Showing papers by "Wageningen University and Research Centre published in 1989"

Relationship between density and stiffness of apple flesh

Abstract: The parenchyma of a number of varieties of apple was tested in torsion. It is necessary to use small samples (cylinders 10 mm long × 5 mm diameter) orientated to take account of the radial air spaces. Over a range of nine varieties of apple, the torsional stiffness (0.5 to 7 MPa) is largely dependent on the average density (0.6 to 0.9 g cc−1) both within and between varieties. At a given density, the outer parenchyma is stiffer than the inner. As the apple matures, density and stiffness reduce and their mutual dependence is also less. A model is presented which can convert density (or volume fraction) of packed cells into the degree of mutual cellular contact. The calculated degree of contact (never greater than 0.4 of the wall area of a cell) correlates well with stiffness, though the nature of the correlation varies with the variety of apple and its maturity. The anisotropy and density/stiffness relationship must be considered in any mechanical (and presumably, therefore, organoleptic) testing of apples.

Serial effects of host infestation on egg allocation by the mediterranean fruit fly: a rule of thumb and its functional significance

Abstract: SUMMARY (1) Prior infestation of host kumquats (Fortunella japonica) with the eggs of the Mediterranean fruit fly, Ceratitis capitata, had a number of effects on the oviposition behaviour of conspecific flies under semi-field conditions. Overall, infestation markedly reduced the rate at which clutches were laid by a female searching within a host tree, a consequence of effects on three separate components of behaviour. (2) Egg infestation decreased the probability that a female (i) bored with her ovipositor after landing on a fruit and (ii) deposited a clutch once oviposition-boring was initiated, and (iii) deposited additional clutches at new sites on the fruit before leaving. (3) In addition, egg infestation decreased the duration of an oviposition (and thus probably the size of a clutch) and tended (although not significantly) to decrease the persistence with which a female foraged on fruit (expressed in terms of terminal search time (TST) and giving-up time (GUT)). Infestation had no effect on the persistence with which a female foraged within a tree (expressed in terms of TST and GUT) or on the rate at which a female landed on fruit.

Epidemics of diseases and pests of winter wheat at different levels of agrochemical input : a study on the possibilities for designing an integrated cropping system

Abstract: A study to what extent the level of fertilization effects epidemics of pests and diseases, compared to the well-known effects of pesticides and cultivars

Overweight: fat distribution and health risks. Epidemiological observations. A review.

Abstract: Several expert panels have recommended the use of a body mass index (BMI = weight/height2) to assess obesity. Excessive risks of chronic diseases and mortality are clear when BMI exceeds 30 kg/m2. Probably more important in assessing the health risks of excessive fat stores is the distribution of fat over the body. Accumulation of fat in the abdominal cavity (mesenteric and omental fat) predisposes to important metabolic aberrations and leads to an increased incidence of diabetes mellitus, cardiovascular disease, and stroke. Importantly, the increased risks associated with abdominal obesity are seen in obese as well as in non-obese individuals.

Evaluation of Ozone Effects on Vegetation in the Netherlands

Abstract: The current knowledge concerning ozone-induced effects on vegetation in the Netherlands is discussed. Results with indicator plants show that ozone occurs in phytotoxic concentrations throughout the country each year. Foliar injury 1s generally most severe in the western part of the country. The region with the highest average effect intensities does not necessarily coincide with the region with the highest average ozone concentrations. Ozone is considered as the most important air pollutant in terms of crop loss. It is estimated for 1983 that ambient air pollution reduced crop production with 5%, of which 70% is caused by ozone. Especially horticultural crops are affected. From literature data maximum acceptable ozone concentrations. for protection of vegetation have been proposed: 150,μg.m for 1 h, 65 μg. m for 8 h and 50 μg. m for the growing season. Ambient ozone concentrations in the Netherlands, measured in the period 1980-1985, substantially exceeded these values. The frequency of exceedances appears to increase with an increase in the duration of exposure.

Nodule physiology of a supernodulating pea mutant

Abstract: Physiological and biochemical parameters of the supernodulating pea (Pisum sativum L.) mutant nod3 were compared to those of its wild-type parent cv. Rondo in a nil nitrate environment. Plants of cv. Rondo produced more biomass and accumulated more N than plants of nod3. Accordingly, seed yield of the wild type was twice that of the supernodulating mutant. Although the nodule number of nod3 was 10-fold that of cv. Rondo, the nodule mass of nod3 was only twice that of cv. Rondo as individual nodules were smaller in nod3 than in cv. Rondo. The maximum rate of acetylene reduction activity, determined in an open flow-through gas system, was higher in the wild type than in nod3 when expressed on a nodule dry weight basis. However, when expressed on a whole plant basis, the nitrogenase activity (acetylene reduction) was similar in the two symbioses. The net carbon costs of nitrogenase activity was 25% lower in nod3 than in cv. Rondo. An equal proportion of the net CO2 efflux from the root system was for growth and maintenance of the tissue in the two symbioses. However, growth and maintenance respiration was higher in nod3 than in cv. Rondo per gram dry weight of the nodulated root system. The nodules of nod3 had a reduced soluble protein concentration as compared to those of the wild type. The specific activities of nodule glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 1.4.1.14) and asparagine synthetase (EC 6.3.5.4) were lower in nod3 than in cv. Rondo. The root bleeding sap of nod3 contained lower amounts of glutamine and higher amounts of asparagine than that of cv. Rondo. The results suggest that the use of carbon directly related to the dinitrogen fixation and nitrogen assimilation may be less in nod3 than in cv. Rondo, and that there may be differences between the two symbioses in the pathway for assimilation of fixed nitrogen.

The effects of long‐term open‐air fumigation with SO2 on a field crop of broad bean (Vicia faba L.) I. Depression of growth and yield

Abstract: In an open-air Held exposure system for the controlled release of air pollutants, broad bean (Vida faba L.) crops were exposed to elevated SO2 concentrations in three growing seasons, in order to analyse the effects on crop growth under field conditions. The treated plots were exposed to a mean concentration of 165μgm-3 in 1985, 62μgm -3 in 1986 and 74μgm-3 in 1988. The background concentration was about 10μ m-3 . A reasonably uniform distribution of SO2 concentration was obtained over an area of 8m × 8m and concentrations exceeding the target concentration were rare. In 1985 and 1988, the growth rate of the crop was depressed at the end of the pod-filling period. This resulted in a reduction of total dry-matter production of 17% in 1985 and 9% in 1988, and a seed yield reduction of 23% in 1985 and 10% in 1988. In 1986, dry matter growth was not analysed up to the end of the growing season due to a severe infection of Botrytis fabae (Choclate spot disease) infection in the control plot in the middle of the pod-filling period. Slight B. fabae infections in the control plots only were also observed in 1985 and 1988. In all experiments no significant reductions of dry matter growth were observed in the vegetative and early reproductive phases.

The effects of long-term open-air fumigation with SO2 on a field crop of broad bean (Vicia faba L.) : II. Effects on growth components, leaf area development and elemental composition

Abstract: SUMMARY Faba bean crops (Vicia faba L.) were exposed to elevated SO2 concentrations in three different years in an open-air field exposure system for the controlled release of air pollutants. The treated crops were exposed to an average SO, concentration of 165μg m-3 in 1985, 62μg m-3 in 1986 and 74μg m-3 in 1988. The ambient SO2 concentration was about 10 μg m-3. Plant height, number of internodes and number of pods were not affected by SO2. The specific leaf area was reduced in the plants exposed to SO2 at the end of the growing season. Leaf area development was strongly affected during the pod-filling period in 1985 and 1988 as a result of leaf injury and defoliation in the fumigated plots. In 1986 a similar trend in leaf area reduction was observed in the early reproductive phase. N and Mg content of the different organs was unaffected by SO2. The S content was strongly elevated in the leaves and pods of the fumigated plants, and the Ca content of the leaves was reduced by SO2. Chlorophyll content of different leaf numbers was unaffected by SO2.

Value of a control decision rule for leek moth infestations in leek

Abstract: Fourteen commercial leek fields with first and second generation Leek moth, Acrolepiopsis assectella Z., (LM) injury were sampled during 1986 in The Netherlands. For both generations, plant injury was more prevalent in the perimeter of the field than in interior portions. A sequential sampling program for use in making treatment decisions for LM was developed. An economic analysis of the value of sampling information derived from the sequential sampling program was performed. The parameters used for the analysis were crop yield and value, expected level of LM infestation, potential loss of value due to LM infestation, effectiveness of insecticide application, and cost of sampling. Due mainly to the high value of the crop and low cost of treatment, analysis indicates that there is little difference between a sampling-based management plan and prophylactic application of insecticides in terms of pest control costs. Additionally, such a sampling-based management plan is relatively insensitive to changes in the parameters used in the model. Thus, development of a threshold linked to a sampling procedure will not reduce pest control costs. Use of the sampling-based management plan will also not significantly increase pest control costs and will likely result in reduced insecticide use compared with a prophylactic treatment program. Zusammenfassung Bewertung einer Entscheidungsregel fur Bekampfung von Lauchmottenbefall in Porree In den Niederlanden wurde 1986 der durch den Befall der ersten und zweiten Generation der Lauchmotte (Acrolepiosis assectella Z.) verursachte Schaden auf 14 kommerziell genutzten Porreefeldern ermittelt. Fur beide Generationen wurde an den Feldrandern ein deutlich hoherer Befall als in dem inneren Bereich eines Feldes festgestellt. Zur Bekampfung der Lauchmotte wurde als Entscheidungsmodell ein sequentielles Probenahmeverfahren entwickelt. Der Informationsgehalt der sequentiellen Befallserhebung wurde einer okonomischen Bewertung unterzogen. Hierbei wurden folgende Parameter zugrunde gelegt: Erntemenge und Ertrag, erwarteter Befallsgrad sowie hierdurch verursachter moglicher Ertragsverlust, Wirkungsgrad einer Insektizidbehandlung und Kosten der Stichprobennahme. Die Analyse der einzelnen Parameter ergab nur eine geringe Kostendifferenz zwischen einer gezielten Bekampfung nach sequentieller Probenahme und prophylaktischen Insektizidspritzungen, bedingt durch den hohen Wert der Kultur und die niedrigen Kosten einer Bekampfung. Daruber hinaus ist das Verfahren einer gezielten Lauchmottenbekampfung gegeuber Veranderungen der obengenannten Parameter relativ unempfindlich. Deshalb wird die Entwicklung eines Schwellenwertes der mit Probenahmeverfahren verbunden ist die Bekampfungskosten nicht reduzieren. Die Anwendung der Probenahmeplans wurde Bekampfungskosten auch nicht erhohen und wurde wahrscheinlich Insecktizidverbrauch reduzieren im Vergleich zu einen prophylaktischen Behandlungsprogramm.

Sequential sampling to measure the infiltration rate within relatively homogeneous soil units

Abstract: The statistical prediction techniques Trend Surface Analysis, Kriging and Co-kriging are regularly used to provide predictive single-value soil maps. Kriging and Co-kriging perform well in situations where regionally distributed variables show clear spatial structure. If the amount of variation of the variables under study is relatively small, however, no gain in precision is gained by Kriging and Co-kriging, as compared with simply averaging over an area or by applying Trend Surface Analysis. This study was carried out on an older terrace of the Allier river in Central France where attention was focused on the infiltration rate (Inf). Kriging log(Inf) values did barely improve the predictions as compared with Trend Surface Analysis, whereas deleting part of the observations did not result in serious changes of predictions. A satisfactorial first approach was obtained by regarding the observations as being independent. To determine the sample size which provides sufficient information with respect to the soil characteristic under study use can be made of the sequential t-test as is illustrated. Application of this test resulted in eight measurements which represented a saving of 70% as compared with the original standard scheme.