Effects of flat plastic film covering and tunnel protection on the development of early lettuce

The results of trials with lettuce that was given a temporary cover of polythene sheets of 0.05 mm thickness after being planted in the open in March, indicate that the covering should not be removed until the minimum soil temperature at a depth of 10 cm reaches 4°C. This occurred in 1973 after 14 days when planting on March 7th, and after 7 days when planting on March 19th. The results obtained with perforated polythene were better than with unperforated sheeting.It is possible to advance cropping by 1 week at least. A temporary cover always improves the weight of heads and this is attributed to the increased water content of covered plants and to their larger number of heavier — and therefore probably also larger — leaves. The $\text{length}\text{width}$ ratio of leaves was smaller in plants that were given temporary cover than in those that had not been covered.The differences referred to were considered to be mainly due to the more favourable temperatures under the plastic film and therefore also with improved root development in the first stages of the plant's life.     

Effect of freezing and thawing on microbial activity and glyphosate degradation in two Norwegian soils

Little research has been done on pesticide dissipation in cold climates and there is a need to focus on the influence of climate on pesticide degradation in soil. Glyphosate, N-(phosphonomethyl)glycine, is a herbicide frequently used for controlling perennial weeds through application after harvest and was used as a model compound for this study. The effect of freeze-thaw activity on the availability of glyphosate in soil, and consequently its mineralization by soil microorganisms, was studied through laboratory incubations of repacked soil cores treated with 14C-labelled glyphosate and subjected to different freeze-thaw treatments. Winter simulation regimes applied were constant thaw (+5 degrees C), constant freezing (-5 degrees C), unstable conditions with short fluctuations (24 h of -5 degrees C followed by 24 h of +5 degrees C), and long duration fluctuations (3 weeks of -5 degrees C followed by 3 weeks of +5 degrees C). Distribution of 14C-glyphosate was followed during the incubation through measurements of the mineralized fraction (14CO2), soil water fraction, KOH extractable fraction, and non-extractable fraction. Microbial parameters used to characterize the soils were estimates of size of microbial biomass, overall microbial activity and microbial diversity. The constant freezing treatment exhibited the lowest amount of glyphosate mineralization. The constant thawed treatment and the treatments with fluctuating temperature exhibited significantly increased mineralization. These results were in accordance with the observed concentration of glyphosate in soil water; the higher the activity, the lower the concentration. The amount of glyphosate extractable with KOH and the resulting non-extractable fraction, however, were not significantly affected by soil type or temperature regime. The glyphosate mineralization pattern was comparable with the overall microbial activity in the soils. Observed different levels of diversity might explain some of the difference in total glyphosate mineralization between soils.     

Prediction and Mapping of the Impact of Winter Temperature on the Development of Phytophthora cinnamomi-Induced Cankers on Red and Pedunculate Oak in France

ABSTRACT Phytophthora cinnamomi is the causal agent of a perennial canker that develops on the lower bole on northern red oak and pedunculate oak. The disease has a limited range in Europe, being reported only in southwest France. This limited distribution is probably linked to the susceptibility of P. cinnamomi to frost. A model was developed in previous work to estimate the impact of temperatures of <0 degrees C on the winter survival of P. cinnamomi in trunk cortical tissues and on the subsequent development of cankers. In this article, we report the use of this model to simulate canker development in 503 locations across France during a 30-year period. The predicted canker extension decreased sharply when the median P. cinnamomi winter survival index decreased from 0.95 to 0.65, with cankers that poorly developed when the median survival index was lower than 0.5 to 0.6. The actual incidence of the disease in 192 stands located across southwest France was compared with that of the model outputs. Both presence of disease in stands and frequency of cankered trees in infected stands, but not canker size on infected trees, were strongly related to the median P. cinnamomi survival index. No disease was present in stands with median survival index lower than 0.65, and the frequency of cankered trees in infected stands remained very low in stands with a median survival index between 0.65 and 0.70. Aspect was an additional factor explaining disease incidence, while the effect of elevation was likely due to its effect on winter temperatures. Maps of winter suitability to P. cinnamomi-induced cankers on oaks in France are presented.     

In vivo imaging of quantum dots encapsulated in phospholipid micelles

Fluorescent semiconductor nanocrystals (quantum dots) have the potential to revolutionize biological imaging, but their use has been limited by difficulties in obtaining nanocrystals that are biocompatible. To address this problem, we encapsulated individual nanocrystals in phospholipid block-copolymer micelles and demonstrated both in vitro and in vivo imaging. When conjugated to DNA, the nanocrystal-micelles acted as in vitro fluorescent probes to hybridize to specific complementary sequences. Moreover, when injected into Xenopus embryos, the nanocrystal-micelles were stable, nontoxic (<5 x 10(9) nanocrystals per cell), cell autonomous, and slow to photobleach. Nanocrystal fluorescence could be followed to the tadpole stage, allowing lineage-tracing experiments in embryogenesis.     

Effect of essential oils on the growth of Fusarium verticillioides and fumonisin contamination in corn

Essential oils extracted by hydrodistillation from local plants in Benin, western Africa, and oil from seeds of the neem tree (Azadirachta indica) were evaluated in vitro and in vivo for their efficacy against Fusarium verticillioides infection and fumonisin contamination. Fumonisin in corn was quantified using a fluorometer and the Vicam method. Oils from Cymbopogon citratus, Ocimum basilicum, and Ocimum gratissimum were the most effective in vitro, completely inhibiting the growth of F. verticillioides at lower concentrations over 21 days of incubation. These oils reduced the incidence of F. verticillioides in corn and totally inhibited fungal growth at concentrations of 8, 6.4, and 4.8 microL/g, respectively, over 21 days. At the concentration of 4.8 microL/g, these oils did not affect significantly fumonisin production. However, a marked reduction of fumonisin level was observed in corn stored in closed conditions. The oils adversely affected kernel germination at 4.8 microL/g and therefore cannot be recommended for controlling F. verticillioides on stored corn used as seeds, when used at this concentration. The oil of neem seeds showed no inhibitory effect but rather accelerated the growth of F. verticillioides.     

Alkylpyridiniums. 2. Isolation and quantification in roasted and ground coffees

Recent model studies on trigonelline decomposition have identified nonvolatile alkylpyridiniums as major reaction products under certain physicochemical conditions. The quaternary base 1-methylpyridinium was isolated from roasted and ground coffee and purified by ion exchange and thin-layer chromatography. The compound was characterized by nuclear magnetic resonance spectroscopy ((1)H, (13)C) and mass spectrometry techniques. A liquid chromatography-electrospray ionization tandem mass spectrometry method was developed to quantify the alkaloid in coffee by isotope dilution mass spectrometry. The formation of alkylpyridiniums is positively correlated to the roasting degree in arabica coffee, and highest levels of 1-methylpyridinium, reaching up to 0.25% on a per weight basis, were found in dark roasted coffee beans. Analyses of coffee extracts also showed the presence of dimethylpyridinium, at concentrations ranging from 5 to 25 mg/kg. This is the first report on the isolation and quantification of alkylpyridiniums in coffee. These compounds, described here in detail for the first time, may have an impact on the flavor/aroma profile of coffee directly (e.g., bitterness), or indirectly as precursors, and potentially open new avenues in the flavor/aroma modulation of coffee.     

Measurement of plasma leucine flux in rainbow trout (Salmo gairneri R.) using osmotic pump. Preliminary investigations on influence of diet

A method for the direct measurement of plasma amino acid flux, in rainbow trout, using the continuous infusion of L-[U-¹⁴C]-leucine with ALZET mini-osmotic pumps implanted into the peritoneal cavity, was developed. The fish were fed successively on three different diets (a commercial control diet, a semi-purified diet and a purified diet) during the 4 weeks of experiment. The amounts of radioactivity in the free pool and the protein of both the plasma and skin mucus were measured in these fish. The total flux of leucine was calculated either from the specific activity of leucine in the plasma (61.8 mg leucine. 100 g^-1.d^-1) or from the amounts of labelled and unlabelled leucine flowing into the skin mucus protein (61.5 mg leucine. 100g^-1.day^-1). The total plasma flux was not affected by changes in the diet. The contributions of total leucine oxidation and whole body protein turnover to plasma leucine flux (80% and 20% respectively) were estimated in fish fed the semi-purified diet.     

Fillet texture and muscle structure in brown trout (Salmo trutta) subjected to long-term exercise

Brown trout (Salmo trutta) (2.7 g initial mean weight) were reared in freshwater for 8 months at water velocities of <0.1 (control group), 1 or 2 body lengths per second (BL s^?1) (exercise groups). Growth (body weight, body length and body width), muscle structure (muscle fibre diameter and width of myosepta) and flesh quality parameters (dry matter, muscle pH, collagen content and solubility, instrumental evaluation of texture) were measured at the end of the experiment. The body weight of fish at 1 BL s^?1 was 22% higher than the control group. Muscle development was stimulated at 1 and 2 BL s^?1, leading to a higher condition factor, greater body height and width, and muscle fibre hypertrophy (55 vs. 59.5 μm fibre diameter in the control and 2 BL s^?1 groups respectively). Connective tissue and collagen were only slightly affected by exercise (no difference in collagen solubility, but a greater proportion of γ trimer and fewer α chains in the control compared with the exercised group). Flesh quality was affected, with greater dry matter content and lower post‐mortem pH in the 1 BL s^?1 group compared with the control and 2 BL s^?1 groups. The mechanical resistance of the raw fillets was slightly but significantly increased by exercise. The exercise‐related changes in muscle structure and texture are discussed.