions to 15% VWC did not influence plant performance (root and shoot weight, plant height) or pathogen infection in either inoculated or non-inoculated plants compared to well-watered plants and reduced water inputs by 17%, indicating potential for reducing water usage without increasing disease risk. Further, P. capsici inoculated plants had lower shoot biomass and greater root infection incidence when 15% VWC was applied to older compared to younger plants; the inverse was true for root rot severity, although root rot development was minor overall (P < 0.05). These results indicate that water use reductions pose disease risks, but there is potential to reduce water use and effectively manage plant pathogens in containerized production. Overall, this study indicates that physiological indices should not be solely relied on to develop water reduction methods.