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In the last decade, frequency of late cold incidence has increased in the upland forest nurseries. The aim of present study was to reduce the damage caused by spring frost and to increase the efficiency of Persian maple seedlings production in mountain nurseries. This study was conducted as split plot design with two main treatments and three replications in two consecutive years (2009-2010) in Farim Wood Company nursery, Mazandaran Province, Iran. Maple seeds were collected from a site located near the nursery. The main treatment was seedlings protection in two levels of covering the seedlings during the cold days and without covering. Sowing date was sub-treated and applied at six levels (2^nd week of Dec., mid-Jan., 1^st week of Feb., 3^rd week of Feb., 3^rd week of Mar. and mid-April).The results showed that seedling covered and seed sowing dates had significant (p<0.01) effect on reducing frost damage. Besides, interaction effect of sowing date and seedling cover was significant (p<0.01) in both years. There was no significant (p>0.05) effect between the sowing dates in protected plots. Overall, mortality of seedlings gradually reduced with shifting sowing date to March in uncovered plots. The maximum mortality rate was related to the sowing in 3^rd week of February. Losses of seedlings were the same in covered and uncovered plots in mid-April sowing dates. In the unprotected plots, the maximum losses of seedlings were recorded in the sowing dates before March. In fact, if seed sowing of A. velutinum was postponed until early spring, the seedlings mortality rates were not significantly different in both treatments.

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Isabgol (Plantago ovata Forsk), is an annual herb cultivated as a medicinal plant in recent decades. Its seed contains mucilage, fatty oil, large quantities of albuminous matter, a pharmacologically inactive glucoside, namely Aucubin (C13 H19 O8 H2O), and a plantiose sugar. Medicinal plants are rich in secondary metabolites: their biosynthesis is controlled genetically and is affected strongly by environmental factors. In the present work, the influence of sowing dates (20th April, 5th and 20th May) and nitrogen-fertilizer levels (0, 50, 100 and 150 kg ha-1) was examined on the growth, seed yield and seed swelling factor (content of mucilages) of isabgol. The statistical design was a split-plot arrangement of a randomized complete block design with three replicates: the sowing dates and nitrogen fertilizer were considered as the main and sub-main plots, respectively. The plot experiment was installed in the experimental station of Zanjan region located in the northwest of Iran, under silty-clay soil conditions. According to the resulting data, the best time for sowing isabgol in such a region was 5th May and the suitable amount of nitrogen fertilizer was 100 kg ha-1. To discover any relationship, all measured independent variables were muliple regressed on the dependent variable (seed yield) followed by stepwise regression analysis. This verified that the seed yield among other independent characteristics tested appeared to show a significant positive effect on the seed swelling.

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Two independent field experiments were carried out on two sowing dates. The experimental factors included three herbicides (trifluralin, pendimethalin, and linuron) using the method of incorporation by sowing, inter-row cultivation, and control (weed-free and weed-infested). The density of weeds 45 days after sowing, applying pendimethalin, linuron, and inter-row cultivation on the first sowing date (FSD), was 26.5, 31.8, and 45.9% less than the second sowing date (SSD), respectively. On the contrary, at the flowering stage, weeds on the SSD were 59% less than the FSD, and the average weed density in applying pendimethalin and linuron was 78.7% less than their density in the weed-infested. The height of the plant and the height of the first pod from the soil surface on the FSD were 13% and 11% higher, respectively, compared to the SSD. The average number of branches per plant with experimental treatments was 37% more than the weed-infested ones. The maximum biological yield of chickpeas in the FSD and SSD was obtained by inter-row cultivation (760 g m^-2) and pendimethalin (749 g m^-2), respectively. On the FSD, the seed yield in applying pendimethalin was 82.5%, and its average in linuron and inter-row cultivation was 86.4% more than the weed-infested control. Also, on the SSD, the average seed yield in the three mentioned treatments was 73.6% more than the weed-infested control. However, linuron and inter-row cultivation were identified as the most appropriate treatments for weed control in the early stages of both sowing dates.

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Field experiments were conducted to investigate the effects of sowing dates and irrigation on seed quality of a spring-type safflower cultivar, in Karaj-Iran, during 2008 and 2009 growing seasons. A split plot design based on a randomized complete block layout with three replications was used in which sowing dates and irrigation treatments comprised the main plot and sub-plot, respectively. The results showed the highest oil yield, oil content, protein yield, and linoleic acid content of safflower seed for sowing date of 19^th of April and under non-water stress conditions. The highest seed protein, oleic acid, and palmitic acid contents were obtained for sowing dates of May 5^th and 20^th along with ceasing irrigation at heading, flowering, and seed filling stages, respectively. Under arid and semiarid Mediterranean conditions prevailing in Karaj, late sowing date led to a greater simultaneity of reproductive stages and higher temperature, which made the negative effect of water stress more prominent than in the early sowing dates.

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Cross-acclimation of mild drought stress and cold acclimation may additionally increase the chickpea’s cold tolerance due to transferring sowing date from spring to winter in Mediterranean high lands. Two weeks after sowing in greenhouse, chickpea seedlings were subjected to the following treatments in a controlled environment: (i) Well-Watered under an optimum temperature regime (WW); (ii) Well-Watered under a Cold temperature regime (WWC); (iii) Drought Preconditioned under an optimum temperature regime (DP); and (iv) Drought Preconditioned under a Cold temperature regime (DPC). After three-week acclimation period, plants were frozen on the thermogradient freezer, then, recovered for three weeks in a greenhouse. In the acclimation period, with decreasing temperatures, a clear decrease of the electrolyte leakage (EL) were observed for both genotypes: 51% for cold tolerant MCC252 and 36% for cold sensitive MCC505. Cold acclimation induced the greatest accumulation of proline and MDA contents (about 75% for both genotypes) and drought preconditioning most consistently induced an increase in soluble carbohydrate content (25% for MCC252 and 51.7% for MCC505) during the acclimation period. The survival percentage increased 9.3% for MCC252 and 21.25% for MCC505 by both cold and drought acclimation under freezing conditions. Generally, drought preconditioning had a synergistic effect on the cold acclimation period to improve freezing tolerance (as indicated by the lowest LT50el and LT50su) and leading to an increase in the freezing tolerance for the cold sensitive genotypes (MCC505). Thus, the greatest gains in freezing tolerance for both genotypes were associated with cross-acclimation treatment (DPC).