Survival and inactivation of classical swine fever virus

Classical swine fever virus, like many enveloped viruses, may be regarded as moderately fragile. It shows a short but variable survival time in the environment, depending on physical conditions, but may remain viable for prolonged periods in favourable circumstances as found, for example, in stored meat. Published information is reviewed on the survival time of the virus under a variety of physical and chemical conditions, including the variable influence of environmental factors. The principles of virus inactivation by heat, pH or chemicals are discussed, with a consideration of the principles of containment for laboratories working with the virus.     

Oestradiol Induced Inhibition of Neuroendocrine Marker Expression in Leydig Cells of Adult Rats

The objectives of this work were to determine the changes in the expression of neuroendocrine markers in Leydig cell by oestradiol treatment, and to determine whether testosterone is able to recover partially the effects of hormonal suppression induced by oestradiol. Adult male rats were injected daily with either 50 microg of oestradiol or oestradiol plus testosterone propionate (25 mg every 3 days) for 15 days. The animals were sacrificed and testicles were dissected and processed by routine histological protocols. FSH and LH serum levels were determined by radioimmunoassay. The visualization of antigens was achieved by the streptavidin-peroxidase immunohistochemical method. Antibodies against chromogranin A (CrA), S-100 protein (S-100), P substance (PS), synaptofisin (SYN), neurofilament protein (NF), gliofibrillary acidic protein (GFAP) and neuron specific enolase (NSE) were used. The mean LH and FSH serum concentrations were consistently suppressed with hormonal treatments. Intermediate filaments (NF and GFAP) showed no difference in their expression. The expression of S-100, NSE and SYN was significantly lower in both hormone-treated groups. In oestradiol-treated rats, the immunoreactivity of CrA and SP decreased significantly but was restored after testosterone supplementation. Although the nature and functions of many of these substances in Leydig cells remain unknown, these results are consistent with the hypothesis that the expression of some neuroendocrine markers is hormonally controlled.     

Sustainable management of the western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), in infested areas: experiences in Italy, Hungary and the USA

The western corn rootworm, Diabrotica virgifera virgifera LeConte, is the most important pest of maize in the Midwestern USA, and since its detection in 1992 in Europe, also in several countries of Central and Eastern Europe. Methods for managing this pest vary from region to region, depending upon: the different cultural practices in maize production, climatic conditions, soil types, pest behaviour, infestation level and socio-economic conditions. Factors including date of planting, amount of rotated or continuous maize, irrigation, date of rootworm hatching and differences in behaviour of the pest, necessitate developing different management strategies in different areas of the infested countries. Pest monitoring, damage evaluation, threshold development, use of insecticides, risk estimation and crop rotation are some of the starting points in the development of management strategies. Approaches and experiences in D. v. virgifera control and management in Italy, Hungary and the USA, based on the understanding of local agro-ecosystems and socio-economic conditions, are reported.     

Soil S availability in upland pastures of NE Scotland: relationship of extractable soil S and soil respiration to soil and site characteristics

Abstract. The mean extractable sulphur (S) concentration in 315 upland topsoil samples collected in 1988/89 from beneath pasture in NE Scotland was 13 μg S g⁻¹ (range 2–77 μg S g⁻¹). More than two thirds of the samples had S concentrations less than that acceptable for productive soils. Continued decreases in atmospheric S inputs may have increased this proportion subsequently. The analysis of herbage S also indicated that two-thirds of the samples were below 0.2% S. A 'respirometric index', namely CO₂ produced during cellulose decomposition without added S as a percentage of that produced with added S, was significantly less than 100% in a quarter of the soils. Results of three different extraction procedures suggested that sulphate in the soils was present mainly as free plus adsorbed rather than precipitated forms. Soil extraction identified a significant non-sulphate S fraction, presumably organic S. The variability in extractable S stemmed from a combination of geographical, depositional and local site and soil factors. Extractable S was significantly correlated with soil organic matter content and inversely with soil pH and together these factors explained 37% of the variability. While significant differences in mean concentrations between geographical area, soil association and drainage status were evident, no trends could be observed between the major soil subgroups or with altitude.     

Mechanisms of drought response in Thuja occidentalis L. II. Post-conditioning water stress and stress relief

We examined the extent of osmotic adjustment and the changes in relative water content (RWC) and transpiration rate (i.e., relative stomatal function) that occur in water-deficit-conditioned 6-year-old Thuja occidentalis L. (eastern white cedar) trees in response to a severe drought. Trees conditioned by successive cycles of mild or moderate nonlethal water stress (conditioning) and nonconditioned trees were exposed to drought (i.e., -2.0 MPa predawn water potential) to determine if water deficit conditioning enhanced tolerance to further drought stress. Following drought, all trees were well watered for 11 days to evaluate how quickly osmotic potential, RWC and transpiration rate returned to preconditioning values. Both nonconditioned trees and mildly conditioned trees exhibited similar responses to drought, whereas moderately conditioned trees maintained higher water potentials and transpiration rates were 38% lower. Both conditioned and nonconditioned trees exhibited a similar degree of osmotic adjustment (-0.39 MPa) in response to drought relative to the well-watered control trees. The well-watered control trees, nonconditioned trees and mildly conditioned trees had similar leaf RWCs that were about 3% lower than those of the moderately conditioned trees. Following the 11-day stress relief, there were no significant differences in osmotic potential between the well-watered control trees and any of the drought-treated trees. Daily transpiration rates and water potential integrals (WPI) of all drought-treated trees approached those of the well-watered control trees during the stress relief period. However, the relationship between cumulative transpiration and WPI showed that previous exposure to drought stress reduced transpiration rates. Leaf RWC of the moderately conditioned trees remained slightly higher than that of the nonconditioned and mildly conditioned trees.     

Tree water use and rainfall partitioning in a mature poplar-pasture system

Traditionally, poplars (Populus) have been planted to control erosion on New Zealand's hill-slopes, because of their capacity to dry out and bind together the soil, by reducing effective rainfall and increasing evapotranspiration and soil strength. However, the effect of widely spaced poplars on the partitioning of soil water and rainfall has not been reported. This study determined rainfall partitioning for 18 mid-spring days in a mature P. deltoides (Bart. ex Marsh, Clone I78)-pasture association (37 stems per hectare, unevenly spaced at 16.4 +/- 0.4 m) and compared it with a traditional open pasture system in grazed areas of a hill environment. Tree transpiration was measured by the heat pulse technique. A time-driven mathematical model was used to set a zero offset, adjust anomalous values and describe simultaneous sap velocity time courses of trees. The model showed that daylight sap flow velocities can be represented with a nonlinear Beta function (R(2) > 0.98), and differences in the parameters representing the initiation, duration and conformation of the sap velocity can be tested statistically to discern tree transpiration differences during the day. Evapotranspiration was greater for the poplar-pasture association than for the open pasture (2.7-3.0 versus 2.2 mm day(-1)). The tree canopy alone contributed 0.92 mm day(-1) as transpiration and 1.37 mm day(-1) as interception, whereas evapotranspiration of the pasture understory was only 0.4-0.6 mm day(-1). Despite the higher water use of the poplar-pasture association, soil water in the 0-300 mm soil stratum was higher than, or similar to, that of the open pasture. Tree shading decreased evapotranspiration and pasture accumulation under the trees.     

Seasonal patterns of light-saturated photosynthesis and leaf conductance for mature and seedling Quercus rubra L. foliage: differential sensitivity to ozone exposure

Extrapolation of the effects of ozone on seedlings to large trees and forest stands is a common objective of current assessment activities, but few studies have examined whether seedlings are useful surrogates for understanding how mature trees respond to ozone. This two-year study utilized a replicated open-top chamber facility to test the effects of subambient, ambient and twice ambient ozone concentrations on light-saturated net photosynthesis (P(max)) and leaf conductance (g(l)) of leaves from mature trees and genetically related seedlings of northern red oak (Quercus rubra L.). Gas exchange measurements were collected four times during the 1992 and 1993 growing seasons. Both P(max) and g(l) of all foliage followed normal seasonal patterns of ontogeny, but mature tree foliage had greater P(max) and g(l) than seedling foliage at physiological maturity. At the end of the growing season, P(max) and g(l) of the mature tree foliage exposed to ambient ( approximately 80-100 ppm-h) and twice ambient ( approximately 150-190 ppm-h) exposures of ozone were reduced 25 and 50%, respectively, compared with the values for foliage in the subambient ozone treatment ( approximately 35 ppm-h). In seedling leaves, P(max) and g(l) were less affected by ozone exposure than in mature leaves. Extrapolations of the results of seedling exposure studies to foliar responses of mature forests without considering differences in foliar anatomy and stomatal response between juvenile and mature foliage may introduce large errors into projections of the response of mature trees to ozone.     

Mechanical site preparation effects on understory plant diversity in the Piedmont of the southern USA

Diversity of understory vegetation was compared among four intensities of site preparation and an adjacent 50-year-old pine-hardwood forest. The study site was a six-year-old loblolly pine (Pines taeda) plantation in the lower Piedmont of Georgia. Species richness and Shannon diversity indices were used to evaluate vine and woody (trees and shrubs) species diversity. Biomass distribution was compared among four plant categories: vines, forbs, grasses, and woody. Moderate intensity treatments (chainsaw and shear and chop) consistently ranked highest overall in diversity, with the mature pine-hardwood forest ranking lowest. Distribution of the four plant categories was not significantly affected by intensity of site preparation.Alabama Agricultural Experiment Station Series No. 9-892325P.