ABSTRACT
Hydroponic farming systems play an increasingly important role in the sustainable production of nutrient-rich foods. The contamination of surfaces in hydroponic fresh produce production poses risks to the food safety of crops, potentially endangering public health and causing economic losses in the industry. While sanitizers are widely used in commercial hydroponic farms, their effectiveness against human pathogens on surfaces and their impact on plant health and quality are not known. In this study, we evaluated the efficacy of chemical sanitizers in eliminating Salmonella Typhimurium from inanimate surfaces in commercial hydroponic Nutrient Film Technique (NFT) systems. Further, we assessed the impact of sanitizers on the yield, quality, and nutritional value of lettuce and basil. Sanitizers (Virkon, LanXess, Pittsburgh, PA, USA; SaniDate 12.0, BioSafe Systems, East Hartford, CT, USA; KleenGrow, Pace Chemical Ltd., Delta, BC, Canada; Green Shield, United Labs Inc., St Charles, IL, USA; Zerotol, BioSafe Systems, East Hartford, CT, USA; Bleach, Pure Bright, ON, Canada) were tested against Salmonella Typhimurium inoculated on NFT surfaces (nutrient reservoir, growing channels, top covers, drain lines). The effective treatments were then tested for their impact on lettuce and basil in a split-plot experiment conducted in commercial NFT units. Crop yield, color, and nutrient content (chlorophyll and carotenoids) were measured throughout the crop life cycle. While all quaternary ammonium compounds (QAC), SaniDate 12.0 (200 ppm), Zorotol (5%), and Virkon (1%) eliminated Salmonella Typhimurium from commercial NFT surfaces, chlorine-based sanitizer treatments were statistically similar to water treatments on most surfaces. All chemical sanitizers impacted the yield, color, and nutritional value of lettuce and basil. SaniDate 12.0 (200 ppm) was the least detrimental to crops and was identified as a potential candidate for further validation in commercial hydroponic settings. The findings of this study will be translated into recommendations for the industry and will contribute to the development of future food safety guidelines and policies.
ABSTRACT
Corky root rot is an important disease in tomato production systems and is caused by Pseudopyrenochaeta terrestris and P. lycopersici (formerly Pyrenochaeta lycopersici Types 1 and 2, respectively). The corky root rot pathogens are slow growing and difficult to isolate and quantify in soil and plant tissue. A multiplex hydrolysis probe-based qPCR assay was designed to allow for simultaneous detection and quantification of P. lycopersici and P. terrestris with a competitive internal control to indicate if qPCR inhibitors are present. Single species and multiplex assays for Pseudopyrenochaeta spp. detected DNA levels above 0.013 pg of DNA per reaction. These highly specific assays had no nontarget amplification of other fungal and oomycete pathogens or rhizosphere-associated fungi of tomatoes that were tested. This assay can be used to quantify Pseudopyrenochaeta populations in roots and soils in tomato production systems to better determine the impacts of disease management strategies on Pseudopyrenochaeta spp. and provides a tool to study the biology of Pseudopyrenochaeta spp.
Subject(s)
Solanum lycopersicum , Plant Diseases/microbiology , Polymerase Chain Reaction , DNAABSTRACT
Hydroponic vegetable production is increasing globally, but there is a lack of science-based recommendations to ensure their food safety. Specifically, there is limited evidence for establishing water management strategies. The purpose of this study was to determine the survival of Salmonella Typhimurium and Listeria monocytogenes in commercial nutrient flow technology (NFT) systems during the lifecycle of lettuce exposed to sporadic or extreme contamination. NFT systems were inoculated with Salmonella Typhimurium or Listeria monocytogenes, and nutrient solution, rockwool, roots, and lettuce leaves were collected over the lettuce production cycle for pathogen enumeration and detection. Both human pathogens persisted in the lettuce NFT growing system throughout the growth cycle of lettuce. Salmonella Typhimurium and L. monocytogenes accumulated in rockwool medium and on lettuce roots and were transferred to the leaves at quantifiable levels from the contaminated nutrient solution. In the nutrient solution, Salmonella concentration under sporadic and extreme conditions declined significantly 24 h after inoculation and again 7 days post-inoculation (p < 0.0001). Under extreme conditions, the concentration did not change significantly after 7 days, while under sporadic conditions, the concentration declined again 14 days post-inoculation in the nutrient solution collected from the reservoirs. L. monocytogenes populations in the nutrient solution fluctuated significantly over the 28-day growth cycle (p < 0.0001). Under extreme conditions, L. monocytogenes concentrations in the nutrient solution declined, while under sporadic conditions, the populations increased. The findings of this study, for the first time, describe human pathogen survival in commerical NFT systems and highlight the urgent need for novel approaches to mitigating the risks from nutrient solution contaminaiton in hydroponics.
