Introduction
Wheat, as one of the most important crops, occupies about 20% of the world's cultivated area. In the FAO report, more than 90% of Iran is classified as arid and semi-arid. The impact of drought stress on crops is devastating, resulting in yield losses of 17% every year. It is therefore of high importance to conduct researches to improve crop resilience to drought stress and minimize water losses in agriculture.
Materials and Methods
This study explored the relationships among different traits in bread wheat genotypes. A split-plot experiment was conducted, according to the randomized complete block design with three replications, to investigate 30 genotypes as subfactors. The experiment was carried out at the research farm of Shahid Madani University, Tabriz, northwest of Iran during the 2016-2017 growing season, under normal irrigation and drought stress conditions during the early flowering stage as a main factor (B). The relationship between yield and yield components and the relative importance of traits affecting yield were investigated using an analysis of variance, mean comparison, and canonical correlation analysis after measuring the traits of the studied genotypes.
Results and Discussion
The analysis of variance results revealed significant differences among genotypes for the examined traits. Moreover, the impact of drought stress was significant for all traits except spike straw yield. The interaction effect of stress and genotype was significant for all traits except 1000-grain weight, spike length, grain filling rate, and vegetative growth rate, indicating that the relative performance of the genotypes changed between the two environments. Canonical correlation analysis indicated a significant correlation between pairs of canonical variables resulting from phenological and growth traits with spike-related traits under normal and moisture stress levels. 
Conclusions
Based on the results of canonical correlation analysis, it can be concluded that, under normal field conditions, enhancing desirable characteristics in the spike (such as spike harvest index and grains/ spike) requires considering the traits of vegetative growth rate and grain filling rate. On the other hand, under stress conditions at the flowering stage in the field, selecting criteria should prioritize an increase in the grains/spike, spike harvest index, spikelets/spike, and spike length, as well as a decrease in spike straw yield, vegetative growth rate, length of grain filling period, days to maturity, and vegetative growth rate.