Introduction: Weeds are an important challenge to crop production, particularly in sustainable agriculture. Today, identification of highly COMPETITIVE CULTIVARS is an easy and inexpensive method for weed management in sustainable agriculture systems. Watson et al. in their study of 29 barley varieties found that yield loss due to weed competition varied from 6 to 79 percent, which is related to their ability to compete. In the case of WHEAT, for more than four decades, the difference of the weed COMPETITIVE ability between WHEAT CULTIVARS has been investigated. Two aspects of cultivar COMPETITIVEness can be defined, COMPETITIVE index (CI) and weed interference tolerance index (WITI). CI is the ability of a cultivar to reduce weed growth and WITI is the ability of a cultivar to achieve high yield despite weed competition. These traits differ based on genetical and agronomical aspects. CI is often associated with traits including vigorous growth, allelopathic potential, crop cover, and height and leaf area. Although for environmental stresses high tolerance indexes are important, the COMPETITIVE index is more important in the long-term management of weed management. Trusting the tolerance index alone can lead to a sharp increase in the weed seed bank, which may not tolerate high-tolerance CULTIVARS. So, the present study was carried out to classify Iranian WHEAT CULTIVARS based on traits related to competition and tolerance indices and to determine the correlation between indices with yield and yield components. Material and Methods: This experiment was conducted to classify Iranian WHEAT CULTIVARS based on traits related to competition and tolerance indices and to determine the correlation between indices with yield and yield components in the agricultural research farm of the faculty of agriculture and natural resources, University of Mohaghegh Ardabili at 2015-2016 growing season. For this purpose, 25 WHEAT CULTIVARS were tilled in November 2015 under with or without weed competition. In each plot, 10 WHEAT lines were cultivated at a distance of 20 cm and a length of 5 m. The experiment was conducted in a randomized complete block design with three replications. At the beginning of spring, from each plot, a sample of WHEAT plants was harvested at a surface area of 0. 25 m2, dried at 75 ° C for 48 hours in order to measure the initial dry weight of the CULTIVARS. Sampling from weeds was conducted before the end of growing season. WHEAT plants harvested at maturity stage from 1 m2 and seed yield was reordered. To determine the yield loss, CI and WITI was used appropriate formulas. Results And Discussion: The results showed that there was no significant correlation between weed density with growth traits of WHEAT CULTIVARS, while there was a significant negative correlation between weed dry weight and these traits. The highest correlation was found between the primary cover with dry weeds weight (R2=-0. 70; P

In order to study the COMPETITIVE relations of three WHEAT CULTIVARS with different densities of wild oat, an experiment was conducted in factorial arrangment based on completely randomized block design in field of Abosaeed Agricultural School of Feizabad, with three replications. Experimental factors were consisted of three CULTIVARS of WHEAT (Falat, Sepahan, Pishtaz) and five wild oat densities (0, 5, 10, 20, 40 plant/m2). Result showed that the the highest yield was obtained in weed free conditions for all WHEAT CULTIVARS. Pishtaz showed superiority in respect to competition ability, growth characteristics and yield potential, compared to othere CULTIVARS, so that in density of 40 plant/m2 of wild oat grain yield of WHEAT CULTIVARS reduced about 44.66, 42.6 and 34.12 percent for Falat, Sepahan and Pishtaz, respectively. These differences was significant at P<0.01. The higher the wild oat density (20&40 plant/m2) the lowest vegetative and reproductive growth of WHEAT CULTIVARS, specially in Falat. Finally results confirm that, wild oat can reduce grain yield and harvest index of WHEAT CULTIVARS throughout its effect on productive tillers number, WHEAT leaf area index, plant height, 1000 seed weight and kernel number in spike. These COMPETITIVE effects occurred during the growing season and reproductive period of WHEAT. The yield reduction was different and depended to morphological and COMPETITIVE characteristics of each cultivar.

A field experiment was conducted to study the COMPETITIVEness of WHEAT CULTIVARS against Bromus japonicas at Sistan Agricultural Research Station during 2003. The experimental design was a randomized complete block assigned in factorial arrangement of treatments with four replications. Six WHEAT CULTIVARS comprised two natives (old CULTIVARS; Boulani and Kalak-Afghni), and four new-released CULTIVARS (Chamran, Hirmand, Kavir, and Hamoun) (as factor a) were grown in pure stand and in mixture with B. japonicus (as factor b). Weed density was 100 plants m-2. The old CULTIVARS were found more COMPETITIVE than new-released ones. Boulani was the most COMPETITIVE cultivar, however, had the lowest yield. In contrast, Kalak-Afghani with a good COMPETITIVE ability indicated the highest yield. Cultivar Hirmand with a low yield and the highest weed infestation was indicated the least COMPETITIVE cultivar. The more COMPETITIVE CULTIVARS had more biomass, leaf area, plant height, tiller number, and grain yield than the less COMPETITIVE ones in competition with B. japonicus.

In order to evaluate of yield and yield components of eight WHEAT CULTIVARS against flix weed (Descurainia Sophia), an experiment was conducted using a factorial arrangement of treatments in a randomized complete block design with four replications during 2003-2004 growing season in Varamin region. The WHEAT CULTIVARS were Tabasi, Roshan, Karaj2, Azadi, Niknejad, Mahdavi, Shiraz and Pishtaz. In this experiment traits such as: COMPETITIVE index, grain yield and yield components of WHEAT were measured. The results showed that significant differences between CULTIVARS in yield, so results of analysis of variation showed CULTIVARS were significant differences in (HI), but were not significant differences between CULTIVARS under weed-infested and weed-pure condition. The results showed that cultivar Niknejad from the competition ability was superior to CULTIVARS and had a greater yield compare to other CULTIVARS.

A study was carried out over 2 years (2008/2009 and 2009/2010) in Greece, in order to evaluate the weed control using reduced rates of the herbicide mesosulfuron-methyl+iodosulfuron-methyl-sodium of four major weeds (Avena sterilis, Phalaris minor, Papaver rhoeas and Sinapis arvensis), grain yield and yield components of five WHEAT CULTIVARS (Bob, Cosmodur, Meridiano, Quadrato and Simeto). The results indicated a significant differentiation between the several WHEAT CULTIVARS regarding their weed COMPETITIVE ability, in terms of dry biomass and seed production. In the case of CULTIVARS such as Simeto the efficacy of 50% reduction of the herbicide recommended rate on wild oat remained high, since it resulted to a reduction of biomass and seed production up to 81 and 98% compared with the untreated plots. In most CULTIVARS studied, the reduction of the herbicide rates by 25 to 50% resulted to a no significant reduction of grain yield compared to the recommended rate. The study revealed that some WHEAT CULTIVARS with enhancing weed COMPETITIVEness can improve the efficacy of reduced herbicide rates. Consequently, sustainable cropping systems could be further developed through the integration of such agronomic practices, while in parallel, care on the threat of herbicide resistance development should be also taken.

In order to study the COMPETITIVE performance of spring bread WHEAT (Triticum aestivum) CULTIVARS with wild oat (Avena lodoviciana), a field experiment was conducted in research farm of Ramin University of Agricultural and Natural Resources, Khouzestan in 2010-2011 cropping season. The experimental design was strip blocks with three replications. Four wild oat densities (0, 40, 80 and 120 plant.m-2) were assigned to horizontal plots and spring bread WHEAT CULTIVARS (Chamran, Baz, Atrak, Arvand, Maroon, Shoeleh, Chenab, Vee/Nac and Falat) were randomized in vertical plots. Competition indices calculated and analyzed for each cultivar. The highest competition index was obtained for 40 and lowest at 80 and 120 plants.m-2. Results showed that new index was better than older by many aspects, as there is 8 category scales including; highly susceptible, susceptible, semi susceptible, moderate, semi-tolerant, tolerant, high tolerant, and immune. Newly CULTIVARS Chamran, Daz, Virinak Vee/Nac and Falat with 1.3, 1.4, 1.6 and 1.8 competition indices, respectively, were identified as semi susceptible and Maroon with 7.0 as tolerant, but there is no immune, high tolerant, susceptible, or high susceptible among these 10 CULTIVARS. According to the results of the present experiment, tolerance of Maroon cultivar implies that low tillering CULTIVARS with more than 400 plants.m-2 density may decrease weed damage by earlier WHEAT canopy closure.

In order to investigate the effect of COMPETITIVE ability of WHEAT CULTIVARS with weeds in the Kurdistan region, an experiment was conducted in Agricultural Research Station Qamlv. A split plot design based on a randomized complete block with four replicates was used in growing season of 2004-2005. Main plots consisted of four CULTIVARS of WHEAT (Alvand, Zarin, Back cross Roshan and Shahriar) and sub-plot consisted of four levels of herbicides 2.4.D application time (early spring spraying (2 to 3 leaves), spraying in mid-spring (complete tillering), late spring (grain dough) and non pesticides application) were compared in combination with one another. Factores in this experiment are include: weed dry weight, plant height, stubble yield, biological yield, number of ear per unit area, number of grains per ear, grain weight, grain yield and harvest index. Results of comparison of data showed that the highest plant height, biological yield, number of ear per unit area, number of grains per ear, grain yield and harvest index relevant to Back cross roshan, it showed COMPETITIVE ability towards weeds in comparison with other CULTIVARS. In this experiment, spraying in mid-spring with 1250 kg per hectare, was known as the effective time of spraying to eliminate the competition with weeds and the back cross Roshan as the best cultivar to competition with weed.

To study the effect of salinity stress on some physiological traits in WHEAT CULTIVARS (Triticum aestivum L.), a factorial experiment based on randomized complete block design with three replicates was performed at 2017 in the research greenhouse of Agronomy Department, University of Tehran. Salinity treatments at two levels; control (1.2 dS/m) and sodium chloride treatment (16 dS/m) and seven WHEAT CULTIVARS, Rowshan, Inia-66, Mahdavi, Khazar-1, Karaj-2, Ghods and Shole were the experimental treatments. According to the results, relative water content, yield and its components and potassium/sodium ratio decreased in all genotypes while Na+ content and remobilization of carbohydrates were increased. Salt resistant varieties, Roshan and Inia-66, had the highest level of relative water content, remobilization of soluble carbohydrates and number of grains per spike. In addition, Roshan cultivar showed the highest potassium concentration and K+/Na+ in the shoots, while Ghods and Sholeh as sensitive CULTIVARS had the highest sodium concentration in the shoots. Findings showed that the ability of a cultivar to remobilize soluble carbohydrates is one of the traits that determine salt stress tolerance, hence, this trait is suitable for evaluating salt tolerance of WHEAT CULTIVARS in the future investigations.

Water Water deficit especially after heading is one of the most effective factors of WHEAT yield loss in Iran and across the world and identifying the physiological traits related to plant resilience is of great importance in screening for tolerant varieties. The objective of this study was to evaluate the variation in stem reserves accumulation capacity and its relationship with remobilization in some WHEAT CULTIVARS. 22 WHEAT CULTIVARS were cultivated in a split plot design with three replications, full irrigation and 40% of field capacity being main plots. The amount of accumulation and remobilization was estimated by measuring internodes weight and stem soluble carbohydrates content (WSC). Significant genotypic variation among CULTIVARS was observed under both normal and drought conditions. Maximum accumulation was found in lower internodes followed by peduncle and penultimate using dry weight measurement method. In WSC measurement method, however, maximum accumulation was observed in penultimate followed by lower internodes and peduncle. CULTIVARS ranking based on accumulation was also different in two methods. Drought stress caused decline in internodes weight, WSC and yield and remobilization efficiency. The specific stem weight had the highest correlation with remobilization. Significant correlation was found between grain yield and remobilization, specific stem weight and WSC.

During the 2003-2004 growing season, an experiment was conducted at the Plant Protection Research Institute in Karaj, Iran, to compare the COMPETITIVE ability (CA) of eight WHEAT CULTIVARS released during the last 50 years. Each cultivar (Tabasi, Roshan, Karaj2, Azadi, Niknejad, Mahdavi, Shiraz and Pishtaz) was grown in weed-free conditions or infested with rocket (Eruca sativa). The results indicated that grain yield COMPETITIVE indices differed significantly between the CULTIVARS. An old cultivar, Karaj2, showed a high ability to withstand competition (AWC), high COMPETITIVE indices (CI) and low grain yield in the weed-free plots (3865 kg ha-1). Cultivar Tabasi, a less COMPETITIVE cultivar, had the lowest AWC and CI amongst the CULTIVARS. There was a significant negative correlation between AWC and grain yield in the weed-free plots. Also, no significant correlation was observed between CI and AWC. The number of spikes m-2, number of fertile tillers planr-1, number of plants m-2, and number of kernels spike-1 were the most influenced components of yield in weedy conditions. This study showed that local adaptation is important for the Karaj2 cultivar to prevent yield loss (tolerance) in weed-infested conditions, and more suppression ability in the presence of rocket.