QTL mapping for physiological traits affecting lead tolerance in the Hordeum vulgare L.

Human activities such as mining and industrials activities have increasingly affected soil contamination through the sedimentation of heavy metals. This issue is concerned as a global problem. All heavy metals are potentially poisonous, which vary based on their biologic available concentrations and the sensitivity of organisms which are exposed to the heavy metal. One of the main heavy metals is Lead. lead is a potential pollutant that readily accumulates in soils and sediments. Pb is considered a major troublesome poison, crop productivity sharply declines in soils contaminated by Pb. The poisonous characteristics of lead on plants are attributed to chlorosis, declined growth, blackening of root system, upsets mineral nutrition and water balance, changes in hormone status, and the effects on the structure and permeability of membrane. In recent years, many plants have been destroyed due to the increased pollution of the earth by heavy metals, and which has led researchers are interested in soil improvement, the production and use of resistan. Most of the important agricultural traits, such as yield, grain quality and resistance, or tolerance of live and non-live stresses in nature, are complex qualitative traits. These traits are usually controlled by multiple quantitative traits (QTLs), which are strongly influenced by the genetic context of the creaturet plants, and the identification of mechanisms and genes associated with heavy metal tolerance. This research was carried to identification of QTL traits related to lead toxicity tolerance in barley.

In this study, we used 94 double haploid from Dom and Rec parents that were planted in a completely randomized design with three replications in twenty-cm diameter pots. Then at 2- to 3-leaves stage, seedlings were treated by 0 (control) and 2000 ppm density lead nitrate. Physiological traits such as sub-stomatal CO2, transpiration rate, photosynthesis rate, stomatal concentration and plant greenness after 24 under stress, were measured at the beginning heading stage. In order to investigate the frequency distribution of data and their variation under stress and normal conditions, Spss program version 23 was used. After observing the continuous and quantitative variation among progenies to studied traits, in order to locate the lead-tolerance genes, Using Mapchart2.32 and MapQTLs Software, chromosomal regions associated physiological traits were identified on seven chromosome of barley.

The phenotypic Analysis of the studied traits showed a quantitative and continuous variation. the studied traits showed normal distribution in both non stress and stress conditions The genetic which is lead tolerance is controlled depending on the physiological indices of different parts in the genome of the barely. In this study No QTL was observed for the studied traits under normal conditions. among the traits sub-stomatal CO2, transpiration rate, plant greenness after 24 under stress, stomatal concentration, photosynthesis rate, QTL was observed Under stress conditions with lead, two QTL discovered for sub-stomatal CO2 on chromosome 6, two QTL for transpiration rate on chromosome 3, four QTL for Stomatal Conduction on chromosomes 1 and 3, four QTL for photosynthesis rate on chromosomes 3 and 2, four QTL for plant greenness after 24 under stress on chromosomes 1 , 4 and 5. Phenotypic variation justified by these QTLs varied 10.5% to 19.10%.

The results of this study showed that the OWB mass mapping can be used as a proper mass mapping and as a model for studying the genetic of lead tolerance in plants. The results of this study also showed that various physiological traits of barely under lead stress conditions are manipulated by different genes. Precisely locating lead resistant QTL is the most important step in cloning and finding the function of the genes involved in lead resistance. In order to use QTL detection methods for understanding the attributes related to lead resistance, it is necessary to divide lead toxicity resistance into smaller traits. This task is achieved through considering the events occurring in lead poisoning and the determining the reason why some plants are tolerate.