Enzyme activity in cell cultures infected with herpesvirus suis]

The activity of succinate dehydrogenase (SDH) and lactage dehydrogenase (LDH) was studied in chick-embryo fibroblast cultures after inoculation of the virulent strain "A2" and the avirulent strain "MK" of herpesvirus suum. Strain "A2" reduced SDH activity, and so did strain MK, but here the decrease of enzyme activity was slower, and it did not become evident until the 24th hour. LDH activity fluctuated after "A2" infection but was generally increased, while there was no change in LDH activity, compared with uninfected control cells, after "MK" infection. When interaction of cell and virus took place in the presence of 5-iodo-2-desoxyuridine (IUDR), strain "A2" produced little change in the enzymes, but "MK" infection was accompanied by a definite fall in SDH and a slight increase in LDH. The presence of IUDR inhibited the proliferation of the virulent strain but had no apparent effect on proliferation of the attenuated strain "MK". Investigation of the enzyme activity of cells infected with Aujeszky's disease virus has revealed new biological properties of the virus, which might serve to distinguish between different strains of the virus.     

The effects of ultraviolet-B (UV-B: 290–320 nm) radiation on blister blight disease of tea (Camellia sinensis)

Sunlight is known to reduce the incidence of blister blight disease of tea, caused by Exobasidium vexans . The effects of the ultraviolet-B (UV-B: 290–320 nm) component of solar radiation on the disease and the development of E. vexans were studied in the field in Sri Lanka using UV-screening filter materials held over a commercial crop. Exclusion of UV-B radiation by Polyester, which reduces fluxes in the UV-B region by approximately 75–85%, increased both the number of translucent spots (immature sites of infection) and number of sporulating blisters (mature sites of infection), but it had little or no effect on the sporulation of the pathogen. When basidiospores were artificially inoculated on leaves, and were exposed to full or filtered solar radiation, their survival and germination increased when UV-B wavelengths were removed; significant differences were found 62 h after inoculation. However, UV-B did not affect the extension of germ tubes. This study indicates that the UV-B component of solar radiation plays an important role in the natural regulation of blister blight disease in the field.     

Modelling crop:weed interactions in wheat with ALMANAC

ALMANAC is a dynamic model for plant growth, water balance and soil nitrogen dynamics that can simulate on a daily basis two or more competing species. The simulation of competition for light is based on Beer's law, allowing a different extinction coefficient ( k ) for each species. Light is partitioned between species based on k -values, leaf area index and plant heights. Total hiomass is simulated with radiation use efficiency and grain yield with a harvest index approach, sensitive to water stress. The model simulates competition for water and nutrients based on each species current rooting zone and demand by each species. The effect of crop management on the competition issue can he simulated. The model was evaluated in Dijon (France) using 4 years of experimental data on wheat:oat mixtures, differing in oat ( Avena sativa L.) densities, the period of oat emergence, the date of weed suppression by herbicides and the wheat ( Triticun aestivum L.) genotype. Additional data on oilseed rape ( Brassica nupus L.) and vetch ( Vilcia sauiva L.) competition in spring wheat were also used. The wheat grain yield was reasonably simulated with a root mean square error (RMSE) of 0.10-0.35 t ha^-1. Corresponding values for oats were 0.10-0.55 t ha^-1. The competitiveness of oats, oilseed rape and vetch was correctly simulated. The model appears as a reasonable tool for estimating damage thresholds in integrated weed control programmes.     

敌百虫的液相色谱分析方法

本文采用即以乙腈+水(50+50)为流动相,用CN柱和紫外检测器分离测定敌百虫原药及40%敌·毒乳油中敌百虫反相高效液相色谱法。结果表明,本方法的标准偏差为0.3233,变异系数为0.3551%,平均回收率为99.65%,线性相关系数为0.9997。     

除草剂最低致死剂量(MLHD)使用新技术概述

本文论述了荷兰MLHD技术的基本内容、技术原理、应用程序等．并针对荷兰的农业特点、开发背景，对该技术在荷兰与中国的应用前景及可行性等进行了比较分析．作者认为合理地利用该技术将有利于我国农业的可持续发展。     

Proposals for a Sangay National Park in Ecuador

This paper describes the main features of the Sangay wilderness area in the Ecuadorian Andes. It is a region of great diversity with life zones ranging from tundra to subtropical rain forest. The conservation value of the area is assessed and the feasibility of protection determined. Boundaries based mainly on the limits of human interference are put forward with management proposals for its establishment as a National Park.