Interactions Between French Isolates of Phomopsis/Diaporthe Helianthi Munt.-Cvet. et al. and Sunflower (Helianthus annuus L.) Genotypes

Three artificial infection tests measuring the rate of mycelial growth of 7 Phomopsis/Diaporthe helianthi isolates were used on leaves, stems and capitula of 6 sunflower hybrids. Isolates and hybrids were chosen to cover the range of variability and resistance levels known at the present time. Significant genotype and isolate effects and isolate×genotype interactions were shown in all the tests, with some changes in order of hybrids according to the isolate used for infection. Consequences of interactions in breeding for stable resistance to P./D. helianthi are discussed.     

Effects of Recent Human Colonization on the Presence of Mercury in Amazonian Ecosystems

Three Hg sources were characterised and mass balance calculations were used to determine their relative contributions to the contamination of the Amazonian environment. About an order of magnitude more Hg is emitted to the atmosphere by goldmining activity than by the burning of forest biomass. However, anthropogenic atmospheric Hg cannot account for the high Hg burdens found in terrestrial ecosystems: deposition of Hg from goldmining sources is estimated to account for less than 3% of the Hg present in the surface horizons of soils. We propose that erosion of deforested soils following human colonization constitutes a major disturbance of the natural Hg cycle. Deforestation thus increases soil Hg mobilisation by runoff, which may explain the increase of Hg burdens in Amazonian aquatic ecosystems in newly colonized watersheds.     

Bottled-Water Quality in Metropolitan Mexico City

Bacteriological and physico-chemical parameters of 265 samples from 39 brands sold in 5-gallon plastic and glass bottles and 2-5 L plastic containers were analyzed to determine the quality of bottled water distributed in Mexico City. Tests included fecal and total coliform counts, alkalinity, total hardness, chloride, calcium and magnesium concentrations, pH and conductivity. Correlation and cluster analyses and ANOVA were carried out, and a comparison made of the averages with the maximum permissible levels established in the Official Mexican Norms. Concerning the investigated parameters no differences (p > 0.05) between the brands were found. Physico-chemical parameters were studied and all the samples were within the permissible limits. Most samples taken from the 5-gallon containers exceeded the maximum bacteriological limits. It was concluded that the bacteriological quality of the brands studied was extremely variable. Appropriate sanitary measures, should be established to control this aspect.     

SPRINKMOD – pressure and discharge simulation model for pressurized irrigation systems. 3. Sensitivity to lateral hydraulic parameters and leakage

A computer model, SPRINKMOD, was tested with field data collected from a simple sprinkler irrigation system in operation. The original data for laterals and the amount and way leakage is considered were modified to evaluate the model sensitivity. The model predicted the pump station flow rate within 2% and the pump station pressure head within 5% with the original data collected. For this irrigation system, no practical effect was observed in the system operating point by changing the lateral pipe characteristics, lateral leakage amount and distribution, lateral pipe roughness and lateral local loss coefficient for flow past a riser outlet. The amount of leakage had more effect on the model simulation of pressure heads than the way leakage was considered, localized or distributed along the laterals. The use of a variable local loss coefficient, K _r, along the 350-m hand-move laterals had a negligible effect on both system operating point and distribution of pressure heads along the laterals. Received: 14 February 1998     

Foliage Age and Pollution Alter Content of Phenolic Compounds and Chemical Elements in Pinus nigra Needles

Changes of phenolics and chemical elements [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn), iron (Fe), boron (B), copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni) and cobalt (Co)] content in needles of black pine ( Pinus nigra) as dependent on age of needles (5–6 classes) and pollution were examined. The content of ortho-diphenols (o-dPh) and total phenols (TPh) was significantly higher at a polluted site than at a control one. It increased with age of needles at both sites. At the polluted site contents of N, K, Mg in black pine needles were lower and of Fe, Ni and F were higher than at the control site. An increase of content with age of needles at both sites was detected for Ca, Fe, B and F, and a decrease for N, P, K, Cu and Ni. The content of elements in different age classes of needles is connected with their mobility. The content of phenolics is negatively correlated with main nutrients and positively with some toxic elements.     

Kinetic modeling of the thermal aggregation of patatin.

A kinetic model of the thermal aggregation of patatin is presented based on chromatographic analysis of the proportions of nonaggregated and aggregated patatin. It was observed that the decrease of the amount of nonaggregated patatin proceeded initially quickly and was followed by slower aggregation at longer incubation times. It was shown that this behavior was not due to heterogeneity of the starting material. It was noted that overestimation of the amount of native molecules after a heat treatment, caused by refolding of the unfolded protein during the cooling step prior to the analysis, was significant and could not be neglected. Hence, corrections based on information on the structural properties of patatin were applied. Taking this into account, a model was proposed consisting of a first-order formation of reactive particles, followed by a second-order aggregation reaction. This model described the thermal aggregation of patatin rather accurately and was confirmed by experiments at various protein concentrations.     

Thermal aggregation of patatin studied in situ.

In this work dynamic light scattering was used to study the thermal aggregation of patatin in situ, to elucidate the physical aggregation mechanism of the protein and to be able to relate the aggregation behavior to its structural properties. The dependence of the aggregation rates on the temperature and the ionic strength suggested a mechanism of slow coagulation, being both diffusion and chemically limited. The aggregation rate dependence on the protein concentration was in accordance with the mechanism proposed. The aggregation rates as obtained at temperatures ranging from 40 to 65 degrees C correlated well with unfolding of the protein at a secondary level. Small-angle neutron scattering and dynamic light scattering results were in good accordance; they revealed that native patatin has a cylindrical shape with a diameter and length of 5 and 9.8 nm, respectively.     

Infection of IHHN virus in two species of cultured penaeoid shrimp Litopenaeus vannamei (Boone) and Litopenaeus stylirostris (Stimpson) in Ecuador during El Niño 1997–98

Infectious hypodermal and haematopoietic necrosis virus (IHHNV) was first noted in blue shrimp Litopenaeus stylirostris (Stimpson) in mid-1981. Since that time, at least 12 species of penaeoid shrimp have been reported to be infected with IHHNV. Pacific white shrimp Litopenaeus vannamei (Boone) represents a shrimp species highly refractory to the disease, whereas L. stylirostris was highly susceptible to the disease. Since the beginning of the shrimp farming industry in Ecuador, viral diseases have been observed in L. vannamei and L. stylirostris. Of these, L. vannamei represents ≈ 80% of cultured shrimp. Histopathology, ultrastructure and in situ DNA hybridization confirm the presence and assess the prevalence of IHHNV in pond-reared shrimp, and especially in abnormally small animals of both species. Although IHHNV may be considered enzootic in cultured L. vannamei in Ecuador, we did not find high prevalence (Cowdry A bodies) in specimens of diseased pond shrimp before 1996. From that time to 1998, a higher prevalence of IHHNV has been observed in both species. The epizootic of the IHHNV disease has been related to the oceanographic and climatological conditions caused by El Niño. In addition, it has been suggested that large quantities of wild shrimp post-larvae of both species that were stocked in shrimp farms, infected as latent carriers in 1997, from which the virus could spread to a larger population of these shrimp in 1998.