In order to compare of inheritance, combining ability, heterosis and genes action in the genetic control of 1000-kernel weight, grain per spike, grain yield per spike and grain yield per plant in bread wheat genotypes under drought stress conditions, an experiment was conducted on eight genotypes using fixed method 2 of Griffing. Exception mean squares of grain per spike at specific combining ability (SCA), other traits were significant differences for general and specific combining abilities. It states important of inheritance additive and dominance gene effects under drought stress conditions. The GCA/SCA ratio was significant for grain per spike. For exception of grain per spike, non-additive gene effects were more important than additive. It is concluded that genetic improvement of grain per spike under drought stress conditions is possible at early generations by selecting from the best crosses, while selection for another traits is better that delayed until advanced generations and increase of its heritability.

Providing the main food for people in arid and semi-arid regions such as Iran, bread wheat is considered one of the most important crop plants in the world. The present study was aimed to assess the genetic diversity and the relationship between morphological and agronomic traits under normal and drought stress conditions among thirty-five wheat genotypes. A split-plot in RCB consisting of three replicates was carried out. The morphological and agronomic traits, which were measured, included plant height, awn length, spike length, leaf length, internode length and number of nodes, number of tillers, number of leaves, number of spikelets per a spike, number of grains per spike, number of spikes per plant, grain yield, 100 grain weight and biological yield. And phonological traits containing of number of days to germination and heading were calculated too. According to anova, there were statistically significant differences among various wheat genotypes for the all of traits evaluated. Correlation coefficients among traits demonstrated that in normal conditions, there was a positive correlation between grain yield and spike length, spike weight, number of nodes, number of spikelets per spike, number of grains per spike and number of spikes per plant. However, under stress conditions, grain yield showed a positive correlation with spike weight, number of nodes, number of leaves, number of spikelets per spike, number of grains per spike and number of spikes per plant. In regression analysis, the four variables entered the model in normal conditions, included 100 grain weight, number of spikes per plant, number of grains per spike and awn length. And the six variables under stress conditions which have been entered the model contained number of grains per spike, number of spikes per plant, spike weight, 100 grain weight and leaf length. Path analysis revealed that under normal and stress conditions, 100 grain weight and spike weight had the highest role in increasing grain yield, respectively. In the analysis of the main components, the three main factors justify 77/5٪ of the total variation in normal condition.According to the results, the genotype D1(genomeAA(and Sabalan cultivar,which in all their high performance conditions,can be recognizwd as the most tolerant.

Development of high yielding varieties is the main objective in many wheat breeding programs. However, effectiveness of program depends on relationships between grain yield and its components. In order to investigate the relationships, four varieties of wheat were evaluated for nine traits. Correlation coefficients of simple traits showed the positive and significant relationship of grain yield with harvest index, biological yield, the number of grain per spike and number of grain per m2. The high relationship of grain number per m2, number of grain per spike, weight of thousand grains and number of spiklet per spike with grain yield was also observed in multivariate stepwise linear regression. Path analysis showed positive and direct effect of grain number per m2, number of grain per spike, weight of thousand grains and number of spikelet per spike on grain yield. Grain number is the most important component from grain yield and according to effective role of spikelet number per spike, selection of these two traits will be important to increased grain yield.

In order to investigate path analysis of grain yield and yield components, an experiment was carried out with 20 genotypes of wheat in a randomized complete block design with four replications in two places in North Khorasan Province, dry land Research Station of Shirvan and Sisab, Iran. In 2015-2016. During the growth stages and after harvesting, traits like plant height, number of days to heading, numbers of spikes per square meter, number of grains per spike, number of days to maturity, seed weight and seed yield were recorded. according to the analysis of variance, between genotypes in terms of number of days to heading, days to maturity, numbers of spikes per square meter, number of grains per spike and grain yield, differences were significant. According to the comparison of the averages, genotypes 17 and 12 with 2522 and 2364 kg.ha-1 had the highest grain yield respectively and genotype 20 with 1190 kg.ha-1grain yield was the lowest. Based on the path analysis results, the number of spike per square meter (69.8%), the number of grains per spike (64.9 %) and grain weight (38.9 %) had the highest direct effect on grain yield. The correlation coefficients showed that seed weight and number of grains per spike and number of spikes per square meter had a significant negative correlation and the number of grains per spike and number of spikes per square meter were significant positive correlation with yield.

In a 2-year field experiment (2009-10 and 2010-11) 30 wheat cultivars were compared under with and without late season drought stress conditions. The experiments were conducted as a split plot based on randomized complete block design with four replicates at Research Farm of College of Agriculture, Shiraz University. Drought stress treatments (without stress, as control, and irrigation cutting off at anthesis stage) and wheat cultivars were assigned into main plots and sub plots, respectively. In this study mean productivity (MP), stress susceptibility index (SSI), stress tolerance index (STI), geometric mean productivity (GMP), tolerance (TOL), and yield stability index (YSI) were calculated based on grain yield under both with and without drought stress conditions. The results showed where irrigation cut off at anthesis, Kavir cultivar with 390.48 g/m2 had the greatest grain yield; while, under normal irrigation treatment the greatest grain yield was achieved from Shiroudi cultivar (873.83 g/m2). Comparison of means under normal irrigation conditions showed that Ghods cultivar (57.7 grains per spike) and Yavarous cultivar (20.72 grains per spike) had the highest and lowest grains per spike, respectively. Under drought stress conditions, the highest and lowest grains per spike were obtained by Zarin (39.4 grains per spike) and Souraplata (9.9 grains per spike), respectively. In the present study, 1000- grain weight was significantly different between irrigation treatments. Sistan cultivar had the greatest (45 g) 1000- grain weight under normal conditions, and Omid cultivar produced the greatest (35 g) 1000- grain weight under terminal drought stress conditions. Comparison of the mean of wheat cultivars showed that highest grain yield was achieved under stress and non-stress conditions in Kavir and Derakhshan cultivars, respectively. The lowest grain yield under both conditions was obtained from Veernak cultivar. The results of this investigation indicated that GMP, STI and MP, which had the highest significant correlation with the grain yield under both conditions, were assigned as the most appropriate indices for evaluating the drought tolerance of cultivars.

In order to study of source limitations on traits related with wheat grain yield, an experiment was carried out in split plot design based on RCBD with four replications and 24 genotypes as the main plot factor and source limitation as subplot factor in Research Station of Dryland Agricultural Research Institute (DARI) at 2016-2017. The measured traits were spike length, number of spikelets per spike, spike weight, number of grains per spike and 1000 grains weight. The difference between the compared genotypes was significant in terms of the measured traits. Spike weight had a significant positive correlation with the number of grains per spike. The principal component analysis in control conditions, showed that all traits were placed in one principal component, that number of grains per spike was evaluated as the most effective trait. While, principal component analysis in source limitation conditions indicated that the traits are placed in two principal components, the first principal component represents the number of grains per spike and the second component represents the 1000 grains weight. Generally, both control and source limitations, the number of grains per spike was evaluated as the most effective trait. On the other hand, among the source limitations studied, flag leaf removal had the highest decrease in grain yield related traits.

This study evaluated direct drilling planters used for wheat cultivation in Khorasan-e Razavi province. A randomized complete block design with three replications was used. The treatments were direct drilling of wheat plants into wheat residue using the following direct planters: (1) Sfoggia (13-25), (2) Baldan (SPD3000), (3) Tondar (SPD 2500), (4) Semeato (SHM 11/13). The parameters measured were uniformity of seed depth, planter field capacity, seed germination, mechanical damage to seed, yield, number of spikes per m2, number of grains per spike, 1000 seed weight and harvest index. The results showed that planter type was significant at the 1% probability level for uniformity of seed depth, planter field capacity and harvest index and at the 5% probability level for yield, number of spikes per m2, number of grains per spike and seed germination. Results showed that the Sfoggia planter performed best for uniformity of seed depth and number of spikes per m2. The Sfoggia and Tondar planters performed best for seed germination, yield, and number of grains per spike and harvest index.

To investigate the relationship between yield and its components in wheat under non stress and drought stress conditions an experiment was conducted in on Agricultural Research Station at Bahonar University of Kerman. Experimental trial was split-plot (non-stress and drought stress as main plots and 15 cultivars as sub plots) in randomized complete block design with three replications. The measured traits were relative water content، yield and its components (number of spikes per m2، number of grain per spike and 1000 grain weight)، biological yield and harvest index. The results showed that the effects of drought and cultivar were significant on all traits، and drought stress decreases all traits. Correlation coefficients between grain yield and harvest index under both conditions was positive and highly significant. Correlations of harvest index with the number of spikes per m2، number of grains per spike and 1000 grain weight under drought stress، were significant. However، under non-stress condition was non significant. Correlation between 1000 grain weight and grain number per spike was significant under drought stress and was not significant under non-stress conditions. Under drought stress and non stress conditions، the correlation between 10 grain weight and grain yield was positive and significant. Correlation coefficient between grain yield and relative water content under non-stress condition was not significant; however under stress condition was significant. Based on path analysis، under stress and non stress conditions، harvest index had the highest and positive direct effect on grain yield. Under non-stress condition number of spike per m2 and under stress condition number of grains per spike had the highest direct effect. The number of spikes per m2 via by the number of grains per spike had the highest indirect negative effect under non-stress condition. Under stress condition، the 1000 grain weight by harvest index had the highest indirect negative effects.

With increasing the world population, and needing to feed it, the yield enhancement of cereals crops is of the most important approaches meet this target, which is achieved via identifying the effective factors underlay yield of cereals like wheat. This experiment was conducted to evaluate the grain yield and its association with some contributed traits in a doubled-haploid (DH) wheat population comprising 100 DH lines deriving from across with maize, along with their parents (CK1 & ES32) and 6 Iranian local cultivars. Traits under study were of grain yield per unit area, number of fertile tiller and total number of tillers per plant, number of node, plant height, flag leaf length and width, spike length, number of grains per spike and 100-grain weight. The results indicated significant (P<0.01) correlations between grain yield with grain number per spike, spike length, and flag leaf length and width. According to stepwise regression analysis: spike length, number of tiller, flag leaf length, and number of grains per spike were the most important causing traits mostly (73%) interpreting the grain yield variation. The simple path coefficients analysis revealed that spike length and number of grains per spike contributed the most significantly (P<0.01) direct effects on grain yield. Moreover, the sequential path analysis showed that the number of tiller had a significant (P<0.01) positive direct effect on grain yield. In addition, there was significant direct effect of grain number on 100-grain weight and of spike length effect on number of grain per spike. Orthogonal contrast analyses results indicated also a nonsignificant difference between local cultivars and DH lines for the most important economic trait, yield. The results of this research could be applied for select the important yield contributed characters as selection criteria according to homogeneity of DH lines, and pave the way to potentially increase the yield of bread wheat cultivars.

This research was carried out in a field factorial experiment based on randomized complete block design with three replications in a silty loam soil. Experimental factors were including two levels of Azotobacter chroococcum (seed inoculation with azotobacter at a concentration of 107 bacteria per gram and uninoculation) and five levels of nitrogen (0, 50, 100, 150 and 200 kg N.ha-1 from urea source). Azotobacter effect was significant on grain yield, number of grains per spike, grain protein content (P≤ 0.05), SPAD, number of spike per m2 and thousand grain weight (P≤ 0.01). Effect of nitrogen was significant on all of the traits except of number of grains per spike (P≤ 0.01). Interaction effect of two factors was significant on grain yield, SPAD (P≤ 0.05), plant hight, number of spike per m2 and number of grains per spike (P≤ 0.01). Grain yield was 4899 kg.ha-1 in combination of seed inoculation with azotobacter and nitrogen (100 kg.ha-1), which there was no significant differences with 150 and 200 kg N.ha-1. This fertilizer combination increased seed yield by 13.76%, compared to uninoculation and nitrogen (100 kg.ha-1). There were positive and significant correlation between grain yield and SPAD, number of spike per m2, number of grains per spike, thousand grains, plant hight and leaf area index (LAI). Overall, the inoculation with azotobacter bacteria and nitrogen (100 kg.ha-1) could achieve grain yield potential, reduce the adverse environmental impacts and save the N-fertilizer utilization.