Light Photoperiod Research Articles

Effect of Daily Light Integral on Cucumber Plug Seedlings in Artificial Light Plant Factory

In a controlled environment, in an artificial light plant factory during early spring or midsummer, vegetable seedlings can be uniform, compact, and high quality. Appropriate light parameters can speed up the growth of seedlings and save on production costs. Two experiments were carried out in this study: (1) cucumber seedling growth under different daily light integrals (DLIs) (5.41–11.26 mol·m−2·d−1) and optimum DLI for seedling production were explored (experiment 1: Exp. 1); (2) under the same DLI selected by Exp. 1, the effects of different light intensities and photoperiods on cucumber seedlings were investigated (experiment 2: Exp. 2). The root biomass, root-to-shoot ratio, seedling index, and shoot dry matter rate increased as the DLI increased from 5.41 to 11.26 mol·m−2·d−1, while the shoot biomass and leaf area decreased in Exp. 1. The cucumber seedlings became more compact as DLI increased, but more flowers developed after transplanting when the DLI was 6.35 mol·m−2·d−1. Under the optimal DLI (6.35 mol·m−2·d−1), the optimal intensity was 110–125 μmol·m−2·s−1, and the optimal photoperiod was 14–16 h, in which plant biomass, shoot dry matter rate, seedling index, and photochemical efficiency were higher.

Photoperiod controls egg laying and caudodorsal cell hormone expression but not gonadal development in the pond snail Lymnaea stagnalis.

Photoperiod is a reliable cue to regulate growth and reproduction for seasonal adaptation. Although photoperiodism has been well studied in Chordata and Arthropoda, less is known about Mollusca. We examined photoperiodic effects on egg laying, body size, gonad-somatic index, oocyte size and relative amounts of caudodorsal cell hormone mRNA in individual rearing conditions in the pond snail Lymnaea stagnalis. Twenty-five weeks after hatching, the percentages of egg-laying snails under a photoperiod of 12h light and 12h darkness (12L:12D) were significantly smaller than those under longer days. The total numbers of eggs and egg masses under 12L:12D were significantly smaller than those under longer days. Significant differences between 16L:8D and 12L:12D were not observed in the soft body and ovotestis weight, and the gonad-somatic index. Photoperiodic effects were also not observed in oocyte diameters twenty-two weeks after hatching. Twenty-seven weeks after hatching amounts of caudodorsal cell hormone mRNA were significantly lower in the cerebral ganglia with commissure under 12L:12D than 16L:8D. L. stagnalis exhibited a clear photoperiodic response in egg laying and the amount of caudodorsal cell hormone mRNA, but not in gonadal development. Under 12L:12D suppression of caudodorsal cell hormone expression might suppress egg laying.

Comparative Assessment of Hydroponic Lettuce Production Either under Artificial Lighting, or in a Mediterranean Greenhouse during Wintertime

Butterhead lettuce was grown hydroponically in a vertical farm under high (HLI) and low (LLI) light intensity (310, and 188 μmol m−2 s−1, respectively) and compared to hydroponically grown lettuce in a greenhouse (GT) during wintertime in Athens, Greece (144 μmol m−2 s−1). The highest plant biomass was recorded in the HLI treatment, whereas LLI and GT produced similar plant biomass. However, the LLI produced vortex-like plants, which were non-marketable, while the plants in the GT were normal-shaped and saleable. Net photosynthesis was highest in the HLI and higher in the LLI than in the GT, thereby indicating that light intensity was the dominant factor affecting photosynthetic performance. Nevertheless, the unsatisfactory performance of the LLI is ascribed, not only to reduced light intensity, but also to reduced light uniformity as the LED lamps were closer to the plants than in the HLI. Furthermore, the large solar irradiance variability in the GT resulted in substantially higher adaptation to the increased light intensity compared to LLI, as indicated by chlorophyll fluorescence measurements. Light intensity and photoperiod are believed to be the primary reasons for increased nitrate content in the GT than in the vertical farming treatments.

Pulsed LED Light: Exploring the Balance between Energy Use and Nutraceutical Properties in Indoor-Grown Lettuce

In indoor vertical farms, energy consumption represents a bottleneck for both a system’s affordability and environmental footprint. Although switching frequency (sf) represents a crucial factor in determining the efficacy of light emitting diodes (LED) lighting systems in converting electricity into light, the impact of sf is still underexplored. The aim of this work was to investigate the effect of LEDs sf on the productive and qualitative responses of lettuce (Lactuca sativa L.), also considering the resource use efficiency. Plants were grown for 14 days under red and blue LEDs (215 μmol m−2 s−1 and 16/8 h light/dark, with a red:blue ratio of 3) characterized by two different sf for the blue diode, namely high sf (850 kHz) and low sf (293 kHz). A fluorescent light (same light intensity and photoperiod) was included. LED sf did not alter plant morphological parameters, including fresh or dry biomass, leaf number, leaf area, or water use efficiency. A low sf increased the energy use efficiency (EUE) by 40% as compared to high sf. The latter enhanced the leaf antioxidant capacity, as a consequence of increased concentrations of caftaric and chicoric acids, isoquercetin, and luteolin, consistent with the upregulation of a few genes related to the biosynthetic pathway of phenolic compounds (4C3H and DFR). The study highlights that different sf may significantly affect the EUE as well as crop nutritional properties.

Regulation of carbon assimilation in Skeletonema costatum under diel variations

Here, we explored the molecular responses of photosynthetic carbon fixation in a globally distributed marine diatom, Skeletonema costatum, based on incubation experiments over a 24-h period under natural light. A model of carbon metabolism was proposed based on the transcriptome of S. costatum. We examined the diurnal expression patterns and relative importance of the C4 pathway in S. costatum photosynthesis by analyzing the transcript abundance and key enzyme activities during the day/night cycle. This study suggested that the photosynthetic pathways of S. costatum were diverse and could involve combined CO2-concentrating mechanisms. The analysis at the transcriptional level revealed that the transcripts of the C4 pathway-related genes phosphoenolpyruvate carboxylase (PEPC) and pyruvate-phosphate dikinase (PPDK) were upregulated under the photoperiod and had obvious diurnal rhythms, indicating that light obviously affected photosynthetic carbon fixation. Moreover, we studied the pathway of photosynthetic carbon assimilation in S. costatum with carbon isotope δ13C techniques. The data provided evidence that carbon fixation in S. costatum involves the synergy of C3 and C4 photosynthesis. Under low pCO2 levels in the low light photoperiod, the affinity of inorganic carbon increased, supported by the C4 pathway, to acclimate to variations in the environment. This study promotes a better understanding of the photosynthetic carbon fixation mechanism in S. costatum during the diel cycle.

Storage of Simarouba amara Aubl. seeds

Prior knowledge about the physiological behavior of seeds under storage conditions allows the use of appropriate techniques to maintain viability. The goal of the present study was to classify the behavior of Simarouba amara seeds regarding their physiological potential during storage. The seeds were obtained from mature fruits, collected from five parent plants located at the Joanes-Ipitanga Environmental Protection Area (EPA) (Simões Filho, Bahia) in January 2018. Two experiments were carried out in a completely randomized design. In the first one, seed desiccation tolerance was evaluated with seven moisture contents: 5%, 7.5%, 10%, 12.5%, 15%, 25% and 35.6% (initial moisture). A germination test was carried out to evaluate the seeds’ vigor. In the second experiment, the seeds were stored with moisture contents of 7.5%, 12.5% and 35.6% at temperatures of 8 °C, 15 °C and 20 °C) for two storage periods, two and four months, and samples were taken to determine moisture content and conduct the germination test. Germination tests were performed in BOD chambers at 30 °C and with 12-hour light photoperiod. Daily counts were performed for the number of germinated seeds. We measured germination percentage, mean germination time, uncertainty index, percentage of normal seedlings, and percentage of unviable seeds. Simarouba amara seeds tolerate desiccation up to 7.5% moisture content, but lost viability when stored under this condition. At four months of storage all seeds lost viability. Simarouba amara seeds are recalcitrant and lose viability before reaching two months of storage.

Optimization of Culture Conditions for Mycelial Growth and Sporulation of Myrothecium roridum

Culture and nutrition conditions of Myrothecium roridum Tode were optimized by conducting a series of interlined experiments on a growth medium, temperature, pH, and photoperiod. In contrast, relation of culture age with virulence was measured by fungal development on young leaves of bitter gourd. The physiological response was measured on colony radial growth and spore production. Among the six test growth media, i.e., nutrient agar (NA), potato dextrose agar (PDA), Czapek-Dox agar (CDA), glucose agar (GA), malt extract agar (MEA), and bitter gourd agar (BGA), the highest radial growth (77 mm) and the highest number of spores (239 × 106 spores/ml) were observed on PDA. Incubation temperature was evaluated between a range of 15-40 °C, and the highest colony growth (87 mm) was observed at 30 °C, whereas the highest spore production (315 × 106 spores/ml) was at 35 °C. Different pH levels, i.e., 5, 5.5, 6, 6.5, 7, and 7.5, were optimized, and the highest colony growth (87 mm) and spore production (504 × 106 spores/ml) was recorded at pH 5.0. Impact of photoperiod was studied, and the highest mycelial growth (88 mm) and maximum spore production (524 × 106 spores/ml) was observed at 16/8 h alternate light and dark period. It was concluded that the optimum conditions for mycelia growth and spore production was pH 5.0-6.0 and at 30 ± 2 °C in PDA with 16/8 h alternate light and dark photoperiod.

Supplemental light exposure improves sleep architecture in people with type 2 diabetes.

People with type 2 diabetes (T2D) suffer from sleep disorders, with the mechanism not clearly understood. In T2D, the light transducing retinal photoreceptors that regulate sleep behaviours are dysfunctional; hence, we determine here whether supplemental light exposure ameliorates sleep quality and daytime sleepiness in T2D. Supplemental light (10,000Lux, polychromatic) was self-administered for 30min every morning for 14days by ten participants with T2D with no diabetic retinopathy (DR). The effectiveness of supplemental light was assessed by comparing subjective sleep questionnaire (PSQI and ESS) scores and salivary dim light melatonin onset (DLMO) before and after the light exposure as well as with a self-maintained sleep diary during the light exposure. Compared to the baseline, supplemental light significantly improved the excessive daytime sleepiness score (p = 0.004) and phase-advanced the DLMO on average by ~ 23min. Sleep diary analyses showed that afternoon nap duration significantly shortened over the first week of supplemental light exposure (p = 0.019). Afternoon naps and midnight awakening were significantly longer in diabetic participants with thinner perifoveal retina. In this case series, we provide initial evidence that supplemental bright light improves daytime sleepiness in T2D with no DR, with the critical period of light exposure showing a beneficial effect after one week. We infer that supplemental light augments photoreceptor signalling in T2D and therefore optimises circadian photoentrainment leading to improved sleep. Our findings inform the development of tailored light therapy protocols in future clinical trials for improving sleep architecture in diabetes.

Short photoperiod attenuates CO2 fertilization effect on shoot biomass in Arabidopsis thaliana.

The level of carbon dioxide (CO2) in the air can affect several traits in plants. Elevated atmospheric CO2 (eCO2) can enhance photosynthesis and increase plant productivity, including biomass, although there are inconsistencies regarding the effects of eCO2 on the plant growth response. The compounding effects of ambient environmental conditions such as light intensity, photoperiod, water availability, and soil nutrient composition can affect the extent to which eCO2 enhances plant productivity. This study aimed to investigate the growth response of Arabidopsis thaliana to eCO2 (800ppm) under short photoperiod (8/16h, light/dark cycle). Here, we report an attenuated fertilization effect of eCO2 on the shoot biomass of Arabidopsis plants grown under short photoperiod. The biomass of two-, three-, and four-week-old Arabidopsis plants was increased by 10%, 15%, and 28%, respectively, under eCO2 compared to the ambient CO2 (aCO2, 400ppm)i.e. control. However, the number of rosette leaves, rosette area, and shoot biomass were similar in mature plants under both CO2 conditions, despite 40% higher photosynthesis in eCO2 exposed plants. The levels of chlorophylls and carotenoids were similar in the fully expanded rosette leaves regardless of the level of CO2. In conclusion, CO2 enrichment moderately increased Arabidopsis shoot biomass at the juvenile stage, whereas the eCO2-induced increment in shoot biomass was not apparent in mature plants. A shorter day-length can limit the source-to-sink resource allocation in a plant inage-dependent manner, hence diminishing the eCO2 fertilization effect on the shoot biomass in Arabidopsis plants grown under short photoperiod.

Photoperiods affect growth, food intake and physiological metabolism of juvenile European Sea Bass (Dicentrachus labrax L.)

Photoperiodism is a vital environmental factor that regulates the growth, development, metabolism, and reproduction of aquatic organisms. Here, we examined how different photoperiods (0L: 24D, 8L: 16D, 12L: 12D, 16L: 8D, 24L: 0D) with a full spectrum LED, influence growth, feeding, digestive enzymes, and antioxidant enzymes in juvenile European Sea Bass (Dicentrachus labrax L.). Specifically, a total of 300 fishes (body length: 13.5 ± 0.54 cm, bodyweight: 45 ± 5.3 g) were randomly divided into 5 different light treatment groups. Sampling and analysis were conducted after 60 days of the experiment. Results revealed significantly higher weight gain, specific growth rate, and daily growth index in the 8L: 16D group, relative to 0L: 24D and 24L: 0D. Conversely, feed conversion ratio (FCR) was significantly lower in 8L: 16D, 12L: 12D, and 16L: 8D treatments than in 24L: 0D and 0L: 24D. Additionally, activities of intestinal amylase (AMS) lipase (LPS) pepsin (PPS) and trypsin (TPS) in the stomach were significantly higher in the 8L: 16D, relative to the other treatment groups. Gills of juveniles exposed to 0L: 24D recorded significantly higher catalase (CAT) and superoxide dismutase (SOD) activities, compared to those in the other groups. Regarding the dorsal muscle, a significantly higher CAT activity was recorded under 0L: 24D light than the other light photoperiods. Moreover, kidneys of juveniles exposed to 24L: 0D recorded the highest CAT and SOD activity. In summary, 8L: 16D, 12L: 12D, and 16L: 8D light photoperiods increased the digestive enzyme activity, reduced oxidative stress, and enhanced growth in fish, despite long-term exposure to light or darkness being unsuitable. These findings indicate that light and dark combinations are more conducive for culturing sea bass, with the 8L: 16D regime being the optimal photoperiod for the growth of juveniles.

Effect of Light Regulation on the Quality of Sweetpotato Sprouts

Sweetpotato sprouts are buds or young shoots formed under dark or low-light conditions that can be eaten directly by people. This study was conducted to investigate the effects of light intensity and photoperiod on the quality and yield of sweetpotato sprouts and to identify the most suitable production conditions to provide a theoretical basis and technical parameters for the production of these vegetables. Four treatments involving different light intensities and photoperiods were set up: WL-1, WL-2, SL-1, and SL-2. The leaf color, nutritional quality, antioxidant capacity, texture characteristics, and yield of the sweetpotato sprouts were analyzed using Duncan’s new complex range method. The results demonstrated the following: 1) an increase in photoperiod improved leaf brightness and enhanced the appearance of the product, whereas light intensity had little effect on these parameters; and 2) low light intensity increased the yield of sweetpotato sprouts, whereas high light intensity reduced their yield. Under weak light conditions, the quality and yield of sweetpotato sprouts were improved, and their taste was unaffected. Therefore, the condition of 750 μmol·m−2·s−1 for 2 hours/day was chosen to produce crispy, high-quality, and high-yielding sweetpotato sprouts.

First report of Mycoleptodiscus terrestris causing root rot of soybean in Indiana.

During the summers in 2019 and 2020, 137 soybean (Glycine max (L.) Merr) seedlings (V1-V3 stage) showing stunting, delayed emergence, and/or crown lesions were collected at Purdue's Agronomy Center for Research and Education in West Lafayette, Indiana. Four seedlings were stunted with reddish-brown girdled lesions along the hypocotyl and crown, rotted tap and lateral roots, and brown discoloration of the cortex and vascular tissues. Four fungal isolates (AC4, AC58, AC96, and AC127) were recovered by plating surface-sterilized symptomatic root tissue onto water agar plates and incubating on the benchtop until mycelia emerged. The growing hyphal tips were transferred to the semi-selective medium DCPA (Andrews and Pitt 1986). On potato dextrose agar, the fungal colonies developed olivaceous green mycelia which melanized into a mat of black microsclerotia with time and no conidia were observed. On 1.5% water agar plates amended with twice autoclaved soybean leaf and root tissue collected from flowering soybean plants, conidia were formed in sporodochia in darkness at 28 οC within one week. Conidia were 1-2 septate, cylindrical with two setae on either end, and measured 20.8 to 26.4 x 4 to 5.6 μm (average 23.9 x 4.7 μm, n=20). The morphological characters matched with the description of Mycoleptodiscus terrestris (Gerd.) Ostaz (Gerdemann 1953). Species identification was further confirmed by sequencing the internal transcribed spacers (ITS) region of rDNA amplified by ITS1 and ITS4 primers (White et al. 1990) and the translation elongation factor 1 alpha (TEF1-α) gene using 983F and 1567R primers with annealing temperature at 53 ○C (Rehner and Buckley 2005). The sequences were deposited in GenBank under the following accession numbers: ITS: MW002684, MT998441, MW010258, and MW010260; and TEF1-α: MW015941-MW015944. The GenBank BLAST searches revealed 100% identity in the ITS region (accession NR_145373.1) and 99.75% identity in the TEF1-α region (MK495977.1) to M. terrestris. Pathogenicity test was conducted on soybean seedlings (cv. Williams) at V1 growth stage using a root dip assay. Isolate AC58 was grown in a modified cotton seed meal broth (CSMB) to produce microsclerotia as inoculum (Gray 1978; Shearer and Jackson 2006). Microsclerotia concentration was measured using a hemocytometer and adjusted to 1.5 x 104 per ml. Five soybean seedlings each were dipped into inoculum or sterile CSMB for 30 minutes then planted individually in vermiculite-filled Styrofoam cups placed on flooded trays in 16-hr photoperiod light racks at room temperature. Seven days after inoculation, all inoculated plants were visibly stunted with root and crown symptoms identical to field symptoms while all controls were healthy. M. terrestris was successfully re-isolated from inoculated plants, but not from the controls, and identified by morphology and sequencing as above. M. terrestris has been previously reported causing root rot of soybean in Illinois (Gray 1978) and Wisconsin (Smith et al. 1998). To our knowledge, this is the first report of M. terrestris infecting soybean in Indiana. Increased geographic distribution of this pathogen warrants more attention for its control. M. terrestris has been proposed as a biological control agent against multiple aquatic weeds (Verma and Charudattan 1993; Shearer and Jackson 2006). Introduction of this fungus into soybean production regions should be avoided.

The Physiological Response of Lettuce to Red and Blue Light Dynamics Over Different Photoperiods.

This study aimed to evaluate the effect of dynamic red and blue light parameters on the physiological responses and key metabolites in lettuce and also the subsequent impact of varying light spectra on nutritive value. We explored the metabolic changes in carotenes, xanthophylls, soluble sugars, organic acids, and antioxidants; the response of photosynthetic indices [photosynthetic (Pr) and transpiration (Tr) rates]; and the intracellular to ambient CO2 concentration ratios (Ci/Ca) in lettuce (Lactuca sativa L. “Lobjoits Green Cos”). They were cultivated under constant (con) or parabolic (dyn) blue (B, 452 nm) and/or red (R, 662 nm) light-emitting diode (LED) photosynthetic photon flux densities (PPFDs) at 12, 16, and 20 h photoperiods, maintaining consistent daily light integrals (DLIs) for each light component in all treatments, at 2.3 and 9.2 mol m–2 per day for blue and red light, respectively. The obtained results and principal component analysis (PCA) confirmed a significant impact of the light spectrum, photoperiod, and parabolic profiles of PPFD on the physiological response of lettuce. The 16 h photoperiod resulted in significantly higher content of xanthophylls (neoxanthin, violaxanthin, lutein, and zeaxanthin) in lettuce leaves under both constant and parabolic blue light treatments (BconRdyn 16 h and BdynRdyn 16 h, respectively). Lower PPFD levels under a 20 h photoperiod (BdynRdyn 20 h) as well as higher PPFD levels under a 12 h photoperiod (BdynRdyn 12 h) had a pronounced impact on leaf gas exchange indices (Pr, Tr, Ci/Ca), xanthophylls, soluble sugar contents, and antioxidant properties of lettuce leaves. The parabolic PPFD lighting profile over a 16 h photoperiod (BdynRdyn 16 h) led to a significant decrease in Ci/Ca, which resulted in decreased Pr and Tr, compared with constant blue or red light treatments with the same photoperiod (BconRdyn and BdynRcon 16 h). Additionally, constant blue lighting produced higher α + β-carotene and anthocyanin (ARI) content and increased carotenoid to chlorophyll ratio (CRI) but decreased biomass accumulation and antioxidant activity.

Germination biology of four climatically varied populations of the invasive species African lovegrass (Eragrostis curvula)

AbstractAfrican lovegrass [Eragrostis curvula (Schrad.) Nees] is a highly invasive C4 perennial grass that threatens global biodiversity. Appropriate management of this species has been hampered by a lack of knowledge concerning its seed ecology, resulting in significant economic and environmental impacts within various environments. Consequently, this study explored the effects of a selection of environmental factors (photoperiod, alternating temperature, pH, and salinity) by analyzing several measures of germination on four geographically distinct populations of E. curvula to assist in its extirpation from infested sites. Seeds were collected in Australia from Maffra and Shepparton, VIC; Tenterfield, NSW; and Midvale, WA. Key results showed that seeds from Maffra (54% vs. 79%), Tenterfield (38% vs. 61%), and Shepparton (34% vs. 71%) had significantly reduced germination in complete darkness compared with an alternating 12-h light and 12-h dark photoperiod, whereas Midvale had consistent germination (91% vs. 99%). Temperatures between 17/7 C reduced germination for Maffra (42% vs. 73%), Tenterfield (34% vs. 55%), and Shepparton (33% vs. 59%) compared with the mean of all other temperature combinations, whereas Midvale had consistent germination. Furthermore, germination for all populations was consistent between pH 4 and 9. For salinity, germination was significantly reduced at ≥100 mM for Maffra (29% vs. 67%), ≥150 mM for Tenterfield (29% vs. 94%) and Shepparton (39.5% vs. 81.5%), and 250 mM for Midvale (39% vs. 82%) compared with the mean of all other concentrations. Although each trial was conducted independently, the data can be used to generate species-targeted management. Such strategies include maintaining high levels of quarantine and hygiene programs to avoid future spread; where practical, applying light-limiting strategies (mulching, tilling, or scraping) for the Maffra, Tenterfield, and Shepparton populations; and maintaining management efforts year-round, as the species can germinate under a wide range of conditions.

Seasonal variation in UVA light drives hormonal and behavioural changes in a marine annelid via a ciliary opsin.

The right timing of animal physiology and behavior ensures the stability of populations and ecosystems. In order to predict anthropogenic impacts on these timings, more insight is needed into the interplay between environment and molecular timing mechanisms. This is particularly true in marine environments.Using high-resolution, long-term daylight measurements from a habitat of the marine annelid Platynereis dumerilii, we find that temporal changes in UVA/deep violet intensities, more than longer wavelengths, can provide annual time information, which differs from annual changes in photoperiod. We developed experimental setups that resemble natural daylight illumination conditions, and automated, quantifiable behavioral tracking. Experimental reduction of UVA/deep violet light (app. 370-430nm) under long photoperiod (LD16:8) significantly decreases locomotor activities, comparable to the decrease caused by short photoperiod (8:16). In contrast, altering UVA/deep violet light intensities does not cause differences in locomotor levels under short photoperiod. This modulation of locomotion by UVA/deep violet light under long photoperiod requires c-opsin1, an UVA/deep violet-sensor employing Gi-signalling. C-opsin1 also regulates the levels of rate-limiting enzymes for monogenic amine synthesis and of several neurohormones, including PDF, Vasotocin (Vasopressin/Oxytocin) and NPY-1.Our analyses indicate a complex inteplay between UVA intensities and photoperiod as indicators of annual time.

Influence of light intensity and photoperiod on energy efficiency of biomass and pigment production of Spirulina (Arthrospira platensis)

Biomass and photosynthetic pigments production of cyanobacteria, in particular Spirulina (Arthrospira platensis), depend on light intensity. Production cost of Spirulina cultivation in photobioreactor illuminated with LED is strongly related to light cost. This work is aimed to evaluate the effects of light intensity and photoperiod on the energy efficiency of biomass and pigment production of Spirulina platensis UTEX 1926. Cultures illuminated with white light-emitting diodes (LED) were carried out in batch mode cultivation. Three lighting scenarios with different light intensities were tested: two with a constant light intensity at 80 and 160 μmol · m−2 · s−1 and one with modulated light intensity. Concerning photoperiod, three cycles of light:dark (h:h) (24:00, 20:04 and 16:08) were studied under light intensity at 160 μmol · m−2 · s−1. Concerning Spirulina biomass and pigment production (phycocyanin, chlorophyll and carotenoids), it is found that the lower intensity tested allows a substantial increase of the process energy efficiency. Concerning the influence of the photoperiod, it has been found that the longer the off time is (up to 08 h 00 a day), the higher is the energy efficiency for Spirulina biomass as well as for pigmentary production.

Effects of Light Intensity and Photoperiod on the Growth Performance of Largemouth Bass (Micropterus salmoides) in Recirculating Aquaculture Systems

HighlightsLight design is needed in recirculating aquaculture systems.A long photoperiod is beneficial to largemouth bass growth.Low light intensity is beneficial to largemouth bass growth.Abstract. In this study, recirculating aquaculture systems (RAS) were used to culture juvenile largemouth bass, and the effects of LED light intensity and photoperiod on the survival and growth performance of juvenile largemouth bass were studied. In the light intensity experiment, largemouth bass juveniles with an initial weight of 0.53 ±0.02 g were subjected to a two-month feeding experiment under two different light intensities: group A, at 0.5 W m-2 in the first month and 5 W m-2 in the second month; and group B, at 5 W m-2 in the first month and 0.5 W m-2 in the second month. The results showed that in the first month of the experiment, the growth rate of fry was faster in group A than in group B. After changing the light intensity, the weight of the fry in group B after one month of growth had exceeded and was significantly higher than that in group A. Based on the above experimental results, we conducted a photoperiod experiment. Largemouth bass juveniles with an initial weight of 0.56 ±0.02 g were cultured for two months under four different photoperiods (24L:0D, 16L:8D, 8L:16D, and 0L:24D). The light intensity of the four groups was 0.5 W m-2. The fry growth rate was fastest in the 24L:0D photoperiod group and slowest in the 0L:24D photoperiod group. The growth rate of the 24L:0D photoperiod group was significantly higher than that of the 0L:24D photoperiod group (p < 0.05). The final fry weight was highest in the 24L:0D group, followed by that in the 16L:8D group and 8L:16D group, with the lowest weight observed in the 0L:24D group (p < 0.05). Although the different light conditions in the two experiments had no significant effect on the survival rate of juvenile largemouth bass (p > 0.05), a low-intensity light environment with a continuous photoperiod during the juvenile largemouth bass culture process promoted growth and development. Keywords: Growth, Largemouth bass, Light intensity, Photoperiod, RAS.

Effects of Modification of Light Parameters on the Production of Cryptophycin, Cyanotoxin with Potent Anticancer Activity, in Nostoc sp.

Cryptophycin-1 is a cyanotoxin produced by filamentous cyanobacteria. It has been evaluated as an anticancer agent with great potential. However, its synthesis provides insufficient yield for industrial use. An alternative solution for metabolite efficient production is to stress cyanobacteria by modifying the environmental conditions of the culture (Nostoc sp. ATCC 53789). Here, we examined the effects of light photoperiod, wavelength, and intensity. In light photoperiod, photoperiods 24:0 and 16:8 (light:dark) were tested while in wavelength, orange-red light was compared with blue. Medium, high, and very high light intensity experiments were performed to test the effect of light stress. For a 10-day period, growth was measured, metabolite concentration was calculated through HPLC, and the related curves were drawn. The differentiation of light wavelength had a major effect on the culture, as orange-red filter contributed to noticeable increase in both growth and doubled the cyanotoxin concentration in comparison to blue light. Remarkably, constant light provides higher cryptophycin yield, but slightly lower growth rate. Lastly, the microorganism prefers medium light intensities for both growth and metabolite expression. The combination of these optimal conditions would contribute to the further exploitation of cryptophycin.

Occurrence of Plasmopara destructor causing Downy Mildew on Impatiens walleriana in Brazil.

Impatiens walleriana (Balsaminaceae), popularly known as Impatiens, is an African succulent and a popular ornamental plant worldwide (GBIF, 2019). In Brazil it is broadly grown indoors and outdoors, including in public parks of Curitiba, State of Paraná (Viezzer et al. 2018). In September 2018, I. walleriana plants showing typical downy mildew symptoms were observed in wastelands and gardens in Curitiba. The symptoms included adaxial chlorotic leaf spots with abundant white sporulation on abaxial side (Supplementary figure 1). The disease led to severe defoliation of the plants and the incidence of the plant disease varied from 20 to 80% of plants in an area ranging from 400 to 40,000 m2. A representative sample was deposited in herbarium of the Museu Botânico Municipal de Curitiba (MBM 331601). The following morphology was observed: Sporangiophores (n = 30), hyaline, thin walled, emerging through stomata, 407.3 to 551.1 μm long, slightly swollen base, first branch at 165.8 to 324.7 μm from base, end branches 5.1 to 13.1 μm long, sporangia (n = 50) hyaline, thin-walled subglobose to ovoid, from 12.8 to 21.9 μm x 12.5 to 17.9 μm, slightly papillate. Due to morphological and genetic variations within the species Plasmopara obducens, Görg et al. (2017) proposed the new species P. velutina and P. destructor. The morphology of the Curitiba specimen was equivalent to that described for P. destructor (Görg et al. 2017). DNA was extracted from LEMIDPRTf-19-02 isolate and the ITS1 and cox2 regions were PCR amplified as described in Görg et al. (2017). The resulting sequences were deposited in GenBank (ITS1, MT680628; cox2, MT952335). A BLASTn analysis of the sequences revealed 100% homology with ITS (MF372742) and cox2 (MF372728) sequences of type strain of P. destructor (GLM-F107554). A Bayesian phylogenetic analysis was performed to compare the sequences from this study with reference sequences for P. obducens, P. destructor and P. velutina (Görg et al. 2017; Salgado-Salazar et al. 2018). The oomycete from Curitiba grouped in a reliable clade with P. destructor (Supplementary figure 2). Pathogenicity was carried out by ex vivo and in vivo tests. For ex vivo, stems with approximately four healthy leaves of I. walleriana (n = 10) were embedded in aluminum grid inside of gerbox with the stem bases immersed in distilled water. The inoculation of five stems was carried out by spraying a suspension with 6 x 104 sporangia mL-1 on the abaxial side of the leaves. Five stems with leaves inoculated with sterile water were used as controls. They were incubated in a growth chamber in the dark for 48 h at 20 °C and another 12 days in a 12 h light photoperiod. The confirmation of pathogenicity in plants (in vivo) was obtained with the inoculation of I. walleriana seedlings (one-month old) grown in 2 dm3 aluminum pots. The inoculation methodology and number of plants were the same as the stems test. After the inoculation, plants were incubated in a growth chamber for 48 h in the dark at 20 °C with 100% RH with nebulization, and another 10 days at a photoperiod of 12 hours of light. For both tests, abundant sporulation was observedwith morphology equivalent to Plasmopara destructor described by Görg et al. (2017). No disease developed on control plants. To our knowledge, this is the first report of P. destructor on I. walleriana in Brazil (Farr and Rossman 2019, Silva et al. 2019) representing a potential loss to flower production and a reduction in flowering period in public gardens and parks.

First report of Fusarium proliferatum causing root rot disease in Salvia miltiorrhizae in China.

Salvia miltiorrhiza Bunge is a herb plant used as a traditional Chinese medicine to cure cardiovascular disease. In December 2018, a root rot disease was observed on S. miltiorrhiza in four surveyed counties (Song, Yuzhou, Fangcheng, and Mianchi) in Henan province in China. The disease incidence ranged from 15 to 50% in 12 surveyed fields. At the early stage, the diseased plants were wilting with purple leaves. Leaves and branches became withered and fibrous roots became brown and rotted. The main roots of severely diseased plants also became rotted. The color of the stem surface turned from red to black, and the color of the stem xylem and phloem turned from dark red to brown. Eventually, the roots of diseased plants became completely rotted and the whole plants became dead, but no stink, which is different from Fusarium solani (Mart.) Sacc. (Yuan et al. 2015). Diseased root tissues (5×5×5 mm in size) were cut from diseased plants, surface-sterilized with 1% sodium hypochlorite for 1 min followed by dipping in 75% alcohol for 30 sec, rinsed in sterile distilled water for 3 times, air-dried on a sterilized filter paper in a laminar flow hood, placed on potato dextrose agar (PDA) containing 250 mg/l of streptomycin sulfate, and incubated at 28℃. Five isolates of Fusarium were obtained and purified using the single-spore isolation method. On PDA plates, the colonies were purple in color with formation of white aerial mycelia and reached 50 to 60 mm in diameter after incubation for 5 days. The colonies produced abundant microconidia on the colonies. The microconidia were 4.3 to 12.3 (10.0) × 2.1 to 3.5 (3.1) μm in size (n = 40), hyaline, ovoid or ellipse in shape. The conidiogenous cells were polyphialides. On mung bean media, the isolates formed macroconidia with 3 to 6 septae, fusiform in shape, slightly curved, 21.8 to 32.7 (31.4) × 2.6 to 4.3 (3.4) μm in size (n = 50). The morphological features of the five isolates were consistent with the description for Fusarium proliferatum (Matsush.) Nirenberg ex Gerlach & Nirenberg (Leslie and Summerell 2006). To further define the identity of the five isolates, molecular phylogenetic analysis was performed. The genomic DNA was extracted from all five isolates using the cetyl trimethylammonium bromide (CTAB) method. Five genes [nuclear ribosomal internal transcribed spacer (ITS) region, translation elongation factor 1-α (EF1α), β-tubulin gene, partial sequence for calmodulin (PRO), and RNA-dependent DNA polymerase II subunit (RPB2)] in F. proliferatum were amplified using primers pairs ITS1/ITS4, EF1T/2T, β-tubulin 2a/b, PRO1/2, and RPB2F/R, respectively (Glass and Donaldson 1995; Liu et al. 1999; Mulè 2004; O'Donnell et al. 1998; O'Donnell et al., 2010). The sequences (GenBank accession numbers: MT371373, MT371384, MT925651, MT925652, and MT934441, respectively) showed 99.6 to 100% identities to the corresponding DNA sequences in F. proliferatum (GenBank Acc. Nos. MK243486, MN245720, KJ12896, MN245721, and MK144327, respectively). All five isolates were tested for pathogenicity to fulfill the Koch's postulates. The 45-day-old healthy plants of S. miltiorrhiza grown in sterilized soil in pots (20 cm in diameter), one plant in one pot, were inoculated with conidial suspensions (1.0 × 107 cfu/ml) by pouring 10 ml conidial suspensions around the stem base in one pot. For each isolate, four plants were inoculated. Four plants were treated with sterilized water in the same volume as a control. The tested plants were placed in a growth room at 25°C (RH > 60%) with a 12 h photoperiod of fluorescent light. The pathogenicity assay was repeated for three times. The similar wilt symptoms were observed on the roots in the inoculated plants 30 days after inoculation but were not observed in the control plants. F. proliferatum was re-isolated from the infected roots, and its identity was confirmed by PCR with the primers described above. To our knowledge, this is the first report of F. proliferatum casing root rot disease on S. miltiorrhiza in China.