Assessment of genetic diversity of bread wheat under the late season drought stress

Draught is considered as one of the most important threats of successful crop production in Iran and in the world. In agronomic year of 2011-2012 in the research farm of Islamic Azad University of Ardabil Branch in factorial form with 30 genotypes and two drought stress levels with completely randomized block design an experimental was conducted. In under drought stress treatments, after pollination the irrigation was eliminated. In this study traits such as fertile tillers, plant height, spike length, spike weight, number of spikes per square meter, biomass weight, seed weight, grain weight per spike, grains per spike, the number of days to pollination, the number of days to heading, days to ripening, grain filling period, grain yield and harvest index were measured. Analysis of variance demonstrated that there is a significant difference among the studied genotypes, from all considered traits point of view except the number of days to pollination, at 1% probability level. Comparing the average of mutual effects of stress levels× genotype demonstrated that the combination (normal × genotype number 6) with an average of 9037 kg per hectare had the maximum yield and the combinations (stress × genotype No. 18; stress × genotype No. 19 and stress ×genotype No. 26) with the averages of 2441, 2296 and 2284 kg per hectare, respectively, allocated to the lowest yields. As a matter of fact the draught stress reduced the grain yield to 40.92 percent, and this was due to the fact that the weight of the one thousand grains after pollination becomes lowered in the draught stress conditions. Heritability of traits including plant height, number of spikes ears per square meter and days to ripening were more than other traits. The heritability of the grain yield was 9.46. The trait yield is poly genetic and so many genetics have affects on its generation and usually heritability of such traits, due to the high proportion of environment is not very high and hence the improvement of these traits will not be as easy as monogenic traits.