JWSS - Journal of Water and Soil Science

---

Sorghum grain is an important cereal to be cultivated in tropical and sub-tropical areas. The extension of its cultivation and application in animal and poultry diets may reduce the need for imported corn. In order to determine the nutritive value of sorghum, 36 sorghum grain (SG) varieties and one type of corn were grown at the same location. The grains were analyzed for their nutrient composition. Results from of proximate analyses showed that the ash, crude protein (CP), phosphorous (P) and acid detergent fiber (ADF) contents of SG were 1.72±0.54, 11.6±1.18, 0.34±0.03 and 8.35±3.93, respectively. The ether extract (EE) of SG was lower than Iranian and imported corns. Iranian corn had higher amounts of CP (10.7%), EE (5.9%) and CF (3.3%) than the imported one (7.8, 4.2 and 2.25). Tannin contents of low and high SG varieties were 0.021% and 0.998%, respectively. The apparent and true metabolizable energies (AME and TME) of SG were decreased due to increasing the tannin contents. The values of TME_n (3853, 3771 and 3213 Kcal/kg) showed significant differences (p < 0.05) among low, medium and high tannin sorghum (LTS, MTS and HTS) varieties. However, in comparison with the SG, the corn had higher amounts of TME (3853, 3771 and 3213 VS. 3947 Kcal/kg). LTS had the highest AME (3453 Kcal/kg) among all the grains, while there were no significant differences (P > 0.05) between MTS (3458 Kcal/kg) and the two corn grains (3406 Kcal/kg).

---

Growth and grain yield of irrigated barley cultivars (Valfajr, Binam and Raihaneh) was investigated at 4 sowing dates (6, 22 Oct. and 14, 20 Nov.) in Karaj region. The effect of sowing date, genotype and their interaction on grain yield were statistically significant. Early and late sowing enhanced cold damage. However, the damage was more in late sowings. It was estimated that the optimum sowing date would be about 50 days (600 GDD) prior to freeze-up and maximum cold damage would occur when sowing was delayed until some 22 days (230 GDD) before freeze-up but any more delay in sowing would cause less damage. Highest grain yield was obtained from Raihaneh at 22 Oct. sowing. Binam showed good yield stability and relatively high yield, especially in unfavorable sowing dates. In the relatively favorable sowing dates (6 and 22 Oct.), grain weight showed positive correlation with linear grain filling rate, storage and translocation of reserves. LAI, LAR, RGR, CGR and LAD of each cultivar were higher in the second sowing date compared to the first one. The “ratio of post anthesis growth to maximum TDM” showed a high correlation with the harvest index. Raihaneh was the highest cultivar in resistance to lodging, harvest index, storage and retranslocation of assimilates, and linear grain filling rate. It is suggested that at favorable sowing dates, Valfajr and Binam had source limitation or disturbed translocation and Raihaneh had sink limitation.

---

The effect of N levels and planting densities on quantitative and qualitative characteristics of grain yield in grain sorghum (cv. Kimia) was studied in summer 1998 at Kushkak Agricultural Research Station, Shiraz University. The experiment was a spilt plot with 4 replications in which 4 levels of planting densities (7.7, 10, 15.4, 20 seeds m^-2) were applied as main plots and 4 levels of N (0, 40, 80, 120 Kg N ha^-1) as subplots.

 N application rates up to 120 kg N ha^-1 increased grain yield (7240 kg ha^-1), but due to increased planting density (5336 kg ha^-1) the highest yield obtained from 15 seeds m^-2. Interaction of N and planting density was also significant. Application of 80 kg N ha^-1 and highest planting density produced 8702 kg ha^-1 of grain. Different grain yields in different levels of N and planting densities were due to increased number of grains per basic branches of panicle and increased number of panicle per m^-2. The trend of variation of crop growth rates (CGR) was similar to the trend of grain yield. Nitrogen application increased grain protein contents but planting density had no significant effect on grain protein. Phenolic compounds (tannins) decreased with increasing N application and with decreasing planting density. A negative correlation was observed between increased N content and increased phenolic compounds.

---

Effects of different levels of nitrogen fertilizer and cutting time of forage on grain and forage yield of barley (Hordeum vulgare L.) Karoon cultivar was studied during 1995-1996 at Ramin Agricultural Research and Educational Center, University of Shahid Chamran, Ahwas, by using a split plot design in randomized complete block with 4 replications. Main plots were assigned to five levels of N fertilizer (45, 90, 135, 180 and 225 kg N/ha) as urea fertilizer and subplots to three cutting times (no cutting, cutting forage at early stem elongation without removing reproductive meristem and cutting forage in the middle of stem elongation with cut reproductive meristem).

The effects of N rates and cutting time on grain yield were significant. Maximum yield was obtained with 281.6 g/m² when crop plants received 90 kg N/ha and cutting time at early stem elongation and minimum yield was obtained (158.2 g/m²) with 45 kg N/ha and cutting forage in the middle of stem elongation. Interactive effect of levels of N and cutting time on spike number per m², grain number in spike and grain weight were significant. Among yield components, spike number and grain weight showed the highest sensitivity to both. Different levels of N increased forage protein concentration and protein yield significantly, but delay in cutting time decreased protein concentration and increased protein yield. Results indicated that high levels of N could not compensate for the delay in cutting time of forage for grain yield. It was concluded that application of 90 kg N/ha and cutting time in early stem elongation was preferable for grain and forage production as compared to other treatments.

---

To study grain quality traits and their relationships with high molecular weight (HMW) and low moleculor weight (LMW) glutenin subunits, 104 durum wheat genotypes were used. Six grain quality characteristics comprising wet and dry gluten content, test weight, grain hardiness, protein content and SDS sedimentation volume were studied. HMW and LMW glutenin subunits were evaluated using SDS-polyacrylamid gel electrophoresis (SDS-PAGE) in 33 genotypes. Statistical analysis including correlation coefficients, factor analysis, cluster analysis of genotypes based on qualitative traits, analysis of variance in qualitative traits based on HMW, LMW, and combination of subunits as well as all of subunits, and canonical correlation analysis between glutenin subunits and qualitative traits were used. Factor analysis of the genotypes detected 2 factors, which explained 65 percent of the total variation among the data. These were named quantitative protein and qualitative protein. Based on cluster analysis, the genotypes were classified into four clusters. The genotypes in groups 2 and 4 were beneficial in terms of protein quantity and quality. In evaluating glutenin subunits, 7 HMW subunits and 2 LMW subunits were detected. Subunit null of Glu-Al was observed. Subunits 7+8, 6+8, 13+16 and 20 at Glu-Bl were observed however, neither of them had significant differences in qualitative traits, but 6+8 and 7+8 had a higher SDS sedimentation rate than 20. LMW-1 and LMW-2 had significant differences in protein content and SDS sedimentation LMW-1 had higher protein content whereas LMW-2 had higher SDS sedimentation. Combibation of subunit LMW-1 / HMW 7+8 had the highest protein content and LMW-2/HMW 7+8 had the highest SDS sedimentation. Results of canonical correlation showed that presence of LMW-2 and HMW 7+8, and absence of LMW-1 and HMW 20 in durum wheats caused an increase in SDS sedimentation and a reduction in protein and gluten content.

---

Genetic variation of 300 genotypes of durum wheat comprising CIMMYT/ICARDA and Iranian germplasm was evaluated in 1999-2000 at Researh Farm of College of Agriculture, Isfahan University of Technology located at Lavark, NaJaf-Abad. Days to heading, days to maturity, plant height, spike length, grain weight per spike, number of grain per spike, number of spikes per m², 1000-grain weight, test weight, grain yield, biological yield, and harvest index were recorded. Coefficients of correlation, step-wise regression, factor analysis and cluster analysis of characters and genotypes were conducted using the studied traits. Results indicated that considerable genetic variations exist for the traits and, in particular for grain yield, harvest index, number of spikes per unit area and number of grain per spike. Grain yield had a positive and significant correlation with days to heading, days to maturity, number of grain per spike and grain weight per spike. Factor analysis for the genotypes detected 6 factors, which explained 76.7 percent of the total variation among data. These factors basically involved potential of assimilate distribution, different aspects of plant storage, source-sink relationships, plant height and tillering potential. Cluster analysis was similar to factor analysis in grouping the characters. According to cluster analysis, the genotypes were calssified into 6 clusters with significant differences among all groups. Mean comparisons of traits in these groups showed that genotypes of groups 5 and 6 were superior in grain yield and harvest index and are beneficial to the local durum breeding objectives.

---

Planting density, through its impact on the level of available environmental factors may have significant impacts on grain yield in safflower (Carthamus tinctorius L.). In order to investigate the impacts of plant density on grain yield, yield components and growth characteristics of safflower, a randomized complete block design field experiment with four replicates was conducted in spring-summer, 2000, at Lavark Research Farm (Lat. 32⁰ 32^, N and Long. 51⁰ 23^, E), College of Agriculture, Isfahan University of Technology, Isfahan, Iran. Arak-2811 and Kouseh safflower genotypes were seeded at 16.6, 22.2, 33.3 and 50 plants/m². For establishing these plant densities, plants were seeded in 12, 9, 6 and 4 cm distances, respectively, on ten 8-m-long rows spaced 50 cm apart in each plot. Plant density had no impact on plant growth stages with the exception of button formation. Genotype had significant effects on days to seedling emergence, button formation, and 50% flowering. While both number of days and accumulated growing degree-days for all growth stages decreased with an increase in plant density, Arak-2811 was earlier than Kouseh for most growth stages. Number of branches and heads per plant, number of heads per branch, number of seeds per head and harvest index showed significant decreases with increasing plant density. The decrease in the mentioned grain yield attributes was mainly negated by greater number of plants per m², leading to no significant variation in grain yield between plant densities of the two genotypes. Arak-2811 produced a significantly greater number of heads per branch and 1000-grain weight however, these differences did not lead to any greater grain yield compared to Kousehdue, mainly due to the greater number of branches in the latter. Neither of the leaf area index, leaf area duration, and crop growth rate varied significantly with plant density and between two genotypes, suggesting no difference in dry matter production capabilities of the two genotypes under environmental conditions of the present study.

---

In order to study the effects of different levels of nitrogen fertilizer and plant density on grain yield and its components in sunflower, an experiment was conducted using 'Record' cultivar at the Research Farm of College of Agriculture, Isfahan University of Technology in 1996. Four levels of nitrogen (0, 75, 150 and 225 kg/ha) and four plant densities (65000, 75000, 85000 and 95000 plants/ha) were used in a split plot arranged in a randomized complete block design with three replications. Developmental stages, plant height, stem diameter, head diameter, number of head per m2, grain yield, biological yield, harvest index, 1000-grain weight, number of grains per head, grain oil percentage, oil yield and grain protein content were measured. The results indicated that N fertilizer caused an extension of the growth period and means of days to physiological maturity. It also increased plant height, stem diameter and head diameter. While increasing plant density had an incremental effect on plant height, it negatively affected stem diameter and head diameter. N fertilizer up to 150 kg/ha increased the grain yield and biological yield, whereas higher levels of N fertilizer decreased both. Plant density of 85000 plants per hectare was observed as a suitable plant density, whereas the higher plant density had a negative effect on grain yield. N fertilizer via increasing the number of grains per head, and plant density via increasing the number of heads per unit area and also decreasing the number of grains per head influenced the grain yield. One-thousand grain weight was not affected by neither N fertilizer nor plant density. Considering the superiority of 150 kg/ha of N fertilizer and plant density of 85000 plants/ha for grain yield and oil yield, it appears that they could be recommended for producing desirable yield in the regions similar to the study region.

---

An experiment was conducted at Rasht Rice Research Institute, in 2001 to study trait relationships and to determine the direct and indirect effects of different characteristics on grain yield of rice (Orgza sativa L.). A 9x2 factorial experiment in complete randomized block design with 3 replications was used. The two factors were 9 cultivars, namely: Hashemi, Ali Kazemi, Binam, Sepeedroud, Nemat, Khazar, Taichung, Chanto, and Usen, and 2 planting patterns (15x15 cm and 30x30 cm). Significant differences were detected among cultivars, between planting patterns, and their interaction effects. The direct effect of the number of panicles/m² on grain yield was positive and significant in both planting patterns and their combined analysis. Heading date had a positive and significant direct effect on the number of panicles/m² in both planting patterns and their combined analysis. Only in 30x30 cm planting pattern, a positive correlation was found between biomass at heading date and the number of panicles/m². Grain weight per plant had a direct and positive effect on panicle weight in the 3 cases studied. Also, in all the cases studied, flag leaf area had positive direct effects on grain weight per plant. Grain filling rate and effective grain filling period increased in 30x30 cm planting pattern. Native cultivars demonstrated longer latent period. Grain filling rate and effective grain filling period showed positive direct effects on grain yield in both plantings. According to the results obtained, an increase in the number of panicles/m², rate of grain filling, and effective grain filling period would enhance grain yield. Selection for heading date, grain yield per plant, and flag leaf area would also indirectly increase grain yield.

---

To evaluate heritability, phenotypic and genotypic correlation coefficients, phenotypic and genotypic variances as well as relationships between some of the grain quality traits, an investigation was conducted in a randomized complete block design replicated three times in 2001, using four durum wheat genotypes PI40100, Dipper-6, Oste/Gata, Shova and their F₂ and F₃ progenies derived from their crosses. Grain quality characteristics including seed hardiness, protein content, SDS sedimentation volume and gluten content were evaluated. The results indicated that wet gluten content and dry gluten content had the highest coefficient of variation. Statistical analysis showed a significant difference between genotypes for all traits with the exception of SDS sedimentation volume. Dry gluten content had the highest heritability (90.4%) while SDS sedimentation volume had the lowest heritability (48.6%). Results of correlation analysis indicated that seed hardiness correlated significantly with protein content, SDS sedimentation and dry gluten content. Protein content had a positive correlation with wet and dry gluten content. Since dry gluten content showed a high correlation with protein content (quantity) and seed hardiness had a high correlation with SDS sedimentation volume, hence these two traits can be used as the selection criteria for improving quality of protein in durum wheat.

---

The Genetic basis of grain yield and related characteristics were studied by a generation mean analysis in five crosses of winter wheat (Triticum aestivum L.). “Roshan”, “Mahdavi”, “Inia”, “Atila” and “Goscoyin” cultivars along with their F₁, F₂, BC₁ and BC₂ populations were evaluated by a split-plot design with crosses as the whole plot in a randomized complete block design with two replications and generations were applied as the subplots. Analysis of variance revealed significant differences among generations for studied characteristics including the grain yield per plant, the number of spikelet per plant, the number of spikelet per spike and grain weight per spike. For the majority of traits and crosses, F/DH^1/2 was less than one, indicating that the sign and magnitude of gene actions were different. Estimates of broadsense and narrow sense heritabilities were low for the grain yield per plant compared with other traits, rating from 28.5% to 58.6% and 24% to 48,5% for the five crosses, respectively. Genetic components of generation means were calculated by fitting different models and choosing the best model indicated that the impact of additive, dominance and epistasis genetic components in controlling the traits depend on the cross and the trait under study.

---

A major source of photoassimilates deposited into the seeds is the closest photosynthetic source to the latter sinks. While the contribution made to grain yield by floral parts and the adjacent photosynthetic surfaces has been determined for a number of crop plants, such information lacks regarding safflower. Thus the present study was aimed at estimating the contribution of photosynthesis of safflower head and the two adjacent leaves to the grain yield of this oil seed crop. A 4-replicate RCBD field experiment was conducted at Lavark Research Farm, Isfahan U. of Tech., using four genotypes (Nebraska10, Kouseh, Arak2811 and K12) and three levels of shading (heads only, heads and the two adjacent leaves and control) on safflower heads following pollination, using khaki paper bags. Genotypes differed in terms of days to heading and maturity, height, number of heads per plant, number of seeds per head, 1000-seed weight, seed weight per head and grain yield per plant. Shading on safflower head and the two adjacent leaves led to a significant decrease in number of seeds per head, 1000-seed weight, seed weight per head, grain yield per plant and harvest index. There was not a significant difference between the two levels of shading treatment. It could be concluded that, with the environmental conditions experienced during spring 2003 at Isfahan, the photosynthetic products of safflower head and the two adjacent leaves may contribute to grain yield per plant by as much as 37 percent.

---

In order to investigate the effect of different irrigation regimes on some agronomic and physiological characters of three chickpea cultivars (Jam, 301 and Pirooz), a field experiment was conducted in 1998 at the Agricultural Research Farm of Tabriz University, Tabriz, Iran. A split plot experiment based on a randomized complete block design with three replications was used, in which irrigation treatments (full irrigation, irrigation at only branching or flowering and or pod formation stage) were in the main plots and chickpea cultivars were in the sub plots. Under limited irrigation conditions there were no significant differences among irrigation regimes for green cover percentage and the number of pods per plant while rate and duration of grain filling, grain weight and grain yield were significantly higher for irrigation at pod formation than for irrigation at branching or flowering stage. The mean of all the traits, except for the number of seeds per pod were significantly higher for full irrigation than for limited irrigation treatments. Rate of grain filling, maximum grain weight and grain yield were significantly higher for irrigation at flowering than for irrigation at branching stage. While, other characters were not significantly different between these two treatments. Although, green cover percentage and seeds per pod in 301 were higher than those in Jam, but in other cases their response to water limitation was almost similar. All traits, except the number pods per plant, were noticeably lower for Pirooz compared to Jam and 301 cultivars. Green cover percentage showed the highest correlation with the grain yield. This study revealed that among phenological stages of chickpea, pod formation is the most sensitive to water deficit, and that under water limitation conditions chickpea yield could be improved by irrigation at this stage.

---

A field study was conducted at the Zabol Agricultural Research Center during the years (2003-2004) to investigate the effect of irrigation with treated municipal wastewater on the yield and quality of wheat and some soil properties. Irrigation treatments were: T₁: Irrigation of wheat with well water during entire period of growing season T₂: Irrigation of wheat with well water until the begging of flowering stage, and irrigation with wastewater in every other turns of irrigation T₃: Irrigation of wheat with well water until the beginning of booting stage, and irrigation with wastewater in every other turns of irrigation T₄: Irrigation of wheat with well water until the begging of tilling stage, and irrigation with wastewater in every other turns of irrigation and T₅: Irrigation of wheat with wastewater during entire period of growing season. A complete randomized block design with four replications was adopted for this experiment. The soil was sandy loam with no limitation for internal drainage. Chemical and physical aspects of soil were measured during the experiment. Grain yield, yield components and chemical composition of wheat grain were also measured. The results showed that yield of wheat and total biomass production were statistically significant in T₃, T₄ and T₅ compared with the control treatment. Plant height, width and length of flag leaf, numbers of fertile tillers, length of panicle, numbers of grains per panicle and weight of 1000 grains were also statistically significant with the control treatment. Percentages of protein were statistically different among various irrigation treatments. No significant changes in accumulation of heavy metals in soil and plant grains were observed. The increase of SAR, ECe, O.C% and total nitrogen in the T₄ and T₅ were statistical significant compared with the control treatment. In summary, for sustainable use of Zabol municipal wastewater, the growth stages of wheat should be irrigated with municipal wastewater and other growth stages should be irrigated with nonsalinty water, so that the maximum yield is obtained and soil salinitisation and sodication is prevented.

---

Relationship between grain filling rate , grain filling duration, yield components and other physiological traits of rice was investigated in 93 genotypes of rice at Rice Research Institute of Iran (Rasht, Iran) during the growing season of 2001-2002. The experiment was performed without any statistical design. Panicles of main stem were tagged and taken at 3- day intervals during the grain filling period. A cubic polynomial model was used to fit the grain dry weight data (mean of R²= 0.98 for all genotypes) and the grain filling rate and duration estimated for the genotypes. Traits related to sink capacity such as grain weight, grain size and grain number per panicle correlated with grain filling rate but source -capacity- related traits except chlorophyll content of flag leaf and secondary leaf did not correlate with grain filling rate. Stepwise regression showed that final grain weight, grain filling duration and flag leaf angle contributed to grain filling rate, however, path analysis showed that only final grain weight and grain filling duration had the greatest effect on grain filling rate. The results of stepwise regression irrespective of final grain weight showed that chlorophyll content of flag leaf, grain width, grain filling duration and grain length contributed to grain filling rate. Path analysis results showed that the final grain weight had the greatest direct positive effect on grain filling rate, while grain filling duration had negative effect on grain filling rate.

---

Many experiments have been carried out to alleviate the negative effect of drought stress and to obtain suitable growth under water deficient condition. Application of plant growth regulators (especially growth retardants) is one of the proposed methods. In a greenhouse experiment using a completely randomized block design with 4 replications at Kerman University Agricultural Department, the effect of 4 drought levels 25, 45, 65, 85 percent of field capacity and 3 different concentrations of chlormequat chloride 0, 1500, and 3000 mg/liter on some factors of winter barley cultivar Valfajr was investigated. Results indicated that increasing the cycocel concentration from 0 to 3000 milligram per liter leads to significant decrease in plant height. Relative water content affected by growth retardants was increased. Numbers of tillers and root and shoot dry weight, were also decreased because of applying cycocel in dry condition. The result also indicated that the root/shoot dry weight ratio, grain number per ear and ear number in dry condition without stress would increase using cycocel treatment.

---

Drought stress is one of the major limiting factors of crop yield. A field experiment was conducted to study the effects of drought stress on yield and yield components of nine bread wheat and one durum wheat genotypes during 2003-2004 growing season. The experiment was designed as two separate randomized complete blocks design with three replicates under well-watered and unwatered conditions during the post-anthesis period. Post-anthesis drought stress reduced the grain yield and yield components in all genotypes. Mean of each trait significantly(p≤%5) decreased under drought stress conditions, except for spikeletes number per spike and ear number per square meter. The highest yield loss was caused by the grain number per ear and 1000- grain weight reduction under drought stress conditions.“Gahar” genotype had the highest grain yield (4149 kg/ha) under drought stress conditions, whereas the highest grain yield (6674 kg/ha) was obtained for “Nikenejad” genotype under optimum conditions. Based on stress susceptibility index, “Koohdasht” and “Boholh-15” genotypes showed the lowest and the highest yield loss in response to drought stress, respectively. Correlation analysis of yield and yield components indicated that, under drought stress conditions, ear number per square meter (r=0.751) and biological yield (r=0.707) had the highest correlation with the grain yield(p≤%5), whereas these traits were grains number per ear(r=0.864) and biological yield (r=0.848) for the well-watered conditions. Therefore, it might be possible to select genotypes for greater grain yield with the means of the traits which have the highest correlation coeficient with the grain yield under each moisture regime. Generally, it appeared that “Gahar”and “Nikenejad” genotypes with greater yield potential might be recommended for agronomic conditions similar to the present investigation.

---

Understanding the nitrogen remobilization by plant, in order to obtain cultivars with higher quality, has specific importance in plant physiology. In this experiment, a bread and a durum wheat cultivar, were treated with different rates and times of nitrogen application, by using split factorial on the basis of randomized complete block design with three replications at Shiraz region during 2001-2002. Main plots consisted of two levels of cultivars ( Falat and Yavaros) and sub plots included nitrogen (40, 80 and 160 (kg ha^-1) and times of nitrogen application (T1= all N fertilizer at planting , T2= 1/2 at planting + 1/2 during stem elongation and T3= 1/3 at planting + 1/3 during stem elongation + 1/3 at heading stage). The results showed that there was a significant difference between cultivars in flag leaf nitrogen content at maturity stage, N remobilization and its efficiency from flag leaf to grains and also grain protein percentage. Durum wheat was more efficient in nitrogen remobilization and therefore, had a higher grain protein percentage. Increase in rates and times of nitrogen application had significant effect on most of the measured traits. There were significant interactions between cultivars, rates and times of N application, indicating that durum wheat was more efficient in N remobilization from flag leaf to the grain. It appeared that N remobilization efficiency was the important factor affecting the grain protein percentage. Also increases in yield are associated with corresponding decreases in wheat protein.

---

To evaluate the effect of plant density and detopping on grain yield, protein content biological yield harvest index, growth indices, number of cob in each plant, No. of row per ear, No. of grain in each row, thousand seed weight of corn (Zea mays L. ar. SC 704), an experiment was conducted at the experimental statues of Research Center of Uremia Agricultural College in 2004. The Treatment design was split plot in randomized complete block design with four replications. The main plots included plant density at three levels (53000, 66000, and 88000 Plants/ha) and the subplets comprised three levels: (1) no detopping (control) (2) removing canopy only and (3) removing canopy and three leaves above the node. Analysis of Variance of data showed that both detopping treatment and plant density influenced the number of kernel per ear ,1000 grain weight, ear weight, total dry weight of biomass, seed yield and harvest index. Canopy detopping led to a marked increase in photo assimilateion import grains. The highest plant density evaluated, 88000 plants per hectare with detopping of three above leaves had the highest number of cobs per square meter. In plant density of 53000 plants per hectare and canopy detopping treatment, the number of grain per ear was greater than other densities. The efficiency of harvest index increased under corn detopping compared with control, and this increase with an increase in photosynthesis contributed to grain yield. It was concluded that major increase in grain yield under high plants density and tassel detopping was due to improvement of physiological indices.

---

  Application of selection index for screening desired plants based on complex quantitative traits can be more effective than direct selection. This study was conducted using an F₂ rice population consisting of 87 plants derived from a cross between two cultivars Gharib and IR28. The purpose was to establish suitable selection indices for increasing yield and its related traits in research farm of Rice Research Institute of Iran (RRII), Rasht, in 2005. Studied traits included the days from sowing, germinated grain to maturity (MD), plant height (PH), panicle length (PL), flag leaf length (FL), flag leaf width (FW), number of panicles per plant (PP), number of grains per panicle (GP), number of spikelets per panicle (SP), 100-grain weight (GW), grain yield per plant (GY), biomass (BM), harvest index (HI), grain length (GL) and grain breadth (GB). Among the studied traits, 100-grain weight (GW), biomass (BM) and harvest index (HI) (0.99) and flag leaf width (FW) (0.35) showed the highest and lowest broad-sense heritability, respectively. Path coefficient analysis revealed that BM, HI, GP had positive direct effects on GY. Calculation of five different selection indices based on optimum and base indices indicated that selection for BM, HI and GP using genotypic path coefficients and their heritability as economic values would be a suitable selection criterion for improving population. Moreover, this study showed that both optimum and base indices show the same genetic progress for the studied traits. Since evaluation of base index, is much easier than the optimum index, it is highly recommended.