Iranian Journal of Crop Sciences
Year:2003 | Volume:5 | Issue:3|Papers Count:8

To study the extent of yield loss that weeds may cause, and the most suitable index for estimating the reduction of wheat yield a survey has been conducted in Ghaemshahr in 1998-1999. For this purpose 27 plots in a farm with dimensions of 5×5 were identified, and in different stages the density of weeds were counted and recorded. At the end of growing season, every single species in each plot was measured, separately. For calculation and comparison of coefficient of damage in species, indices such as dry weight, plant equivalent ratio, and also average dry weight of a single weed plant was measured. The results shown that the ratio of weeds biomass to their number provided a better index for estimating of wheat reduction in wheat yield. Yield eguation was developed using multivariate regression, in which the effect of weeds in wheat crop is divided in two different groups; the first inhibiting and the second as positive effect. Intra specific competition of wheat plants was more than inter specific competition. Two species (Rapistrum reugosum) and (Avena fatua) had the most effect on reducing wheat yield in this study. However Veronica persica and Artemisia sp. had the least effect on wheat yield reduction. In the next survey conducted, we found the positive effect of some species of weeds in inhibiting of those species with the of high competitive ability in wheat crop.      

In order to determine a wheat ideotype for competition with weeds, two field experiments were conducted in Agricultural Research Station of Mashad University in 2001. The experiments were carried out as factorial in a Randomized Complete Block Design with four replications. In the first experiment, the factors included wheat densities at 3 levels (300, 450 & 600 plants/m2) and wild oat densities at 5 levels (0, 20, 40, 80 & 160 plants/m2). The factors of the second experiment consisted of the same wheat densities but turnip weed densities at 5 levels (0, 4, 8, 16 & 32 plants/m2). ldeotypes were selected based on the absorbed PAR by INTERCOM model. The results indicated that wheat ideotypes in comparison to normal plants have taller plant height and larger leaf area index and less extinction coefficient (K). Wheat ideoype in competition with turnip weed are different from wild oat. A high correlation was observed between the amount of radiation absorbed by weeds and wheat yield loss.      

Studying relationships between agronomic traits would assist breeders to identify the effective traits and use proper selection intensity in their breeding programs. Forty-eight elite entries of chickpea (Cicer arietinum L.) as well as one Iranian cultivar (Jam) were used to estimate genetic variation for 11 morphological and phonological characters, at Kurdistan Agricultural Research Center, west of Iran. The experimental design was a simple lattice (7×7) with two replications. Genotypic differences among the entries were highly significant for some of the characters. The phenotypic and genotypic correlations among the traits were estimated. Seed yield was positively and significantly correlated with number of pods per plant, number of secondary branches, biological yield and harvest index, and negatively but significantly correlated with number of days from sowing to flowering. In most cases, phenotypic and genotypic correlations were closely correspondent. However in some cases, the differences signified the environmental effects. Path analysis showed that 100 seeds weight has the most direct effect on seed yield.          

In order to study yield and yield components of corn (Zea mays L.) in competition with redroot pigweed (Amaranthus retroflexus L.) an experiment was conducted at Seed and Plant Improvement Institute (SPII), Karaj, Iran during 2000. Field study was carried out based on RCBD with 3 replications to determine the influence of redroot pigweed densities (3, 5, 8 and10 plant per m of row) and times of emergence (same time with corn, 2-3 and 4-5 leaf number of corn) on yield and yield components of corn. Results indicated that early emergence of pigweed caused a decrease in harvest Index (HI), row number, grain number per row and grain yield. Results also revealed that different time of emergence did not show any significant differences in kernel weight. Corn yield loss was 30% in early emerged pigweed and decreased to 25 and 12 percent in 2nd and 3rd time of emergence, respectively. There were no significant differences in corn traits under different redroot pigweed densities.      

High molecular weight glutenin subunits variation was studied at Glu-1 loci in 86 breeding lines and cultivars of bread wheat of lran, using SDS-PAGE method. A total of 14 alleles and 31 allelic composition were detected. An already reported rare subunit pair" 2***+12'" at Glu-D1 locus was found in Sorkhtokhm, and Boulani which are landraces of Sistan and Bluchestan province of Iran and cv. Kavir which is a Sorkhtokhm derivative. The total average of Glu-1 quality scores of these lines and cultivars was 7.6 of 10 and showed that the HMW-GS compositions had generally good quality. Cultivars Inia, Maroon, Sisson, Zagros, Pastour, Tajan and N-75- 11, N-75-15, C-79-16 and C-79-18 lines showed quality scores equal to ten. However, Alamoot, Shahriar, Hamoon cultivers and C-73-18, C-73-20, C-75-5, and C-78-I8 lines showed quality scores between four to five. The quality of former and later lines/ cultivars was considered the highest and lowest in this study, respectively. The results in this study provide a genetic estimation of quality of bread wheat lines/ cultivars in Iran in comparison to those from other countries.      

Agro-technical factors that have effect on grain yield and their optimum control would increase yield. This experiment was carried out in as factorial using RCBD with two factors including distance between rows (a1=40 and a2=60 cm) and distance between plants on row (b1=20 cm, b2=25cm, b3=30cm and b4=35cm) with 3 replications for two years on sunflower cv. Armavirsky. Plant height, head diameter, stem diameter, days to flowering and maturity, number of seeds per head, TKW and grain yield were recorded. Results showed that effects of distance between plants on row was significant (a=%1). Based on results, there are no significant differences in grain yield among treatments. The combination of 60 cm row distance and 35 cm plant distance on rows with 47619 plants per hectare is recommended for growing sunflower cv. Armavirsky under Maragheh dryland conditions. This recommendation will lead to reduce seed rate and soil moisture losses through transpiration. It would also facilitate in the chamical control of weeds.      

Rice is an important nutrient crop and plays strategic role for food security worldwide. Study of genetic variation is essential for yield improvement, increasing quality and other agronomically important traits. Four hundered and nineteen rice accession of several provinces received from National Plant Gene Bank were studied. Sowing, seedling transplanting (single plant) and other husbandry measures carried out according to the cultural practices needed in Mazandaran region. Sixteen physiological and agronomically important traits recorded on the basis of standard evaluation system (SES). Cluster analysis performed according to the minimum variance, using SPSS software. The maximum and minimum variation belonged to the Gillan and Mazandaran provinces and Kohkiluieh-Boyerahmad, Sistan-Baluchestan and Chaharmahal-Bakhtiari provinces, respectively. The cluster of the whole data (total population, 419 cultivars) showed 6 distinct clusters at 35% genetic distance. This dandrogram (total population) indicated that the rice accession from Gillan and Mazandaran located at two independent clusters but most of accessions from Eilam, Khuzestan, Kohkuluih-Boyerahmad and Fars provinces' were very close to the Mazandaran accessions. It is concluded that many accessions of Mazandaran have been transferred to the provinces.