Leaf Lettuce Research Articles

Inoculum Preparation Conditions Influence Adherence of Salmonella enterica Serovars to Red Leaf Lettuce (Lactuca sativa)

Salmonella enterica has been increasingly linked to outbreaks involving consumption of fresh produce. Although researchers have identified genes whose products are involved in mediating S. enterica-plant interactions, the use of various experimental approaches, serovars, and plant types has generated variable and conflicting data. The purpose of this study was to determine whether conditions under which inocula are prepared for in vitro plant interaction studies influence the outcome of these studies. Seven S. enterica serovars were grown in media that differed in salinity and physical state with incubation at 25 or 37°C. These cultures were then used to inoculate red leaf lettuce, and adherent microbes were subsequently recovered. Although all Salmonella serovars were influenced by inoculum preparation conditions, the amount of variation differed. Analysis of pooled serovar data revealed that inocula prepared from either agar plates or biphasic cultures had higher levels of interaction with red leaf lettuce than those prepared from broth cultures. Incubation at 37°C enhanced adherence after 30 s or 5 days of contact time, and adherence after 1 h of contact time was increased in low-salt medium. Broth inoculum cultures were highly influenced by medium salinity and incubation temperature, whereas plate and biphasic inoculum cultures were only minimally affected. Therefore, inocula prepared from bacteria grown on plates or in biphasic culture would be most suitable for evaluation of strategies used to interfere with plant-Salmonella interactions. However, pooled data mask serovar-specific responses, and care should be taken when extrapolating these findings to individual serovars. The previous association of a serovar with outbreaks involving leafy greens was not correlated with levels of interaction with red leaf lettuce, suggesting that the occurrence of these serovars in or on these commodities does not reflect their fitness in the plant environment.

Reduction of Norovirus Surrogates Alone and in Association with Bacteria on Leaf Lettuce and Tomatoes During Application of Aqueous Ozone.

Retail foodservice establishments (FSE) frequently utilize washes with sanitizing agents during fresh produce preparation. This study evaluated the efficacy of ozonated water on the inactivation of viruses, bacteria, and viruses in association with bacteria on produce surfaces. Boston bibb lettuce (BB) and cherry tomatoes were spot inoculated with viruses (murine norovirus (MNV) and MS2 bacteriophage), bacteria (Enterobacter cloacae and Bacillus cereus), or MNV associated with E. cloacae or B. cereus. Following inoculation, produce was held at 4°C for 90min (virus, virus + bacteria) or 24h (virus, bacteria) prior to treatment. A batch wash ozone sanitation system (BWOSS) was prepared with ice (3-5°C) and 0.5ppm initial ozone concentration or no ozone. Produce samples were treated for 40min with an ozonated water (0.86-0.99ppm) or water-only wash with samples taken every 10min. Samples were processed for microbial recovery, and plaque forming units (PFU) and colony forming units remaining on the produce were determined. Although microbial reductions of 99 to 99.99% were achieved during ozone treatments, few statistically significant differences (P > 0.1) were detected when comparing the ozonated water to water-only wash. Notably, a significant difference (P = 0.009) in log reduction of MNV + bacteria and MNV alone on BB was observed after 40min ozonated water wash. Specifically, MNV with B. cereus achieved a 1-log greater reduction (2.60 log PFU/ml) compared to MNV alone (1.63 log PFU/ml). Overall, washing produce in ozonated water did not significantly increase microbial inactivation compared to water alone under the conditions presented here. Variables impacting ozone wash effectiveness should be considered when implementing produce wash sanitation systems within FSE.

Red and blue wavelengths affect the morphology, energy use efficiency and nutritional content of lettuce (Lactuca sativa L.)

Since red (R) and blue (B) LED light has different quantum efficiency and photoelectric conversion efficiency, mixed RB with different proportions of R and B results in varied energy consumption. In order to improve the energy use efficiency of the closed-type plant production systems, the effects of R and B proportions on the electric use efficiency (EUE), light use efficiency (LUE) as well as the quality of butter leaf lettuce were evaluated in this study. Lettuce seedlings were cultivated in a plant factory with artificial lighting (PFAL) and subjected to eleven combinations of R and B (100%R, 90%R, 80%R, 70%R, 60%R, 50%R, 40%R, 30%R, 20%R, 10%R, 0%R; the rest of the photons in each treatment were B) with the same total photosynthetic photon flux density (PPFD) and photoperiod (200 ± 3 μmol·m−2·s−1, 16 h) for 35 days. The results showed that palpable petiole distortion appeared when R proportion was more than 70% and the distortion was aggravated with the increase of R proportion. The highest EUE and LUE were both detected in lettuce under 90%R treatment, which were respectively 3.64% and 1.20%. The least number of photons and the least electricity amount required to produce 1 g dry weight of lettuce was respectively 2.92 mol and 1.67 MJ, which were both detected in lettuce treated with 90%R. The sucrose content in lettuce treated with more than 50%R was significantly higher than those treated with less than 50%R (50%R included). Lettuce treated with 80%R possessed the highest soluble sugar content as well as the lowest crude fiber and nitrate content (not significantly different with the minimum values). R proportion exceeding 50% in mixed RB light was beneficial to the accumulation of hexose and sucrose, as well as the decomposition of nitrate in lettuce. The vitamin C content in lettuce treated with 100%R was significantly higher than that in lettuce under other treatments in the study. On the whole, the study indicated that the proportions of R and B affected the energy use efficiency and quality of lettuce in closed plant factory, however the responses of plants to the proportions of R and B varied according to different indexes. Thus, some indexes of top priority should be determined before choosing the optimal proportions of R and B.

Evaluation of mercury bioavailability to vegetables in the vicinity of cinnabar mine

Knowledge of the concentration of the bioavailable forms of mercury in the soil is necessary, especially, if these soils contain above-limit total mercury concentrations. The bioavailability of mercury in soil samples collected from the vicinity of abandoned cinnabar mines was evaluated using diffusive gradients in the thin films technique (DGT) and mercury phytoaccumulation by vegetables (lettuce, spinach, radish, beetroot, carrot, and green peas). Mercury was accumulated primarily in roots of vegetables. The phytoaccumulation of mercury into edible plant parts was site-specific as well as vegetable species-specific. The mercury concentration in edible parts decreased in the order: spinach leaf ≥ lettuce leaf ≥ carrot storage root ≥ beetroot storage root > radish storage root > pea legume. The translocation index as well as the target hazard quotient indicate the possible usability of soils from the vicinity of abandoned cinnabar mines for planting pod vegetables (peas). A strong positive correlation (r = 0.75 to 0.92, n > 30, p < 0.05) was observed between mercury concentration in secondary roots, the storage roots, leaves of vegetables and the flux of mercury from soil to the DGT units, and the effective concentration of mercury in soil solutions.

Productive and agro-economic benefits in beet-lettuce intercropping under organic manuring and population densities

The use of a cropping system that provides producers with better land use, higher productivity per unit area, greater diversification in production, and consequently agro-economic advantages, has been the choice of vegetables producers. Therefore, the objective of this work was to evaluate the productive and agro-economic benefits of beet-lettuce intercropping under different equitable amounts of Merremia aegyptia and Calotropis procera biomass (20, 35, 50 and 65 t ha-1 on a dry basis) in different lettuce population densities (150, 200, 250, and 300 thousand plants ha-1), in two cropping years in semi-arid environment. In the cultures and in the intercropping, the production and its components and the agro-economic indexes were evaluated. The maximum production of beet commercial roots in intercropping with lettuce was obtained with a productivity of 33.77 t ha-1 in the amount of 65 t ha-1 of M. aegyptia and C. procera biomass incorporated into the soil and in the lettuce population density of 300 thousand plants per hectare, while the maximum lettuce leaf production was achieved with a productivity of 24.40 t ha-1 in the same combination of green manure amounts and lettuce population densities. The greatest agro-economic advantages of the beet intercropping with lettuce were achieved with a system productivity index (SPI) of 32.97 t ha-1, land equivalent coefficient (LEC) of 0.87 and a monetary equivalence ratio (MER) of 1.55, respectively, in the combination of 65 t ha-1 of M. aegyptia and C. procera biomass with a lettuce population density of 300 thousand plants per hectare.

Evaluation of Lettuce Growth, Yield, and Economic Viability Grown Vertically on Unutilized Building Wall in Dhaka City

Production of safe food in the densely populated areas of the developing countries is the most challenging issue due to the speedy urbanization, fragile food transportation facilities, and reduced farmlands. Given this background, a study was conducted to evaluate the agronomic properties and economic viability of lettuce grown vertically in the wall of building in Dhaka city, Bangladesh. Two lettuce cultivars (V1: Green wave and V2: New red fire) and three organic growing media (P1: 40% soil + 40% vermicompost + 20% coir; P2: 50% soil + 50% vermicompost; P3: 20% soil + 40% vermicompost + 40% spent mushroom compost) along with control (P0:100% soil) were used. The results revealed that plant height, leaf area, fresh weight, dry weight, and total yield of leaf lettuce were significantly increased when the green-leafed cultivar (VI) was grown in the P1 compared to all other treatments, but V2 got maximum sensory attribute scores when grown in the P1. Lettuce leaves grown in the formulated growing media (P1, P2, and P3) had higher microbial infestation whereas, a lower content occurred in the P0. The higher economic return was observed in V1P1. These results provided baseline information for further study on urban commercial vertical farming on the building walls. These demonstrate the agronomic and economic potential for vertical farming in densely populated areas but emphasize the need for optimized food safety strategies.

Balancing crop production and energy harvesting in organic solar-powered greenhouses

Summary Adding semitransparent organic solar cells (ST-OSCs) to a greenhouse structure enables simultaneous plant cultivation and electricity generation, thereby reducing the greenhouse energy demand. However, there is a need to establish the impact of such systems on plant growth and indoor climate and to optimize system tradeoffs. In this work, we consider plant growth under OSCs and system-relevant design. We evaluate the growth of red leaf lettuce under ST-OSC filters and compare the impact of three different OSC active layers that have unique transmittance. We find no significant differences in the fresh weight and chlorophyll content of the lettuce grown under these OSC filters. In addition, OSCs provide an opportunity for further light and thermal management of the greenhouse through device design and optical coatings. The OSCs can thus affect plant growth, power generation, and thermal load of the greenhouse, and this design trade space is reviewed and exemplified.

Plasmonic Sensor for Detection of β-Lactam Antibiotics based on the Conjugated Antibody with Gold Nanoparticles

This study aims to detect β-lactam antibiotics using a conjugated antibody with gold nanoparticles (GNPs). For this purpose, the gold nanoparticles synthesized from Chinese lettuce leaf extract (as reductant) were used for the colorimetric detection of β-lactam antibiotics (such as ampicillin, amoxicillin, penicillin G, oxacillin, and carbenicillin). XRD, FTIR spectroscopy, TEM, and dynamic light scattering were utilized to detect the crystallinity, to identify functional groups involved in the synthesis of GNPs, and to measure the size of the GNPs; pH 8 and a concentration of 8.4 μg of antibody at 1 mL GNPs solution were selected as the best pH and concentration of antibody for the conjugation of antibody with GNPs. The maximum wavelengths of the colloidal GNPs, conjugation of antibody with GNPs, and detection of antibiotics (from 1 nM to 1 mM) with GNPs–PAb were recorded using a micro-volume spectrophotometer system. The results indicated that the localized surface plasmon resonance spectrometer absorption wavelength of GNPs red-shifted with increasing concentration of β-lactam antibiotics. With increasing concentration of ampicillin, penicillin G, and carbenicillin, the wavelength of maximum changed, and after saturation of antibiotics concentration, the curve reaches a plateau. This indicated that the antibody showed similar behavior in the detection of these antibiotics. But regarding amoxicillin, the saturation concentration is much higher, indicating that the antibody was more specific for its detection. In contrast, for oxacillin, saturation occurred very soon, which demonstrated that the antibody had an extremely low detection capability for this antibiotic. Finally, the results showed that the antibody was sensitive to 1 nM of the five β-lactam antibiotics studied.

Quantification of gray mold infection in lettuce using a bispectral imaging system under laboratory conditions.

Gray mold disease caused by the fungus Botrytis cinerea damages many crop hosts worldwide and is responsible for heavy economic losses. Early diagnosis and detection of the disease would allow for more effective crop management practices to prevent outbreaks in field or greenhouse settings. Furthermore, having a simple, non‐invasive way to quantify the extent of gray mold disease is important for plant pathologists interested in measuring infection rates. In this paper, we design and build a bispectral imaging system for discriminating between leaf regions infected with gray mold and those that remain unharmed on a lettuce (Lactuca spp.) host. First, we describe a method to select two optimal (high contrast) spectral bands from continuous hyperspectral imagery (450–800 nm). We then explain the process of building a system based on these two spectral bands, located at 540 and 670 nm. The resultant system uses two cameras, with a narrow band‐pass spectral filter mounted on each, to measure the bispectral reflectance of a lettuce leaf. The two resulting images are combined using a normalized difference calculation that produces a single image with high contrast between the leaves’ infected and healthy regions. A classifier was then created based on the thresholding of single pixel values. We demonstrate that this simple classification produces a true‐positive rate of 95.25% with a false‐positive rate of 9.316% in laboratory conditions.

A Rapid Approach to Measure Extracted Chlorophyll-a from Lettuce Leaves using Electrical Impedance Spectroscopy

Chlorophyll-a is a highly measured metric in water quality and plant health monitoring. Current laboratory-based methods exploit spectroscopic techniques and require expensive instrumentation like spectrophotometer or fluorometer. In this work, a rapid approach has been proposed using electrical impedance spectroscopy (EIS) to measure chlorophyll-a that is extracted from lettuce leaves into 95% (v/v) ethanol. Multiple readings of 70 differently concentrated samples were taken, and the corresponding impedances were measured using the proposed EIS system by varying frequency from 1.5 to 7.5 kHz. Pearson coefficient, variance inflation factor (VIF), and backward elimination were used to identify the significant component of the frequency. Finally, a multiple linear regression model with 11 features in the range of 2.3 kHz to 4.7 kHz was chosen based on the lowest root mean square error (RMSE) and mean absolute error (MAE). The results show high index of positive determination of chlorophyll-a with the coefficient of determination being 0.932, RMSE of 1.05 μgL-1, and MAE of 0.904 μgL-1.

Composting Spent Mushroom Substrate from Agaricus bisporus and Pleurotus ostreatus Production as a Growing Media Component for Baby Leaf Lettuce Cultivation under Pythium irregulare Biotic Stress

Composts of spent mushrooms substrates can be an alternative for the partial replacement of peat as growing media in horticulture. Three mature composts from Agaricus bisporus (Ag), Pleurotus ostreatus (Pl), and 70% Ag:30% Pl (AgPl) production were used as partial components of peat growing media, used at a 1:4 compost:peat ratio for growing red baby leaf lettuce. They showed higher yields, between 3 and 7 times more than that for peat itself, even under the pressure of the plant pathogen Pythium irregulare. AgPl showed the higher suppressiveness (50%) against Pythium irregulare than Ag- (38%) or Pl- (15%) supplemented media. The combination of these raw materials and a suitable composting process is important for obtaining mature compost for use as a partial component of peat-based growing media.

Effects of brewer’s spent grain biochar on the growth and quality of leaf lettuce (Lactuca sativa L. var. crispa.)

The need for organic soil amendments is increasing in the Republic of Korea against the backdrop of increased soil acidification and nutrient losses. The pyrolysis of biomass produces biochar which not only increases soil productivity but also provides environmental benefits through carbon sequestration. The portion of the brewer’s spent grain (BSG) recycled is by far less than the amount generated, but pyrolysis can help to reverse this trend by turning BSG waste into a valuable soil amendment. The current study, therefore, evaluated the effects of brewer’s spent grain biochar (BBXXX) produced at three different temperatures of 300 °C, 500 °C and 700 °C on the yield and quality characteristics of the leaf lettuce as well as the effects on soil chemical properties through a pot experiment. Each of the BBXXX and BSG were added to the soil at two rates of 2% and 5% by weight. The pH and carbon content of the BBxxx increased with increasing pyrolysis temperatures and the trend was replicated in the soil upon biochar application i.e. the soil pH and carbon content increased alongside temperatures at which biochar was pyrolyzed. On the other hand, however, the soil electrical conductivity (EC) diminished with the increasing pyrolysis temperatures of the biochar applied. With regards to crop growth, the BB500 5% amendment produced the highest marketable yield of the leaf lettuce and while the lettuce grown on the control produced leaf lettuce with the lowest content of nitrate nitrogen, BB500 5% amendment generally produced the highest quality lettuce. The results indicate that BB500 performed agronomically better than the rest of the amendments and is thus recommended as an effective BSG recycling measure.

Decontamination of Escherichia coli O157:H7 on fresh Romaine lettuce using a novel bacteriophage lysin

Raw vegetables are a key food for a healthy diet, but their increased consumption brings a higher risk for foodborne disease. Contamination of salad greens with Shiga toxin-producing Escherichia coli (STEC) O157:H7 has caused severe disease and important economic losses almost yearly in the United States over the last 10 years. To curb the risk of infections from contaminated produce, approaches based on bacterial virus – commonly known as bacteriophage or phage – have recently started to draw interest among other antimicrobial strategies. Phages enter bacterial cells to reproduce and cause cellular lysis to release their phage progeny at the end of their infection cycle. This lytic effect is caused by lysins, phage-encoded enzymes that have evolved to degrade the bacterial cell wall resulting in hypotonic lysis. When applied externally in their purified form, such enzymes are able to kill sensitive bacteria on contact in a similar way. Their unique bactericidal properties have made lysins effective antimicrobial agents in a variety of applications, from treating multidrug-resistant infections in humans to controlling bacterial contamination in several areas, including microbiological food safety. Here we describe a novel lysin, namely PlyEc2, with potent bactericidal activity against key gram-negative pathogens including E. coli, Salmonella, Shigella, Acinetobacter and Pseudomonas. PlyEc2 displayed high bactericidal activity against STEC to a concentration of 12.5 μg/ml under different pH conditions. This lysin was also able to reduce the bacterial titer of several pathogenic strains in vitro by more than 5 logarithmic units, resulting in complete sterilization. Importantly, PlyEc2 proved to be a powerful produce decontamination agent in its ability to clear 99.7% of contaminating STEC O157:H7 in our Romaine lettuce leaf model. PlyEc2 was also able to eradicate 99.8% of the bacteria contaminating the washing solution, drastically reducing the risk of cross-contamination during the washing process. A sensory evaluation panel found that treatment with PlyEc2 did not alter the visual and tactile quality of lettuce leaves compared to the untreated leaves. Our study is the first to describe a highly effective lysin treatment to control gram-negative pathogenic contamination on fresh lettuce without the addition of membrane destabilizing agents.

Effect of modified atmosphere packaging on the mechanical properties of lettuce during shelf life in cold storage

Lettuce is a perishable vegetable that its shelf life is limited by detrimental texture changes and enzymatic activities during postharvest storage. One of solutions that can be used in storage and distribution of this product is modified atmosphere packaging (MAP). But its effects on the mechanical properties of the product have not been studied. This information would be beneficial in inspection of eating quality and later processing such as cutting and shredding. This research aimed to study effect of active MAP technology on the postharvest mechanical properties of lettuce at different storage periods. It was found that MAP had a significant effect on the tension property of the lettuce leaf. MAP treatment preserved the brittleness of the specimens during storage, but the control ones lost their brittleness and tolerated greater tension. Stiffness and rupture energy were significantly affected by MAP with P values of 0.01 and 0.05, respectively. Also, stiffness of the MAP-treated samples was higher than the control at the same storage time. The findings are due to reducing respiration, transpiration and bacterial growth by MAP which delays nutrient decomposition and maintains the original color and texture.

Supplemental UV-A and UV-B Affect the Nutritional Quality of Lettuce and Tomato: Health-Promoting Phytochemicals and Essential Nutrients

UV radiation plays an important role not only in plant growth and development but also in the accumulation of essential nutrients and health-promoting phytochemicals in plants. The main objective of this study was to examine the effects of supplemental UV-A, UV-B, and UV-AB on the nutritional quality of lettuce (Lactuca sativa, cv. red leaf “New Red Fire” and green leaf “Two Star”) and tomato (Solanum lycopersicum L., cv. BHN-589) grown in a greenhouse. Supplemental UV radiation was provided by UV lamps 5 - 6 days prior to harvest. Supplemental UV-A produced higher accumulation of total phenolic compounds and higher antioxidant capacity in red leaf lettuce compared to other treatments. Overall, supplemental UV-A produced a stronger response than other UV treatments and control in the accumulation of many phenolic compounds including luteolin-7-glucoside, quecetin-3-glucoside, and apigenin-3-glucoside in red leaf lettuce. However, UV-B and UV-AB had a negative response in the accumulation of many phenolic compounds including chlorogenic acid, luteolin-7-glucoside, quercetin-3-glucoside, and apigenin-3-glucoside in both red and green leaf lettuce varieties. In tomato fruits, supplemental UV-A had no effect on their total phenolic concentration. However, supplemental UV-B radiation for 3 h or UV-AB radiation for 9 h exposure produced higher total phenolic concentration in the fruits compared to other supplemental UV treatments. Supplemental UV-AB (3 hexposure) was generally more effective than other UV treatments in increasing the accumulation of a number of phenolic compounds including chlorogenic acid, caffeic acid, chicoric acid, luteolin-7-glucoside, and other flavonoids in ripe tomato fruits. Supplemental UV-A produced higher accumulation of carotenoids including lutein and β-carotene than other supplemental UV treatments, while supplemental UV-AB increased the accumulation of lycopene in fully ripe tomatoes. With regard to the essential nutrients, green leaf lettuce was more responsive to the supplemental UV treatments than red leaf lettuce. All the supplemental UV treatments produced an increase in protein concentration in the leaves of green leaf lettuce. However, supplemental UV-AB produced a stronger response compared to the control and other UV treatments in increasing the accumulation of many nutrients including protein, phosphorus, potassium, sulfur, and zinc in green leaf lettuce “Two Star”. Supplemental UV-treatments did not affect the accumulation of any essential nutrients in fully ripe tomato fruits. The results show that supplemental UV enhances the nutritional quality of lettuce in relation to both health-promoting phytochemicals and essential nutrients. Similarly, supplemental UV enhances nutritional quality in tomato fruits with higher accumulation of both phenolic compounds and carotenoids than does the control treatment.

Genetic parameters and selection indexes for biofortified red leaf lettuce

Abstract: The objective of this work was to determine the genetic parameters and the efficiency of different selection indices for biofortified red leaf lettuce (Lactuca sativa var. crispa) lines with agronomic and nutritional potential. The experiment was carried out in a randomized complete block design with three replicates and 31 crisp-textured and red-tinted leaf lettuce genotypes: the Belíssima cultivar, with a low carotenoid content and rich in anthocyanins; and 30 lines from the cross between the Belíssima and Uberlândia 10000 cultivars, rich in carotenoids and with a low anthocyanin content. The assessed traits were: total green mass (g), stem diameter (cm), leaf count, plant diameter (cm), foliar temperature (°C), soil plant analysis development (SPAD) index, anthocyanin content (mg 100 g-1 sample), and bolting (days after sowing). To estimate selection gains, 12 genotypes were selected through selection indices. The traditional index proposed by Smith &amp; Hazel and the sum of ranks index by Mulamba &amp; Mock provided the highest selection gains in the biofortified lettuce. The coefficient of genotypic determination for leaf count, anthocyanin content, bolting, and SPAD index is of high magnitude.

Erratum: Interactive Effects of Photoperiod and Nitrogen Form on the Growth of Leaf Lettuce and Fluctuation of Nutrient Solution pH in Plant Factory Condition [Shokubutsu Kankyo Kogaku Vol. 32 (2020) No. 3 P 143–152

Erratum: Interactive Effects of Photoperiod and Nitrogen Form on the Growth of Leaf Lettuce and Fluctuation of Nutrient Solution pH in Plant Factory Condition [Shokubutsu Kankyo Kogaku Vol. 32 (2020) No. 3 P 143–152

Time-varying Photosynthetic Photon Flux Density and Relative Spectral Photon Flux Density Distribution to Improve Plant Growth and Morphology in Plant Factories with Artificial Lighting

In contrast to fluorescent lamps and high-power sodium lamps, the use of light-emitting diode (LED) lamps enables the control of not only photosynthetic photon flux density (PPFD) at the plant level, but also the relative spectral photon flux density distribution (RSPD) of light because of the variety, even at different times of day, of producible light emitted by LEDs of different types. Effects of the spectral photon flux density on plant growth and morphology have been investigated using several types of LEDs and plant species. However, few studies on lighting methods with time-varying PPFD or RSPD have been published to date. In this paper, we summarize the effects of time-varying PPFD on the net photosynthetic rate (Pn) and those of time-varying RSPD on plant growth and morphology. Detailed modeling studies have been conducted on the reactions of the photosynthetic pathway under time-varying PPFD at a cycle of milliseconds to seconds. The results of these modeling studies and actual measurements of Pn under pulsed light clearly indicate that pulsed light is not advantageous to improve Pn. Although the integrated PPFD of blue and red light was unchanged, the growth of leaf lettuce was promoted by asynchronous irradiation with blue light and red light compared with growth under simultaneous irradiation. We think that blue-light monochromatic irradiation promotes leaf elongation through leaf expansion as a primary factor in the enhancement of plant growth. In addition, changes in leaf photosynthetic capacity caused by blue-light monochromatic irradiation may be involved in plant growth promotion. An increasing number of studies have investigated the effects of time-varying RSPD on plants. However, the mechanisms underlying these effects remain to be elucidated.

Study of planting media and nutrition concentration on growth rate and yield of Lettuce (Lactuca sativa L.) in NFT hydroponic systems

Lettuce (Lactuca sativa L.) is a vegetable whose commercial value is quite good and the demand for lettuce has increased, including from hydroponic results. The use of rockwool planting media in hydroponics is often not available when needed and is expensive. Therefore it is necessary to study of using local planting media, such as: coconut fiber and rice husk charcoal as a replacement of rockwool planting media and whether the increased concentration of nutrients given to the planting media affects the rate of plant growth and yield of lettuce. The purpose of this research to study are interaction between planting media and nutrient concentrations (AB Mix) on the growth and development rate of plants, as well as the yield of lettuce hydroponically with the NFT system. The research was arranged in factorial with two factors using a Split Plot Design. The the main plot is AB Mix nutritional concentration (K) consisting of 3 levels (600 ppm, 900 ppm and 1200 ppm), while the subplot is a planting media (M) consisting of 3 treatment, namely: Rockwool, Coconut Fiber, and Rice Husk Charcoal. The results showed that the combination treatment of rice husk charcoal planting media and AB Mix concentration of 1200 ppm (M3K3) produced the best growth and increased the fresh weight of lettuce plants by 447,54% compared to the combination treatment of rockwool media and AB mix concentration of 600 ppm (M1K1). Rice Husk Charcoal planting media increases the growth rate of plant length and leaf area respectively by 26% and 81,54% compared to rockwool planting media. AB Mix concentration of 1200 ppm gives the best response and increases the growth rate of plant length and lettuce leaf area respectively by 367,5% and 165% compared to the concentration of 600 ppm.

The effect of physico-chemical treatment in reducing Listeria monocytogenes biofilms on lettuce leaf surfaces

The purpose of this research was to characterize Listeria monocytogenes from several environmental and clinical sources and assess the efficacy of single and combined physico-chemical treatments in reducing biofilm on lettuce leaves. PCR analysis of L. monocytogenes isolates collected from different clinical (10 strains) and environmental sources (12 strains) was used to look for the presence of one Listeria-specific gene and five virulence genes. Biofilms of L. monocytogenes were developed on lettuce leaves over 24 h. A 5-min ultrasound and a 300-ppm sodium hypochlorite (NaOCl) wash resulted in similar reductions in cell numbers of 0.82 log CFU cm−2. For chlorine dioxide (ClO2) at 60 ppm, the cell numbers were reduced by ∼5.45 log CFU cm−2. A combined treatment of 5 min of ultrasound plus 300 ppm NaOCl or 40 ppm ClO2, provided maximal efficacy, reducing the number of L. monocytogenes on the lettuce surface to non-detectable levels. Therefore, ClO2 has the potential to replace NaOCl for the disinfection of food products in the food industry.