evaluation of critical traits for improving wheat yield under drought stress

drought stress is one of the most important abiotic stresses which can affect the growth of a plant, thereby curbing crop yield. identification of effective morphological traits is the main aim of each breeding program. our objective was to identify agronomic traits associated with changes in grain yield of wheat under irrigated and drought conditions. to address this objective, grain yield and its components of 81 iranian wheat genotypes were tested using two simple lattice designs with two replications under irrigated and drought conditions at research farm of agriculture college, university of tehran, karaj during 2007-2008 and 2008-2009. drought stress was imposed when plants were at the heading stage by withholding watering. grain yield, biological yield, harvest index, kernel weight per spike, 1000 kernel weight, number of kernels per spike and plant height were evaluated. five statistical procedures including: simple correlation, multiple linear regression, stepwise regression, factor analysis and principal components were used to study the relationship between wheat grain yield and its components under irrigated conditions and drought stress. results revealed that biological yield and harvest index were the most effective variables influencing grain yield. based on the results, biological yield and harvest index were found to be the most important agronomic traits for selecting high-yielding cultivars under irrigated and drought stress conditions. the effects of these traits under irrigated and drought stress conditions were not similar. the role of biological yield was less sensible than harvest index under drought stress. however, yield increase in wheat cultivars could be attributed to partitioning enhancement of photo-assimilates to the grain (higher harvest index) under drought stress.