جستجوی مقالات مرتبط با کلیدواژه « gene bank » در نشریات گروه « زراعت »

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.

Leaf rust is one of the most important wheat diseases in the world and Iran and the use of resistant cultivars is the most effective tool against this disease, however, the resistance of the cultivars becomes ineffective following a selective pressure on the pathogen, which makes the search for new resistance genetic resources unavoidable. The present study was performed to identify these sources of resistance in wheat germplasm. Therefore, 97 accessions from the bread wheat collection of National Plant Gene Bank of Iran were investigated under natural infection condition at Eraghi-Mahale Research Station, Gorgan, Iran, in 2017-2018. The results showed that 46.4% of the studied accessions had a zero infection coefficient that were selected for evaluation at the seedling stage. Seedling evaluation was performed in greenhouse using four pathotypes with determined virulence-avirulence factors. The results of qualitative and quantitative analyzes grouped the studied accessions into different groups with specific resistance to one or more pathotypes. Comparison of resistance response of the accessions with avirulence/virulence formula in the pathotypes indicated the possibility of presence of Lr14a in the accession 5127. Furthermore, these comparisons revealed the possibility of presence of unknown resistance genes in many of the accessions under study. The results of this study showed the valuable capacity of the bread wheat germplasm to possibly identify new genes and sources of resistance to leaf rust. Therefore, it is suggested that additional research be done to evaluate and screen the bread wheat germplasm.

Soil salinity and poor irrigation water quality are a global problem in crop production. Thedevelopment of tolerant cultivars is one of the most important solutions to overcome theproblem of salinity, but it requires access to and identification of genetic resources withgenetic diversity for this trait. In order to identify germplasm tolerant to salinity stress andeffective traits, 413 accessions from the bread wheat collection of the National Plant GeneBank of Iran were cultivated in the 2012-2013 crop year in saline lands of ArdakanResearch Station and also under normal condition in Karaj research filed in Augmentedstatistical design and evaluated by measuring agronomic traits. Based on the results ofdescriptive statistics under salinity stress, spike density (20.27%) and five-spike grainweight (19.99%) were the highest and days to spike (7.90%) and days to full maturity(4.90%) had the lowest coefficient of variation. The highest mean decrease in theevaluated traits under salinity stress compared to normal condition belonged to the grainweight of five spikes (31.02%) and 100-grain weight (21.82%). Under salinity stress,accessions of KC 11791 (5.6 g) and KC 11622 (5.4 g) had highest value of 100 grainweight, and accessions KC 11946 (9.0 g) and KC 11816 (8.78 g) possessed highest valueof grain weight of five spikes. Under salinity stress, the first four principal componentsaccounted for 77.76% of the data variation. The studied genetic materials weredifferentiated into five groups using K means cluster analysis. The results of the presentstudy led to the identification of a large number of wheat bread tolerant to salinity stresswith a range of diversity in the evaluated traits that can be used as diverse raw materials inbreeding programs

One of approaches to reach sustainable agriculture is to exploit crop diversity, especially in legume species. Since Melilotus spp. (sweet clover) is a forage crop with a suitable yield especially in the marginal lands; therefore collection and characterization of this germplasm is the first effective step for its conservation and utilization in the country. Few accessions of Melilotus genetic resources had been collected in the National Plant Gene Bank of Iran, before this study.

Sweet clover genetic resources were collected all over the country using standard descriptors during two years. Twenty-six characteristics of collection sites were recorded and their descriptive statistics were estimated. The collected materials were planted in an experimental field to identify their life cycle. The seeds of collected germplasms were conserved in mid (2-4 °C)- and long (-20 °C)-terms conditions for further using.

A total of 258 accessions were collected. The geographical altitude of plant origin differed from -11 m in Babolsar to 3090 m in Noor Abad in Lorestan. The materials were mostly collected from non-saline habitats. However, eight accessions were collected from mid to high salinity locations. Taxonomically, M. albus, M. officinalis, and M. indicus were identified with a number of 21, 201 and 36 accessions, respectively. M. dentatus and M. sulcatus, which have been mentioned in the former researches in Iran, were not collected in the recent study.

The collected germplasms from marginal lands (saline, low drainage and low fertility lands) may be tolerant to such marginal lands, therefore they can be exploited for the future research. All M. indicus species were annual; whereas there were annual as well as facultative and obligate biennial accessions in the two other species. Lack of access to M. dentatus and M. sulcatus may be an alarm that they may be threatened species in the country. Collected materials in this study along with the former collection in the Iranian National Plant Gene Bank (80 accessions) have provided high potentials of Melilotus genetic resources for exploitation in the further. Highlights: 1- The three-fold increase in the Melilotus germplasms in the ex-situ conservation system. 2- Alarm for M. dentatus and M. sulcatus which may be threatened with extinction in the country.

In order to study changes of agronomic traits under drought stress and identification of tolerant germplasm, a total of 484 accessions of bread wheat collection of National Plant Gene Bank were studied in Yazd field under normal and drought stress conditions by planting tolerant cultivars (Kavir, Roshan and Mahooti). Drought stress was applied by irrigation stoppage after cultivation. Evaluation of agronomic traits was carried out in accordance with international descriptor both for 71 drought survived accessions and the same accessions under normal condition. Analysis of descriptive statistics showed that the grain weight of five spikes under normal condition and the number of fertile tillers under drought stress had the highest coefficient of variation. The highest mean reduction in traits under drought stress was observed for grain weight of five spikes (23.8%) and then for the number of fertile tillers (21.1%). In almost all traits evaluated, some accessions were superior to control cultivars in both normal and drought conditions. Grain weight of five spikes under drought stress was significantly correlated with florets number per spikelet (r = 0.272*), grain number per spike (r = 0.742**), one-hundred-grain weight (r = 0.663**), grain filling period (r = 0.314**) and days to spike emergence (r = -0.238*). The accessions were divided into four groups under drought stress and normal conditions using cluster analysis dendrogram. Distinction among clusters was confirmed by discriminant analysis. The superior accessions identified in this study can be used in drought tolerance wheat breeding programs.

To study genetic diversity in pomegranate germplasm collected from Kerman province, 94 accessions from the pomegranate collection of the National Plant Genetic Bank of Iran in Yazd were evaluated. For this purpose, 21 qualitative attributes were evaluated using the international descriptor for pomegranate. Analysis of Shannon index showed that shape of fruit base, seed color and vigour of tree had the highest, and color of one-year-old shoot, growth habit and bearing habit had the lowest diversity. Variation of Shannon index in each type of sweet, sweet-sour and sour genotypes followed similar pattern. Dendorgram of the cluster analysis divided sweet, sweet-sour and sour genotypes into five, seven, and eight groups, respectively. The results of boxplot study based on genotype origins indicated higher variation in the genetic distances of Ravar, Baft and Rafsanjan areas with other regions. The origins of the genotypes were divided into five groups using dendrogram. Ravar, Rafsanjan and Baft formed one group. Jiroft and Shahdad also belonged to a common group, and Sharababak and Bam, in a separate group. Sirjan and Chatroud regions stood individually in dendrogram. Results of cluster analysis by K-means method, using the principal components, showed that based on the Bayesian information criterion (BIC), the maximum genetic differentiation obtained at K = 10. The characteristics of each of the ten groups were studied. The results of this research in the field of genetic differentiation and germplasm grouping will be useful in future studies to identify genotypes and to select accssions with high levels of differentiation.

One of the most common methods for conservation of plant genetic resources is their ex situ storage as seed gene banks. Seeds that are stored in the gene banks must be regenerated due to exchange and seed deterioration; if they not be regenerated the potential benefits of infrastructure investments for germplasm ex situ conservation may not be attained. Prediction of seed longevity is based on viability equation that has four constants which are species specific. The aim of this project was estimation of these constants and then using them for predicting the regeneration time of Thymus transcaspicus،T. daenensis،Salvia officinalis، Satureja hortensis، Dracocephalum moldavica، Descurainia sophia،Eruca sativa andMelilotus officinalis. The seeds were placed in three environments with relative humidity of 20، 40 and 60% and their moisture content was measured after equilibrium. Then the seeds sealed in nylon pockets and stored at 30، 35 and 40 ºC. The TP germination tests with three replications were done monthly. The Excel software was used for estimation of viability constants (i. e. KE، Cw، CH، CQ). The KE was estimated 5. 065، 5، 5، 4. 46، 3. 837، 4. 33 and 4. 21 for T. transcaspicus، T. daenensis، Salvia officinalis، Satureja hortensis، Dracocephalum moldavica، Descurainia sophia، Eruca sativa and Melilotus officinalis respectively. The maximum and minimum seed longevity estimated for T. transcaspicus and Eruca sativa respectively. If viability be 100% at the beginning of the storage، the seeds of T. transcaspicus and E. sativa with 8% moisture content in the active collection (5 ºC) must be regenerated after 123 and 15 years respectively.