مجله علوم گیاهان زراعی ایران
سال چهلم شماره 3 (پاییز 1388)

Water deficit is one of the most important problems facing crop production in arid and semiarid regions in Iran. Application of super absorbent polymers may somehow control yield reduction in some crop plants under drought stress conditions. In this investigation, the effect of different levels of super absorbent polymer, SUPERAB A200 (0, 100, 200, 300 Kg/h), and three irrigation intervals (7, 9, 11 days) on growth and yield of forage corn (single cross 704) was evaluated under field conditions during summer 2004. Results revealed that the utilization of super absorbent polymers did increase yield, height and relative growth rate of forage corn crop. In contrast, an increase in irrigation interval, although accompanied by reduction in water consumption, caused decrease in the above-mentioned traits. A linear relationship was observed in either case of increase or decrease in traits as affected by either of the experimental factors.

The experiment was aimed at investigating the effects of defoliation (i. e. amanipulation of source size) at different times and with different intensities on yield, grain protein content and remobilization of dry matter from shoot to grain under various levels of soil moisture and nitrogen in winter wheat. Two separate field experiments were conducted simultaneously under water stress vs irrigated conditions at research farm of College of Agriculture, University of Tehran, Karaj, during 2004-2005 growing season. The experimental design was a factorial one of RCB of 3 replications. A combination of four levels of defoliation (D0= control or intact plants, D1= excision of all leaf blades except flag leaf at booting stage, D2= same as D1 but excision at anthesis stage and D3= removal of all leaf blades at booting stage) along with two levels of nitrogen (none vs 250 kg ha-1 of urea fertilizer applied at jointing stage) were randomly assigned to plot units. Water stress was induced by withholding irrigation from late booting stage until plant maturity. Variance analysis of each experiment revealed that defoliation did not affect grain yield in either of the moisture regimes. Extent and efficiency of dry matter remobilization were promoted by defoliation, predominantly in water stress conditions. However, a clear relationship, between this parameter and grain yield, was not observed. Protein content decreased by defoliation only in drought stress conditions. The effect of nitrogen was significant on grain protein content and on remobilization in stress conditions, increasing both. Results of combined analysis showed the significant effect of defoliation on grain yield. The effect of defoliation depended on the environment, was significant for grain weight and as well for grain protein and remobilization. The effect of nitrogen depended on the environment, was significant for grain protein content, and as well for remobilization. Nevertheless, the highest grain protein percent was observed in intact plants with the application of nitrogen fertilizer in water stress conditions.

Physiological study of wheat varieties under abiotic stress conditions is a very important factor for improving their future productions. This research work was conducted in the Research Greenhouse of Faculty of Agriculture, Tarbiat Modarres University in 2006, to study leaf quantitative traits of durum wheat under different levels of carbon dioxide (400 and 900 ppm), ultraviolet radiation (UV A, B and C) and water deficit (up to 60% of field capacity). The experiment was factorially performed in a complete block design arrangement of three replications. In total, decreases were observed in: grain yield (157.27-38.05 g/m2), plant height (60.69-50.69 cm), leaf relative water content (68.00-54.90%), chlorophyll content (50.53-17.62%) and maximum quantum efficiency in photosystem II (from 0.565 to zero), in durum wheat under water deficit and when ultraviolet radiation intensity increased from A to C level. In this situation, proline increased from 3.28 to 24.46 (µg g-1 FW). Proline and grain yield variations were different as affected by carbon dioxide. At UVA, B and C radiations and no water deficit condition, durum wheat grain yield decreased (from 157.27 to 89.48 g/m2) with CO2 enrichment, while proline being increased from 3.28 to 12.45 (µg g-1 FW). Under water deficit accompanied by CO2 enrichment, durum grain yield increased, while proline being decreased. Carbon dioxide enrichment in the absence of water deficit increased vegetative growth while decreasing reproductive growth. This was while at stress conditions, grain yield increased due to an improvement in leaf relative water content along with reduction in stomatal conductance. The above results indicate that the three main environmental stresses which reduce leaf chlorophyll content, specific leaf area and plant protection (due to negative effects of these stresses) decrease yield and yield components in this variety of wheat.

To study the root allelopathic effects of cool season crops on germination and early growth of three crops (sorghum, corn, and soybean), an experiment was conducted in seed research laboratory and greenhouse of College of Agriculture, University of Tehran. The experiment consisted of four cool season crops (wheat, barley, rye and pea) and control as the main plots, three spring-crops (corn, soybean and sorghum) as sub-plots and three sowing times (sowing immediately after physiological maturity, 2 and 4 weeks past physiological maturity) as sub-sub plots. The experiment was arranged as a split-split plot in a completely randomized design of three replications. All traits (seedling emergence percent, seedling emergence rate, as well as plant height and biomass weight) were affected by experimental treatments. Rye had the highest allelopathy effect on the evaluated crops. Soybean had the greatest susceptibility to root allelopathism as compared with corn and sorghum. Delay in sowing time decreased the root allelopathic effects in a way that 4 weeks of delay in sowing time exerted a significant influence on growth traits. Mean germination percent and mean germination rate of the evaluated crops increased with a 4 weeks delay in sowing time. Also, an increased trend of biomass weight was observed with delay in sowing time.

To study the effect of water deficit and plant density on yield and yield components of cumin (Cuminum cyminum), an experiment was conducted during the 2002 - 2003 growing season at Research Farm of Zabol University. In this study, the effects of plant density (25, 50, 100, 150, and 200 plants per m²) and water stress (before flowering, flowering, seed filling and seed hardening vs adequate irrigation) were investigated. The experiment was a split plot one, with RCBD of 3 replications. The results showed that the effect of plant density on number of umbels per plant, number of seeds per umbel, plant yield and seed yield per hectare was significant (?<0.01) but the effect of plant density on one thousand seed weight was not significant. The effect of water stress on number of umbels per plant, number of seeds per umbel, one thousand seed weight, plant yield and seed yield per hectare was significant (?<0.01). The effect of plant density on one thousand seed weight was non significance. Water stress reduced the number of umbels per plant, number of seeds per umbel, one thousand seed weight, plant yield, as well as seed yield per hectare. In a high plant density, seed yield per hectare was maximum but the number of umbels per plant, number of seeds per umbel, and plant yield were at their minimum. According to the results of this study, to achieve maximum yield, cumin must be supported with sufficient moisture especially in early reproductive stages and optimum plant density.

To study the physiological effects of different levels of salt stress on germination and on seedling stages, two seperate experiments were undertaken in Rice Research Institute of Iran, Amol in 2006. The experiments were conducted in a completely randomized design of three replications in greenhouse. Sixteen rice genotypes namely: Ahlamitarum, Shafagh, Gharib, Taromzavarak, Khazar, Mosatarom, Ghashange, PSBR-C88, Hybride- bahare –1, Nemat–A, Hassansaraie, Anbarboo, Gerde, Tichong and four salinity levels (O, 4, 8, 12 ds m-1) were tested. Characters assessed were percent and rate of germination, length and dry weight of rootlet and of stemlet, total dry weight, Na+ and K+ contents, K+/Na+ ratio, dry weight as well as length of roots and shoots, leaf area and total biomass. Results indicated that the effects of salinity, genotype as well as their interactions were highly significant on all the evaluated traits. In germination stage, in response to salinity effects all characters significantly differed with their correlation coefficients being positive and highly significant. Except in Na+ content and K+/Na+ ratio in roots and shoots, all the other assessed traits at the seedling stage showed reduction with increasing salinity trend and in a number of traits the correlation coefficients were positive and significant. Genotypes PSBR-C88 and Bahar-1 exhibited the highest and the lowest growth rates. They were determined as the respectively tolerant and susceptible genotypes to salinity for using in future further experiments. Finally, for a prediction of the relationships of total biomass and its components, and also exclusion of removal the less important variables for path analysis, stepwise regressions was employed. Results obtained from stepwise regression indicated that only two out of seven traits (rootlet and stemlet dryweight) at the germinating stage and merely two out of thirteen traits (root and shoot dryweight) at seedling stage contributed to total biomass production. However, results optained from path analysis indicated that only the variables of stemlet and shoot dry weight were very important. These traits directly and to a very large extent affect total biomass and thus can be employed in rice breeding programs. Also, path analysis revealed that a major portion of correlations of other traits (rootlet and root dryweight, in both germinating and seedling stages) with total biomass were related to their indirect effects via other variables.

One hundred and twenty Iranian accessions of Aegilops crassa with origin from different geographical areas of Iran, were evaluated for variation in high molecular weight glutenin subunit (HMW-GS) composition. The results showed different banding patterns between hexa (6x) and tetra-ploid (4x) as well as within different ploidy accessions. Eleven allelic variants were observed in Glu- Dcr1 locus with the highest (30.90%) and the lowest allele (0.5%) frequency in 3+12 and 2+10 variants, respectively. Moreover, six new alleles likely belonging to M genome and one new allele belonging to D genome (between 12.1 and T2 alleles) were observed. The first two principal coordinate analyses (PCOs) along with cluster analysis could not clearly separate accessions according to geographical origin. Results revealed that the evaluated Iranian accessions of Aegilops crassa formed an interesting source of favourable glutenin subunits that might be very desirable in breeding activities for improving bread wheat quality.

To investigate the effect of plant density and supplemental irrigation on agronomic characteristics, chlorophyll content and light interception beneath the canopy of three chickpea genotypes under dryland conditions, an experiment was conducted at Research Station of Lorestan Agricultural Research Center located at Chegini, Khoramabad, during 2004-2005. The study was conducted using a split-split plot design with a randomized complete block layout, replicated four times. Dry farming (no supplemental irrigation (control)), dry farming supplemented with irrigation at 50% flowering, and dry farming supplemented with irrigation at pod filling period; three genotypes of Flip 93-93, Arman, and Gerit; and four planting densities of 30, 42, 54, 66 plants/m2 were taken as the main, sub, and sub-sub plots, respectively. The results revealed that on average of two supplemental irrigations led to increase of grain yield (556 kg/ha), biological yield (1102 kg/ha), plant pod number (6.8) and number of seeds per pod (2.52). All experimented factors significantly influenced the agronomic and physiological traits with the exception of cultivar × supplementary irrigation, and the three factor interaction. Cultivar Flip 93-93 as an early maturing genotype produced the highest grain yield and harvest index under all treatments. By increasing plant densities grain yield was increased, accordingly. The greatest grain yield of 1388 kg/ha and biological yield of 3823 kg/ha were obtained from the density of 66 plant/m2. Moreover, increasing plants per unit area resulted in an increment in leaf chlorophyll content accompanied by a reduction of interception under the canopy. The least light interception under the canopy was obtained by plant densities of 54 and 66 plants per m2. Supplementary irrigation at 50% flowering stage led to a significant increase of grain yield in all cultivars. Flip 92-93 was a superior genotype for grain yield.

To study seed dormancy and the after-ripening period in barley genotypes (57 Dutch genotypes and two Iranian cultivars (Gorgan and Valfair)), an experiment of randomized complete block design (two replications) was conducted at the Research Farm of Collage of Agriculture and Natural Resources, University of Tehran in 2004-2005. In the growing stage of ZGS92, panicle was collected. The percentage of seed dormancy and germination were assessed at 20?c in three replications. Among the 57 genotypes, 38 had a low percentage of germination (dormant) while the rest (21) were non-dormant. The control cultivars exhibited a high level of dormancy and low percentage of germination. To evaluate the duration period of dormancy in seeds, test of after-ripening was conducted on the dormant genotypes and on control cultivars for a duration of five weeks (three replications). The length of after-ripening on water uptake rate was studied. For seed water uptake experiment Gorgan and CGN00962 genotypes were selected. The effect of dormant seed coat extract and dormant embryo extract on percentage of germination, length of coleoptile and length of radicle in the non-dormant seeds were investigated. Finally the superficial changes in the seed coat after the period of after-ripening were investigated with the aid of an electron microscope. The results revealed that there existed significant genetic variations for seed dormancy and the duration length of after-ripeining among genotypes. This will facilitate selection for these traits among genotypes. During after-ripening, germination and water uptake increased. The results of seed extract showed that percentage of germination, length of coleoptile and length of radicle, in non-dormant seeds, decreased when non-dormant seeds placed in the extract solution of dormant seeds. The highest inhibition was observed when the non-dormant seeds put in the extract of dormant seed's coats. The results of electron microscopic studies revealed that after-ripening brought about some changes in the seed coat. After having under gone the passing of this period, spiral threads were found as deleted and splits detected appearing on the seed coat.

Nowadays, tobacco is considered as one of the important world industrial plants. In the present study, for a creation of somaclonal variation, calli were produced on MS medium supplemented by 2 mg/l of Naphthalene Acetic Acid (NAA) and then regenerated on MS medium supplemented with 1 mg/l Benzyl Amino Purine (BAP) and 0.1 mg/l of NAA. To determine correlations among traits and to fit multiple regression model to the green leaf yield, the produced somaclones and cv. Burley21 (as control) were investigated at the experimental field of Tirtash Research and Education Center. Different morpho-physiological traits were evaluated. Simple and canonical correlations were assessed and multiple regression was fitted on green leaf yield. Coefficients of canonical correlation indicated that there existed relationships between nicotine percentage and leaf yield, plant height and also between sugar percentage and plant height, leaf width as well as internode length. The most important characters entering multiple regression model were leaf length, stem diameter, nicotine percentage and plant height (R2=0.8). These traits can be employed, as some most important yield factors, by researchers in their future works.

To study the effect of strip intercropping pattern with cowpea and soybean on sorghum fodder yield an experiment was conducted at research farm of University of Tehran (Karaj) during 2005. The experiment was arranged in a randomized complete block design of four replications. The plant proportions included pure culture of sorghum (SSS); cowpea (CCC) and soybean (GGG) each in 12 rows; vs different patterns of strip intercropping of 4 rows cowpea: 4 rows sorghum: 4 rows soybean (CSG); 4 rows soybean: 4 rows sorghum: 4 rows soybean (GSG); 4 rows cowpea: 4 rows sorghum: 4 rows cowpea (CSC); 4 rows soybean: 8 rows sorghum (GSS) and 4 rows cowpea: 8 rows sorghum (CSS). The results revealed that strip intercropping patterns exerted significant effects on sorghum fodder yield, and as well, on legumes seed yield. The highest biomass yield of fodder sorghum (22079 kg/ha) was obtained from pure sorghum culture (SSS) while the lowest biomass yield (10469 kg/ha) obtained from the combination of four rows of each of the three crops (CSG). The highest legumes seed yield was obtained from the legume's pure cultures (CCC or GGG). The different strip intercropping patterns significantly affected the quality of fodder sorghum (p?0.05) too. The highest fodder digestibility (71%) was obtained from strip intercropping patterns of CSS and GSS; the highest crude protein (15.2%) from CSG and finally the highest crude fiber (48.1%) from pure sorghum (SSS). Considering the extra sorghum biomass and the extra legumes seed yield (8-30 percent) from strip intercropping pattern of CSG, and also the good quality of fodder sorghum at CSS, GSS and CSG intercropping patterns as compared to pure sorghum culture (SSS), conclusion can be drawn that the intercropping of the two legume crops (cowpea and soybean) together with sorghum in a 4:4:4 row pattern is assuredly beneficial. Besides, the increasing crop biodiversity and reducing crop intra-specific competition, would result in higher Land Equivalent Ratio (LER= 1.25) for both sorghum fodder yield & quality.

To study the genetic variation among 24 genotypes of tall fescue (F. arundinacea), a randomized complete block design of three replications was conducted under spaced plant conditions in Karaj Research Institute of Alburz, Iran. Analysis of Variance showed high and significant differences (P<0.001) for between genotypes all the 15 morphological characteristics of: heading date, stem height, fertile tiller number, seed yield, panicle length, panicle seed yield, seed number in panicle, thousand grain weight, harvest index, stand of plant, flowering date, forage dry matter, viability percentage, speed of germination, and germination vigor. Genotypes G1, G2, G4, G6 and G8 appeared to be the most suitable genotypes for both seed and forage production. Principal component analysis, the most effective variable among seed yield characters was identified. Four independent components accounted for 87.7% of total variations. The first principal component indicates that stem height, fertile tiller number, seed yield, forage dry matter yield were important characters for classification. Viability percentage and germination vigor were the important characters of the second component. Based on Ward’s cluster analysis, the 24 entries were divided into 4 groups. Genotypes in clusters 1 and 2 averaged higher than the overall means for seed and forage dry matter yields.

Twenty five durum wheat lines were evaluated under drought stress and non-stress conditions employing Randomized Complete Block Design of 4 replications. Significant differences were observed among the lines for most traits in either stress or non-stress conditions. Correlation analysis under non-stress conditions indicated that grains per spike and number of spikes per m2 and while under stress conditions, 1000 kernel weight and number of spiklets per spike had high positive significance with grain yield. Stepwise regression revealed that the 1000 kernel weight and peduncle length were the most affected characters both under stress and non- stress conditions. Path analysis illustrated that peduncle length had the highest direct effect on grain yield under either one of the environmental conditions. Among the drought resistance indices, harmonic mean, geometric mean productivity and stress tolerance index, were the most suitable ones to be considered in drought resistance selection. Based upon bi-plot display, lines 14, 20, 16, 17, 1 and 15 were found to be the most resistant.

To assess the effects of different levels of nitrogen and phosphorous on yield and nutrient use efficiency of sugar beet (polygerm seed (Cv. 7233)), this study was carried out in 1999-2001 in Ardabil Agricultural Research Station (Alarough). The experiment contained two factors of: nitrogen in 4 levels (control, 100, 200 and 300 Kg N/ha) and phosphorous in 3 levels (control, 100 and 200 Kg P2O5/ha) in four replications based on a randomized complete block design. Each plot consisted of 8 rows each with a length of 10 meters and interspacing of 65 cm. During the study, Agronomic or Economic (AE), Physiological Efficiency (PE), Apparent Recovery Efficiency (ARE), and Mineral Nutrient Efficiency (MNE) were assessed. Results indicated no significant effects of nitrogen and phosphorous application on crude and saleable seed yield. But application of nitrogen significantly (<0.01) affected the standard and viable seed yield, in a way that control levels until 200 kg/ha had statistically the same viable standard seed yield with the further increase in nitrogen application up to 300 kg/ha leading to a significant decrease in seed yield to 833 kg/ha. Although phosphorous application led to a higher PE as compared with N application (1.269 kg/kg), but of each kilogram addition of phosphorous result in an increase in crude, saleable and viable standard seed yield of only 0.365, 0.590 and 0.460 kg, respectively. PE, as a result of phosphorous application (1.269 kg/kg) was higher than that of nitrogen (0.225 kg/kg), while ARE due to nitrogen application (77.3%) was greater than ARE due to phosphorous application (12.9%) by sixfold

To study the effect of seed sowing rate, different levels of nitrogen and different sowing dates on canola cultivar Hyola401, a field experiment was conducted during 2005-2006 at Safiabad Agricultural Research Center. The design was a split split plot in a completely randomized block basis of 3 replications. Main plots consisted of 3 levels of sowing dates (6, 26 Nov and 16 Dec), sub plots of 3 levels of nitrogen (180, 220 and 260 kg/ha) and sub sub plots of 3 sowing rates (4, 6 and 8 kg/ha). Results indicated that a significant difference was observed among different sowing dates and seed sowing rates. The highest yield (4501.65 kg/ha) was obtained from 8 kg/ha of seed sowed. Application of planting date of 6 Nov, produced the highest grain yield (4777.65) while the lowest grain yield (3910.86 kg/ha) was achieved from 16 Dec. treatment, indicating that the grain yield was lower by 18.15% in the third sowing date in comparison with the first one. The interaction effect between sowing dates and nitrogen applications was significant on grain yield. Application of 260 kgN/ha at the first sowing date yielded 5138.7 kg/ha of grain. The highest oil content (93.45%) was obtained from the treatment Nov 6th sowing date. Delay in sowing date caused a, decrease in oil percentage. Delay in the sowing date also caused decrease in the number of pods per plant. The highest (325.2) and the lowest (98.13) number of pods per plant were obtained for the first and the third sowing date treatments respectively. The results reveal that from among the factors studied in this experiment, sowing date is the most important one affecting the grain yield. A sowing date of 6 Nov with an application of 260kg/ha of nitrogen, yielding the highest grain is finally recommended.

To evaluate genetic variation and to study of dry matter remobilization towards seed, 64 bread wheat genotypes were examined in two separated experiments using Alpha-Latic design of 2 replications during 2002–2003. Significant differences observed for most traits in normal and drought conditions. There were considerable variations among genotypes for independent parameters of dry matter remobilization to different plant parts in the two environments. Seven factors explained 77. 5% and 78. 6% of total variance in normal and drought conditions, respectively. Assessment of drought resistance indices indicated that the four indices of: MP (Mean Productivity), GMP (Geometric Mean Productivity), HARM (Harmonic Index), STI (Stress Tolerance Index) were more effective than the others for a selection of drought tolerant genotypes.