Commercial Lettuce Research Articles

Silencing of RDR1 and RDR6 genes by a single RNAi enhances lettuce's capacity to express recombinant proteins in transient assays.

Enhanced recombinant protein expression was achieved in Salinas lettuce and commercial lettuce by designing a unique RNAi that knockdown the gene-silencing mechanism in transient assays. Improved yields of recombinant proteins (RP) are necessary for protein-production efficiency and ease of purification. Achieving high yield in non-tobacco plants will enable diverse plants to be used as hosts in transient protein-expression systems. With improved protein yield, lettuce (Lactuca sativa) could take the lead as a plant host for RP production. Therefore, this study aimed to improve RP production in lettuce var. Salinas by designing a single RNA interference (RNAi) construct targeting LsRDR1 and LsRDR6 using the Tsukuba system vector. Two RNAi constructs, RNAi-1 and RNAi-2, targeting common regions of LsRDR1 and LsRDR6 with 75% and 76% similarity, respectively, were employed to evaluate simultaneous gene silencing. Quantitative transcription analysis demonstrated that both RNAi constructs effectively knocked down LsRDR6 and LsRDR1, but not LsRDR2, at both 3 and 5days post-infiltration (dpi), with RNAi-1 exhibited slightly higher efficiency. Based on the protein yield, co-expression of RNAi-1 with enhanced green fluorescent protein (EGFP) increased EGFP expression by approximately 4.9-fold and 3.7-fold at 3dpi and 5dpi, respectively, compared to control. A similar but slightly lower increase (2.4-fold and 2.33-fold) was observed in commercial lettuce at 3and 5 dpi, respectively. To confirm these results, co-infiltration with Bet v 1, a major allergen from birch pollen, resulted in a 2.5-fold increase in expression in Salinas lettuce at 5 dpi. This study marks a significant advancement in enhancing transient protein production in lettuce, elevating its potential as a host for recombinant protein production.

A portable, easy-to-use paper-based biosensor for rapid in-field detection of fecal contamination on fresh produce farms

Laboratory-based nucleic acid amplification tests (NAATs) are highly sensitive and specific, but they require the transportation of samples to centralized testing facilities and have long turnaround times. During the Coronavirus Disease 2019 (COVID-19) pandemic, substantial advancement has been achieved with the development of paper-based point-of-care (POC) NAATs, offering features such as low cost, being easy to use, and providing rapid sample-to-answer times. Although most of the POC NAATs innovations are towards clinical settings, we have developed a portable, paper-based loop-mediated isothermal amplification (LAMP) testing platform for on-farm applications, capable of detecting Bacteroidales as a fecal contamination biomarker. Our integrated platform includes a drop generator, a heating and imaging unit, and paper-based biosensors, providing sensitive results (limit of detection 3 copies of Bacteroidales per cm2) within an hour of sample collection. We evaluated this integrated platform on a commercial lettuce farm with a concordance of 100% when compared to lab-based tests. Our integrated paper-based LAMP testing platform holds great promise as a reliable and convenient tool for on-site NAATs. We expect that this innovation will encourage the fresh produce industry to adopt NAATs as a complementary tool for decision-making in growing and harvesting. We also hope that our work can stimulate further research in the development of on-farm diagnostic tools for other agricultural applications, leading to improved food safety and technology innovation.

A Loop-Mediated Isothermal Amplification (LAMP) Assay for the Detection of Bremia lactucae in the Field.

A real-time loop-mediated isothermal amplification (LAMP) assay for the detection of Bremia lactucae, the causal pathogen of lettuce downy mildew, was developed and validated to aid in-field detection of airborne inoculum. Assay specificity was confirmed against a range of other pathogenic oomycete and fungal spp., and sensitivity of the assay for the detection of DNA extracted from sporangia was evaluated. The B. lactucae LAMP assay reliably detected DNA equivalent to 1 spore/reaction (16.7 pg DNA/reaction). Following extraction of DNA from Rotorod air samplers, to which sporangial suspensions were added, the assay reliably detected 25 sporangia/Rotorod. Detection of airborne inoculum of B. lactucae collected through the season from air samplers deployed in-field in plots infected with B. lactucae and in commercial lettuce fields in Scotland over two growing seasons was assessed. The method can be deployed on samples collected from commercial lettuce production to inform disease management strategies and limit the use of unnecessary prophylactic pesticide applications.

Detection of Fusarium oxysporum f.sp. lactucae race 1 and 4 via race-specific real-time PCR and target enrichment

Fusarium oxysporum f.sp. lactucae (Fol) causes a vascular disease in lettuce that results in significant yield losses. Race-specific and sensitive real-time PCR assays were developed for Fol races 1 and 4, which are prevalent in Europe. Using genotyping-by-sequencing, unique DNA loci specific to each race were identified and subsequently used for the design of primers and hydrolysis probes. Two assays per race were developed to ensure specificity. The two assays of each race could be run in duplex format, while still giving a sensitivity of 100 fg genomic DNA for all assays. Sample preparation methods were developed for plant tissue, soil, and surfaces, with an extra enrichment step when additional sensitivity was required. By controlling the incubation conditions during the enrichment step, the real-time PCR signal could be matched to the number of spore equivalents in the original sample. When enriching naturally infested soil, down to six conidiospore equivalents L-1 soil could be detected. As enrichment ensures sensitive detection and focuses on living Fol propagules, it facilitates the evaluation of control measures. The developed detection methods for soil and surfaces were applied to samples from commercial lettuce farms and confirmed the prevalence of Fol race 4 in Belgium. Monitoring of soil disinfestation events revealed that despite a dramatic decrease in quantity, the pathogen could still be detected either immediately after sheet steaming or after harvesting the first new crop. The detection method for plant tissue was successfully used to quantify Fol in lettuce inoculated with race 1, race 4 or a combination of both. Under the temperature conditions used, race 4 was more aggressive than race 1, as reflected in larger amounts of DNA of race 4 detected in the roots. These newly developed assays are a promising tool for epidemiological research as well as for the evaluation of control measures.

Testing Cultivar-specific Tipburn Sensitivity of Lettuce for Indoor Vertical Farms

Low evaporative conditions in indoor (vertical) farms reduce mass-flow–driven transport of calcium (Ca), resulting in tipburn of lettuce. Lettuce tipburn symptoms develop along the margins of young leaves and the growing shoot tip, where necrotic tissue forms as a result of Ca deficiency. For indoor farms, lettuce tipburn poses a major economic risk because the crop becomes unmarketable as a result of its appearance. Difference in tipburn sensitivity among cultivars has been thought to be related to differences in growth rate, morphology, or anthocyanin production, whereas most commercial lettuce cultivars have been known to express tipburn symptoms in the indoor farm setting. We created a tipburn-inducing growing condition in walk-in growth chambers that limits plant potential transpiration rate while achieving relatively high growth rates, and examined 10 commercial cultivars selected for tipburn sensitivity. Selected cultivars differ in morphology (butterhead, romaine, and leafy type) and color (red or green; resulting from anthocyanin production). All cultivars expressed visually detectable tipburn symptoms 22 ± 2.6 days after transplanting, and varied tipburn rates of 7% to 41% of all leaves at the time of harvest (28 days after transplanting). Despite cultivar-specific variation, neither lettuce morphology nor anthocyanin content were significantly correlated with the incidence or severity of tipburn. However, cultivars recommended for “indoor” production by seed suppliers had less tipburn severity than those recommended for outdoor or both indoor and outdoor production systems. Although tipburn risk may vary under other environmental conditions, low evaporative conditions in this experiment caused tipburn symptoms in all tested cultivars at varying degrees of severity. Cultivar-specific average yield and tipburn severity were not correlated with the Ca concentrations in the inner leaves, suggesting that the amount of tissue Ca required to prevent tipburn is cultivar specific and not related to yield. Our selected tipburn-inducing condition was found to be effective in comparing tipburn sensitivity of lettuce cultivars for indoor farm settings, and similar fast-growing but low-evaporative conditions should be used to assess cultivars for indoor farm production.

Rhizosphere Bacteria Biofertiliser Formulations Improve Lettuce Growth and Yield under Nursery and Field Conditions

Rhizosphere bacteria can provide multiple benefits to plants, including increased nutrient supply, pathogen/disease control, and abiotic stress tolerance, but results from pot trials do not always translate to field conditions. This study tested whether rhizosphere biocontrol bacteria can also provide plant growth promotion and how benefits can be provided at a commercial farm. Commercial lettuce seeds and plants were treated with rhizosphere biocontrol bacteria Bacillus velezensis UQ9000N, B. amyloliquefaciens 33YE, Brevibacillus laterosporus 4YE, and Pseudomonas azotoformans UQ4510An. 33YE increased the head diameter, plant height, and fresh weight of the Green Moon cultivar, while 33YE, UQ4510An, and UQ9000N increased the fresh and dry weight of Liston, a more heat-tolerant cultivar, via a single seed treatment or repeat root treatments under nursery and field conditions across different inoculation schedules and growth stages. Significant growth promotion was also demonstrated when inoculating field plants after transplanting (in particular for 33YE). Applications of these microbial biostimulants to lettuce seeds or plantlets potentially enable earlier transplanting and earlier harvests. Repeat inoculations using irrigation water and long-lasting formulations may further advance the benefits of these biostimulants as microbial biofertilisers for plant growth promotions in the field.

Performance analysis of two typical greenhouse lettuce production systems: commercial hydroponic production and traditional soil cultivation.

Due to the shortage of land and water resource, optimization of systems for production in commercial greenhouses is essential for sustainable vegetable supply. The performance of lettuce productivity and the economic benefit in greenhouses using a soil-based system (SBS) and a hydroponic production system (HPS) were compared in this study. Experiments were conducted in two identical greenhouses over two growth cycles (G1 and G2). Three treatments of irrigation volumes (S1, S2, and S3) were evaluated for SBS while three treatments of nutrient solution concentration (H1, H2, and H3) were evaluated for HPS; the optimal levels from each system were then compared. HPS was more sensitive to the effects of environmental temperature than SBS because of higher soil buffer capacity. Compared with SBS, higher yield (more than 134%) and higher water productivity (more than 50%) were observed in HPS. We detected significant increases in ascorbic acid by 28.31% and 16.67% and in soluble sugar by 57.84% and 32.23% during G1 and G2, respectively, compared with SBS. However, nitrate accumulated in HPS-grown lettuce. When the nutrient solution was replaced with fresh water 3 days before harvest, the excess nitrate content of harvested lettuce in HPS was removed. The initial investment and total operating cost in HPS were 21.76 times and 47.09% higher than those in SBS, respectively. Consideration of agronomic, quality, and economic indicators showed an overall optimal performance of the H2 treatment. These findings indicated that, in spite of its higher initial investment and requirement of advanced technology and management, HPS was more profitable than SBS for commercial lettuce production.

Epidemiology and Economic Impact of Impatiens Necrotic Spot Virus: A Resurging Pathogen Affecting Lettuce in the Salinas Valley of California.

The Orthotospovirus impatiens necrotic spot virus (INSV) is a thrips-transmitted pathogen of lettuce that has rapidly emerged as a serious threat to production in the Salinas Valley of Monterey County, California. As a first step toward understanding the severity of the virus, we utilized Spatial Analysis by Distance IndicEs (SADIE) to characterize the distribution and progression of INSV outbreaks and thrips infestations in two commercial lettuce fields. In both fields, INSV incidence rapidly increased from 15.86% ± 1.77 to 80.24% ± 2.60 over the course of 7 weeks and aggregated at specific edges in both fields as early as 3 weeks after planting (Ia = 1.63, Pa = 0.0100, and Ia = 1.53, Pa = 0.0300). In one of the fields, thrips populations aggregated in areas that also experienced the most INSV (Ia = 1.2435, Pa = 0.0400, week 3; Ia = 1.4815, Pa < 0.0001, week 6; Ia = 1.5608, Pa < 0.0001, week 9), while in the second field, thrips were distributed randomly despite the aggregated effects that were observed for INSV incidence. Economic analysis estimated that the virus accounted for over $475,000 in losses for the two fields, while stakeholder surveys documented over 750 fields that experienced INSV infection during the 2021 season in Monterey County alone. These studies enhance our knowledge on the epidemiology of thrips and INSV under current lettuce production practices in the Salinas Valley, while elucidating the economic consequences and broader challenges that are associated with managing thrips-transmitted viruses.

Lettuce Production in Intelligent Greenhouses-3D Imaging and Computer Vision for Plant Spacing Decisions.

Recent studies indicate that food demand will increase by 35-56% over the period 2010-2050 due to population increase, economic development, and urbanization. Greenhouse systems allow for the sustainable intensification of food production with demonstrated high crop production per cultivation area. Breakthroughs in resource-efficient fresh food production merging horticultural and AI expertise take place with the international competition "Autonomous Greenhouse Challenge". This paper describes and analyzes the results of the third edition of this competition. The competition's goal is the realization of the highest net profit in fully autonomous lettuce production. Two cultivation cycles were conducted in six high-tech greenhouse compartments with operational greenhouse decision-making realized at a distance and individually by algorithms of international participating teams. Algorithms were developed based on time series sensor data of the greenhouse climate and crop images. High crop yield and quality, short growing cycles, and low use of resources such as energy for heating, electricity for artificial light, and CO2 were decisive in realizing the competition's goal. The results highlight the importance of plant spacing and the moment of harvest decisions in promoting high crop growth rates while optimizing greenhouse occupation and resource use. In this paper, images taken with depth cameras (RealSense) for each greenhouse were used by computer vision algorithms (Deepabv3+ implemented in detectron2 v0.6) in deciding optimum plant spacing and the moment of harvest. The resulting plant height and coverage could be accurately estimated with an R2 of 0.976, and a mIoU of 98.2, respectively. These two traits were used to develop a light loss and harvest indicator to support remote decision-making. The light loss indicator could be used as a decision tool for timely spacing. Several traits were combined for the harvest indicator, ultimately resulting in a fresh weight estimation with a mean absolute error of 22 g. The proposed non-invasively estimated indicators presented in this article are promising traits to be used towards full autonomation of a dynamic commercial lettuce growing environment. Computer vision algorithms act as a catalyst in remote and non-invasive sensing of crop parameters, decisive for automated, objective, standardized, and data-driven decision making. However, spectral indexes describing lettuces growth and larger datasets than the currently accessible are crucial to address existing shortcomings between academic and industrial production systems that have been encountered in this work.

Investigating the pilot-scale performance of a hydroponic nutrient solution as potential draw solution for fertilizer drawn forward osmosis and hydroponic agriculture of lettuce

The objective of this research is to test the feasibility of a large-scale application of fertilizer drawn forward osmosis using a concentrated hydroponic nutrient solution as the draw solution. This large-scale application will help to mitigate the ever-growing issue of freshwater resources, by providing an alternative source of freshwater for agriculture. This method can then be used to grow crops hydroponically in arid regions that have access to both brackish groundwater and freshwater. The nutrient solution was prepared by dissolving industrial-grade fertilizer salts in dechlorinated tap water and was tested as a draw solution (DS) on a pilot-scale forward osmosis membrane module. The feed solution (FS) for the process was NaCl dissolved in dechlorinated tap water, in a 10 g/L (10% w/w) NaCl concentration to represent the salinity level of brackish groundwater. The performance of the draw solution was measured based on the water flux, water recovery, specific solute flux, and salt rejection. Two hydroponic basins were utilized to hydroponically grow lettuce. The first basin was grown using a commercial hydroponic nutrient solution, while the other basin was grown using the diluted draw solution from the pilot-scale. The growth of the lettuce in both basins was compared based on wet and dry weights of the stem, percent reduction in weight by drying, total length, stem length, and the ratio between stem and total lengths. Results showed that average water flux on the pilot-scale was found to be 1.11 L/m2/hr (LMH), while it was found to be 7.7 LMH in previous research on the bench-scale; this is in line with previous experiments conducted on both bench-scale and pilot-scale forward osmosis. The highest value specific reverse solute flux on the pilot-scale was found to be 7.48 g/m2/h for the K+ ion, which is also comparable to the results obtained on the bench-scale. Finally, salt rejection was found to be high, the lowest value was 90.7%, indicating high membrane selectivity against feed ions. The lettuce grown hydroponically using the resultant diluted draw solution from the pilot-scale was comparable to the lettuce grown using a commercial nutrient solution, with the draw solution lettuce being 16.23% less in terms of weight than the commercial lettuce, and 27.18% in stem length. This decrease in size and weight of the lettuce grown with the diluted draw solution can be attributed to the ratio of macro- and micro-nutrients in the Resh Florida/California solution not being optimized for the species of lettuce grown (loose leaf). It was concluded that concentrated hydroponic nutrient solution is a valid draw solution for large-scale fertilizer drawn forward osmosis, and this application mitigates some of the drawbacks of fertilizer drawn forward osmosis and increases the feasibility of large-scale application of forward osmosis as a desalination technology.Graphical abstract

Preemergence and postemergence spiny amaranth (Amaranthus spinosus) and common lambsquarters (Chenopodium album) control in lettuce on organic soils

AbstractSuccessful weed management, particularly use of chemical control, is very important for commercial lettuce production on organic soils in the Everglades Agricultural Area in south Florida. Field experiments were conducted in 2016 and 2017 to determine the efficacy of herbicides (pronamide, bensulide, imazethapyr, or oxyfluorfen) applied preemergence (PRE) either alone or followed by a postemergence (POST) application of imazethapyr for weed control and lettuce (romaine and iceberg) yield. Preemergence-applied oxyfluorfen (0.56 kg ha−1) resulted in significant lettuce injury, including stand loss, while PRE applications of pronamide (4.44 kg ha−1), bensulide (5.6 and 10.1 kg ha−1), or imazethapyr (0.035 g ha−1) resulted in transient lettuce injury and no significant stand loss. Similarly, PRE-applied pronamide, bensulide, and imazethapyr followed by POST-applied imazethapyr did not result in significant lettuce stand loss or injury. When contrasted as a group, PRE-applied herbicides followed by a POST application of imazethapyr provided better spiny amaranth and common lambsquarters control compared with PRE-applied herbicides or POST-applied imazethapyr-only treatments. Lettuce yield was highest with PRE herbicides followed by POST imazethapyr compared with PRE herbicides or POST-applied imazethapyr-only treatments, indicating a yield benefit of having a PRE followed by POST herbicide weed control program in lettuce grown on organic soils. However, oxyfluorfen is not an option for lettuce on organic soils because of unacceptable stand reduction and crop injury. Whether to apply pronamide, bensulide, or imazethapyr PRE followed by a POST application of imazethapyr for broadleaf weed control in lettuce on organic soils depends on the species present, cost, and ease of application.

Sporobolomyces lactucae sp. nov. (Pucciniomycotina, Microbotryomycetes, Sporidiobolales): An Abundant Component of Romaine Lettuce Phylloplanes.

Shifts in food microbiomes may impact the establishment of human pathogens, such as virulent lineages of Escherichia coli, and thus are important to investigate. Foods that are often consumed raw, such as lettuce, are particularly susceptible to such outbreaks. We have previously found that an undescribed Sporobolomyces yeast is an abundant component of the mycobiome of commercial romaine lettuce (Lactuca sativa). Here, we formally describe this species as Sporobolomyces lactucae sp. nov. (Pucciniomycotina, Microbotryomycetes, and Sporidiobolales). We isolated multiple strains of this yeast from commercial romaine lettuce purchased from supermarkets in Illinois and Indiana; additional isolates were obtained from various plant phylloplanes in California. S. lactucae is a red-pigmented species that is similar in appearance to other members of the genus Sporobolomyces. However, it can be differentiated by its ability to assimilate glucuronate and D-glucosamine. Gene genealogical concordance supports S. lactucae as a new species. The phylogenetic reconstruction of a four-locus dataset, comprising the internal transcribed spacer and large ribosomal subunit D1/D2 domain of the ribosomal RNA gene, translation elongation factor 1-α, and cytochrome B, places S. lactucae as a sister to the S. roseus clade. Sporobolomyces lactucae is one of the most common fungi in the lettuce microbiome.

Postharvest Changes in the Nutritional Properties of Commercial and Traditional Lettuce Varieties in Relation with Overall Visual Quality

Nowadays the cultivation and consumption of traditional lettuce varieties are growing as they are particularly appealing to consumers for their diversity, and high nutraceutical quality. However, lettuce is a highly perishable product, which results in significant nutritional loss from harvest to final consumers. In this work, the content of some bioactive compounds (chlorophylls, carotenoids, anthocyanins, ascorbic acid, phenols), overall antioxidant capacity and mineral content was monitored in five landraces and four commercial lettuce varieties to compare their variation during the storage period. Visual characterization was conducted during the postharvest period, as was the determination of the parameters indicative of oxidative stress, to establish the preservation capacity of their physico-chemical attributes. As a general trend, lettuce varieties showed individualized behavior during the postharvest period, which was not necessarily better in the commercial varieties compared to the landraces. Of all the varieties, landrace L10 stood out for not showing excessive variations in its general appearance or nutritional quality throughout its life cycle. However, in terms of initial concentration of bioactive compounds, the reddest varieties (CL4 and L11) stand out. These results indicate variability among varieties, which emphasizes the potential of lettuce landraces in postharvest practices.

Genome-wide core sets of SNP markers and Fluidigm assays for rapid and effective genotypic identification of Korean cultivars of lettuce (Lactuca sativa L.).

Lettuce is one of the economically important leaf vegetables and is cultivated mainly in temperate climate areas. Cultivar identification based on the distinctness, uniformity, and stability (DUS) test is a prerequisite for new cultivar registration. However, DUS testing based on morphological features is time-consuming, labor-intensive, and costly, and can also be influenced by environmental factors. Thus, molecular markers have also been used for the identification of genetic diversity as an effective, accurate, and stable method. Currently, genome-wide single nucleotide polymorphisms (SNPs) using next-generation sequencing technology are commonly applied in genetic research on diverse plant species. This study aimed to establish an effective and high-throughput cultivar identification system for lettuce using core sets of SNP markers developed by genotyping by sequencing (GBS). GBS identified 17 877 high-quality SNPs for 90 commercial lettuce cultivars. Genetic differentiation analyses based on the selected SNPs classified the lettuce cultivars into three main groups. Core sets of 192, 96, 48, and 24 markers were further selected and validated using the Fluidigm platform. Phylogenetic analyses based on all core sets of SNPs successfully discriminated individual cultivars that have been currently recognized. These core sets of SNP markers will support the construction of a DNA database of lettuce that can be useful for cultivar identification and purity testing, as well as DUS testing in the plant variety protection system. Additionally, this work will facilitate genetic research to improve breeding in lettuce.

Characterization of Multidrug-Resistant Escherichia coli Isolated from Two Commercial Lettuce and Spinach Supply Chains

Leafy green vegetables have increasingly been reported as a reservoir of multidrug-resistant pathogenic Enterobacteriaceae, with Shiga toxin-producing Escherichia coli frequently implicated in disease outbreaks worldwide. This study examined the presence and characteristics of antibiotic resistance, diarrheagenic virulence genes, and phylogenetic groupings of E. coli isolates (n = 51) from commercially produced lettuce and spinach from farms, through processing, and at the point of sale. Multidrug resistance was observed in 33 (64.7%) of the 51 E. coli isolates, with 35.7% (10 of 28) being generic and 100% (23 of 23) being extended-spectrum β-lactamase/AmpC producing. Resistance of E. coli isolates was observed against neomycin (51 of 51, 100%), ampicillin (36 of 51, 70.6%), amoxicillin (35 of 51, 68.6%), tetracycline (23 of 51, 45%), trimethoprim-sulfamethoxazole (22 of 51, 43%), chloramphenicol (13 of 51, 25.5%), Augmentin (6 of 51, 11.8%), and gentamicin (4 of 51, 7.8%), with 100% (51 of 51) susceptibility to imipenem. Virulence gene eae was detected in two E. coli isolates from irrigation water sources only, whereas none of the other virulence genes for which we tested were detected. Most of the E. coli strains belonged to phylogenetic group B2 (25.5%; n = 13), B1 (19.6%; n = 10), and A (17.6%; n = 9), with D (5.9%; n = 3) less distributed. Although diarrheagenic E. coli was not detected, antibiotic resistance in E. coli prevalent in the supply chain was evident. In addition, a clear link between E. coli isolates from irrigation water sources and leafy green vegetables through DNA fingerprinting was established, indicating the potential transfer of E. coli from irrigation water to minimally processed leafy green vegetables.

A simple graphene modified electrode for the determination of antimony(III) in edible plants and beverage

Antimony(III) is a rare electroactive specie present on Earth, whose concentration is not typically determined. The presence of high concentrations of antimony is responsible for a variety of diseases, which makes it desirable to find convenient and reliable methods for its determination. We have developed a convenient glassy carbon modified electrode with electroreduced graphene oxide GC/rGO for the first time determination of Sb(III) in commercial lettuce, celery, and beverages. The surface of the electrode was characterized by scanning electron microscopy (SEM) and cyclic voltammetry, indicating a heterogeneous and rough surface with a real area of 0.28 cm2, which is ~2.5 times the area of GC. The optimal chemical and electrochemical parameters used were: sodium acetate buffer (pH = 4.3), an accumulation potential of −1.0 V and an accumulation time of 150 s. The analytical validation was developed evaluating the linear range (10–60 µg L−1), limit of detection (2.5 µg L−1), accuracy, repetibility and reproducibility with satisfactory results (relative standard deviation (RSD) values lower than 10%). All the analyzes performed in real samples by stripping voltammetry were compared with GF-AAS, showing statistically similar values, demonstrating that GC/rGO could be effectively applied in the analysis of food samples.

Genetic Variation in Root Architectural Traits in Lactuca and Their Roles in Increasing Phosphorus-Use-Efficiency in Response to Low Phosphorus Availability.

Low phosphorus (P) bioavailability in the soil and concerns over global P reserves have emphasized the need to cultivate plants that acquire and use P efficiently. Root architecture adaptation to low P can be variable depending on species or even genotypes. To assess the genetic variability of root architectural traits and their responses to low P in the Lactuca genus, we examined fourteen genotypes including wild species, ancient and commercial lettuce cultivars at low (LP, 0.1 mmol. L–1) and high P (HP, 1 mmol. L–1). Plants were grown in cylindrical pots adapted for the excavation and observation of root systems, with an inert substrate. We identified substantial genetic variation in all the investigated root traits, as well as an effect of P availability on these traits, except on the diameter of thinner roots. At low P, the main responses were a decrease in taproot diameter, an increase in taproot dominance over its laterals and an increase in the inter-branch distance. Although the genotype x P treatment effect was limited to root depth, we identified a tradeoff between the capacity to maintain a thick taproot at low P and the dominance of the taproot over its laterals. Regardless of the P level, the phosphorus-use-efficiency (PUE) varied among lettuce genotypes and was significantly correlated with total root biomass regardless of the P level. As taproot depth and maximum apical diameter were the principal determinants of total root biomass, the relative increase in PUE at low P was observed in genotypes that showed the thickest apical diameters and/or those whose maximal apical diameter was not severely decreased at low P availability. This pre-eminence of the taproot in the adaptation of Lactuca genotypes to low P contrasts with other species which rely more on lateral roots to adapt to P stress.

Estimation of the Allowable Concentration of Chlorides in Soaking Effluents from the Tanning Process Using Ecotoxicological Tools

The use of sodium chloride for the preservation of pelts and skins destined for tanning is a very widespread technique in Peru, therefore the quantities used of this salt represent high concentrations of chlorides in the liquid effluents that are generated, which can affect the environmental quality of ecosystems and human health. The present study aimed to estimate an allowable concentration of chlorides in tanning effluents using ecotoxicological tools so that it would serve as a guide for the tanning industry and the authorities in their efforts to establish better conservation practices and effluent control parameters, which are currently absent from national environmental legislation. The permissible concentration of chlorides was determined using bioassays with seeds of Lactuca sativa species (lettuce), which was exposed to soaking effluents obtained from local tanneries. The studied species was determined based on sensitivity tests to zinc sulfate (ZnSO4) applied to three commercial lettuce species. The selected lettuce seed presented a germination rate higher than 90%, a CV lower than 30% and an IC50 of 38.97 mg/L of Zn+2 with a confidence interval between 19.30 mg/L and 58.65 mg/L of Zn+2. The admissible guide concentration determined for chlorides in soaking effluents from IC50 was 582.30 mg/L with a minimum value of 258.45 mg/L and a maximum of 906.15 mg/L. Additionally, because of the presence of other pollutants in the soaking effluents, such as bactericides, organic matter, enzymes and salts added in soaking process, tests with synthetic solutions of sodium chloride at the same concentrations of the soaking effluents were conducted, to evaluate the effect produced by those substances.

Daily lettuce supplements promote foraging behavior and modify the gut microbiota in captive frugivores.

For captive primates, greater provisioning of leafy greens or foliage can promote natural foraging behavior while boosting fiber intake. Recalcitrant fiber, although minimally available to endogenous metabolism, is readily fermented into nutrients by gut microbes. Whereas most primates in captivity consume fiber-limited diets and harbor imbalanced gut microbiota compared to their wild conspecifics, the importance of fiber provisioning to primate gut microbiota has predominately been studied in folivores. We, therefore, determined if commercial lettuce could be used to encourage foraging behavior and modify the gut microbiota of captive frugivores. We provisioned ruffed lemurs (Varecia rubra and V. variegata) with romaine lettuce, on top of the standard dietary fare, for 10 consecutive days. Before and across the period of lettuce supplementation, we collected observational data of animal feeding and fecal samples for microbiome analysis, determined via amplicon sequencing. The ruffed lemurs and their gut microbes responded to lettuce provisioning. In particular, younger animals readily ate lettuce and showed no decline in consumption across study days. When controlling for the effects of host species and social-group membership, lettuce consumption shifted the composition of the gut microbiome away from each lemur's own baseline, an effect that became stronger as the study progressed. In the final study days, Ruminococcaceae UCG-008 and Akkermansia, microbes typically and respectively associated with fiber metabolism and host health, were significantly enriched in the consortia of lettuce-provisioned subjects. Ultimately, the routine offering of lettuce, leafy greens, or foliage to captive frugivores may benefit animal wellbeing.

Behavior of three lettuce cultivars in a hydroponic system

The cultivation of lettuce in a hydroponic system is an alternative to optimize the production. Lettuce is an important food, being one of the most consumed vegetables in Brazil. The objective of this study was to evaluate the agronomic behavior of commercial cultivars of lettuce under a single nutritive solution in a hydroponic system. The experiment was carried out under greenhouse conditions. The experimental design was completely randomized, with five replicates. The treatments were composed of commercial lettuce cultivars (Americana Great Lakes, Rafaela-Americana, and Simpson Black Seed). At the time of harvest, the following parameters were evaluated: number of leaves, length of leaves and roots, fresh mass of shoot and root, and stem diameter. The collected data were submitted to an ANOVA. The cv. Rafaela-Americana presented higher leaf length. The evaluated cultivars did not present significant differences in the number of leaves, aerial green mass, green root mass, root length, and stem diameter. The cultivars showed similar variations in the number of leaves, aerial green mass, green root mass, root length, and stem diameter. The cultivar Rafaela-Americana presented a superior performance in the development of leaf length regarding the other cultivars.