Genetic diversity in spring wheat cultivars and relationships between traits under terminal drought stress

For evaluation of the traits related to water deficit stress in 20 spring wheat (Triticum aestivum L.) cultivars and subsequently  determination of the most tolerant and sensitive cultivars, an experiment was carried out in split plot based on randomized complete block design (RCBD) in the research farm of the University of Tabriz, Iran during 2010-2011 and 2011-2012 crop seasons. The first factor was different levels of water stress including water stress (no irrigation after booting stage) and well-watered conditions, and the second factor comprised 20 spring wheat cultivars. The results indicated that there was significant difference between cultivars and irrigation conditions related to nearly all the traits studied here. The mean comparison and cluster analysis of the cultivars showed that Marvdasht, Niknejhad, Moghan3, Darya and Kavir cultivars had the highest values, but Pishtaz, Bam, Sistan, Sepahan and Bahar cultivars had the lowest values for almost of all the traits. Generally, Kavir and Bahar cultivars were recognized as the most tolerant and susceptible cultivars under drought stress, respectively. According to stepwise regression, some traits entered into the final model, as the maximum amounts of correlation coefficient and direct effects were achieved for the number of spike per plant under two conditions. So, screening for higher values of this trait can bring an improvement in wheat grain yield under two conditions. Factor analysis detected three and four factors which explained 89.95 and 88.01 % of the total variation in non-stress and stress conditions, respectively. Under drought stress condition the factors of 1, 2, 3 and 4 named as root, yield and yield components, physiological, and biomass factors, respectively. These coefficients showed that cultivars with higher values of these factors had the highest values for the traits related to names of each factor.