Effects of Set-Point Substrate Moisture Control on Oomycete Disease Risk in Containerized Annual Crops Based on the Tomato–Phytophthora capsici Pathosystem

Abstract

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 midrange SM (15% volumetric water content [VWC]) and low-range SM (10% VWC) with 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 with noninoculated plants. Furthermore, incidence of fine root infections in inoculated asymptomatic plants was greater under reduced SM (10% VWC) compared with in well-watered plants (P < 0.05). Mild reductions to 15% VWC did not influence plant performance (root and shoot weights and plant height) or pathogen infection in either inoculated or noninoculated plants compared with well-watered plants and reduced water inputs by 17%, indicating potential for reducing water usage without increasing disease risk. Furthermore, P. capsici inoculated plants had lower shoot biomass and greater root infection incidence when 15% VWC was applied to older compared with 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.

Improving Containerized Nursery Crop Sustainability: Effects of Conservation-driven Adaptations in Soilless Substrate and Water Use on Plant Growth and Soil-borne Disease Development

“…Further, studies with pathogens indicate that reduced irrigation regimes that are not harmful physiologically may still compromise production by enhancing disease impacts when a pathogen is present (Swett, 2020). Our work is consistent with previous studies of the tomato-P. capsici pathosystem, in which reducing irrigation inputs increased crown and root rot severity and enhanced incidence of vine decline (Del Castillo M unera et al, 2019a). Although there are limited studies of chrysanthemum, in a study of the ornamental crop poinsettia, Pythium root rot (caused by Pythium aphanidermatum) was also enhanced under severe water reductions (Del Castillo M unera et al, 2019b).…”

“…Interactions of soilless substrate with sustainable water use. Previous studies of reduced irrigation methods indicate that, although in many cases irrigation reductions can be achieved without physiological impacts on plant growth, certain reduced irrigation practices can also incur a growth cost to many crops, including greenhouse tomatoes (Chand et al, 2021;Del Castillo M unera et al, 2019a;Pulupol et al, 1996) and chrysanthemums (Giordano et al, 2021). Further, studies with pathogens indicate that reduced irrigation regimes that are not harmful physiologically may still compromise production by enhancing disease impacts when a pathogen is present (Swett, 2020).…”

“…Inoculations were conducted with a single isolate per pathogen; P. capsici isolate SL897 was recovered from infected peppers in St. Mary's County, MD, and Phytopythium helicoides isolate SL1617 was recovered from an ornamental nursery retention pond in Frederick County, MD. Both isolates were confirmed to be pathogenic to their respective hosts in previous studies (J. Beaulieu et al, unpublished data;Del Castillo M unera et al, 2019a). For each pathogen, infested millet inoculum was prepared by transferring 10 plugs (1 cm diameter) of actively growing mycelia on 1-week-old V8 petri dish cultures to flasks containing 40 g of millet seed mixed with asparagine (0.032 g) and water (30 mL) that had been autoclaved twice (Quesada-Ocampo et al, 2009).…”

“…These studies evaluated performance of both a containerized vegetable and a floricultural crop in two peat-replacing wood-based substrates, bark and Hydrafiber (wood fiber blended with peat), in comparison with peat. For the vegetable pathosystem we examined tomato (Solanum lycopersicum L.)-Phytophthora capsici (Phytophthora root rot) interactions; tomatoes are an important greenhouse vegetable crop worldwide, and this is a common model system for plant-pathogen-water stress interactions (Bostock et al, 2014;Del Castillo M unera et al, 2019a). For the floriculture pathosystem, we examined chrysanthemum (Chrysanthemum ×morifolium)-Phytopythium helicoides (root rot) interactions.…”

Monitoring for a new I3 resistance gene-breaking race of F. oxysporum f. sp. lycopersici (Fusarium wilt) in California processing tomatoes following recent widespread adoption of resistant (F3) cultivars: Challenges with race 3 and 4 differentiation methods

“…Due to these challenges, in planta-based methods continue to provide the standard for the accurate differentiation of pathogenic from nonpathogenic strains, segregation of the different formae specialis, and differentiation of Fol races (e.g., Loṕez-Benıtez et al, 2018;Cabral et al, 2020;Munawar et al, 2020;Armenta-Loṕez et al, 2021;de Oliveira et al, 2021). In planta identification methods vary in terms of plant age, inoculation method, and the duration needed for symptom development, with results in 2-12 weeks, depending on the method.…”