جستجوی مقالات مرتبط با کلیدواژه « نمونه ژنتیکی » در نشریات گروه « زراعت »

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.

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.

Safflower is the most suitable crop plant for oil production in dry areas and regarding the fact of climate change, it has been come in consideration in recent years. A broad genetic base and rich germplasm is necessary for breeding of this crop. This research was performed in 2011 to investigate variability of safflower germplasm. A total of 345 accessions of safflower collection of National Plant Gene Bank of Iran were planted and evaluated in research field of Seed and Plant Improvement Institute in Karaj. Preliminary evaluation showed that many accessions consisted of several diverse morphotypes, hence, by isolating and morphotype determination, the number of accessions reached to 534, which were investigated in an observational design. The results indicated that corolla color and spine intensity of outer involucral bracts had considerable amount of Shannon index. The highest (85.62) and the lowest (7.24) coefficient of variation belonged to seed weight of single plant and days to flowering, respectively. The first three principal components justified 56.13% of variation, the first one emphasized on yield components and the second on vegetative traits. The accessions were located in five groups by K means clustering method. Distribution of country origin of the accessions was consistent with their geographical situation in some cases. Totally, results showed that the studied accessions have a considerable variation which could be exploited in breeding programs.