Progress 06/01/20 to 12/31/24
Outputs
Target Audience:The target audiences served by this project consisted primarily of hydroponic leafy greens (i.e. lettuce) producers, consultants, horticultural supply companies and allied businesses, and controlled environmental agriculture (CEA) researchers and extension personnel in the United States. Consumers of hydroponic leafy greens were beneficiaries of this project, which aimed at investigating strategies to improve the safety and resilience of food crops. Efforts to disseminate the science-based knowledge during the final year of this project included presentations and workshops at the Root Health Symposium (rootalliance.org/events) in Gainesville, FL, and at the Floriculture Research Alliance (floriculturealliance.org) and Root Alliance (rootalliance.org) joint stakeholder meeting in Oceanside, CA. The stakeholders at both events included commercial greenhouse and hydroponic growers, plant breeders and marketers, allied companies (fertilizer, substrate, plastics, chemical companies, etc.), university researchers and educators and extension faculty, graduate students, and members of the general public. The information generated by this project and covered at the Root Health Symposium and Floriculture Research Alliance/Root Alliance meetings included (i) managing micronutrients as a strategy to mitigate Pythium root rot in hydroponic lettuce, (ii) the custom-formulating of recirculating hydroponic solutions to optimize yield, (iii) the potential for food-borne pathogens to contaminate the hydroponic solution, growing substrate, and plant, and (iv) the challenges of measuring/monitoring the microbiome in hydroponic and CEA production. These efforts included both oral and poster presentations. The dissemination efforts from this period also consisted of developing a step-by-step protocol for formulating hydroponic solutions, including target levels for metal micronutrients and silicon for optimal lettuce growth and disease control, for easy use by growers and other stakeholders. It was not possible to disseminate these efforts before the project ended, however, they are being published and presented during a Root Health Webinar Series (June through August of 2025, https://aaes.uada.edu/news/root-zone-webinar-series/) hosted by PI Dickson as well as at the second annual Root Health Symposium in Gainesville, FL (date TBD). Changes/Problems:There were a couple of unforeseen and noteworthy challenges that resulted in changes to the project approach. First, it was challenging to obtain a Pythium isolate that had an appropriate level of virulence and pathogenicity towards hydroponic lettuce. We discovered in this project that lettuce is relatively immune to Pythium in hydroponic culture, especially compared to highly susceptible plant species like spinach. Approximately 30 isolates were initially screened from a variety of sources. Lettuce showed resistance to nearly all isolates tested of P. dissoticum, P. ultimum, and P. aphanidermatum at various stages of plant growth and development. Fortunately, during this project, a colleague (Dr. Rosa Raudales, Univ. of Connecticut) isolated P. myriotyllum from hydroponic lettuce showing significant pathogenicity, and we obtained samples of this isolate for this project. The decision was made to switch to P. myriotyllum as the model pathogen. Finding a suitable Pythium isolate and developing the subsequent inoculation protocols required far more time, labor, and effort than originally planned. The impact was the research team did not have the time or resources remaining to complete substrate testing with Pythium (part of Objective 3) or the Safe Grow survey and outreach (part of Objective 4). However, the team did complete excellent experimentation testing the effects of metal micronutrients and silicon on Pythium root rot (Objective 2), which was a critical component of the project. During the project the nation-wide eXtension program was discontinued and therefore the research and extension team were not able to develop a new stakeholder eXtension COI group. However, in place of the proposed eXtension group, PD Dickson instead co-founded a new academia-industry collaborative group called Root Alliance (discussed earlier), through which he disseminated the results of project, even after the project-end. As of year-end 2024, the Root Alliance consisted of six university research/extension specialists focused on advancing the science around root health of hydroponic food and medicinal crops. What opportunities for training and professional development has the project provided?A graduate student working on this project took several professional development courses offered by the University of Florida IFAS Online Greenhouse Training program and included "Nutrient Management", "Advanced Nutrient Management", "Irrigation Water Quality and Treatment', and "Basic Hydroponic Production". They also participated in giving stakeholder presentations during the Root Health Symposium and Root Alliance annual meeting, which also served as an industry networking opportunity. How have the results been disseminated to communities of interest?A major dissemination of this project was the initiation of a Root Health Symposium (also discussed in Target Audience), in which the inaugural meeting was held at the University of Florida in Gainesville, FL, in May of 2024. The symposium focused on improving root zone management for optimal yield with edible food crops grown in hydroponic and soilless culture. There were presenters from the University of Arkansas (PI Dickson), University of Florida IFAS, University of Georgia, and Purdue University. There were also hands-on workshops and technology demonstrations in the university greenhouses, which also included presentations and demos from various industry sponsors. In attendance were primarily hydroponic and CEA growers, allied CEA companies (suppliers of substrate, fertilizer, plastics, and agrichemicals), university researchers/educators/extension specialists as well as graduate and undergraduate students. This event was also co-organized by the Florida Nursery, Greenhouse and Landscape Association. The symposium had over 100 attendees (not including presenters, sponsors, etc.) and received positive industry feedback. The second annual Root Health Symposium has been tentatively scheduled for late fall of 2025. Another major dissemination of information from this project was through the development of the Root Alliance (rootalliance.org), a collaborative academia-industry group with a mission to develop research-based solutions to major sustainability challenges impacting the hydroponic and CEA industry. PI Dickson co-founded this group in 2024, which consists of five universities: University of Arkansas (PI Dickson), University of Florida (Drs. Paul Fisher and Jeb Fields), University of Connecticut (Dr. Rosa Raudales), Purdue University (Dr. Celina Gomez), and the University of Georgia (Dr. Rhuanito Ferarrezi). Each university researcher focuses on a different aspect of root zone management (e.g. fertilizer, pathogens, substrate, water quality, root zone environment and microbiome) in hydroponic/CEA production, and partners with different industry stakeholders to help secure funding and collaborate on research. The priorities and benefits of this alliance include (i) fostering a collaborative research environment between industry and academia, (ii) promoting the professional networking and development of students, (iii) developing science-backed solutions to the industry's major problems for the collective benefit of all stakeholders, and (iv) advancing the hydroponic/CEA industry to promote the safe and sustainable production of food crops. The Root Alliance debuted in 2024 and had a soft launch during the first Root Health Symposium. The first annual stakeholder meeting, presentation of results, and official initiation of the Root Alliance was held in Oceanside, CA, in October 2024 in conjunction with a similar group called the Floriculture Research Alliance (floriculturealliance.org). Feedback on the Root Alliance was well received, and the university partners collected stakeholder input to set research and funding priorities for 2025. These priorities included inviting USDA members to join the Alliance. PI Dickson initiated a Root Health Webinar series (discussed in Target Audience section) to showcase research from this project, however, the series was not able to launch in 2024 and was postponed to summer of 2025. The webinar series was designed to deliver presentations, but also industry trade publications, to stakeholders covering topics from this CARE project: custom-formulating recirculating hydroponic solutions, management of micronutrients and silicon for disease control, water-treatment systems and design considerations, and soilless substrate considerations. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Objective 1. Characterizing food safety risks during production in recirculating hydroponic systems. Several experiments were conducted to investigate human pathogen (Salmonella Javiana and Listeria monocytogenes surrogates) persistence and internalization in "Rex" lettuce during production in recirculating hydroponic systems. All experiments were conducted at the University of Arkansas Horticulture Field Laboratory greenhouse complex in 20-L deep water culture systems. The nutrient solution for all experiments consisted of a half-strength modified Hoagland's solution. Experiments also evaluated the effects of the solution electrical conductivity (EC), pH, and temperature on pathogen persistence, since these parameters are often controlled in hydroponic production and were thought to potentially influence pathogenicity. Solution temperature varied from 17 to 29 °C, pH varied from 5.11 to 6.90, and electrical conductivity from 1.5 to 3.0 mS/cm. The concentrations of S. Javiana and L. monocytogenes (log CFU/mL or log CFU/g) were measured in the nutrient solution, roots, and rootzone (rockwool substrate + roots) at 0, 1, 3, 7, 14, and 21 days after transferring lettuce seedlings into the systems. Experiments were replicated in triplicate. Effects of sample day and sample type were evaluated by pathogen and by solution pH, EC, and temperature treatment (depending on experiment). Solution temperature, EC, and pH had no statistical effects on pathogen concentration in the hydroponic solution, roots, or rootzone (substrate + roots). Sampling date impacted pathogen concentration where S. Javiana and L. monocytogenes were greatest at day 0 (3 to 7 log CFUs) and steadily decreased (across all sample types) over time. At day 7, concentrations of both pathogens were greater in the roots and rootzone compared to the nutrient solution, whereas pathogen concentrations were similar across sample types for the remaining sample dates. These results suggest the greatest risk in terms of the hydroponic solution would occur immediately following a contamination event, and that the risk would be significantly reduced by 21 days. The fact that solution pH, EC, and temperature did not influence pathogen concentrations indicates that the management of these solution parameters presents little risk, but also little opportunity in terms of mitigating S. Javiana and L. monocytogenes. Overall, pathogen concentrations in the roots and rootzone paralleled those measured in the hydroponic solution. Objective 2: Evaluating hydroponic nutrient effects on plant disease risk. Several experiments were conducted to investigate the effects of increasing metal micronutrient concentrations and silicon (Si) concentrations on plant growth and susceptibility to Pythium root rot with hydroponically grown lettuce (Lactuca sativa). All experiments were conducted at the University of Arkansas Rosen Alternative Pest Control Center greenhouse complex in 20-L deep water culture systems. The nutrient solution for all experiments consisted of a half-strength modified Hoagland's solution. In the first experiment, "Rex" lettuce was grown in hydroponic solutions with metal micronutrients iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) supplied at either 0, 2.5, 5, or 10 mg/L. A standard hydroponic solution was also included as a control, with metal micronutrients supplied at 2 Fe, 1 Mn, 0.5 Cu, and 0.5 Zn mg/L. In the second experiment, hydroponic lettuce was grown with Si at 0, 7, 14, 28, and 56 mg/L. Hydroponic treatment solutions for both experiments were either dosed with Pythium myriotylum (Pythium treatment) at 1.80 x104 oospores per L or deionized water as a non-Pythium control. Data were collected on leaf SPAD chlorophyll content, shoot height and width, total plant fresh mass, and root disease severity. Increasing the Cu concentration in solution decreased Pythium disease severity but reduced lettuce growth and yield. Increasing the concentration of the other metal micronutrients also tended to reduce lettuce growth but had no significant influence on root disease. Supplementing the hydroponic solution with Si had no effect on Pythium root disease severity and slightly decreased lettuce growth at 56 mg/L Si. Results of this study suggest that the management of micronutrients and Si nutrition is not an effective strategy and, at best, a risky strategy for controlling Pythium in hydroponic lettuce. Growers would likely benefit from maintaining metal micronutrient and Si concentrations within the ranges of (in mg/L) 0.5 to 5.5 for Fe, 0.1 to 2.0 for Mn, 0.1 to 0.6 for Cu, 0.1 to 0.6 for Zn, and 0 to 28 for Si for many hydroponic crops. Supplementing Si has the potential to negatively influence plant growth and quality for certain plant species, and testing is necessary to evaluate phytotoxicity risks prior to implementing in commercial practice. Overall, successful mitigation of root rot pathogens in commercial hydroponic production requires the combination of proper sanitation, best management and cultural practices, appropriate hydroponic system design, and the implementation of a water treatment system with proper design and a multi-barrier approach. Objective 3: Evaluating soilless substrates and root zone pH effects on food and waterborne pathogens. Several experiments were conducted to investigate the impact of soilless substrate type no L. monocytogenes and S. Javiana persistence during recirculating hydroponic cultivation of "Rex" leaf lettuce. All experiments were conducted at the University of Arkansas Horticulture Field Laboratory greenhouse complex in 20-L deep water culture systems. The nutrient solution for all experiments consisted of a half-strength modified Hoagland's solution. The substrates tested consisted of rockwool (stonewool), Oasis foam cubes, and sphagnum peat moss. The remaining experimental details and data collection were the same as for Objective 1, with the exception that pathogens were also measured in the edible shoot tissue of lettuce. A mixed model was used to analyze bacterial recovery by sample type, sample day, and bacteria type. Least-square means were compared between treatments, with statistical analysis consisting of ANOVA and means separation used a Tukey-Kramer honest significance test at the 0.05 significance level. Trends in pathogen concentrations for Objective 3 were similar to those observed for Objective 1. Substrate type had little to no effect on pathogen concentration in the roots or solution. Pathogen concentrations were greatest in the solution at day 0, and steadily decreased over time, where root and rootzone concentrations were statistically similar to solution pathogen concentrations. L. monocytogenes and S. Javiana were not detected in the edible lettuce shoot tissue, indicating internalization and root uptake of these pathogens did not occur. Overall, the main risk of a contaminated hydroponic solution appears to be the potential for cross contamination or splashing of solution onto edible plant parts. Objective 4: Developing and delivering novel extension outreach materials targeting CEA producers. The novel outreach materials developed from this project consisted of a step-by-step protocol for customizing hydroponic nutrient solutions and managing micronutrients and silicon, which were delivered through the new Root Health Symposium and Root Alliance initiatives previously discussed. Some of the outreach materials and deliverables originally planned had to be modified due to insignificant results in disease testing as well as unforeseen changes in the project (discussed in greater detail under Project Changes).
Publications
- Type:
Peer Reviewed Journal Articles
Status:
Published
Year Published:
2024
Citation:
Dhulappanavar, G. R., & Gibson, K. E. (2023). Persistence of Salmonella enterica subsp. enterica ser. Javiana, Listeria monocytogenes, and Listeria innocua in hydroponic nutrient solution.Journal of Food Protection,86(10), 100154. https://doi.org/10.1016/j.jfp.2023.100154
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Progress 06/01/23 to 05/31/24
Outputs
Target Audience:The primary target audience is hydroponic and soilless greenhouse growers producing leafy greens and herbs crops. Changes/Problems:This project received a no cost extension to provide more time to meet the outreach and delivery objectives. The next report will be the final report. What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Novel outreach and deliverables were provided at an annual Root Alliance (rootalliance.org) stakeholder meeting in Oceanside, CA. Audience members included professional hydroponic growers, soilless substrate and fertilizer companies, biocontrol and pest management companies, researchers (university, USDA, private sector), and university students (undergraduate and graduate).
Publications
|
Progress 06/01/22 to 05/31/23
Outputs
Target Audience:The target audience for this research is primarily producers of hydroponic leafy greens in greenhouse and indoor/vertical farming systems as well as allied horticultural companies. Allied horticultural companies include but are not limited to distributors of hydroponic supplies and equipment, soilless substrate manufacturers, fertilizer companies, plant breeders, consultants working in hydroponics, and companies producing horticultural softwares and related technologies. Other intended audiences include students, researchers, and extension specialists working in hydroponics, soilless culture, and controlled-environment agriculture. Changes/Problems:We have been delayed on implementing the Safe Gro survey, collecting samples, and analyzing these samples. In addition, we have minor work to still complete related to the investigation of human pathogen risk and risks based on substrate type. Initial delays in starting and gaining momentum were a result of this grant being awarded in the peak of the COVID-19 pandemic, and although we have overcome these and some challenges in the research, more recent delays have been caused by personnel hiring challenges, supply chain issues, and unexpected turnovers in personnel and students (PD Dickson) within the last year. In addition, Co-PD Rojas left the University of Arkansas in 2023 for employment at Michigan State University, requiring PD Dickson's lab to take on additional responsibilities under short staffing, which created challenges in advancing the project to completion. We are requesting a second NCE for 6 months (until December 31, 2024) to complete our ongoing work, and continued access to the remaining funds will enable completion of this work. In the request we have outlined a new timetable to completion over the next six months. The Safe Gro Survey and remaining projects are near ready to implement and execute, and the staffing issues that prevented progress have been resolved as April 2024. We are confident we can acheive completion within the next 6 months. What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?Research results have been presented at scientific meetings for the American Society for Horticultural Sciences, American Pathological Society, and International Association for Food Protection. They have also been presented through grower meetings, articles, and field days including the Horticulture Industry Show (2022), e-GRO (2021 through 2023), and the Root Health Symposium (Gainesville, FL 2024). What do you plan to do during the next reporting period to accomplish the goals?We are currently requesting a second NCE for 6 months (until December 31, 2024) to complete our ongoing work. Specifically, we are still aiming to implement the Safe Gro survey, collect samples, and analyze these samples. In addition, work related to the investigation of human pathogen risk in recirculating DWC systems as well as risk based on substrate type will be fully completed by December 2024. Continued access to the remaining funds will enable completion of this work. For context, we were awarded this grant in June 2020 in the peak of the COVID-19 pandemic and were delayed in starting and gaining momentum on numerous aspects of this project due to personnel hiring challenges, supply chain issues, etc. Co-PD Rojas moved from the University of Arkansas to Michigan State University in 2023. In addition, PD Dickson has had unexpected turnovers in personnel within the last year which has also created challenges in advancing the project to completion.
Impacts
What was accomplished under these goals?
Hydroponic systems are "closed loop" systems, meaning the hydroponic solution (fertilizer nutrients + water) is reused and recirculated continuously among all plants. The problem being addressed is the recirculated solution poses a contamination risk for human and plant diseases. Co-PD Gibson has investigated the persistence of a human norovirus surrogate, (Tulane virus, TV), Salmonella Javiana, Listeria monocytogenes, and Listeria innocua in recirculating hydroponic solutions as a function of temperature (15°C, 25°C, 30°C, and 37°C) and time (over 21 day period, typical crop time). In completing this work, the internalization of these pathogens into the root and shoot tissues of lettuce was measured. Mixed models were used to determine the effects of temperature and time (day) on pathogen concentration in solution and tissues. In addition, decimal reduction values (D-values) were calculated using the slope from linear regressions by plotting each data point from each temperature. D-values indicate the time needed to reach 90% reduction in virus or bacterial loads (in days) in solution for each temperature. Infectious TV persisted in nutrient solution throughout the 21-day study period at 15°C, 25°C, and 30°C. Meanwhile, TV was not detected after day 5 in nutrient solution at 37°C. Similarly, decimal reduction values (D-values) of TV at 15°C, 25°C, 30°C, and 37°C were 48.0, 11.3, 8.57, and 7.02 days, respectively. At all temperatures, S. Javiana persisted in solution throughout the 21-day study period. However, L. monocytogenes and L. innocua persisted for only 3 to 4 d and 7 to 8 d, respectively. Similarly, decimal reduction values (D-values) of S. Javiana indicate longer persistence than L. innocua and L. monocytogenes at all temperatures. For instance, at 15°C and 25°C, D-values for S. Javiana were estimated at 82 and 26 d, respectively, compared to D-values of 3.6 and ~3 d for L. monocytogenes. The initial concentrations of S. Javiana and L. monocytogenes were 4.10 and 4.62 log CFU/g in roots, 3.15 and 4.19 log CFU/g in rockwool, and 5.86 and 6.66 CFU/ml in solution, respectively. S. Javiana persisted in roots, rockwool, and NS throughout the 21 sampling days with a log reduction of 2.85 log CFU/g, 3.66 log CFU/g, and ≥5.50 CFU/ml, respectively. L. monocytogenes population declined to <1 log CFU/g in roots, rockwool, and NS between 7 to 14 days. No pathogens were recovered from the edible portion of the lettuce. Pathogen populations in rockwool, roots, and solution were positively associated across sample type (R=0.78 to 0.96). Weak to moderate (R=-0.18 to -0.46) and weak (R=-0.02 to -0.12) associations with pH and temperature, respectively, were calculated for pathogen populations. PD Dickson and Co-PD Rojas investigated the virulence of different species and strains of Pythium (water-borne plant pathogen) in the hydroponic solution and with lettuce. Eighteen isolates of P. aphanidermatum, P. dissoticum, and P. myriotylum were screened for pathogenicity with 'Rex' lettuce (butterhead variety) and tested at concentrations ranging up to 105 oospores per L of hydroponic solution. Overall, 'Rex' lettuce showed tolerance to most P. aphanidermatum and P. dissoticum isolates but was susceptible to P. myriotyllum isolated from commercial hydroponic lettuce by researchers at the University of Connecticut, and therefore P. myriotylum was used for subsequent testing. Studies were then conducted to evaluate the effects of increasing metal micronutrient concentrations and silicon (Si) concentrations on plant growth and susceptibility to Pythium root rot with hydroponically grown lettuce (Lactuca sativa). In the first study, 'Rex' lettuce was grown in recirculating hydroponic solutions with metal micronutrients iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) supplied at concentrations ranging from 0 to 10 mg?L−1. A standard and commonly used commercial hydroponic solution was included as a control in all experiments, with metal micronutrients supplied at 2 Fe, 1 Mn, 0.5 Cu, and 0.5 Zn mg?L−1. In the second study, hydroponic 'Rex' lettuce was grown with Si at 0, 7, 14, 28, and 56 mg?L−1. Hydroponic treatment solutions for replicate systems in both studies were either dosed with P. myriotylum (Pythium treatment) at 1.80 × 104 oospores per L or deionized water as a non-Pythium control. Data were collected on leaf SPAD chlorophyll content, shoot height and width, total plant fresh mass, and root disease severity. Increasing the Cu concentration in solution decreased Pythium disease severity but reduced lettuce growth and yield. Increasing the concentration of the other metal micronutrients also tended to reduce lettuce growth but had no significant influence on root disease. Supplementing the hydroponic solution with Si had no effect on Pythium root disease severity and slightly decreased lettuce growth at 56 mg?L−1 Si. Results suggest that the management of micronutrients and Si nutrition is not an effective strategy and, at best, a risky strategy for controlling Pythium in hydroponic lettuce. Based on these results and those from other researchers, we concluded that growers would likely benefit from maintaining metal micronutrient and Si concentrations within the ranges of (in mg?L−1) 0.5 to 5.5 for Fe, 0.1 to 2.0 for Mn, 0.1 to 0.6 for Cu, 0.1 to 0.6 for Zn, and 0 to 28 for Si for many hydroponic crops. Supplementing Si has the potential to negatively influence plant growth and quality for certain plant species, and testing is necessary to evaluate phytotoxicity risks prior to implementing in commercial practice. Overall, successful mitigation of root rot pathogens in commercial hydroponic production requires the combination of proper sanitation, best management and cultural practices, appropriate hydroponic system design, and the implementation of a water treatment system with proper design and a multi-barrier approach.
Publications
- Type:
Journal Articles
Status:
Under Review
Year Published:
2024
Citation:
Dickson, R.W., M.E. Humphrey, S. Padhye, J.B. Tebow, and L.M. Machesney. Quantifying temperature effects on crop timing and quality for compact container-grown pepper. Submitted to HortScience, in review.
- Type:
Journal Articles
Status:
Published
Year Published:
2023
Citation:
Dhulappanavar, G. R., & Gibson, K. E. (2023). Persistence of Salmonella enterica subsp. enterica ser. Javiana, Listeria monocytogenes, and Listeria innocua in hydroponic nutrient solution. Journal of Food Protection, 86(10), 100154.
- Type:
Journal Articles
Status:
Published
Year Published:
2024
Citation:
Dhulappanavar, G. R., & Gibson, K. E. (2024). Hydroponic nutrient solution temperature impacts Tulane virus persistence over time. Food and Environmental Virology, 1-8.
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Progress 06/01/21 to 05/31/22
Outputs
Target Audience:The target audience for this research is primarily producers of hydroponic leafy greens in greenhouse and indoor/vertical farming systems as well as allied horticultural companies. Allied horticultural companies include but are not limited to distributors of hydroponic supplies and equipment, soilless substrate manufacturers, fertilizer companies, plant breeders, consultants working in hydroponics, and companies producing horticultural softwares and related technologies. Other intended audiences include students, researchers, and extension specialists working in hydroponics, soilless culture, and controlled-environment agriculture. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This project opened training and development opportunities for graduate students and staff within the research group. Students and staff participated at the Horticulture Industries Show in various educational sessions on plant disease, food safety, and horticultural topics. Students also enrolled in a specialty hydroponics course offered by the University of Florida Institute of Food and Agricultural Sciences and leading hydroponic research and extension specialists. How have the results been disseminated to communities of interest?Results have been disseminated to hydroponic growers, representatives from allied horticultural companies, researchers, extension specialists, and students at the Horticulture Industries Show in Fayetteville, AR, in 2022. In addition, results have been disseminated to research scientists and extension specialists through peer-reviewed scientific publications and also to industry stakeholders through e-GRO Alerts and trade publications. What do you plan to do during the next reporting period to accomplish the goals? Our research and dissemination plants for the next reporting period are summarized as follows: Evaluate effects of soilless substrate on mitigation of Pythium and various foodborne pathogens Evaluate the effects of hydroponic solution temperature, pH, and electrical conductivity on foodborne pathogen persistence in hydroponic systems. Finish the SafeGrow Survey of water quality at commercial grower locations Planning a major field day plus a webinar for CEA stakeholders Finish publications and outreach objectives, including the SafeGrow final report.
Impacts
What was accomplished under these goals?
Several key research accomplishments were achieved during this period and are summarized. We found in hydroponic culture that increasing the concentrations of micronutrients supplied in solution did not increase plant resistance to Pythium root rot, and in some cases reduced plant growth and yield. The exception was with copper, where increasing copper concentration decreased Pythium disease severity and mitigated yield losses. However, the copper concentrations needed in solution to reduce root disease also significantly reduce lettuce yield, likely a result of copper toxicity. Omitting micronutrients from solution had either a negative effect or no effect on plant yield and resistance to Pythium depending on the micronutrient. In scenarios where omitting a micronutrient had no effect on yield, it was likely that enough leached into solution from the hydroponic equipment. Overall, we determined that the optimal concentrations of micronutrients were within many of the common recommended ranges for growers, ranging from about 0.15 to 2.5 ppm depending on micronutrient. In contrast to recently published research from other researchers, we do not recommend increasing micronutrient concentrations above 1 ppm for manganese, zinc, and copper and above 2.5 pom for iron; our results indicate this would cause minimal to no reduction in Pythium disease risks, may even increase plant susceptibility to Pythium, and would likely reduce yield. Supplementing the hydroponic solution with silicon (Si) did not increase lettuce resistance to Pythium root rot, and at the highest level of soluble Si (56 ppm Si) there was a slight reduction in growth compared to no Si. Lettuce was also found to be a Si "non-accumulator" species, which means little Si is taken up into shoot tissues (Si represents <1% of shoot dry tissue). Although lettuce a Si "non-accumulator" there is evidence and data to support Si alleviates metal micronutrient toxicity in lettuce, and therefore supplementing the hydroponic solution with up to 14 ppm Si is still recommended for lettuce if it is not cost prohibitive. Survival and persistence of foodborne pathogens varied in hydroponic systems and depended on pathogen. Salmonella javiana and Listeria innocua persisted for >21 days in hydroponic solutions kept at 25 degrees Celsius, whereas Listeria monocytogenes persisted for only 5 days. These results indicate a potentially greater food safety risk with the former pathogens since longevity in hydroponic solutions was longer following a contamination event.
Publications
- Type:
Journal Articles
Status:
Accepted
Year Published:
2021
Citation:
Tebow, J.B., L.L. Houston, and R.W. Dickson. 2021. Silicon foliar spray and substrate drench effects on plant growth, morphology, and resistance to wilting in container-grown edible species. Horticulturae. 7 (9), 263.
- Type:
Journal Articles
Status:
Submitted
Year Published:
2022
Citation:
Houston, L.L., Dickson, R.W., Bertucci, M.B., Trenton, R.L. Evaluation of species-specific replenishment solutions for hydroponically grown arugula and basil. Horticulturae.
- Type:
Journal Articles
Status:
Submitted
Year Published:
2022
Citation:
Helms, K.M., Dickson, R.W., Rojas, A.J., Gibson, K.E. Micronutrient and silicon concentration effects on plant growth and resistance to Pythium with hydroponic lettuce. Horticulture.
- Type:
Journal Articles
Status:
Submitted
Year Published:
2022
Citation:
Dickson, R.W. Evaluating average daily temperature and daily light integral effects on plant growth rate and quality with container-grown fruiting vegetables.
- Type:
Journal Articles
Status:
Accepted
Year Published:
2022
Citation:
DeGenring, L., R.W. Dickson, and A. Poleatewich. Inhibition of Botrytis cinerea growth and suppression of grey mold on petunia leaves using chitosan. 2022. Plant Disease. Accepted, in press.
- Type:
Journal Articles
Status:
Accepted
Year Published:
2022
Citation:
Harrison, D., M. de Oliveira, C. Wu, L. Florez-Palacios, A. Acuna, M. da Silva, F. Ravelombola, J. Winter, K. Brye, R.W. Dickson, A. Rojas, P. Chen, H. Nguyen, and L. Mozzoni. 2022. Developing a high-throughput method to screen soybean germplasm for hypoxia tolerance in a hydroponic system. Crop Science. DOI: https://doi.org/10.1002/csc2.20674
- Type:
Journal Articles
Status:
Accepted
Year Published:
2022
Citation:
Estepp, C.M., R.W. Dickson, and D.M. Johnson. 2022. Rapport, course technology, and self-regulated learning as predictors of student satisfaction in an online horticulture program. NACTA. Volume 66; pg 9-17.
- Type:
Journal Articles
Status:
Accepted
Year Published:
2022
Citation:
Dickson, R.D., K.M. Helms, B.E. Jackson, L.M. Machesney, and J.A. Lee. 2022. Evaluation of peat blended with pine wood components for effects on substrate physical properties, nitrogen immobilization, and growth of petunia (Petunia x hybrid Vilm.-Andr.). HortScience. DOI:
https://doi.org/10.21273/HORTSCI16177-21
- Type:
Journal Articles
Status:
Accepted
Year Published:
2021
Citation:
Dickson, R.W., J.B. Ebba, P.R. Fisher, C.H. Harris, and T.R. Guerdat. 2021. Fertilizer and plant growth regulator strategies to improve consumer success with containerized plants. HortTechnology. 31 (3), 304-314.
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Progress 06/01/20 to 05/31/21
Outputs
Target Audience:The target audiences reached by efforts during this reporting period include but the following. Commercial producers of edible food crops in hydroponic and soilless substrate culture systems. Production can be in greenhouses, high tunnels, indoor vertical farms, and other types of protected and controlled-environment agriculture. Members of the scientific community conducting applied research for protected and controlled-environment agriculture. Members may include researchers, professors, technical staff, post-docs, graduate and undergraduate students, and other members of universities and/or research institutes. Allied horticulture companies associated with crop production in protected and controlled environments. These include manufacturers and suppliers of electric lighting technologies, soilless substrates, fertilizers, agrichemicals, various plastic products, greenhouses, high tunnels, vertical farming units, and plant breeders. University students enrolled in coursework related to horticulture and crop production in protected and controlled environments. Courses include Greenhouse Management and Operation as well as Introduction to Hydroponic and Soilless Food Crop Production. Changes/Problems:The most significant and disruptive problems this past period either resulted from or were related to COVID-19. Like all universities, the University of Arkansas implemented strict social distancing guidelines and restrictive access to campus during 2020. The PI and Co-PIs on this project all had to immediately transition from in-person to remote course lectures and labs with minimal notice, and increase teaching efforts significantly to learn new online platforms and accommodate students. In addition, we had reoccurring student worker absences due to COVID-19 exposures, COVID-19 positive tests, and quarantining. In addition, the lead graduate student on this project had a serious health issue and underwent brain surgery (complicated by COVID-19), and was out of office for parts of summer and fall 2020. In addition to health concerns, there were significant delays in shipping of plastics and materials needed to build hydroponic systems, which we were told by suppliers that shipping delays were also related to COVID-19 shutdowns. Despite some delays from COVID-19, the research team feels confident we can overcome any setbacks from 2020 during the next reporting period, and goals for future reporting periods should not be impacted negatively. Other challenges/problems with experimentation were briefly discussed in the previous section (i.e. managing solution temperature, plant age at inoculation, and proper identification of pathogens strains and surrogates), and have been overcome with additional engineering of hydroponic systems, pilot testing, and fine-tuning of the methods and experimental approach. New approaches include conducting experiments at warm temperatures (30C), inoculating hydroponic systems with pathogens at 14 days after germination, using appropriate surrogates and Pythium strains, and evaluating plants in new leak-free (sealant-free) hydroponic systems. While conducting preliminary studies during the last reporting period, the research team has identified a severe lack in standardized operating procedures (SOPs) on how to effectively screen and evaluate hydroponic leafy greens crops for pathogen resistance, which has been confirmed by some of our industry research partners. During the next reporting period, we will discuss the feasibility of adding a research output that consists of protocols and methodology to develop reliable screening SOPs for use by other university researchers, plant breeders, and hydroponic R&D companies. What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals? Conduct experiments focusing on nutrient concentrations (micronutrients and silicon) and substrate effects on Pythium root infection and uptake of food-borne pathogens. A major issue has been getting repeatable Pythium infection and identifying a virulent Pythium strain. We will therefore grow lettuce at high temperatures (30C), inoculate seedlings at 14 days, and use the most virulent strain we have been able to isolate. Another challenge during preliminary experiments was designing a reliably leak-free hydroponic system, which is also common in commercial production. We custom-ordered special rubber gaskets that would eliminate the need for sealants and glue, for which the degradation was a common cause of leaking over time. We will use our newly designed leak-free recirculating systems. PI Dickson and Co-PI Gibson will present on research from this past reporting period and the next reporting period at the Horticulture Industry Show in Fayetteville, AR. The whole research team will execute outreach activities including the SafeGrow survey, workshops, and initiation of the eXtension group. A challenge and opportunity identified during the last period is a lack of standardized and published protocols on screening hydroponic leafy greens for Pythium resistance and resistance to food safety risks. Therefore, the research team plans to address this problem by setting up standard operating procedures supported by data collected during this period for future publication. Considering the importance as well as the inherent difficulties in screening for Pythium and food-borne pathogen resistance, the research team believes this could have a large impact for both the scientific and commercial communities.
Impacts
What was accomplished under these goals?
In order to meet our research objectives and goals, our first accomplishment was to effectively design and test research-scale hydroponic systems that are both recirculating and deep water culture, mimicking the larger analogs used by commercial hydroponic operations for growing leafy greens (PI Dickson). Our research partners collaborated and gave input to the PI and Co-PIs on the system design. In the meantime, strains of Pythium causing root disease were isolated from commercial operations and established in the laboratory (PI Dickson and Co-PI Rojas). Both graduate and undergraduate students have been trained in techniques related to Pythium strain isolation, deep freeze storage, initiating sporulation, and the development of concentrated spore solutions used to inoculate hydroponic systems during experiments. In addition, we have identified the proper food-borne pathogen surrogates (non-pathogenic to humans) for characterizing food safety risks in hydroponics (Co-PI Gibson), including surrogates for common viruses (human norovirus) and bacteria. For Pythium and water-borne pathogens, preliminary experiments were conducted to (i) identify the appropriate and most virulent isolate for experimentation, (ii) determine the proper plant age and spore concentration for inoculating hydroponic systems with Pythium, (iii) determine whether Pythium should be added to the substrate or directly to the hydroponic nutrient solution, (iv) determine the persistence of Pythium spores in hydroponic systems, (v) determine the effects of nutrient solution and air temperature on disease severity/pathogen risk, and (vi) practice measuring the severity of Pythium lesions using digital imaging software and visual analyses. For food-borne pathogens, preliminary experiments were conducted to achieve the same goals as for Pythium and water-borne pathogens, with the exception of measuring lesions on plant roots. Instead, protocols are currently being tested for the quantification of food borne pathogens in plant leaf tissues. We have learned that Pythium spores and food-borne pathogen surrogates can survive in hydroponic nutrient solutions; however, conditions must be optimal for the pathogen to infect the crop. For example, higher temperatures above 27 degrees Celsius favor Pythium infection of roots, particularly for warm-weather Pythium species, partially because Pythium performs well at higher temperatures and plants are under a greater degree of temperature stress. Young lettuce plants at the 2-4 leaf stage are more susceptible to Pythium infection compared to lettuce with established heads and large root systems. This is because (i) young plants are growing more slowly until more leaves develop, (ii) root systems are small and can be overwhelmed by high pathogen loads, and (iii) there is simply more time in the crop life cycle for Pythium to infect roots and cause yield and growth losses. In contrast, we have seen that larger lettuce plants are naturally more resistant to Pythium infection, likely because plants are growing at more rapid rates and simply "outgrow" the pathogen, particularly when spore concentrations are low in solution. We have found that seedlings between 7 and 14 days after germination are more susceptible to Pythium compared to seedlings that are 14 days old or greater. We have also found that lettuce is particularly sensitive to Pythium at greater than 27 degrees Celsius, and that disease occurrence is significantly reduced at lower temperatures despite high spore concentrations in solution. Our trials indicate that it is possible to dip seedling trays in Pythium spore solutions to provide inoculation as opposed to adding spore solution directly to the recirculating nutrient solution, which may serve as a more practical research method for future studies and experimentation. We are still analyzing similar trials for food borne pathogens, but preliminary results suggest higher temperatures may create more of a food safety risk for hydroponic leafy greens, because plants are stressed at higher temperatures and also transpiring nutrient solution at more rapid rates (one of the main ways plants internalize food-borne pathogens). A food-borne pathogen contamination event would likely create a higher food safety risk when plants are nearer to maturity, because of the greater leaf area per plant and higher demands for water/nutrient solution uptake. Most activities to meet these goals will be concluded during the next two reporting periods, and therefore more detailed accomplishments can be expected in future reports.
Publications
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