2018 ASHS Annual Conference

The nursery crop production sector is a large agricultural consumer of fresh water. With rising concerns related to water insecurity, interest in precision irrigation scheduling to reduce water inputs is increasing, but adoption is hindered in part by perceived disease risks. The objectives of this study were to: (1) evaluate the effects of reducing soil volumetric water content (VWC) on oomycete pathogen colonization and root rot in a containerized crop, and (2) determine whether alteration of soil moisture at different host developmental stages influenced disease risk. All studies were conducted using the Phytophthora capsici-tomato model system. The effects of reducing soil VWC were evaluated for three soil moisture (SM) levels: well-watered (20% VWC), mid-range SM (15% VWC) and low-range SM (10% VWC). Plants were simultaneously inoculated and placed under irrigation regimes, with non-inoculated plants as pathogen controls. In inoculated plants, low-range SM increased the extent of root infection in asymptomatic plants (p< 0.05), as well as wilt progress (p = 0.006) and root rot severity (p = 0.03) compared to higher SM treatments. Low-range SM reduced stem water potential in inoculated plants to -0.94 ±0.04 MPa (p < 0.05), which corresponds to levels resulting in pathogen predisposition. In contrast, in inoculated plants mid-range soil moisture (15% VWC) did not alter pathogen colonization or plant health compared to well-watered controls, and reduced water use by 18%. To evaluate whether soil moisture effects vary by developmental stage of deployment, both 15% VWC and 10% VWC were initiated at vegetative (12 wks old), flowering (14 wks old) and fruit set (16 wks old). Irrigation treatments were applied until plants were 18 weeks old, and then returned to well-watered conditions and inoculated or left untreated (controls). Root rot was more severe and disease progress tended to be more rapid when 15% VWC was initiated at the vegetative stage, compared to later time points (flowering, early fruit set) (p < 0.05); similar results were obtained for 10% VWC. These studies indicate that in containerized production systems, oomycete pathogen management must to be considered when deploying adaptive water use strategies which decrease soil moisture (and thus water inputs), but there is potential to effectively co-manage oomycete pathogens and water use by deploying moderate reductions in soil moisture and initiating reductions at later plant developmental stages.