ABSTRACT Biotic and abiotic factors influence bacterial communities in the rhizosphere. This project aimed to characterize bacterial communities in the lettuce rhizosphere, assess the relationships between bacteria and root rot, and evaluate the impact of reused nutrient solutions on bacterial communities. Lettuce (Lactuca sativa cv. Rex) was grown in deep-water culture hydroponics in reused autoclaved or non-autoclaved nutrient solutions for five cycles, with or without Pythium myriotylum. Bacterial composition was determined via high-throughput sequencing of the 16S rRNA gene. Quantitative real-time PCR was used to detect P. myriotylum. Spearman’s correlation coefficient (ρ) was performed to assess relationships between variables. The expression of PR1, PDF1.2, and LOX1 was quantified to determine if there were differences in plant defenses. The predominant phyla and genera across all cycles in the nutrient solution and roots were Proteobacteria (67%) and Cyanobacteria (47%) and Acinetobacter (13%) and Ideonella (22%), respectively. Bacterial communities in the nutrient solution (R2= 0.35) and roots (R2= 0.24) were significantly dissimilar between cycles. Bacterial communities were significantly dissimilar by the presence of P. myriotylum in nutrient solution (R2= 0.02) and roots (R2= 0.10). Bacterial correlations with health variables mostly differed by the presence/absence of P. myriotylum. Bacterial communities or individual bacterial isolates in recirculating hydroponic solutions that activate plant defenses resulting in the suppression or prevention of Pythium root rot in lettuce should be investigated further to be utilized as viable strains or synthesized compounds for the development of commercial products.IMPORTANCEPythium myriotylum is the causal agent of root rot and wilt disease, which can cause significant damage to lettuce in hydroponic systems. Root rot can be challenging to treat with traditional methods once it develops, often resulting in the destruction of the entire crop. Reused nutrient solutions have been reported to harbor microorganisms that may affect disease suppression. Examining how bacterial communities in recycled nutrient solutions change and trigger plant-defense genes may contribute to the reduction of Pythium root rot and provide chemical-free and cost-effective alternatives for soilless cultivation systems. Future studies focusing on specific microorganisms and their bioactive compounds will be essential for advancing biological control methods in hydroponic crop systems.

Biofilm development in pressurized drip irrigation systems impairs emitter performance and irrigation uniformity, increasing production risks in greenhouse systems where small substrate volumes limit moisture buffering capacity. The present study evaluated the effects of pipe material and peat-derived organic total suspended solids (TSS), representative of recirculated greenhouse irrigation water, on biofilm accumulation, microbial community composition, and emitter performance. Polyvinyl chloride (PVC; main lines) and polyethylene (PE; lateral lines) were tested using nutrient solutions containing 0, 30, 60, and 120 mg L⁻¹ organic TSS (<150 µm). The system incorporated pressure-compensated drip emitters with anti-drain mechanisms and operated under short-pulse irrigation typical of greenhouse production (twice daily for 2 min over 8 weeks). Biofilm accumulation was quantified by dry mass and heterotrophic plate counts, and microbial communities were characterized using 16S rRNA and ITS2 sequencing. Surface hydrophobicity and roughness were evaluated before and after biofilm exposure. PVC pipes accumulated more biofilm than PE pipes and exhibited greater changes in surface properties. Pipe material explained more variation in bacterial community composition than organic TSS. No emitters fully clogged; however, organic TSS ≥ 60 mg L⁻¹ increased emitter discharge, indicating early-stage performance drift in anti-drain emitters. These findings highlight the importance of pipe material selection and organic TSS management for maintaining irrigation performance in greenhouse systems.

Runoff from greenhouse production can impair water bodies if nitrate-nitrogen (N) or phosphate-phosphorus (P) leach from container substrates. This study quantified and compared water and nutrient runoff from three irrigation systems combined with two controlled-release fertilizer (CRF) rates during greenhouse production of petunias (Petunia milliflora F1 'Picobella Pink'). The gray water footprint (GWF), defined as the volume of fresh water required to assimilate pollutants and meet water quality standards, was used to standardize environmental impacts among treatments. The experiment followed a 3 3 2 factorial design with irrigation system (mist, drip, and subirrigation) and CRF rate [2.1 g N-1.26 g P-1.68 g potassium (K) or 1.8 g N-1.08 g P-1.44 g K per container]. Irrigation volume was adjusted to supply 110% container capacity. Plant growth, irrigation input, leachate volume, and nutrient concentrations were measured weekly. Differences in plant growth, water use efficiency, nutrient leaching, and GWF were significant by irrigation system, but not by CRF rate or the interaction of irrigation and CRF. Mist irrigation used approximately five times more water than drip or subirrigation and generated the highest nutrient concentrations and GWF values. In contrast, subirrigation produced no discharge, resulting in a GWF of zero, whereas plant growth was comparable with drip irrigation. These findings demonstrate that irrigation system selection strongly influences the environmental footprint in greenhouse container production and that closed or recirculating systems can reduce water use and nutrient losses substantially without compromising crop quality.

Reducing irrigation inputs is essential for sustainable container crop production; however, the ability of biostimulants to mitigate the effects of deficit irrigation on ornamental crop quality and postharvest often may be crop-specific, product-specific, and application-specific. Two independent experiments were conducted to evaluate whether chitosan applied as a substrate amendment or arbuscular mycorrhizal fungi (AMF) applied during germination could improve growth, physiology, and postharvest performance of petunia (Petunia milliflora ‘PicobellaTM Pink’) under sustained water content reduction. Plants were grown under three container capacity (CC) treatments (100%, 70%, and 40%) combined with chitosan application timing (no application, week 1, or week 3) or AMF application (with or without). After production, plants were exposed to postharvest environments at 30 °C or 40 °C for 2 weeks. The growth index and canopy area decreased by 10% to 40% relative to plants grown at 100% CC under 70% and 40% CC; however, flower coverage percentage remained unaffected during production. Water use reduced by 20% at 70% CC and by up to 50% at 40% CC, while irrigation water use efficiency (IWUE) was maintained with all CC treatments. In the AMF experiment, plants grown at 40% CC with AMF exhibited the highest IWUE and increased root colonization under severe deficit irrigation. Photosynthetic pigment concentrations were generally maintained under deficit irrigation, whereas malondialdehyde concentrations temporarily increased at week 4 under 40% CC, indicating increased oxidative stress. Neither chitosan nor AMF consistently enhanced plant growth or reduced biochemical stress indicators under the evaluated conditions. Chitosan application timing strongly influenced plant responses, with week 3 applications reducing growth and increasing oxidative stress across CC treatments. During the postharvest evaluation, temperature was the primary factor affecting plant performance, with plants maintained at 40 °C exhibiting lower flower coverage and canopy area compared with plants maintained at 30 °C. The combination of deficit irrigation and chitosan application showed limited potential to improve postharvest heat tolerance, whereas AMF application did not improve postharvest performance. Overall, petunia demonstrated substantial tolerance to sustained deficit irrigation, and 70% CC appeared to be a practical strategy for reducing irrigation inputs while maintaining marketable crop quality.

This study quantified water-use metrics under five sustained container capacity (CC) levels (100%, 85%, 70%, 55%, and 40%) during greenhouse production of Petunia milliflora F1 (Picobella Pink) production. Total irrigation input and leachate volumes were measured weekly, and plant growth and quality parameters were measured at harvest. Plant size declined gradually with decreasing CC; however, flower coverage was unaffected. Irrigation water use efficiency (IWUE; grams of dry biomass per volume of water) increased as CC decreased; highest IWUE was observed at 40%. No leachate was recovered at 55% and 40% throughout the experiment. Irrigation input and leachate volumes were significantly reduced at 70% and 55% while maintaining marketable quality, suggesting a practical balance between water conservation and crop marketability. Although the greatest IWUE occurred at 40% CC, the reduction in plant size at 40% limits the practical application of this irrigation strategy for commercial production.

Adventitious root development (ARD) in vegetative cutting propagation is a critical process triggered by wounding and resource isolation from the stock plant. We hypothesized that the exogenous application of stresssignaling compounds during the initial hours post-excision in the induction phase of ARD could alleviate the stress conditions arising from the cuttings severance from the mother plant, ultimately enhancing the quality of rooted cuttings. In this project, we aimed to determine whether the exogenous application of melatonin, ascorbic acid, boron, or abscisic acid during the sticking and root development stages of ARD would influence adventitious root formation, thereby improving root growth and overall cutting quality. The experiment included ten foliar spraying treatments with a negative control (distilled water) and four compounds at different concentrations: melatonin (100 and 200 mu M), ascorbic acid (100 and 500 mu M), boron (15 and 30 mg center dot L-1), and abscisic acid (10 and 20 mu M). The root and shoot lengths and dry matter, number of leaves, leaf chlorophyll content, rootto-shoot ratio (based on dry matter), protein, amino acids, and nonstructural carbohydrate contents were measured. The results showed that most responses were dose-dependent. Treatments with boron, applied during sticking or root development stages, significantly improved root length, root dry matter, and increased sucrose and protein content compared to the untreated control, mainly by facilitating sugar transport. In contrast, treatments with melatonin, ascorbic acid, and abscisic acid produced less favorable results, especially at higher concentrations, with trends toward reduced growth, dry matter, and sugar accumulation. This study provides insight into the application of exogenous chemical compounds in ARD and highlights the potential role of stresssignaling molecules and antioxidants in optimizing root development for vegetative propagation.

An understanding of how amendments influence the sink-to-source relationship in leafy crops can be used to optimize plant resource allocation for enhanced growth and quality. Variations in growth rates and carbon pools across individual leaves or groups of leaves at similar developmental stages allow us to comprehend plant strategies of carbon allocation and partitioning. We hypothesized that products enhancing the carbon source-to-sink relationship during leaf development can increase growth and dry matter accumulation. This project aimed to determine whether exogenous applications of a cytokinin-B-Mo-based product during the leaf development of lettuce plants impact the carbon source-to-sink relationship, thus influencing plant growth and quality. The experiment was a complete randomized design with two treatments: a negative control and the application of the product twice during the growing cycle. Each experimental unit consisted of a deep-water culture reservoir with three lettuce plants. Destructive sampling was conducted five times throughout the cycle. At each sampling time (n = 4 per experimental run), the phenological stage was determined, and measurements of root and shoot length, root and shoot dry matter, leaf length, leaf width, leaf area, chlorophyll contents, and nonstructural carbon contents were performed. These data were used to estimate growth indices. The results indicated that the cytokinin-B-Mo-based product increased the number of true unfolded leaves by 1 ± 0.4 and the overall size of the lettuce head by 9%. The treated lettuce reached marketable size 4 days earlier than that of the control treatment. Statistically significant differences were observed in shoot and root dry matter accumulation and foliar length and width at some sampling points. Some growth indices indicate an increase in leaf surface area investment and enhanced conversion efficiency of assimilates into biomass in plants treated with the product. Plants exhibiting these alterations had higher sucrose and total soluble sugar contents. There was a noticeable pattern of higher concentrations of nonstructural carbohydrates, proteins, and amino acids in the leaves compared with those in the roots across all plants and treatments. Overall, the cytokinin-B-Mo-based product appears to strengthen the source-to-sink relationship during lettuce development, resulting in a high-quality plant within a shorter timeframe.

ABSTRACT Water quality classification systems aim to assess the overall risk of clogging in micro-irrigation systems. However, their ability to predict potential clogging based on water quality characteristics remains untested, particularly in controlled environment agriculture. This project aimed to evaluate if the existing classification systems could be used to identify the cause of clogging in micro-irrigation systems in greenhouses. Water from eight commercial greenhouses with reported clogging was analyzed for physical, chemical, and biological properties to rate the risk of clogging according to the classification systems. In general, iron and manganese from the fertilizers and high microbial load resulted in high ratings. However, the ratings lacked insight into the specific causes of clogging, disregarding interactions among chemical and microbial factors and qualitative characteristics of specific microbial phenotypes (e.g., production of polysaccharides or iron oxidation) that lead to clogging. Furthermore, the systems overemphasize nutrient levels typically used in greenhouse fertigation as the cause of clogging – which is not commonly observed in practice. Enhancing these systems requires parameters reflecting these interactions and microbial traits influencing clogging. Further research needs to develop these parameters in new systems with robust and precise thresholds in which emitter performance, profitability, and sustainability are affected.

Reusing irrigation water has technical, environmental, and financial benefits. However, risks are also associated with the accumulation of agrochemicals, in addition to ions, plant and food safety pathogens, and biofilm organisms. In this project, we measured the concentration of paclobutrazol (a persistent and widely used plant growth regulator) in recirculated water in greenhouses producing ornamental plants in containers. Solutions were collected from catchment tanks at nine commercial greenhouses across seven states in the United States in Spring and Fall 2014. Paclobutrazol was detected in all samples, with differences observed by season, greenhouse operation, paclobutrazol application method, and irrigation method. Across operations, the residual concentration of paclobutrazol was higher in spring for most greenhouses (ranging from 0 to 1100 µg·L −1 ) compared with the fall (ranging from 0 to 8 µg·L −1 ). The spray-drench application method resulted in the highest residual concentrations (up to 35 µg·L −1 ), followed by substrate drench (up to 26 µg·L −1 ) and foliage spray (concentrations under 3 µg·L −1 ). Residual concentrations were higher with overhead irrigation (up to 35 µg·L −1 ) compared with subirrigation systems (up to 15 µg·L −1 ). Our results indicate that paclobutrazol is likely to be a growth retardant risk in greenhouse operations recirculating water. A clear understanding of the risks associated with recirculated water intends to support the development and implementation of risk management strategies to ensure and promote safe use of recirculated water in greenhouses. Overall, the most effective preventative strategy is to ensure the use of the minimum amount of the a.i. necessary per unit of space and time.

The spatial distribution and diversity of plant pathogens and other microbial communities in commercial operations is the first step in identifying critical control points where crops may be at risk of disease. Our objective was to characterize the spatial variation of oomycete pathogens and bacteria across the production system of a greenhouse producing lettuce in hydroponics. We utilized DNA metabarcoding to identify oomycetes and 16S rRNA gene sequencing of bacteria from different production stages and sample types (surfaces, solutions, and roots) collected from a commercial greenhouse producing lettuce in deepwater culture. Pythium was the genus with the highest relative abundance (41 to 100%) across all production stages. P. dissotocum was detected in most samples, except for sowing and seedling surfaces and municipal water, where P. myriotylum was the most abundant species. Oomycete communities showed distinct clustering by production stages and sample types, where sowing and seedling surfaces and municipal water were separated from the rest. Proteobacteria had the highest relative abundance in the surfaces at the sowing (98%) and seedling (85%) stages. Municipal water was the only sample with less than 20% relative abundance of Proteobacteria and dominated by Cyanobacteria. Negative correlations between Pythium and 13 bacteria genera point to potential antagonists in hydroponics that should be further studied. Mapping the spatial variation of oomycetes and bacterial communities in a commercial greenhouse indicates that production stage and sample type influence microbial composition and potentially the risk to disease.

A large group of horticulture species are propagated vegetatively through shoot-tip cuttings harvested from stock plants and planted to form adventitious roots. Adventitious rooting leads to establishing a carbohydrate sink in the region of root regeneration that is highly dependent on energy and carbon skeletons. We hypothesized that the timing of exogenous applications of cytokinin (CK) and boron (B)–molybdenum (Mo)-based products during adventitious root development can affect the flow of sugars from leaves to sinks, carbon allocation to the adventitious roots, and the quality of rooted cuttings. During this project, we aimed to determine if the application time of a CK/B-Mo-based product during the adventitious root development of unrooted cuttings would impact the source-to-sink relationship and, hence, affect plug growth and quality. A sink-strengthening commercial product based on cytokinin, B, and Mo was applied at four plug development stages plus a negative control as follows: T1, plants without product (control); T2, sticking stage (starting 24 hours after the sticking); T3, callus formation stage; T4, root development stage; and T5, toning stage. The root and shoot lengths and dry matter, number of leaves, leaf chlorophyll content, root-to-shoot ratio (based on dry matter), and nonstructural carbohydrate contents were measured. The timing of the application of the product impacted the root development, quality of the cuttings, and nonstructural carbohydrate content. Product application during the adventitious root dedifferentiation and induction phases (T2) resulted in the shortest root and shoot lengths, lowest dry matter accumulation, lowest nonstructural carbohydrate contents, and some phytotoxicity. Application during the initiation phase (T3) resulted in greater root length, total dry matter, and total soluble sugar contents compared with the control. Application during the expression phase (T4) resulted in the largest root length and mass and the highest sucrose contents. Applying the product when the roots had grown and reached all the edges of the growing media (T5) did not have any benefits compared with the control. This study provides new insights into the application timing of exogenous CKs, B, and Mo to generate a well-toned rooted coleus cutting and potential explanations in relation to nonstructural carbohydrate metabolism.

Increasing demand on agricultural water resources have caused a greater need for the use of municipal recycled wastewater (MRW) globally. However, in the United States, greenhouse growers have been slow to use it in their greenhouse operations. In this study, we seek to understand the factors that motivate and limit use of MRW among US growers. Using national survey data from 2019 through 2020, we developed a logistic regression model to understand the many factors influencing growers’ willingness to use MRW on food crops. We find that MRW quality is a primary concern and that growers’ willingness to use MRW is shaped by their direct and indirect knowledge of MRW, garnered from their own and others’ experiences using it. Given these findings, improving adoption of MRW requires collective experiential learning opportunities that gather target audiences with educators, policymakers, end users, and local authorities to simultaneously provide hands-on experience tailored to growers’ particular knowledge and concerns with feedback from peers.

Chlorine is a disinfectant commonly used to treat water. The United States Environmental Protection Agency (USEPA) has set a standard limit of up to 4 mg·L−1 chlorine for drinking water. The objective of this project was to identify chlorine phytotoxicity thresholds on ‘Rex’ lettuce (Lactuca sativa) when the water source contained chlorine levels within the USEPA standard limits. The nutrient solution to grow lettuce was prepared with reverse osmosis–treated water treated with 0, 0.5, 1, 1.5, 2, and 4 mg·L−1 chlorine and then fertilizers were added. Lettuce plants were grown in a deep-water culture hydroponic system. Visual toxicity symptoms on leaves, relative leaf greenness, and fresh and dry biomass were measured. Our results indicate that irrigation water sources with ≥1 mg·L−1 chlorine used to prepare nutrient solutions can cause phytotoxicity in lettuce plants in just 3 days. Compared with the untreated control, lettuce shoot biomass was lower by 30%, 55%, 66%, 83%, and 92% at 0.5, 1, 1.5, 2, and 4 mg·L−1 of chlorine, respectively. Water sources with ≥ 1 mg·L−1 chlorine can cause significant marketable yield reduction in lettuce grown in deep-water culture.

Oomycetes and fungi were recovered from coconut coir and rockwool substrates where marijuana (Cannabis sativa L. cv. Silver and Citron) plants with root rot and wilt symptoms were grown in a commercial growing facility in Connecticut. The objectives of this study were to identify the isolates collected from these substrates, determine the pathogenicity of the isolates on hemp seedlings in vitro and in vivo, and evaluate the pathogens' sensitivity to mefenoxam. Pythium and Globisporangium isolates were identified by sequencing the mitochondrially-encoded cytochrome oxidase genes (COI and COII) and Fusarium sp. with the translation elongation factor (EF-1α) region and internal transcribed spacer region (ITS4 and ITS5) genes. Three isolates were identified as Globisporangium irregulare (formerly Pythium irregulare), 21 isolates were Pythium myriotylum, and one was Fusarium oxysporum. All the isolates tested were pathogenic to hemp plants in vitro and in vivo, with disease incidence between 6.7 and 100%. Inoculated plants were smaller by 32% or more compared with the non-inoculated control. On average, hemp plants infected with Pythium myriotylum produced the lowest biomass and relative greenness values. None of the Pythium and Globisporangium isolates were resistant to mefenoxam—all were sensitive to ≥5 μg·mL−1 mefenoxam. This is the first report of G. irregulare causing root rot on marijuana and hemp plants. The results of this study provide information about the characteristics of pathogens that can be found potentially in soilless substrates in controlled environment agriculture.

As climate change and agriculture burden water resources globally, there is a need for more efficient water use including irrigation with recycled water in greenhouses. While research has proven that properly treated recycled water can be safe for use, many growers still express concern. Underlying most studies on growers' perceptions is the assumption that they understand recycled water the same way scholars and policy makers do-as municipally treated wastewater. We question this assumption and explore whether the ways in which growers conceptualize recycled water is associated with the ways they perceive its usability. Our findings reveal that growers define recycled water in four different ways-captured water, treated water, recirculation and in a general sense as 'reuse'. These definitions do appear to suggest trends in the way recycled water is perceived by growers. While these definitions do not significantly affect growers' willingness to use, other factors such as prior experience using recycled water appear to be significant.

Pythium spp. are the causal agents of Pythium root rot and damping-off on microgreens. The objective of this project was to assess the efficacy of biofungicides on Pythium root rot and damping-off caused by Pythium aphanidermatwn and Pythium dissotocwn on microgreens in greenhouses. In the first experiment, arugula (Eruca saliva Mill.), kale (Brassica oleracea var. sabellica L), radish (Raphanus raphanistrum subsp. sativus L.), and mustard (Brassica juncea L. Czern) microgreens were treated with Companion* (Bacillus subtilis GB03), Triathlon BA* (Bacillus amyloliquefaciens D747), or RootShield Plus* (Trichoderma harzianum KRL-AG2 and Trichoderma virens G-41) in a hydroponic nutrient film technique system. Two days after treatment, the plants were inoculated with 3 x 10(5) zoospores of Pythium spp. After seven days, we measured root necrosis, damping-off incidence and severity, and plant biomass. All plants infected with Pythium spp. were smaller by 28% or more compared with non-inoculated plants. Overall disease was low, but biomass was lower in all treatments inoculated with Pythiwn spp. Arugula infected with Pythium spp. and treated with Triathlon BA* resulted in 8% lower disease incidence compared with the positive control, yet Triathlon BA* resulted in the highest root necrosis. On a separate experiment, arugula and mustard were grown in propagation trays, irrigated manually, and treated with the biofungicides mentioned above or Cease* (Bacillus subtilis QST 713). Arugula and mustard plants inoculated with Pythiwn spp. had 74.4% reduction of shoot dry weight. Arugula and mustard treated with Cease*, with and without Pythium spp., resulted in >= 59% more biomass compared with the untreated inoculated control. In the tray experiment, all the infected plants treated with biofungicides had more biomass than plants with no biofungicides. Results from this experiment suggest that microbial biofungicides can be introduced in nutrient solutions in nutrient film technique or applied in the irrigation to prevent Pythium root rot and damping-off in brassica microgreens. However, biofungicides can reduce plant biomass and growers may need to extend production time to achieve target yields.

The recent increased market demand for locally grown produce is generating interest in the application of techniques developed for controlled environment agriculture (CEA) to urban agriculture (UA). Controlled environments have great potential to revolutionize urban food systems, as they offer unique opportunities for year-round production, optimizing resource-use efficiency, and for helping to overcome significant challenges associated with the high costs of production in urban settings. For urban growers to benefit from CEA, results from studies evaluating the application of controlled environments for commercial food production should be considered. This review includes a discussion of current and potential applications of CEA for UA, references discussing appropriate methods for selecting and controlling the physical plant production environment, resource management strategies, considerations to improve economic viability, opportunities to address food safety concerns, and the potential social benefits from applying CEA techniques to UA. Author's viewpoints about the future of CEA for urban food production are presented at the end of this review.