Genetic variation of bread wheat geneotypes for some important physiological traits under chiling stress

Food productivity is declining due to the effect of different abiotic stresses. Stress is the result of abnormal physiological processes that influence by one or a combination of biological and environmental factors. Cold, salinity and drought are important among the other stresses. Three types of cold stress has been identified that include: Frost, Freezing and Chilling Stress. The relationship between plant growth and climate change is a seemingly contradictory event. In fact, warming increases danger of cold stress. In the spring, at the same time of started wheat growth, it is increase its sensitivity to low temperatures and it damaged. This model of cold stress called rapidly falling temperatures in the spring or in short term called "chilling". Chilling stress reduced leaf expansion, wilting, chlorosis (yellowing of leaves) and may lead to necrosis (death of tissue) and strongly disturbed the reproductive development of plants. Low temperature stress limit the grain production in cold and ultra-cold climates and makes high damages in some years. Therefore produce resistant cultivars is necessary. Management of genetic resources, and knowledge of the genetic diversity are tow important principles of breeding projects. This study examines the genetic diversity of some of bread wheat cultivars for some physiological characteristics associated with chiling stress using multivariate statistical methods and compare these methods.
This survey performed in 2013 at the Faculty of agriculture, Tarbiat Modares University. In this study an experiment with 20 varieties of wheat with four treated cold levels of stress (8 (control), , 0, -2 Celsius) in factorial arrangement in randomized completely design implemented. In early of reproductive stages (Zydaky code 50 to 68), the plant transferred to growth chamber under 14/10 hours and 16/8 °C day/night photoperiod. To impose stress, temperature reduced 2°C per one hours from 8 °C then the pots were placed for 2 h under stress in each of stress temperature levels (2, 0 and -2 °C). After stress, temperature up to 8 °C with ramp 2 °C per hours. Sampling was done after 24 h and then electrolyte leakage, chlorophyll (a, b, ab and cartenoids), proline and fructan, were assessed.
The results of this study showed that the effects of interaction between gentopyes and chiling stress were significant at 1% level. Based on results of the cluster analysis twenty genotypes were classified into four groups in -2 celsius temperature and two groups in control temperature. The principal component and principal coordinate ,confirmed grouping created based on of cluster analysis. The principal component analysis decrease all treats in to 3 components in control (with cumulative of variance 80) and sever stress (with cumulative of variance 85). Also the principal coordinate analysis decrease all component to 3 components with cumulative variance 94.11 (for control) and 96.59 (for sever stress). Based on cluster analysis Pishgam and Aflak genotypes in control condition and Alvand and Sivand in -2°C had the maximum genetic distance. The minimum genetic distance was observed between Mv17 and Navid genotypes (in control condition) and Kaskojen and Pishgam (sever stress).
(1) Chiling stress detects the diversity amoung studied gentopyes; (2) In order to grouping of genotypes, cluster analysis provided more accurate grouping than principal component analysis and principal coordinate analysis ; (3) Alvand and Sivand cultivars can be use as potential parents to provide the necessary population in classical breeding programs, in order to detect of QTLs for chiling tolerance and also for marker assisted selecion.