Journal of Agricultural Science and Technology
Volume:4 Issue: 1, Apr 2002

The relationship between female oviposition preference and offspring performance is a key area of study on the evolution of host specificity. This study investigates host preference of the polyphagous hover fly Syrphus ribesii (Diptera: Syrphidae) and compares it with some components of its offspring`s performance. Females and offspring were tested on six naturally used aphid hosts (blackberry, dock, nettle, pea, rose, and sycamore aphids). In the laboratory, larvae were able to develop successfully on aphids which were rarely selected for oviposition by gravid females. Despite the relatively small differences in performance resulting from feeding on different aphids, there was evidence for a preference-performance correlation in the generalist S. ribesii.

In this research, an apparatus was made and utilized to determine the friction coefficient of chickpea grains on steel surfaces. Experiments were carried out on two black and galvanized surfaces and at four sliding velocities of 5, 20, 100 and 500 mm/min, at three moisture content of 7.5%, 15% and 21% wet basis (w.b.) and at three vertical pressure values of 14.28, 100 and 150 kPa. The following results were obtained.1) For surface conditioning, the steel plates need to be passed through the grains for at least 7 times. 2) At low sliding velocity, by increasing the velocity from 5 to 20 mm/min, the dynamic friction coefficient of chickpea grains increased, and at a sliding velocity of 500 mm/min it was decreased. 3) For the black steel surface, by increasing the moisture content of chickpea grains from 7.5% to 15% w.b., the value of the friction coefficient increased; but at a moisture content of 21% w.b., it decreased. For galvanized steel surfaces, and sliding velocities of 5 and 20 mm/min, increasing the moisture content, the value of friction coefficient was found to decreased, but for sliding velocities of 100 and 500 mm/min it’s behaviour was similar to the black steel surface. 4) Normal pressure has no significant effect on the friction coefficient (at 0.01 level) and the difference between the mean values of the coefficient of friction associated with the normal pressure of 14.28 kPa and 100 kPa, as well as 100 kPa and 150 kPa was not significant at the 0.05 significance level.

In western Canada, durum wheat cultivars (Triticum durum) have low to moderate levels of seed dormancy and are susceptible to pre-harvest sprouting. The aim of this study was to evaluate the dormancy level of Canadian durum wheat cultivars and to identify tetraploid wheat accessions with elevated levels of seed dormancy. First, the level of seed dormancy and length of after-ripening of 17 North American durum wheat cultivars were evaluated. The plants were grown under field conditions in 1995 and 1996, harvested at maturity (Zadok’s Growth Stage 92, ZGS 92), dried at room temperature for one week, and assessed for level of seed dormancy over seven weeks of after-ripening at 20°C. Seed dormancy was characterized by the extent of germination at 20°C. The results indicated that five durum cultivars exhibited moderate levels of seed dormancy at maturity while the remaining cultivars were non-dormant. Likewise, a rapid loss of dormancy (within 2-3 weeks of after-ripening) was characteristic of all durum cultivars. In a second experiment, 78 accessions of T. turgidum, T. turanicum, T. carthlicum, T. polonicum, and T. durum from the USDA germplasm collection grown under field conditions in 1995 and 1996 were evaluated for seed dormancy with the idea of identifying potential sources of increased seed dormancy. At ZGS 92, eighteen accessions were classified as dormant. Accession 93-282 was the only highly dormant genotype in this study. The seven most dormant accessions, identified in two years of field tests, were tested for length of the dormancy period. Accession 93-282 was the only genotype that had a longer period of dormancy than the durum cultivar, Kyle. The intensity of seed dormancy was quantified at five germination temperatures. A dormancy index was calculated from germination data at 10 and 20°C. The dormancy indices of tetraploid accessions 93-62 and 93-177 were 37% higher than that of the durum cultivar Kyle.

The objective of this study was to test whether the stimuli of osmotic pressure (OP), VFA or pH in the omasum would affect the passage of digesta from the rumen and feed intake in sheep. Five experements were carried out. Different solutions with specific, OP, VFA concentration and pH were infused into the omasal body. Rumen digesta volumes and outflow rates (liquid and solid) were measured by pulse dosing of liquid and solid marker into the rumen. Feed intake, solid and liquid outflow rates from the reticulo-rumen were (not always significant) reduced by increasing the (OP) of the infusate in the range of 400 to 2000 mOsmol/kg which gave calculated omasal OP up to 480 mOsmol/kg (perfect mixing with digesta was assumed). Feed intake and fractional ruminal liquid outflow rate were significantly increased by increasing VFA concentration of infusate in the range of 50 to 250 mMol/l or calculated omasal VFA concentrations up to 150 mOsmol/kg with the suggestion of a decrease above this range. pH in the range of 5.0 to 7.0 was without effect. Serum OP was not affected by any infusate. There was no or only a weak response to abomasal infusion compared with omasal infusion when the same infusate was used. The study demonstrated that omasum responds to changes in the composition of digesta. Increasing OP reduced DMI (dry matter intake) and reduced digesta outflow from the reticulo-rumen. Increasing VFA concentration increased DMI and liquid outflow, high VFA concentration decreased DMI and liquid outflow rate. It can be concluded that omasum has a role in the control of digesta outflow from the rumen.

Samples from five sturgeon species including Persian sturgeon (Acipenser persicus), Russian sturgeon (A. gueldenstaedti), Great sturgeon (Huso huso),Ship sturgeon (A. nudiventris) and Stellate sturgeon (A. stellatus) were collected from the South Caspian Sea. DNA was extracted from the fins, eggs and skeleton muscle of the five species. RAPD markers were used for identifying different kinds of black caviar and sturgeon meat. The polymorphic band from RAPD amplification of DNA from two out of five sturgeon species was purified, cloned and sequenced. RAPD analysis was carried out in order to compare the five species using an operon primer set. Sequence Characterised Amplifed Region (SCAR) primers were designed and used to amplify caviar DNA from five sturgeon species. A marker of potential economic importance was discovered that is able to distinguish three species from caviar and also to distinguish Ship sturgeon caviar from osetra caviar (from Russian and Persian sturgeon) and also other species. This marker could assist international conservation and legal efforts to save what is left of the commercial Ship sturgeon populations which are endangered and whose caviar is at present substituted for the more expensive osetra caviar.

This study was carried out to investigate the morphological and anatomical aspects of somatic embryogenesis in date palm. Lateral bud and shoot tip explants excised from young offshoots were cultured on MS medium with 2,4-D. Somatic embryogenesis was induced by transferring the calli produced on the same medium without hormones. Microtome sectioning of paraffin-embedded specimens was carried out using the callus tissue and its differentiated structures. The sections were stained with safranin and fast green. Observation of three-celled proembryos with the longitudinal and oblique division of the top cell, which in later stages results in wedge-like cell(s), supports the ASTERAD type of embryogenesis in date palm. Polyembryonic structures were raised from the embryonic callus formed in different regions of both the proembryos and germinating embryos and the secondary embryos formed directly from primary embryos.

The increasing production and use of fossil fuels increase the probability of soil source contamination by oil and petroleum products, and pose a hazard to life. There are over 43,000 chemical contaminated sites in Canada and USA, with 2,200 of them classified as high risk. In the US, over $10 billion are spent annually on the cleanup of contaminated sites. The primary objective of this study was to develop and test an innovative in situ soil washing system that could extract contaminants from the soil, quickly and effectively, without causing any threat to water sources. We proposed the use of an organic solvent in our system that is not only lighter than water but is also immiscible with water. It was introduced into the soil profile from below using a system of horizontal, underground perforated pipes, and collected from the soil surface. Since the solvent was being introduced from the bottom, it “wete” the soil completely and thus removed the contaminant effectively. To understand and evaluate the performance of the system for remediation, a preliminary experiment was performed using two stainless steel columns (1m long x 0.2m diameter) packed with two diesel fuel contaminated soils (fresh and old contamination). The proposed technique is innovative, unique and very fast for the remediation of diesel fuel contaminated soils. It is the first study of its kind employing a subirrigation system for delivering organic solvents (lighter than water and immiscible in water) for in situ soil washing. Some preliminary applications of the system to diesel fuel contaminated sand soils have proved very promising for both fresh and old contaminated sites. The method could be equally suited for other contaminants also.

Spatial patterns of soil fertility parameters, and other extrinsic factors need to be identified to develop farming practices that match agricultural inputs with local crop needs. Little is known about the spatial structure of yield and weed density across fields. In this study, geostatistics was used to describe and map spatial patterns of soil total nitrogen, available phosphorus, available potassium, grain yield and density of Sisymbrium irio L. (tumble mustard), as a common annual weed of wheat fields at Shahre Kord university. The spatial continuity of each variable was examined by variogram function. The variograms showed that the distribution of all variables is not random but spatially-dependent as their estimated variogram values increase with increasing distance. The average range values were 26.5, 23.4, 31.4, 27.7, and 27.2 m for total nitrogen, available phosphorus, available potassium, grain yield and weed density, respectively. Thus, the range beyond which the property is not longer spatially dependent was almost the same for total nitrogen, grain yield and weed density. This implied close spatial interactions among these variables over the field. Applying the variogram models with the kriging algorithm, the values for each variable were estimated on a 5´5 grid. The disrribution of all variables is spatially dependent and continuous over a short distance. Furthermore, the maps illustratc a joint spatial dependence between grain yield and weed density. Spatial patterns of soil properties identified by these geostatistical techniques are of great importance in the fertility management of spatially variable soils. By studying the spatial structure of yield and mapping, it could be used in determining different factors controlling yield over the field. Moreover, a better knowledge of annual or perennial weed density distribution over fields might be helpful in better designing long-term field experiments in weed control programs.