yousef arshad

In the Mediterranean climates with mild winters like Khuzestan province, Iran, wheat is planted in autumn, and heat stress occurs only during the reproductive growth stage of wheat. In these regions, delayed planting causes the flowering and grain filling stages to be exposed to high temperatures, and the quantitative and qualitative performance of wheat decreases. Genetic improvement is one of the strategies to combat heat stress. Considering the importance of genetic resources for tolerance to environmental stresses tolerance, the present research was conducted to screen the wheat genetic collection of the National Plant Gene Bank of Iran for tolerance to terminal heat stress and to identify tolerant accessions.

In plant materials of this experiment were 236 bread wheat accessions along with three control varieties (Chamran, Chamran2 and Aflak), which were planted in an augmented design in the research field of Agricultural and Natural Resources Research Center of Khuzestan province, Ahvaz, Iran, in 2015-2016 crop year. The experiment was carried out in two planting dates, on-time planting date according to the region's custom at late November as normal conditions, and delayed planting at early January with the aim of heat stress during the reproductive growth stage of wheat. The measured traits included spike length, 100-grain weight, plant height, number of grains per spike, number of spikelets per spike, number of florets per spikelet, number of days to heading, number of days to maturity, grain filling duration, and five spikes grain weight. For data statistical analysis, descriptive statistics were firstly estimated under both normal and heat stress conditions, and then the relationships among traits were investigated using correlation coefficients. Principal component analysis was used to reduce the volume of data and cluster analysis was perfomed to group the studied genotypes.

The results of this experiment showed that terminal heat stress reduced the average of all studied traits, so that the highest decrease was observed in five spikes grain weight and the number of grains per spike. Based on the results of correlation coefficients under both normal and heat stress conditions, a positive and significant correlation was observed between five spikes grain weight and yield components traits, and a negative and significant correlation between five spikes grain weight and days to heading and days to maturity. Based on the results of principal component analysis, 72.54% and 80.53% of the total variance were explained by two and three main components under normal and heat stress conditions, respectively. The results of principal component analysis also indicated that the wheat accessions KC12977, KC12980, KC13013, KC13043, and KC13087, with the characteristics of early flowering and early maturity and higher values of five spikes grain weight, number of grains per spike, grain filling duration and number of florets per spike, were valuable accessions and have the sufficient potential to be used in breeding programs for heat stress tolerance. The results of cluster analysis separated the studied accessions into six group, and the fourth group including 62 accessions along with the control cultivars, had the highest average for number of florets per spike, number of grains per spike, and five spikes grain weight, as well as the lowest average for days to heading and days to maturity under both normal and heat stress conditions. and were recognized as the most tolerant group to heat stress. by three main components. In addition, the studied accessions were divided into six groups using cluster analysis.

The results of this study showed that there was a high genetic diversity among the studied bread wheat accessions in terms of terminal heat stress tolerance. Some genetic samples such as KC12977, KC12980, KC13013, KC13043 and KC13087, were valuable genotypes for the traits of early flowering and early maturity, as well as grain yield and yield components. The high diversity in these genetic resources, especially the tolerant accessions identified in this experiment as above mentioned, can be used to improve heat stress tolerance in future breeding programs.

Wheat ranks second among cereals in term of global production, but it has been affected by ongoing global climate changes. Drought stress is one of the important factors contributing to the reduction in wheat production. Developing drought-tolerant wheat varieties currently presents a major challenge for wheat breeders. Complex multigenic and multitrait genetic control, high genotype-environment interaction, low heritability, and challenges associated with high-throughput screening of plant traits and genes effective in drought tolerance due to the involvement of numerous traits and positive and negative correlations among them are some of the factors that have made wheat variety improvement for drought tolerance a challenging task. Selecting drought-tolerant genotypes as a cost-effective and biologically superior approach to increasing wheat production in low humidity areas has always been considered by breeders. Screening wheat genotypes to identify drought tolerance sources is essential and can be useful in selecting appropriate and desirable parents for implementing beneficial breeding programs. Local plant populations such as landraces are valuable resources for environmental stress tolerance, including drought stress. Local plant varieties are heterogeneous populations with local adaptation that provide genetic resources capable of meeting the needs imposed by new and emerging agricultural challenges under highly stressful conditions. The aim of this study was to identify wheat accessions tolerant to drought stress for use in future breeding programs.

A total of 512 wheat accessions from the National Plant Gene Bank of Iran, along with the varieties Kavir, Roshan and Mahouti as controls, were evaluated for drought stress tolerance in the research field of Agricultural and Natural Resources Research Center of Yazd, Iran. The experiment was conducted in two separate augmented designs, one of which was considered to drought stress and the other to normal irrigation conditions. Drought stress was induced by limiting the irrigation cycle. Considering that out of the total studied genetic materials, 141 accessions survived, the evaluation of traits was perfoemed on both those surviving accessions and their corresponding counterparts in the normal experiment. For data analysis, descriptive statistics including minimum, maximum, average, and coefficient of variation were calculated. Correlation coefficients were estimated and tested to study the relationship between traits. Stepwise regression analysis was used to determine the role of each trait and to identify the important and influencing traits on five-spike grain weight. K-means cluster analysis method was used to separate the accessions. All statistical analyzes were performed using R and SPSS softwares.

The results of descriptive statistics showed that the highest coefficient of variation under normal and drought stress conditions were attributed to five-spike grain weight (23.35%) and number of fertile tillers per plant (31.67%), respectively. Five-spike grain weight had the highest decrease in range (51.3%) under drought stress compared to normal conditions, and the highest decrease in mean was observed for number of fertile tillers per plant (59.3%) and five-spike grain weight (40.5%), respectively. A large number of accessions showed superiority over control varieties under both normal and drought stress conditions, so that 97 accessions had five-spike grain weight more than the control varieties. The accessions KC12856, KC12776, KC12783, KC12767, and KC12697 with values of 6.77, 6.75, 6.22, 5.94 and 5.86 g, respectively, had the highest five-spike grain weight under drought stress conditions. Number of spikelets per spike, number of florets per spikelet, 100-grain weight and number of grains per spike had significant and strong correlation coefficients at 1% probability level with five-spike grain weight under drought stress conditions. Based on the results of stepwise regression analysis under drought stress conditions, three traits including number of grains per spike, 100-grain weight and spike length were the most effective traits on five-spike grain weight and explained 90.6% of it’s variation. The studied genetic materials were grouped into five separated clusters using K-means cluster analysis.

The results of this experiment showed the valuable potential of the studied germplasm to drought stress tolerance. Evaluating the relationships among traits revealed the significance of number of grains per spikelet, number of spikelets per spike, number of florets per spikelet, and 100-grain weight under both normal and drought stress conditions. A considerable number of accessions were superior to the control varieties under both normal and drought stress conditions, indicating the richness and valuable potential of these genetic resources for drought tolerance related traits. Therefore, it is recommended to continue screening and evaluating the wheat collection of National Plant Gene Bank of Iran to identify drought stress-tolerant genetic resources. Based on the results of cluster analysis, the control cultivars with different characteristics were grouped in the separate clusters, and a distinguished cluster of the studied wheat accessions with superior traits was also formed. The diverse germplasm or superior accessions identified in this study can be used to develope the genetic base in crosses or as parents in breeding programs.

Soil salinity, as one of the most important environmental stresses, is a serious threat to agricultural production. Currently, more than 20% of the agricultural lands, which includes 954 million hectares of the world's lands, is affected by soil salinity. Salinity is expanding daily and it is predicted that by 2050, more than 50% of the world's arable lands will be saline. The decrease in yield due to salinity stress in wheat is considerable and worrying, so that a 50% decrease in yield of durum wheat due to salinity of rainfed lands, and an 88% decrease in yield of bread wheat under irrigation with high salinity and and a 70% decrease in yield of bread wheat in sodic soils has been reported. The high levels of salt in soils and irrigation waters are worrying factors for agriculture, therefore it is necessary to develop the effective strategies to improve yield through salinity stress tolerance. The present study was carried out due to the importance of genetic accessions as sources of tolerance to biotic and abiotic stresses including salinity, and the existence of considerable genetic diversity in wheat germplasm to salinity stress tolerance. The objective of this experiment is to investigate the diversity of genetic accessions of bread wheat collection of Iran's National Plant Gene Bank, to compare the accessions with the tolerant control varieties, and to identify the new genetic resources for salinity tolerance.

To identify the genetic resources of salinity tolerance in wheat germplasm, 512 accessions from the bread wheat collection of the National Plant Gene Bank of Iran along with salinity tolerant varieties, Kavir, Roshan and Mahoti as controls, were investigated in two different augmented designs under normal and salinity stress conditions. The normal experiment was carried out at the research field of Yazd Research Center and the salt experiment was done at saline lands of Ardekan Research Station. The studied traits included spike length, spike density, 100-grain weight, number of tillers, plant height, number of spikelets per spike, number of florets per spikelet, number of grains per spike, days to heading, days to maturity, grain filling period and grain weight of five spikes,  which were recorded according to the international description. To perform data statistical analyses, descriptive statistical indices were first calculated and then the studied accessions were grouped using K-means cluster analysis. Discriminant function analysis based on principal components was used to investigate the differentiation between the groups resulting from cluster analysis. Statistical analyzes were performed by SPSS and R softwares.
 
 
Research

The results showed that grain weight of five spikes (with a minimum of 4.15 and a maximum of 12.26 g in normal conditions and a minimum of 2.19 and a maximum of 9.78 g in stress conditions) and the number of spikes (with a minimum of 3 and a maximum of 8 in normal conditions and a minimum of 3 and a maximum of 7 in stress conditions) had the highest coefficients of variation, while days to heading (with a minimum-maximum of 130-163 days and 126-168 days in normal and salinity stress conditions, respectively) and days to maturity (with a minimum-maximum of 173-189 days and 168-196 days in normal and salinity stress conditions, respectively) had the lowest coefficient of variation under both normal and salinity stress conditions. A large number of superior accessions were identified for various traits compared to the control cultivars under both normal and salinity stress conditions. The results of stepwise regression indicated the importance of three characteristics, 100-grain weight, number of grains per spike and number of florets per spikelet, in describing the variation of grain weight of five spikes. The investigated accessions were divided into five groups using K-means cluster analysis and the control cultivars were separated into different groups so that Roshan and Mahooti along with 70 accessions were grouped in the first cluster and Kavir along with 53 accessions in the fifth cluster.

The results of this experiment showed the presence of significant and valuable genetic diversity in traits related to salt stress tolerance in the studied bread wheat germplasm. The effect of salinity stress on different traits of the studied accessions was different. Among the studied traits, 100-grain weight, number of grains per spike and number of florets per spike were more important, so they can be used in breeding programs. A large number of accessions were also superior to control cultivars for various traits. Cluster analysis grouped the control cultivars into distinct clusters, which indicates different aspects of salt stress tolerance in these cultivars. The superior accessions identified in this research can be used to improve salt stress tolerance in bread wheat breeding programs.

Terminal heat stress has been recognized as the most widespread and detrimental type of heat stress in the world. In southern regions of Iran like Khuzestan, delay in planting date causes pollination and grain filling stages to be exposed to high temperatures, resulting in yield reduction. Developing heat tolerant cultivars is one of the ways to deal with heat stress. In this study, to identify resources of heat tolerance in wheat germplasm, a total of 203 bread wheat accessions with three control cultivars were planted in normal and delayed planting dates as an augmented experimental design in Ahwaz and the agronomic traits were evaluated. The results showed that almost all the evaluated traits were reduced in heat stress conditions compared to normal conditions. In both normal and heat stress conditions, some superior accessions were identified in terms of the studied traits compared to the control cultivars. In the biplot based on the principal components under heat stress conditions, 64 accessions along with control cultivars were located in the area of superior characteristics in terms of grain weight of five spikes, number of florets per spike, number of grains per spike, number of spikelets per spike, spike length and plant height. The studied accessions were divided into five groups by cluster analysis. The results showed a high diversity in the studied genetic material and the accessions superior to the control cultivars in terms of the studied traits were identified which can be used in future breeding programs.

Salinity is one of the most important environmental stress which limits growth and yield of crops. Breeding and development of tolerant varieties is the most effective approach to confront salinity. Improvement of tolerance to salinity in crops necessitates existence of diverse genetic resources. Genetic variability for salinity tolerance has been reported. Wheat germplasm is a valuable genetic resource for tolerance to abiotic stresses including salinity. This research was performed with the objective of screening and selecting salinity tolerant genotypes in wheat germplasm.

A total of 97 bread wheat genotypes selected from previous studies along with three tolerant check cultivars of Kavir, Roshan and Mahooti were planted in research filed of Karaj (normal condition) and Meybod (saline soil and irrigation water, EC=6.55 ds/m and 5.61 ds/m, respectively) in lattice statistical design with three replications. Agronomical traits were evaluated according to international descriptor. Stress tolerances indices were calculated and the superior genotypes were distinguished by analyses of cluster and principal components. Stepwise regression was used in order to identify effective trits in tolerance to stress.

Grain yield of the check cultivar Kavir was higher than Roshan and Mahooti in stress condition. A total of nine genotypes had higher grain yield in stress condition than Kavir. Genotype KC.4419 had the highest amount of grain yield in normal condition (966.67 g/plot) and the highest values for the indices STI, GMP, HM and HM. The indices STI, GMP and MP had high correlations with grain yield in both normal and stress conditions. The studied genotypes were separated in the biplot of grain yield in normal and salinity stress conditions. A total of 38 genotypes along with all three check cultivars having higher grain yield in normal and salinity stress conditions were located in Region A of biplot. The results of principal component analysis based on the evaluated traits along with STI indicated that three PCs comprised 74.79% of the total variation. While the first PC emphasized on obtaining higher grain yield in stress condition through increasing grain filling period and producing larger seeds, the second PC highlighted the accumulation of dry matter in vegetative tissues. The results of stepwise regression for STI showed that harvest index entered in both models of normal and salinity stress conditions. The trait appeared specifically in regression model of stress condition.

The genotypes KC.1514, KC.4382, KC.4419 and KC.4407 (from Esfahan), KC.142 (from Khoy), KC.3100 (from Mashhad), KC.1143 and KC.388 (from Iran with unknown province) and KC.106 (from USA) with higher grain yield in stress condition than check cultivars were selected as tolerant genotypes. STI, GMP and MP were suggested as the most suitable criteria for selecting superior genotypes in salinity stress condition due to their high correlations with grain yield in both normal and stress conditions.

In order to evaluate the traits related to nitrogen utilization and to identify the superior genotypes, 33 bread wheat landraces along three check cultivars of Chamran and Koohdasht (from Iran) and Gobustan (from the Republic of Azerbaijan) were studied in simple lattice statistical design with two replications under two treatments of non-usage and application of 200 kg/ha ammonium nitrate fertilizer in research field of Seed and Plant Improvement Institute located in Karaj, Iran. The results indicated that the diversity of nitrogen uptake was higher than that of nitrogen use efficiency based on coefficient of variation. Genotype 4 (from Iran) and Chamran showed the highest value of nitrogen uptake efficiency. The highest amount of nitrogen use efficiency belonged to the genotypes 4 and 7 (from Iran). In the biplot of nitrogen uptake and use efficiency, check cultivar Chamran along with genotypes 4, 19, 21 and 23 (from Iran) and 2, 3 and 9 (from the Republic of Azerbaijan), which were superior for both traits were located in region A of Fernandez grouping. Generally, based on the results , a high varation in nitrogen components was revealed in the studied germplasem, particullary in Iranian landraces which could be used as gene pool for breeding programs.

In order to identify drought tolerant germplasm, 97 bread wheat landraces, mostly Iranian genotypes, were evaluated in two separate experiments of normal and drought stress conditions in the field of Agriculture and Natural Resources Research Center of Varamin. The experiments were performed in lattice statistical design with three replications. Drought conditions in the stress experiment was exerted by irrigation stoppage at the spike emerging stage. Agronomic traits were measured and drought tolerance indices were calculated. The results of combined ANOVA indicated significant differences among genotypes and between conditions as well as genotype × conditions interaction for all the evaluated traits. STI, GMP, HM and MP were known as the best indices for the selection of drought tolerant genotypes. Thirty genotypes, located in A region of Fernandez grouping method, had a higher grain yield in both stress and normal conditions. Four principal components explained 71.44% of the total variation. The first component differentiated drought tolerant genotypes with early spike emerging and the second one emphasized on later spike emergence, larger harvest index and shorter plant height. The results of this research identified a large number of superior drought tolerant genotypes which could be exploited in wheat drought breeding programs.

In order to study genetic variation and relationship between traits، 615 accessions of local bread wheat from wheat collection of National Plant Gene Bank of Iran were evaluated. Seeds of the accessions were planted in 2. 5 meter long rows in an observatory design and 17 agro-morphological traits were measured. Grain yield of 5 spikes، number of tillers and number of seeds per spike were of highest diversity among quantitative traits based on coefficient of variation. Among qualitative traits، glume color had the highest Shannon index. Two independent variables of number of seeds per spike and 100-seed weight were entered the model of stepwise regression determining 98% of grain yield of 5 spikes as dependent variable. The results of PCA indicated that the first five components comprised 63. 28% of the total variation in data. Based on coefficient of variables the components were designated as large seed size and high yield، yield components، biomass production، qualitative characteristics of spike and lodging resistance indices، respectively. The results of principlal component analysis distinguished accessions 200 (West Azarbayjan)، 763 (Gilan)، 835 (Lorestan) and 845، 846 (Isfahan، Both) as superior ones. The cluster analysis distinguished origins of the accessions in four groups. The result of this investigation showed a valuable variation in local wheat germplasm which could be exploited in breeding programs.

Wheat landraces are considered as valuable sources of tolerance specially for severe environmental stresses. Exploiting local genetic resources has become doubly important regarding narrow genetic base due to plant breeding. Twenty seven local and foreign genotypes selected from 4096 populations of wheat collection of National Plant Gene-Bank of Iran along with three control varieties، Mahooti، Kavir and Roshan، were evaluated in three separate experiments، one normal and two saline (Ardekan and Meybod) conditions. STI and GMP were identified as the most favorable indices to select salt tolerant cultivars based on correlations with grain yield in stress and non-stress conditions. Two genotypes of 4383، from Isfehan، and 7122، from Argentina، were superior based on stress tolerance indices، and yield in both stress environments. Despite the lowest amount of yield of the genotype 4419 in non-stress condition، it possessed the lowest amount of yield loss due to salt stress، and the lowest amount of TOL and SSI which could be an indication for a specialized mechanism for salt tolerance. Based on Frenandez classification، genotypes of 3888، 4383، 7097، 7122، 7258 and Mahooti were placed in group A، genotypes of 142 and 4407 were placed in group B، Kavir was placed in group C and genotypes of 1143، 3700 and 4355 were placed in group D commonly in both Ardekan and Meibod experiments. Cluster analysis based on stress tolerance indices could discriminate the genotypes consistent with Fernandez classification.