Young Lettuce Research Articles

Unde venis? Bacterial resistance from environmental reservoirs to lettuce: tracking microbiome and resistome over a growth period.

Fresh produce is suggested to contribute highly to shaping the gut resistome. We investigated the impact of pig manure and irrigation water quality on microbiome and resistome of field-grown lettuce over an entire growth period. Lettuce was grown under four regimes, combining soil amendment with manure (with/without) with sprinkler irrigation using river water with an upstream wastewater input, disinfected by UV (with/without). Lettuce leaves, soil, and water samples were collected weekly and analysed by bacterial cultivation, 16S rRNA gene amplicon sequencing, and shotgun metagenomics from total community DNA. Cultivation yielded only few clinically relevant antibiotic-resistant bacteria (ARB), but numbers of ARB on lettuce increased over time, while no treatment-dependent changes were observed. Microbiome analysis confirmed a temporal trend. Antibiotic resistance genes (ARGs) unique to lettuce and water included multidrug and β-lactam ARGs, whereas lettuce and soil uniquely shared mainly glycopeptide and tetracycline ARGs. Surface water carried clinically relevant ARB (e.g. ESBL-producing Escherichia coli or Serratia fonticola) without affecting the overall lettuce resistome significantly. Resistance markers including biocide and metal resistance were increased in lettuce grown with manure, especially young lettuce (increased soil contact). Overall, while all investigated environments had their share as sources of the lettuce resistome, manure was the main source especially on young plants. We therefore suggest minimizing soil-vegetable contact to minimize resistance markers on fresh produce.

Moderate salinity and high ammonium/nitrate ratio enhance early growth in “summer wonder” lettuce cultivar

Because its impact in plant development and growth and its interaction with Na+ and Cl−, the supply of different N-forms to crops can be an easy-to-use tool with effective results on salinity tolerance. Here the effect of four N–NO3-/N–NH4+ ratios (mM; 2/0, 1.6/0.4, 0.4/1.6, 0/2) on adaptation to salt conditions (15 mM NaCl in a first experiment and 40 mM NaCl in a second experiment) was studied in young lettuce (cv “Summer wonder”) plants. The experiments were carried out in greenhouse and under hydroponics conditions. The results show that this cultivar tolerates and adapts to moderate salinity by deploying several structural and physiological mechanisms; (i) increasing allocation of biomass to the root, (ii) increasing root Na+ uptake and storing it in the shoot and root tissues, (iii) increasing intrinsic water use efficiency and (iv) increasing root N and P uptake. The beneficial effect of salt exposure on growth was greater when the predominant N-form was N–NO3-. These plants with higher tissue N–NO3- concentration, decreased Cl− uptake and shoot and root Cl− concentration. Regardless of salt conditions, plants with a high proportion of N–NH4+ (1.6 mM) and a low proportion of N–NO3- (0.4 mM) had a greater growth and nitrogen use efficiency, that was associated with the improved uptake of nutrients, and the maintenance of water status.

Quantitative and Qualitative Analysis of Agricultural Fields Based on Aerial Multispectral Images Using Neural Networks.

This article presents an integrated system that uses the capabilities of unmanned aerial vehicles (UAVs) to perform a comprehensive crop analysis, combining qualitative and quantitative evaluations for efficient agricultural management. A convolutional neural network-based model, Detectron2, serves as the foundation for detecting and segmenting objects of interest in acquired aerial images. This model was trained on a dataset prepared using the COCO format, which features a variety of annotated objects. The system architecture comprises a frontend and a backend component. The frontend facilitates user interaction and annotation of objects on multispectral images. The backend involves image loading, project management, polygon handling, and multispectral image processing. For qualitative analysis, users can delineate regions of interest using polygons, which are then subjected to analysis using the Normalized Difference Vegetation Index (NDVI) or Optimized Soil Adjusted Vegetation Index (OSAVI). For quantitative analysis, the system deploys a pre-trained model capable of object detection, allowing for the counting and localization of specific objects, with a focus on young lettuce crops. The prediction quality of the model has been calculated using the AP (Average Precision) metric. The trained neural network exhibited robust performance in detecting objects, even within small images.

Predictive Population Dynamics of Escherichia coli O157:H7 and Salmonella enterica on Plants: a Mechanistic Mathematical Model Based on Weather Parameters and Bacterial State.

Weather affects key aspects of bacterial behavior on plants but has not been extensively investigated as a tool to assess risk of crop contamination with human foodborne pathogens. A novel mechanistic model informed by weather factors and bacterial state was developed to predict population dynamics on leafy vegetables and tested against published data tracking Escherichia coli O157:H7 (EcO157) and Salmonella enterica populations on lettuce and cilantro plants. The model utilizes temperature, radiation, and dew point depression to characterize pathogen growth and decay rates. Additionally, the model incorporates the population level effect of bacterial physiological state dynamics in the phyllosphere in terms of the duration and frequency of specific weather parameters. The model accurately predicted EcO157 and S. enterica population sizes on lettuce and cilantro leaves in the laboratory under various conditions of temperature, relative humidity, light intensity, and cycles of leaf wetness and dryness. Importantly, the model successfully predicted EcO157 population dynamics on 4-week-old romaine lettuce plants under variable weather conditions in nearly all field trials. Prediction of initial EcO157 population decay rates after inoculation of 6-week-old romaine plants in the same field study was better than that of long-term survival. This suggests that future augmentation of the model should consider plant age and species morphology by including additional physical parameters. Our results highlight the potential of a comprehensive weather-based model in predicting contamination risk in the field. Such a modeling approach would additionally be valuable for timing field sampling in quality control to ensure the microbial safety of produce. IMPORTANCE Fruits and vegetables are important sources of foodborne disease. Novel approaches to improve the microbial safety of produce are greatly lacking. Given that bacterial behavior on plant surfaces is highly dependent on weather factors, risk assessment informed by meteorological data may be an effective tool to integrate into strategies to prevent crop contamination. A mathematical model was developed to predict the population trends of pathogenic E. coli and S. enterica, two major causal agents of foodborne disease associated with produce, on leaves. Our model is based on weather parameters and rates of switching between the active (growing) and inactive (nongrowing) bacterial state resulting from prevailing environmental conditions on leaf surfaces. We demonstrate that the model has the ability to accurately predict dynamics of enteric pathogens on leaves and, notably, sizes of populations of pathogenic E. coli over time after inoculation onto the leaves of young lettuce plants in the field.

Effects of light quality, photoperiod, CO2 concentration, and air temperature on chlorogenic acid and rutin accumulation in young lettuce plants

Environmental stimuli modulate plant metabolite accumulation, facilitating adaptation to stressful conditions. In this study, the effects of blue and red light, photoperiod, CO2 concentration, and air temperature on the chlorogenic acid (CGA) and rutin contents of lettuce (Lactuca sativa L.) were evaluated. Under continuous blue light and a high CO2 concentration (1000 ppm), the CGA level increased. The increased expression of phenylalanine ammonia-lyase (PAL) and activity of its product were correlated with high expression of cinnamate 4-hydroxylase (C4H) and coumarate 3-hydroxylase (C3H). Furthermore, changes in PAL activity altered the CGA content in lettuce exposed to the three environmental factors, blue light, continuous lighting and high CO2 concentration. In addition, the expression levels of genes related to flavonoid biosynthesis increased in accordance with the promotion of CGA accumulation by the environmental factors. Under continuous blue light, 400 ppm CO2 promoted rutin accumulation to a greater degree compared to 1000 ppm CO2, by downregulating DFR expression. Low air temperature induced CGA accumulation in lettuce grown under continuous blue light and 1000 ppm CO2. Therefore, light quality, photoperiod, CO2 concentration, and air temperature exert synergistic effects on the CGA and rutin contents of lettuce by modulating activity in the corresponding biosynthesis pathways.

Continuous blue lighting and elevated carbon dioxide concentration rapidly increase chlorogenic acid content in young lettuce plants

Chlorogenic acid (CGA) is a strong antioxidant that potentially reduces oxidative damage in human cells. In this study, the effects of environmental factors such as photoperiod, light quality and intensity, and CO2 concentration on the growth and CGA content of lettuce (Lactuca sativa L.) were evaluated. CGA content in fresh lettuce increased under high light intensity treatments, doubling in concentration under 200 μmol m−2 s-1 compared to 100 μmol m−2 s-1. Elevated CO2 concentration also increased CGA content in fresh lettuce, quadrupling in concentration when grown at 1000 ppm compared to 400 ppm. Furthermore, there was a compound effect of light intensity and CO2 concentration whereby a light intensity level of 200 μmol m−2 s-1 and CO2 of 1000 ppm produced an even higher concentration of CGA, 199 mg per 100 g of fresh lettuce. Increased CGA concentration because of continuous lighting and elevated CO2 was observed under both fluorescent light and blue LED, but not under red LED treatment. Increased day length also induced higher CGA content in lettuce plants. These results show that continuous lighting, including blue spectrum and elevated CO2 concentration can cause higher CGA accumulation in lettuce plants. The observed increase in CGA content was induced only for 2 days after treatment was initiated. One possible interpretation of the data is that physiological stress caused by excess photosynthesis under continuous lighting results in higher CGA content to protect the plant body from high levels of reactive oxidative species. In addition, blue light and CO2 could be stimulus signals for inducing high CGA accumulation via metabolite changes.

Essential Tea Tree Oil Activity against Bremia lactucae in Lettuce

Downy mildew caused by the oomycete Bremia lactucae Regel is a serious disease of lettuce in field and greenhouse production. Here we report on the antifungal activity of essential Australian tea tree oil (TTO) derived from Melaleuca alternifolia against downy mildew in lettuce. Preventive treatments with Timorex Gold (STK Ltd., Petach Tikva, Israel), fungicide containing TTO, suppressed the development of B. lactucae on cotyledons and young lettuce plants. Epifluorescence microscopy showed that TTO had a moderate inhibitory effect on spore germination of the pathogen but a strong inhibitory effect on sporophore emergence and hence on sporulation. Timorex Gold (22.3 EC W/V) was as effective as copper hydroxide in controlling the disease in organic field plots. It was as effective as the fungicides Bellis (Boscalid + Pyraclostrobin; BASF, Germany) and Commet (pyraclostrobin; BASF, Germany) in conventional production. The results demonstrate that Timorex Gold effectively suppresses the development of downy mildew in lettuce in growth chambers as well as in the field, and thus suitable biopesticide for its control.

Tam Spektrumlu Gün Işığı Floresan Lamba ile Yapay Işıklandırmanın Marulda Fide Kalitesine Etkisi

Amaç: Bitkiler büyüme ve gelişmeleri için ışığa ihtiyaç duymaktadırlar. Ancak, kış aylarındaki kısa ve bulutlu gün sayısından kaynaklanan doğal ışık miktarındaki azalma bitkilerde büyüme ve gelişmeyi sınırlandırmaktadır. Bu durumda elektriksel yolla yapay ışıklandırma yapılabilmektedir. Materyal ve Metot: 2016 yılı Aralık ayında Ege Üniversitesi Ziraat Fakültesi Bahçe Bitkileri Bölümü fide üretim seralarında yürütülen bu çalışmada, 1-2 gerçek yapraklı genç marul fideleri dikim büyüklüğüne gelene kadar (1) karanlık koşulda lamba kullanılarak (2) gün ışığı altında lamba kullanılarak ve (3) gün ışığı (kontrol) altında yetiştirilmiştir. Karanlık koşul fidelerin üstüne konulan ahşap iskeletin siyah örtüyle kaplanması ile, yapay ışıklandırma LifeLite negatif iyon yüklü tam spektrumlu gün ışığı floresan lambası kullanımı ile sağlanmıştır. Fideler bir ay boyunca yetiştirilmiş ve haftada bir defa marul için kullanılan kışlık besin solüsyonu reçetesine göre hazırlanmış besin solüsyonu ile sulanmıştır. Dikime hazır hale gelen fidelerde morfolojik gelişim, biyolojik kütle, klorofil ve renk ölçümleri yapılmıştır. Bulgular: Karanlık koşulda lamba kullanımı ile fideler daha uzun boylu ve daha açık renkli olmuş, ancak fide kalitesi diğer uygulamalardan daha düşük olmuştur. En iyi fide gelişimi ve kalitesi gün ışığı + lamba uygulamasından elde edilmiş; bunu gün ışığı uygulaması izlemiştir. Sonuç: Çalışma sonucunda tam spektrum lamba ile yapılan yapay ışıklandırmanın marulda fide gelişimi ve kalitesini artırdığı belirlenmiştir.

Xenon lamps used for fruit surface sterilization can increase the content of total flavonols in leaves of Lactuca sativa L. without any negative effect on net photosynthesis.

One (1P), two (2P), three (3P) or four (4P) pulses of light supplied by a xenon lamp, were applied to young lettuce plants grown in pots. The lamp used in the trial was similar to those used for fruit surface sterilization. Total flavonols were measured in leaves using the Dualex method. In a first trial conducted in greenhouse conditions, 6 days after the pulsed light (PL) treatment, flavonols were increased by 312% and 525% in the 3P and 4P treatments, respectively, in comparison to the those in the untreated control. Changes in the chlorophyll fluorescence parameters suggest that the PL treatment may induce limited and transient damage to the photosynthetic machinery and that the damage increases with the increasing number of pulses. The performance parameters were not significantly affected by PL and recovered fully by 6 days after the treatments. The 1P and the 2P treatments 6 days after the treatment showed a 28.6% and a 32.5% increase, respectively, in net photosynthetic assimilation, when compared to that of the control. However, 8 days after the treatment, there was no longer a difference between the treatments and the control in net photosynthetic assimilation. Eight days after the light treatment, the 3P treatment showed a 38.4% increase in maximal net photosynthetic assimilation over that of the control, which is an indication of positive long-term adaptation of photosynthetic capacity. As a whole, our observations suggest that PL could be used on field or greenhouse crops to increase their phytochemical content. No long-lasting or strong negative effects on photosynthesis were associated with PL within the range of doses we tested; some observations even suggest that certain treatments could result in an additional positive effect. This conclusion is supported by a second trial conducted in phytotrons. More studies are required to better understand the roles of the different wavelengths supplied by PL and their interactions.

Genetic variation and relationship among content of vitamins, pigments, and sugars in baby leaf lettuce.

Baby leaf lettuce harvested approximately 30 days after planting is the primary component of spring mix salads, a popular type of packaged salads. Very little is known, however, about the content of vitamins, sugars, and pigments in young lettuce plants. Therefore, plants of 42 accessions harvested at baby leaf stage were analyzed for the contents of vitamin C, ß‐carotene, anthocyanins, chlorophylls, glucose, fructose, and sucrose. Significant differences among accessions were found for content of all seven compounds plus sucrose sweetness equivalency (SSE) and average vitamin load (AVLAC). “Floricos” was highest in all sugars, SSE and vitamin C; “Taiwan” was highest in ß‐carotene and AVLAC, and “Annapolis” and “Darkland” were highest for anthocyanins and chlorophyll contents, respectively. The lowest content of glucose and sucrose was found in iceberg “Salinas,” fructose in L. serriola accession UC96US23, vitamin C in PI 257288, and β‐carotene in “Solar.” The lowest relative sweetness (SSE) was calculated for UC96US23, followed by “Salinas,” while the lowest AVLAC was estimated for PI 257288. There were very strong, positive correlations among contents of the three sugars, and between β‐carotene and vitamin C, and β‐carotene and anthocyanins. Composition profiles of accessions presented in this study, together with identified associations between compounds, can be used by breeders, growers, and producers to select lettuces with desirable combinations of sugars, pigments, and vitamins. This information can help in development of new cultivars and breeding lines with desirable combination of traits, pleasing taste, and higher vitamin content.

Non-destructive Phenotyping of Lettuce Plants in Early Stages of Development with Optical Sensors.

Rapid development of plants is important for the production of ‘baby-leaf’ lettuce that is harvested when plants reach the four- to eight-leaf stage of growth. However, environmental factors, such as high or low temperature, or elevated concentrations of salt, inhibit lettuce growth. Therefore, non-destructive evaluations of plants can provide valuable information to breeders and growers. The objective of the present study was to test the feasibility of using non-destructive phenotyping with optical sensors for the evaluations of lettuce plants in early stages of development. We performed the series of experiments to determine if hyperspectral imaging and chlorophyll fluorescence imaging can determine phenotypic changes manifested on lettuce plants subjected to the extreme temperature and salinity stress treatments. Our results indicate that top view optical sensors alone can accurately determine plant size to approximately 7 g fresh weight. Hyperspectral imaging analysis was able to detect changes in the total chlorophyll (RCC) and anthocyanin (RAC) content, while chlorophyll fluorescence imaging revealed photoinhibition and reduction of plant growth caused by the extreme growing temperatures (3 and 39°C) and salinity (100 mM NaCl). Though no significant correlation was found between Fv/Fm and decrease in plant growth due to stress when comparisons were made across multiple accessions, our results indicate that lettuce plants have a high adaptability to both low (3°C) and high (39°C) temperatures, with no permanent damage to photosynthetic apparatus and fast recovery of plants after moving them to the optimal (21°C) temperature. We have also detected a strong relationship between visual rating of the green- and red-leaf color intensity and RCC and RAC, respectively. Differences in RAC among accessions suggest that the selection for intense red color may be easier to perform at somewhat lower than the optimal temperature. This study serves as a proof of concept that optical sensors can be successfully used as tools for breeders when evaluating young lettuce plants. Moreover, we were able to identify the locus for light green leaf color (qLG4), and position this locus on the molecular linkage map of lettuce, which shows that these techniques have sufficient resolution to be used in a genetic context in lettuce.

Biological Control of Lettuce Drop and Host Plant Colonization by Rhizospheric and Endophytic Streptomycetes.

Lettuce drop, caused by the soil borne pathogen Sclerotinia sclerotiorum, is one of the most common and serious diseases of lettuce worldwide. Increased concerns about the side effects of chemical pesticides have resulted in greater interest in developing biocontrol strategies against S. sclerotiorum. However, relatively little is known about the mechanisms of Streptomyces spp. as biological control agents against S. sclerotiorum on lettuce. Two Streptomyces isolates, S. exfoliatus FT05W and S. cyaneus ZEA17I, inhibit mycelial growth of Sclerotinia sclerotiorum by more than 75% in vitro. We evaluated their biocontrol activity against S. sclerotiorum in vivo, and compared them to Streptomyces lydicus WYEC 108, isolated from Actinovate®. When Streptomyces spp. (106 CFU/mL) were applied to S. sclerotiorum inoculated substrate in a growth chamber 1 week prior lettuce sowing, they significantly reduced the risk of lettuce drop disease, compared to the inoculated control. Interestingly, under field conditions, S. exfoliatus FT05W and S. cyaneus ZEA17I protected lettuce from drop by 40 and 10% respectively, whereas S. lydicus WYEC 108 did not show any protection. We further labeled S. exfoliatus FT05W and S. cyaneus ZEA17I with the enhanced GFP (EGFP) marker to investigate their rhizosphere competence and ability to colonize lettuce roots using confocal laser scanning microscopy (CLSM). The abundant colonization of young lettuce seedlings by both strains demonstrated Streptomyces' capability to interact with the host from early stages of seed germination and root development. Moreover, the two strains were detected also on 2-week-old roots, indicating their potential of long-term interactions with lettuce. Additionally, scanning electron microscopy (SEM) observations showed EGFP-S. exfoliatus FT05W endophytic colonization of lettuce root cortex tissues. Finally, we determined its viability and persistence in the rhizosphere and endorhiza up to 3 weeks by quantifying its concentration in these compartments. Based on these results we conclude that S. exfoliatus FT05W has high potential to be exploited in agriculture for managing soil borne diseases barely controlled by available plant protection products.

Effect of the Spectral Quality and Intensity of Light-emitting Diodes on Several Horticultural Crops

Light-emitting diode (LED) lamps signify one of the most important advances in artificial lighting for horticulture over the last few decades. The objective of this study was to compare the cultivation of four horticultural plants using a conventional white LED tube (T0) light against one with a good spectral fit to the maximum photosynthetic response (T1) at two intensities. The experiment was carried out with two types of young lettuce, tomato, and bell pepper plants. In a controlled environment chamber, six and four lamps per square meter were used to achieve high (H) and low (L) intensity, respectively. We measured the lighting parameters illuminance (lux) and photosynthetic photon flux (PPF) intensity (µmol·m−2·s−1). The dry and fresh weight, leaf area (LA), and specific index were measured to gauge plant growth. The photosynthetic activity and energy efficiency (EE) were recorded for each species over 60 days of cultivation. The results clearly demonstrate that, compared with conventional LED lamps, the specific horticultural LED lamps with an improved light spectrum increased the EE of the evaluated vegetables by 26%. At both the studied light intensities, plant growth was clearly more closely linked to the spectral fit of the light to the maximum photosynthetic response recorded by McCree (1972) than to PPF or illuminance (lux). We therefore suggest that a specific, detailed spectral distribution study be conducted to predict the effect of the specific quantity and quality of light used in this study on a single parameter of plant growth.

Rise of nightly air humidity as a measure for tipburn prevention in hydroponic cultivation of butterhead lettuce

The physiological disorder tipburn remains a constant threat for growers of butterhead lettuce in greenhouses. In standard soil cultivation, tipburn is controlled reasonably well by using traditional growing methods, combined with the selection of tolerant cultivars. However, when applying novel growing techniques such as hydroponics, current practices to prevent tipburn show to be no longer sufficient. Therefore, a research project was started up, aiming at the development of a more rational tipburn prevention strategy. In the first year, tipburn occurrence was studied in successive soil-grown lettuce crops at two locations. Out of several environmental factors, which might induce tipburn according to literature, low nightly air humidity (RH.) appeared to be the most important one in commercial growing conditions. Several successive experiments with hydroponic lettuce (NFT) confirmed that maintaining RHn at a high level is an efficient measure to decrease tipburn occurrence. Whereas 60 to 100% of the control plants was affected by tipburn, maintaining RHn above 95% markedly reduced tipburn injury to 3 to 50%, respectively. This effect was associated with an improved Ca transport to the leaf margins (1 cm zone) of young lettuce leaves and values higher than 2-3 g Ca kg(-1) DM were obtained. The most efficient technique to decrease tipburn occurrence by raising RHn was the combination of water spraying underneath the gullies with nebulization above the plants. Second best techniques were the mere spraying of water under the gullies and covering the plants with plastic foil.

Effect of postharvest short-term radiation of near infrared light on transpiration of lettuce leaf

We investigated the physiological effects of short-term postharvest near infrared (NIR) radiation on relative transpiration rates, stomatal apertures, and reactive oxygen species (ROS) levels in guard cells on excised young lettuce leaves and on transpiration of leaf lettuce at commercial maturity. When the young leaves were radiated by NIR of wavelengths longer than 850nm at 100μmolm−2s−1 for short duration (10–60)min, relative transpiration rates during subsequent storage were reduced, but not by visible light radiation and by longer radiation (180min) of NIR. The reduction in transpiration rates by the short-term NIR radiation was greater at 10°C than at 25°C under both dark and light conditions during subsequent storage. The short-term NIR radiation enhanced stomatal closure and ROS accumulation in guard cells of young lettuce leaves. These results indicate that the suppression of transpiration by short-term NIR radiation is likely to be mediated through stomatal closure due to NIR-induced ROS accumulation. The reduction of transpiration by short-term NIR radiation was obtained not only in excised young leaves but also in leaf lettuce at commercial maturity, resulting in keeping freshness. The short-term NIR radiation could be an additional means to extend shelf life of leaf vegetables.

Laboratory and semi-field evaluation of Beauveria bassiana (Ascomycota: Hypocreales) against the lettuce aphid, Nasonovia ribisnigri (Hemiptera: Aphididae)

The lettuce aphid, Nasonovia ribisnigri (Mosley), is an economically important pest of lettuce worldwide. The entomopathogenic fungus Beauveria bassiana strain GHA has recently been reported as a potential biocontrol candidate for use against the lettuce aphid. This study provides information on the mortality inflicted by B. bassiana when applied against different life stages of the lettuce aphid under laboratory conditions and how fungus infection affects the aphid fecundity. In addition, temporal changes in persistence of fungus inoculum applied to foliage of young lettuce plants under semi-field conditions was analysed. Immature life stages were generally the least susceptible to fungal infection and the susceptibility of all stages was dose-dependent, with the highest mortality occurring at the highest dose. B. bassiana significantly affected the rate of nymph production by the lettuce aphid, with the highest effect seen when the alatoid fourth instar of N. ribisnigri was inoculated with B. bassiana. The persistence of B. bassiana conidia on lettuce foliage was not influenced by leaf position. Within 5days, the cumulative percentage decline in the conidial population was 38% which declined further to 92% and 99% on day 11 and 20 post-spraying, respectively. In accordance, the infectivity to second instar lettuce aphid nymphs of B. bassiana conidia deposited on leaves declined according to an exponential decay model predicting an intercept of 0.59±0.03 (S.E), a reduction in aphid mortality at a rate of 11% with each increasing day after fungal application and a fungus half-life of 6.34±0.69days.

Contamination of Lettuce Plants Irrigated with Waste Water in Yaounde, Cameroon

Aims: To evaluate the effects of various treatment combinations of water contaminated with faecal sludge on the growth and microbiological characteristics of lettuce (Lactuca sativa L.) cultivated around the river Avo'o discharged zone. Study Design: We used randomized plots in which young lettuce plants obtained from a nursery were planted in four sites (S0, S1, S2 and S3) situated 3000, 810, 100 and 350 m from the raw discharge area along river Avo'o. Place and Duration: Field studies were carried out in Nomayos (Yaounde) during the 2009-2010 growing seasons while laboratory analysis were effected at the waste water research unit of the Department of Plant Biology at the University of Yaounde I. Original Research Article Tsama et al; AJEA, 6(6): 402-409, 2015; Article no.AJEA.2015.097 403 Methodology: Faecal streptococci, faecal coliforms and parasitic characteristics were determined in raw discharged sludge from river Avo’o water samples collected at three different points (P1, P2, P3) and in lettuce using standard protocols. Growth parameters of the lettuce plants were also evaluated. Results: Faecal sludge, water from river Avo'o and L. sativa showed high levels of bacteriological and parasitological pollutants. The results also revealed high concentrations of faecal coliforms and faecal streptococci (6092 and 3390 CFU/100 ml respectively), and helminth eggs (> 273 eggs / L) in water. Treatment 3 (S3) showed the largest number of leaves with an average of 34.63 leaves in the ninth week for site 1 and 40.33 leaves for site 2. Plant height increased gradually with time and treatments. The mean values of leaf surfaces obtained after nine weeks were 11.5 cm2 and 13.99 cm2 for treatment S3 in sites 1 and 2 respectively. Conclusion: Though the best growth of lettuce was observed in plots irrigated with water from river Avo’o, the high levels of parasite concentrations on their leaves (43 eggs/100 g) highlight the necessity for a better management of faecal sludge in Yaounde city.

Characterization of Circadian Rhythms Through a Bioluminescence Reporter Assay in Lactuca sativa L.

Circadian rhythms are observed in many physiological events in plant, and clock genes orchestrate the rhythms of expression of many genes. Precise environmental control of circadian rhythms provides a key technology for enhancing plant growth in artificial environments. In this study, we investigated the basic properties of a circadian rhythm for establishment of its control engineering in lettuce (Lactuca sativa L.). Bioluminescence of transgenic lettuce carrying an AtCCA1::LUC construct as a reporter of circadian gene expression was measured in young lettuce seedlings. We observed three basic properties; free-running circadian rhythms under constant conditions without day-night cycles, entrainment to red and blue light cycles with 12 h light-12 h dark period, and temperature compensation of a free-running period in three lettuce cultivars (Cisco, Cos, Greenwave). In addition, a light-quality dependence of the free-running period and sensitivity to blue-light cycles with small amplitude (20% of variance in average light intensity) and non-24 h period were also observed. The results in this study indicated that it is possible to control lettuce circadian rhythms by non-24 h period light cycles in LED illumination. It will play an important role in the research of control engineering for the circadian clock of lettuce in closed plant factories with artificial lighting.

The effect of competition from neighbours on stomatal conductance in lettuce and tomato plants.

Competition decreased transpiration from young lettuce plants after 2 days, before any reductions in leaf area became apparent, and stomatal conductance (g(s) ) of lettuce and tomato plants was also reduced. Stomatal closure was not due to hydraulic signals or competition for nutrients, as soil water content, leaf water status and leaf nitrate concentrations were unaffected by neighbours. Competition-induced stomatal closure was absent in an abscisic acid (ABA)-deficient tomato mutant, flacca, indicating a fundamental involvement of ABA. Although tomato xylem sap ABA concentrations were unaffected by the presence of neighbours, ABA/pH-based stomatal modulation is still likely to underlie the response to competition, as soil and xylem sap alkalization was observed in competing plants. Competition also modulated leaf ethylene production, and treatment of lettuce plants with an ethylene perception inhibitor (1-methylcyclopropene) diminished the difference in g(s) between single and competing plants grown in a controlled environment room, but increased it in plants grown in the greenhouse: ethylene altered the extent of the stomatal response to competition. Effects of competition on g(s) are discussed in terms of the detection of the absence of neighbours: increases in g(s) and carbon fixation may allow faster initial space occupancy within an emerging community/crop.

Screening for genotype and environment effects on nitrate accumulation in 24 species of young lettuce.

Nitrate accumulates in plants in response to N supply, aerial environment (predominantly light), and genotype. This paper characterises the effects of genotype, environment, and their interactions on nitrate accumulation by 24 cultivated and wild lettuce accessions grown hydroponically in winter and summer. The results will inform future strategies for selecting for low-nitrate varieties. A preliminary study in which two accessions were sampled for nitrate over time showed largest differences between cultivars in the early-middle period of growth. Sampling the whole population of lettuce at this stage revealed significant effects of genotype, environment (with nitrate concentrations generally higher in winter), and genotype × environment interactions (largely due to a wider range of concentrations in summer). Changes in the ranking of accessions for nitrate accumulation between the two growing seasons were generally small for cultivated morphotypes. Shoot nitrate concentrations and water contents were positively associated, particularly in summer when separate relationships for different cultivated morphotypes (butterhead, cos/Romaine, crisp, leaf, and stem lettuce) were detected. Expressing nitrate concentration on either a shoot fresh or dry matter basis had relatively little effect on the ranking of most cultivated accessions, but not for the wild types. There is a well-defined sampling window when differences in nitrate accumulation between lettuce genotypes are at a maximum. Delaying sampling may allow morphological changes in head form to mask earlier genotypic differences. Genotype × environment interactions are predominantly of the non-crossover type and have only a small effect on changes in the ranking of accessions between seasons, allowing selections to be made at any time of year. At least part of the genotypic variation in nitrate accumulation is associated with differences in shoot water content.