جستجوی مقالات مرتبط با کلیدواژه « تغییرات فصلی » در نشریات گروه « کشاورزی »

The natural products of seaweeds have been taken into consideration due to their application in various fields of medicine, nutrition, and agriculture in the world. Recent research has shown that marine metabolites can form the future of the bioeconomy. There are many populations of Ulva and Sargassum algae on the southern coasts of Iran, and therefore, in this research, the populations of U. lactuca and S. vulgare were collected from the shores of Bushehr, and their photosynthetic pigments, soluble carbohydrates, total protein and compounds in essential oils were investigated in the winter and spring seasons. The results showed that S. vulgare in spring and U. lactuca in winter had the highest amount of chlorophylls and total carotenoids. The amount of soluble carbohydrates in U. lactuca significantly increased in spring compared to winter. The amount of total protein in both species significantly increased in winter compared to spring. The main components of the essential oils of both species included alkane hydrocarbons, which often had a higher abundance percentage in winter. In spring, fatty acids and aromatic compounds with phenyl ring(s) were observed in the essential oils of these species. Considering the changes in the content of metabolites in these species along with seasonal changes, the present results can be effective in the targeted selection of algal species and the appropriate harvesting time for special applications.

Vegetation cover is an important component of terrestrial ecosystems that changes seasonally. Accurate parameterization of vegetation cover dynamics through developing indicators of periodic patterns can assist our understanding of vegetation-climate interactions. The current study was conducted to investigate and model vegetation changes in some phytogeographical regions of Iran including, Khazari, Baluchi, semi-desert, temperate steppe, warm semi-steppe and arid forest and to compare their stochastic behavior. To study the vegetation changes the net primary production (NPP) was used, based on the products of Moderate Resolution Imaging Spectroradiometer (MODIS) sensor (MOD17A2 series). Seasonal Auto Regressive Integrated Moving Average (SARIMA) time series model was used for modeling NPP. The Autocorrelation Function (ACF) and Partial Autocorrelation Function (PACF) of time series showed that these areas were static with seasonality in 12-month periods. It also showed that the vegetation in Khazari region was more stable, which indicates a stable environmental condition with the least deviation in water, light and nutrients. We also found that most of the vegetative regions of Iran can be modeled with SARIMA and its changes can be reliably predicted. Estimated models for Khazari (Root-Mean-Square Error, (RMSE) = 0.12, R2 = 0.87, Mean Relative Absolute Error (MARE) = 0.083) and semi-desert (RMSE = 0.12, R2 = 0.95, MARE = 0.048) were more suitable models than other regions.

Many marine invertebrates, such as sponges, produce secondary metabolites that have some pharmaceutical uses. This study was carried out to determine the antibacterial properties and the effect of seasonal variations on methanolic extracted from sponge Niphates furcata against Gram-positive bacteria Bacillus subtilis, Staphylococcus aureus and Gram negative bacteria Escherichia coli and Pseudomonas aeruginosus using broth dilution method. The experiment results showed that methanolic extracts of sponge extracted in summer did not show any antibacterial effect on E. coli and P. aeruginosus and did not have the ability to inhibit the growth of the mentioned bacteria, and naturally the concentrations determined could not have any bactericidal effect on the gram-negative bacteria of E. coli and Pseudomonas aeruginosus. In winter, this extract had an inhibitory effect on all four gram positive and gram negative bacteria used in this study, In contrast to methanolic extract from summer, methanolic extract of winter season on Escherichia coli had a bactericidal effect, although it did not show any bactericidal effect, similar to that of summer on Pseudomonas aeruginosus. Comparison of the data shows that the methanolic extract of Niphates furcata sponge has a more severe inhibitory effect on the bacteria than in the winter, although the comparison of the bacterial pathogenic effects in both summer and winter shows similar results, and the concentrations have not shown any bactericidal effect on Pseudomonas aerosinosis.

Aphids are small insects which are famous as pests in agriculture, horticulture and forestry. They cause economic damages directly by feeding plants’ sap and indirectly by transmitting plant viruses. Sitobion avenae (F.) is one the important pests in the United States, Europe and Asia. In Iran, it has been reported on wheat, barley, and the other cereals from the different provinces including Kermanshah. Investigating on the population dynamics of pests is a major factor in evaluation of the pest management. The aim of the present study was to determine the most appropriate life stage of S. avenae for sampling to investigate its population dynamics and identify natural enemies of S. avenae in Sar-Pole Zahab region in Kermanshah province.

This study was conducted in a wheat field in Sar-Pole Zahab region in Kermanshah province during years 2015 and 2016. None of pesticides were used to control the insect pests during experiments.  Population survey and sampling were began each year in the middle of February and continued weekly until the end of wheat growth season in the middle of June. Sampling pattern was X-shaped and totally 30 samples were collected from the field. The selected plants were separately put in plastic bags and transferred to the laboratory for counting the number of nymphs, winged and wingless adults. To examine probable emergence of parasitoids, the aphids were kept in Petri-dishes in laboratory for two weeks and the results were recorded. A standard insect collecting net was used for sampling of the predators. The collected predators were transferred to the laboratory in glass jars for identification. The aphids and collected natural enemies were sent to Plant Protection Research institution in Tehran for confirmation.

At the first sampling date in 2015, there were a few adult aphids in the field. However, the population of adults and nymphs were gradually increased and the highest population of aphids was observed between March 12th 2015 and April 30th 2015.The peak density of adult aphids was on April 9th 2015 (9.5 aphids per spike) and for nymphs, it occurred a week earlier, on April 2nd 2015. In the second year, however, the population fluctuation pattern was very different. Although some aphid colonies were seen in the field from 25th of February, 2016, the number of aphids was decreased due to severe cold happened in March, thus no aphids was found in the samples in the next two weeks. The peak population of adult aphids was observed on 14th of April 2016 (36.9 aphids in spike) and then gradually decreased during the next weeks. Coccinella septempunctata L. (Coleoptera: Coccinellidae), Eupeodes corolla (Fabricius) (Diptera: Syrphidae) and Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) were reported as aphid’s predators in the field. All predators were present at the field from the first sampling date. In the first year, E. corolla showed two distinct peak in its population during sampling including 19th of March 2015 and 16th of April 2015. In the second year, there were 17 adult flies per net in the first day of sampling, but the number of flies was increased gradually and reached to a maximum of 35.5 flies per net on 14th April 2016. C. septempunctata and C. carnea populations’ dynamics also followed the same patterns and showed two peaks in the first year and one peak in the second year of studies. No parasitoid was emerged from the aphids in Petri dishes

Due to presence of active predators in the wheat fields of Sar-Pole Zahab region and their high population, using of chemical pesticide should be restricted. Thus, if spray of pesticides is essential, the most appropriate time is when it has the least detrimental effects on natural enemies.

In the current study, the effect of seasonal variation on the type and percentage of phytochemical compounds of Artemisia fragrans</em> Willd. essential oil was investigated. Herbal samples were collected in 4 different seasons and then their essential oils were extracted by the Clevenger type apparatus. In the following, the essential oil compositions of each season was analyzed by GC-MS apparatus. In total, 50 different compounds were identified in four sentential oil. The major components of the essential oil were camphor, thujone, and 1,8-cineole in different seasons. Also, the results showed that monotreptans were the major class of essential oil compounds in September (91.87%), December (90.55%), May (96.32%) and July (95.4%). The highest amount of phenolics (5.49 mg GAE/g) and antioxidant capacity (28.98%) were observed in essential oil of Septebmer.   Antibacterial effects of the different essential oils using paper disc diffusion method were carried out on Escherichia coli</em>, Proteus vulgaris</em>, Klebsiella pneumonia</em>, Staphylococcus aureus,</em> and Bacillus subtilus</em>. Based on the results of the study, gram negative bacteria (E. coli</em>, Proteus vulgaris,</em> and K. pneumonia</em>) were more susceptible to artemisia essential oils in comparison with gram positive bacteria (S. aureus</em> and B. subtilus</em>). The results of this research can be useful in determining the best sampling date of this plant for pharmaceutical and antibacterial uses.