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Showing papers by "Agriculture and Agri-Food Canada published in 1995"


Journal ArticleDOI
TL;DR: Molecular interactions between anthocyanins and some of the other red wine molecules are shown to be associated with development of new pigments whose formation explains the subtle color changes and stabilization occurring on aging of red wines.
Abstract: The types of anthocyanins occurring in grapes, wines, and juices are described and their distribution documented. Recent work on the evaluation of red wine color during storage and aging is reviewed. Molecular interactions between anthocyanins and some of the other red wine molecules are shown to be associated with development of new pigments whose formation explains the subtle color changes and stabilization occurring on aging of red wines. A detailed description of the recovery of anthocyanins from grape pomace and production of natural red colorants is also given.

533 citations


Journal ArticleDOI
TL;DR: Two improvements to the Logan model of temperature-dependent development were proposed, first eliminated a redundant parameter then incorporated an intercept parameter, thereby resolving the inability of the original model to estimate a low-temperature developmental threshold.
Abstract: We proposed two improvements to the Logan model of temperature-dependent development. We first eliminated a redundant parameter (modification 1) then incorporated an intercept parameter (modification2), thereby resolving the inability of the original model to estimate a low-temperature developmental threshold. The three model versions were compared using temperature-dependent developmental rates in six insect species (a total of 11 life stages).The original model and modification 1 produced identical curves. In 10 of the 11 cases, modification2 had the highest r2 and the least estimation bias.

518 citations


Journal ArticleDOI
TL;DR: A physiological model is described to explain how the precision of estrus is improved following PGF(2 alpha)-induced luteolysis, via the effect of pretreatment with GnRH on follicular development and luteal functions in cattle.
Abstract: Treatment with GnRH and PGF2 alpha is a practical method for controlling ovarian follicular and luteal functions and increasing the precision of estrus synchronization in cyclic and acyclic postpartum cows and heifers. This method reduces considerably the period of time needed for estrus detection; it synchronizes the estrous cycle of 70 to 80% of the cyclic cows to within a 4-d interval without any detrimental effect on the fertility rate (65 to 85%). Moreover, resumption of ovarian activity and normal fertility in acyclic cows in favored. Administration of GnRH eliminates the large follicles by ovulation or atresia and induces emergence of a new follicular wave within 3 to 4 d after treatment at any stage of the estrous cycle, but it limits further growth of these emerging follicles by increasing atresia. The precision of estrus and the unaltered fertility rate is due to the synchronized selection of a new larger growing follicle, which becomes the ovulatory follicle after PGF(2 alpha)-induced luteolysis 6 d after GnRH treatment. Also, fixed-time AI programs without the need for estrus detection may be possible using a second injection of GnRH in a GnRH-PGF(2 alpha)-GnRH protocol to ovulate the selected follicle at a precise time. We describe a physiological model to explain how the precision of estrus is improved following PGF(2 alpha)-induced luteolysis, via the effect of pretreatment with GnRH on follicular development and luteal functions in cattle. Application of this model to the development of reliable methods of fixed-time insemination is also explored.

318 citations


Journal ArticleDOI
TL;DR: Chlorophyll fluorescence ranks high among stress detection tests in forestry applications, because it is rapid, reliable, non‐destructive, quantitative, diagnostic, and the physiological basis of the assessment is understood.
Abstract: The practical utility of chlorophyll fluorescence to forestry applications is reviewed. Major subjects include a review of past applications, sampling protocols, important fluorescence features, and instrumentation. Applications including the study of various stress effects, seasonal effects, and comparative sun/shade leaf physiology are provided. Chlorophyll fluorescence has been used mainly in applied research, rather than directly in operational forestry, but work has begun in this area. Sampling protocols include the selection and treatment of samples before assessment, and control of environmental conditions during assessment. Instrumentation is evaluated based on accuracy, versatility, ease of operation, and cost. Chlorophyll fluorescence ranks high among stress detection tests in forestry applications, because it is rapid, reliable, non‐destructive, quantitative, diagnostic, and the physiological basis of the assessment is understood.

237 citations


Journal ArticleDOI
TL;DR: The data suggest that Colorado potato beetle larvae compensated for inhibited gut proteolytic activity during chronic intake of papain inhibitors by synthesizing insensitive proteinase(s) via gaseous methyl jasmonate.

217 citations


Journal ArticleDOI
TL;DR: In this paper, the use of microscopy and imaging techniques for evaluating food structure is discussed. But, as mentioned before, these techniques cannot be directly applied to study food structure because the processing conditions that turn biological raw materials into food cause structural and textural changes which, in turn, change the innate properties and behaviour of the foods.
Abstract: Microscopy and imaging techniques are the most appropriate techniques for evaluating food structure because they are the only analytical methods that produce results in the form of images rather than numbers. However, images may now also be converted into numerical data to allow for statistical evaluation. Advances in microscopy and imaging techniques are made, for the most part, outside the field of food science, drawing from the fields of materials science, biology and medicine. Such techniques cannot, in most cases, be directly applied to study food structure. They must be adapted because the processing conditions that turn biological raw materials into food cause structural and textural changes which, in turn, change the innate properties and behaviour of the foods. This necessitates the development of appropriate methods and also the specialization of researchers. Future developments in this field can be divided into the use of new equipment developed for use in other fields, and the application of techniques modified to solve specific food science problems, such as the development of new foods with particular properties and texture or the detection of defects in foods.

195 citations


Journal ArticleDOI
TL;DR: Because of their selectivity and minimal environmental impact, microbial control agents will be ideal components of integrated pest management programs in the early 21st century and beyond, but if they are used merely as replacements for chemical pesticides, then eventually these agents will face some of the same fate as the chemicals they replace, particularly with respect to resistance.
Abstract: The role of microbial control in crop and forest protection and the abatement of insects of medical and veterinary importance has expanded considerably with the discovery and development of new microbial control agents and genetic improvement in bacterial and viral pathogens, and improvements in formulation, application options and compatibility with other interventions. A synopsis of the literature regarding the current use of bacteria, viruses, fungi, protozoans and nematodes as microbial control agents is presented along with speculation on their potential in the early 21st century. The most widely used of all microbial control agents isBacillus thuringiensis. The isolation within the past two decades of new strains that are larvicidal for certain Diptera and Coleoptera has increased the utility of the bacterium considerably. Further improvements in efficacy and broadening of its host range are in progress with the isolation of strains with new toxins and the manipulation ofB. thuringiensis genes that encode toxin production using both recombinant and nonrecombinant methods. Genetic manipulation of these genes has also enabled their incorporation into crop plants. The development and commercial availability of entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae expands the options for the control of insects, especially those with soil inhabiting stages. The results of natural epizootics of fungi and viruses often obviate the requirement for additional interventions. Breakthroughs in understanding the genetics ofBaculovirus and subsequent gene manipulation have increased their virulence and utility. Improved production methods that utilize insect cell culture technology may enable affordable use ofBaculovirus in the not too distant future. Fungi continue to offer the only control options using entomopathogens against plant sucking insects. Although fungi have great potential for development as microbial control agents, only a few have been used on an operational scale. Some factors that might limit the full range of entomopathogen potential, including development of resistance, are discussed. Because of their selectivity and minimal environmental impact, microbial control agents will be ideal components of integrated pest management programs in the early 21st century and beyond. However, if they are used merely as replacements for chemical pesticides, then eventually these agents will face some of the same fate as the chemicals they replace, particularly with respect to resistance.

192 citations


Journal ArticleDOI
TL;DR: It is suggested that the detection and avoidance of infected males by female mice through odour cues may function to reduce parasite transmission and potentially serve as a component of female mate selection or choice.
Abstract: The detection and avoidance of parasitized males has been proposed to be a component of female mate choice. We investigated whether or not female laboratory mice, Mus musculus domesticus, could discriminate between parasitized and non-parasitized males on the basis of odour. Female mice were given a choice between the urine and other odorous secretions of either a male mouse sub-clinically infected for five days with the naturally occurring, enteric, single host, protozoan parasite, Eimeria vermiformis, or an uninfected male. Females showed a marked preference for the odours of non-parasitized male mice over those of the parasitized males; as measured by number of investigations, time spent per investigation, and total investigation time of the odours in a choice situation. Female mice also displayed an overwhelming initial, or first choice, preference for the odours of the non-parasitized male mice over those of the parasitized males. These observations show that female mice can distinguish between the odours of parasitized and non-parasitized males, and discriminate against parasitized males on the basis of odour. We suggest that the detection and avoidance of infected males by female mice through odour cues may function to reduce parasite transmission and potentially serve as a component of female mate selection or choice.

192 citations


Journal ArticleDOI
TL;DR: The BEN- and CIN-induced decrease in soybean nutrient absorption may be a consequence of damage to cell membrane integrity caused by a decrease in sulfhydryl groups followed by lipid peroxidation.
Abstract: Benzoic (BEN) and cinnamic (CIN) acids are commonly found in soils and are considered as strong allelochemicals. Published information suggest that BEN and CIN and other phenolic acids decrease plant growth in part by suppressing nutrient absorption. However, studies on the mechanism of action were not conclusive. We examined the effects of BEN and CIN on the cell plasma membrane in intact soybean (Glycine max L. cv. Maple Bell) seedlings. Treating intact root systems with BEN or CIN rapidly increased electrolyte leakage and ultraviolet absorption of materials into the surrounding solution. After 12 hr of treatment, BEN and CIN lowered the extracellular sulfhydryl group content in roots. The two allelochemicals induced lipid peroxidation, which resulted from free radical formation in plasma membranes, inhibition of catalase and peroxidase activities, and sulfhydryl group depletion. Oxidation or cross-linking of plasma membrane sulfhydryl groups is the first mode of action of both compounds. The BEN- and CIN-induced decrease in soybean nutrient absorption may be a consequence of damage to cell membrane integrity caused by a decrease in sulfhydryl groups followed by lipid peroxidation.

190 citations


Journal ArticleDOI
TL;DR: If a piglet's calls provide reliable information about its need for the sow's resources, then this calling can be used as a measure of its welfare, which is consistent with theoretical models of honst signalling.

179 citations


Journal ArticleDOI
TL;DR: In this article, the acidifying effects of urea and anhydrous NH 3 when used as fertilizers for cereal production in Saskatchewan, Canada, were quantified and the major effect of acidification was a depletion of exchangeable Ca and Mg.
Abstract: Acidity generated by N fertilizers depends on factors such as the composition of the fertilizer, climatic and soil conditions, and the crops grown. Our objective was to quantify the acidifying effects of urea and anhydrous NH 3 when used as fertilizers for cereal production in Saskatchewan, Canada. The fertilizers were injected annually (at 10-cm depth) into a medium-textured, moderately acid (pH 5.5) Typic Haploboroll, at rates of 0, 45, 90, and 180 kg N ha -1 for 9 yr. Soil acidity increased as N application rate increased, with anhydrous NH 3 causing greater acidification than urea. Although pH values as low as 4.3 were recorded in soil treated with anhydrous NH 3 , KCl-exchangeable acidity remained low. The major effect of acidification was a depletion of exchangeable Ca and Mg. The solubility of Mn (but not Al) increased substantially as pH decreased, with solution concentrations of almost 30 mg Mn L -1 being recorded 6 d after injection of NH 3 . Acidity generated by anhydrous NH 3 compared well with values predicted assuming that all of the applied NH 3 was oxidized to NO - 3 (with the production of 1 mol H + mol -1 of N) and that these protons were partly neutralized by OH - released when NO - 3 was taken up and assimilated by plants. Acidification due to export of bases in grain was insignificant because wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) remove only a slight excess of cations over anions. Urea failed to realize its full acidification potential because of an apparent loss of urea-N from the soil by NH 3 volatilization.

Journal ArticleDOI
TL;DR: In this article, the authors developed a sensitive method to identify and quantify organic acids in soil extracts from the rhizosphere of quackgrass grown under greenhouse conditions, which involves ion-exchange chromatographic separation using step gradient, and quantification by UV absorption for aromatic acids and by conductivity for aliphatic acids.
Abstract: Low molecular-weight organic acids play a determinant role in nutrient cycling and plant growth in agricultural and forest ecosystems Our study was made to develop a sensitive method to identify and quantify organic acids in soil extracts from the rhizosphere of quackgrass grown under greenhouse conditions The procedure involves ion-exchange chromatographic separation using step gradient, and quantification by UV absorption for aromatic acids and by conductivity for aliphatic acids In a single chromatographic run, 14 aliphatic acids were separated in 55 min and 14 aromatic acids in 25 min The methods have high precision with relative standard deviations of peak areas ranging from 150 to 799% for aliphatic acids and from 065 to 637% for aromatic acids The method for aliphatic acids is recommended for mono- or dicarboxylic acid analysis, whereas the method for aromatic acids constitutes a major improvement over previous procedures We identified 13 organic acids in the quackgrass rhizosphere and 18 organic acids in soil containing decomposing residues of this plant The largest concentrations were found in soils containing quackgrass residues Aliphatic acid concentrations were generally larger than those of aromatic acids Formic and acetic acids dominated the aliphatic group, whereas benzoic and p -hydroxybenzoic acids were found in largest amounts among aromatic acids

Journal ArticleDOI
TL;DR: Methane and CO2 emissions from a herd of 118 lactating cows were measured directly by continuous monitoring with an infrared gas analyzer from 24 gas sampling locations, and values were not corrected for gas emissions from stored manure.

Journal ArticleDOI
TL;DR: In this paper, a model structure for humic acids is proposed to simulate, understand, and predict the trapping and binding of biological and anthropogenic substances in soils, and to follow geochemical processes at the nanochemistry level.
Abstract: Humic substances and soil organic matter are one essential basis for life on earth, and the study of their structures is the aim of a fast-growing, interdisciplinary, scientific community, in particular in the environmental sciences. Modern methods of instrumental analytical chemistry such as analytical pyrolysis combined in an integrated approach with the wide range of standard chemical and biological techniques, have led to proposing a model structure for humic acids. Simultaneously, powerful software programs for computational chemistry and molecular modeling have become available and prompted our present work to develop model structures for humicand organomineral complexes as well as soil particles. The principal aims are to simulate, understand, and predict the trapping and binding of biological and anthropogenic substances in soils, and to follow geochemical processes at the nanochemistry level. The Chemistry of Soil Organic Matter

Journal ArticleDOI
TL;DR: In this paper, the influence of tillage practices on the decomposition of corn residues and turnover of soil organic matter (SOM) was investigated in a maize field and an adjacent meadow, and the results showed that corn-derived C was evenly distributed with depth in the moldboard plow treatment and accumulated at the surface in shallow, reduced-tillage treatments.
Abstract: This study was conducted to determine the influence of tillage practices on the decomposition of corn (Zea mays L.) residues and turnover of soil organic matter (SOM). Measurements of delta 13C were made of the whole soil, the microbial biomass, and two particle-size fractions ( 50 micrometers) in soils that had been under corn production for 11 yr and from an adjacent meadow. Meadow-derived C in total SOM (0-24 cm) decreased under corn cropping at the same rate under all tillage treatments. Corn-derived C was evenly distributed with depth in the moldboard plow treatment and accumulated at the surface in the shallow, reduced-tillage treatments. The incorporation of corn residue C into SOM in the 0- to 24-cm layer was not significantly affected by tillage and was estimated to be approximately 41 g C m-2 yr-1, which represents approximately 30% of the corn residue inputs. Both the macroorganic matter (> 50 micrometers) and microbial biomass had a greater enrichment (up to 35%) in corn-derived C than either the whole soil or the microorganic matter (< 50 micrometers), indicating that these pools are important recipients of plant residue inputs. Nevertheless, the microorganic matter was also a significant sink for C input, accounting for = 50% of the total corn-derived C remaining in the surface (0-8 cm) soil. Under the conditions of this study, tillage practices influenced the vertical distribution of SOM and corn residues but had no detectable effect on SOM turnover and on the fate of corn residues when the whole Ap horizon was considered.

Journal ArticleDOI
TL;DR: Results indicate that mycorrhizas significantly improve tolerance to moderate drought stress imposed at tasselling, especially for the sensitive CO maize cultivar.
Abstract: SUMMARY A greenhouse experiment was conducted to investigate the influence of an arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) on drought tolerance in tropical maize. Freshly regenerated seeds of selection cycles 0 (cv. CO, drought-sensitive) and 8 (cv. C8, drought-resistant) of the lowland tropical population 'TuxpefiQ sequia' were used for this study. Maize plants were subjected to drought stress for three weeks following tasselling (75-95 days after sowing). During the drought stress period, midday leaf water potential (LWP), stomatal resistance (SR) and transpiration rate (TR) were monitored daily, and green leaf area (GLA) determined at alternate days to assess the effects of mycorrhizal inoculation. Mycorrhizal plants of the cultivars CO and C8 had higher (less negative) LWP and TR, and lower SR throughout the experiment. The GLA was 27-5 % higher in mycorrhizal than non-mycorrhizal CO plants under drought conditions. Results indicate that mycorrhizas significantly improve tolerance to moderate drought stress imposed at tasselling, especially for the sensitive CO maize cultivar.

Journal ArticleDOI
TL;DR: In this article, a method for determining 199 pesticides in fruit and vegetables is described, where residuals are extracted from samples with acetonitrile, and coextractives are removed with a miniaturized charcoal-Celite column cleanup.
Abstract: A method is described for determining 199 pesticides in fruit and vegetables. Residues are extracted from samples with acetonitrile, and coextractives are removed with a miniaturized charcoal-Celite column cleanup. Analysis is performed by gas chromatography with mass-selective detection in selective-ion monitoring mode. Two injections per sample are required to cover all compounds. Positive analytes are confirmed by retention time and ion ratios. Carbamates are analyzed by liquid chromatography with postcolumn reaction and fluorescence detection. Recovery data were obtained by fortifying 3 matrixes (pears, carrots, and bananas) at 0.1-0.5 ppm. In addition, the method demonstrated acceptable performance for analysis of other crops such as apple, strawberry, orange, pineapple, asparagus, beet, cucumber, tomato, pepper, squash, green peas, potato, and sweet potato. Limits of detection ranged from 0.02 to 0.2 ppm depending on the compound.

Journal ArticleDOI
TL;DR: It is suggested that the odour-induced analgesic responses and the neuromodulatory correlates are part of an adaptive defence mechanism that facilitates the detection and avoidance of parasitized males by female mice and contributes to female mate choice.

Journal ArticleDOI
TL;DR: Neem insecticides may be suitable for use in integrated pest management programs, as under field use they appear to be relatively benign to aphid predators and parasitoids.
Abstract: Neem [Azadirachta indica (A. Juss.)] seed oil (NSO) applied in three concentrations, 0.5%, 1% and 2%, to potted plants infested with green peach aphid,Myzus persicae (Sulzer), totally prevented adult eclosion of larval coccinellids,Coccinella undecimpunctata L., and reduced adult eclosion of syrphids,Eupeodes fumipennis (Thompson), to 11%, 7% and 0%, respectively, of the controls. Under the same conditions, NSO did not reduce the rate of parasitism ofM. persicae byDiaeretiella rapae (Mcintosh), but emergence of parasitoid adults from aphid mummies collected from treated plants was reduced to 35%, 24% and 0%, respectively, of the controls. Although topical treatment of predator larvae with NSO at concentrations of up to 5% did not affect survival, emergence of parasitoids from mummies dipped in aqueous emulsions of NSO at similar rates was reduced significantly. Under field conditions, sprays of NSO and neem seed extract to plants had no significant impact on the number of aphids parasitized. Although total numbers of predators were reduced, numbers of predators relative to aphid numbers were similar to those in controls. Neem insecticides may be suitable for use in integrated pest management programs, as under field use they appear to be relatively benign to aphid predators and parasitoids.

Journal ArticleDOI
TL;DR: In this article, 16 female Holstein calves were tested alone in an open-field to determine how their behavioural and heart rate responses were affected by: (1) the novelty of the enclosure (5 and 15 weeks of age), (2) a period of previous exercise (7 and 14 weeks), and (3) the presence of a familiar or unfamiliar person (8 weeks).

Journal ArticleDOI
TL;DR: The antibacterial effects of a 3% solution of lactic acid at 55 degrees C were assessed, by examining aerobic bacterial growth on artificially-inoculated pork fat and lean tissue and A. hydrophila was equally sensitive to lactic Acid on lean and fat.

Journal ArticleDOI
TL;DR: In this article, the effects of nitrogen fertilizers and soil water content on N2O and CH4 fluxes in a humisol located on the Central Experimental Farm of Agriculture Canada, Ottawa were investigated.
Abstract: Field and laboratory studies were conducted to determine effects of nitrogen fertilizers and soil water content on N2O and CH4 fluxes in a humisol located on the Central Experimental Farm of Agriculture Canada, Ottawa. Addition of 100 kg N ha−1 as either urea or NaNO3 had no significant effect on soil CH4 flux measured using chambers. Fertilization with NaNO3 resulted in a significant but transitory stimulation of N2O production. Inorganic soil N profiles and the potential nitrification rate suggested that much of the NH 4 + from urea hydrolysis was rapidly nitrified. CH4 fluxes measured using capped soil cores agreed well with fluxes measured using field chambers, and with fluxes calculated from soil gas concentration gradients using Fick's diffusion law. This humisol presents an ideal, unstructured, vertically homogeneous system in which to study gas diffusion, and the influence of gas-filled porosity on CH4 uptake. In soil cores gradually saturated with H2O, the relationship of CH4 flux to gas-filled porosity was an exponential rise to a maximum. Steepening CH4 concentration gradients partially compensated for the decreasing diffusion coefficient of CH4 in soil matrix air as water content increased, and diffusion limitation of CH4 oxidation occurred only at water contents > 130% (dry weight), or gas-filled porosities < 0.2.

Journal ArticleDOI
25 Oct 1995
TL;DR: In this paper, the influence of N resources (fertilizer, legume, soil) on sustainable agriculture in temperate/boreal ecosystems and in the humid, subhumid and semi-arid tropic (exemplified by southeast Asia and central and south America) is discussed.
Abstract: This paper discusses the influence of N resources (fertilizer, legume, soil) on sustainable agriculture in temperate/boreal ecosystems (exemplified by the Canadian prairies), and in the humid, subhumid and semi-arid tropic (exemplified by southeast Asia and central and south America). A sustainable agricultural system is one that is economically viable, provides safe, nutritious food, and. conserves or enhances the environment. Consequently, we discuss the impact of N on crop yields, nitrogen use efficiency (NUE), food quality, environmental quality and on socioeconomic factors. Considerably more long-term research has been conducted in the temperate regions, consequently this was where most information was available. However, the principles governing the behaviour of N are very similar in all ecosystems. It is mainly the rates of nutrient cycling and the socioeconomic constraints that differ. Legumes and N fertilizers, used in a responsible manner, will increase crop production, provide quality food, increase net returns, reduce risk of monetary loss, improve soil quality, and reduce N loss via leaching and gaseous means. The key to sustainable management of N is to synchronize N supply with N use by the crop. Because societies in most temperate ecosystems are more affluent they are better positioned to encourage adoption of management techniques that promote sustainability. In contrast, most producers in the tropics are, subsistence farmers; consequently, their immediate goal is economic survival, not preservation of the environment.

Journal ArticleDOI
TL;DR: Three European biological control agents of the exotic, wetland, perennial plant purple loosestrife, Lythrum salicaria L., were released in North America in 1992 and 1993 and successfully passed the most critical phase for establishment in NorthAmerica; production of the generation following release.
Abstract: Three European biological control agents of the exotic, wetland, perennial plant purple loosestrife, Lythrum salicaria L., were released in North America in 1992 and 1993. Two leaf-feeding beetles, Galerucella calmariensis L. and G. pusilla Duftschmidt, from 2 climatically different source populations in Germany, were released in 10 different states and 6 Canadian provinces. The importance for establishment success of climatic preadaptation, number of individuals released, release of laboratory or field-collected material, and confinement of release were investigated in a series of experimental releases. Both Galerucella species became established at all 1992 release sites regardless of their origin or release method. Higher survival in cages was found for releases of 600 beetles compared with releases of 200 beetles. The amount of litter, number of standing dead stems, or host-plant density clid not affect establishment. A root-feeding weevil, Hylobius transversovittatus Goeze, was released in 9 states and 2 Canadian provinces, and established in the field in 6 states and both provinces. The 3 species successfully passed the most critical phase for establishment in North America; production of the generation following release.

Journal ArticleDOI
TL;DR: In this article, the impact of bulk density and aggregate size distribution of the seedbed on the emergence of Hard Red Spring Wheat (Triticum aestivum L.v.
Abstract: Producers in western Canada are concerned with producing good seedbeds in conservation tillage systems. A thorough understanding of how seedlings interact with the soil surrounding them is required to develop criteria for designing effective furrow openers and packing devices suitable for use in conservation tillage systems. To facilitate interpretation of field evaluations of furrow openers for zero tillage seeders, we conducted a greenhouse experiment designed to assess the impact of bulk density and aggregate size distribution of the seedbed on the emergence of Hard Red Spring Wheat (Triticum aestivum L.). Seeds of wheat (c.v. Lancer) were germinated in seedbeds with five aggregate size distributions with geometric mean diameter ranging from 0.44–12.67 mm, and four bulk densities ranging from 1.0–1.6 Mg m−3 arranged in a factorial design. The soil used in this study was taken from the Ap horizon of a Swinton silt loam (Orthic Brown Chernozemic). A logistic model including bulk density, geometric mean diameter and time since initiation of the experiment explained 90% of the variation observed during the course of emergence, and a logistic model that used penetration resistance and time explained 86% of this variability. Number of seedlings emerged and speed of emergence were affected by bulk density and aggregate size of the seedbed, and by the interaction of both variables. In general, increasing bulk density or aggregate size delayed emergence and reduced total emergence. However, the effect of bulk density was small in seedbeds with large aggregates, and the effect of aggregate size was negligible in compacted seedbeds. Increased bulk density delayed emergence mainly by decreasing the volume of voids in the soil. This elevated the interfacial stress to the elongating coleoptile. The detrimental effect of increased aggregate size was mainly due to increase in the length of the path the coleoptile had to traverse to reach the soil surface, as it elongated through the interaggregate voids. Compaction of the seedbed, necessary to achieve the higher bulk densities in the coarser-aggregate seedbeds, resulted in substantial breakdown of larger aggregates. Consequently, as the interfacial stress was increased by compaction, the path length was decreased, and both effects cancelled each other.

Journal ArticleDOI
TL;DR: In this paper, the authors show that under certain conditions, natural selection can favour the evolution of honest signalling systems, where vocal and other natural signals provide reliable indicators of the signaller's needs.

Journal ArticleDOI
TL;DR: It was confirmed that azadirachtin was largely responsible for both repellent (behavioral) and toxic (physiological) actions of neem on stored-product insects, however, the neem extracts are slightly more active than pure azadIRachtin when applied at equivalent azadorachtin concentrations, indicating that az adiracht in is not the only active compound in neem.
Abstract: Repellency and toxicity of azadirachtin (98% AZA, which contains 98% azadirachtin) and 3 neem extracts (48, 23, and 7% AZA) to 3 stored-product insects, the rusty grain beetle, Cryptolestes ferrugineus (Stephens), the rice weevil, Sitophilus oryzae (L.), and the red Aour beetle, Tribvlium castaneum (Herbst), were investigated in the laboratory. Each test material repelled all 3 species in a standard repellency test using a food preference apparatus. Significant negative correlations were found between insect settling response and extract concentrations. T. castaneum was more sensitive to the repellent action of neem than the other 2 species. The test materials were also toxic to the 3 pest species, with C. ferrugineus being the most susceptible. Six-week LC50 values for 48, 23, and 7% AZA for C. ferrugineus were 18.8, 37.0, and 127.3 ppm, respectively. The F1 adults of all 3 insect species in almost all treatments were significantly reduced compared with controls. This reduction was significantly dose dependent. The relationship between bioactivity of neem materials and their azadirachtin content was established and is discussed. We confirmed that azadirachtin was largely responsible for both repellent (behavioral) and toxic (physiological) actions of neem on stored-product insects. However, the neem extracts are slightly more active than pure azadirachtin when applied at equivalent azadirachtin concentrations, indicating that azadirachtin is not the only active compound in neem.

Journal ArticleDOI
TL;DR: It is concluded that principles of behavioural ecology and sociobiology provide a useful functional and evolutionary perspective to complement other approaches to the study of farm animal behaviour.

Journal ArticleDOI
TL;DR: Postweaning gain performance and individual feed intake on 271 Hereford and 263 Angus bulls were recorded during three 168-d test periods from 1984 to 1986 and genetic and phenotypic correlations were moderately to highly positive for both breeds.
Abstract: Postweaning gain performance and individual feed intake on 271 Hereford and 263 Angus bulls were recorded during three 168-d test periods from 1984 to 1986. Each breed was composed of two lines and within each breed bulls were fed either a high-energy (HD) or a medium-energy (MD) diet. Energy intake was partitioned into energy for maintenance and growth based on predicted individual animal requirements. Estimates of heritability were obtained using Restricted Maximum Likelihood with an individual animal model including fixed effects of year, diet, and covariates of initial weight and backfat change by breed and with line effects for overall data. Bulls fed the HD grew faster and had higher metabolizable energy intake per day (MEI), residual feed consumption (RFC), and gross and net feed efficiency (FE and NFE) (P < .001) than those fed the MD. Estimates of heritability for Hereford and Angus bulls, respectively, were .46 and .16 for 200-d weaning weight (WWT), .16 and .43 for average daily gain (ADG), .19 and .31 for intake per day (MEI), .43 and .45 for yearling weight (YWT), .07 and .23 for RFC, .08 and .35 for FE, and .14 and .28 for NFE. Genetic and phenotypic correlations between MEI and ADG, MEI and YWT, ADG and YWT, ADG and FE, YWT and FE, and FE and NFE were moderately to highly positive for both breeds. Negative genetic and phenotypic correlations between NFE and ADG show partial correlations of FE with ADG after accounting for energy requirement for maintenance. Residual feed consumption was negatively associated with YWT, FE, and NFE, indicating a possible genetic improvement.

Journal ArticleDOI
TL;DR: A reverse transcription and polymerase chain reaction (RT-PCR) system was developed using two 20-mer primers located in the potato leafroll virus (PLRV) capsid gene and a 336-bp PCR product was detected from aphids which had been fed on PLRV-infected plants.