Effect of paclobutrazol levels on grain growth process and yield of three cultivars of wheat (Triticum aestivum L.) under post-anthesis heat stress conditions

IntroductionHormones are the most important crop plant growth regulators in response to genetic and environmental conditions. Paclobutrazol (PBZ) is a triazole plant growth regulators of the categories used in the early 1980s. According to some researchers, paclobutrazol reduced plant height (Yang et al., 2001), increasing the number of tillers per plant and increasing the number of grains per spike (Bayat et al., 2010), increased tolerance to environmental stresses and non-environmental (Berova et al., 2002). Heat stress is one of the major limiting factors of environmental in wheat production and wheat germ stage is the most sensitive periods of high temperatures (Pradhan et al., 2012). The aim of this study was to evaluate the physiological characteristics of wheat grain growth and yield than using different concentrations of paclobutrazol foliar application is in optimal conditions and heat stress.
Materials and MethodsThis study in two independent experiments were conducted each split plot in a randomized complete block design with four replications carried out in Dezful area, Iran in 2013-2014. The first experiments on the cultivation of crop varieties recommended (November) and in order to phenological stages of plant growth to coincide with heat stress after pollination season, planting dates in other experiments the first was in February. In each experiment, four levels of paclobutrazol (0, 50, 100 and 150 mg per liter) at the beginning of stem elongation sprayed on to Shoot applied, As main plots and three cultivars of wheat (Star, Vee/Nac and Chamran) were considered as sub plots.
Results and DiscussionThe results showed that in both optimum conditions and heat stress season, consumption growth regulator paclobutrazol significantly increased the effective grain filling period, 1000-grain weight and grain yield, but the effect of this treatment on the grain growth rate was not significant. Results of stepwise regression analysis showed that the duration of grain filling was the most important attribute of variations grain weight (R2=0.59) and then grain growth rate much of the rest of the changes are determined.
ConclusionsThe yield of the late Star because of the late Star pollination and subsequent exposure to heat stress than in the final stages of the early Vee/Nac and middle Chamran, the gradient of the effective grain filling period, grain weight and higher grain yield under heat stress end of the season was compared to optimum conditions. Overall results showed that the effect of growth regulator paclobutrazol on characteristics of grain growth and yield were positive, therefore can be with the proper use from the damage resulted from heat stress, especially at critical stages of plant growth can be prevented.