The Study of temperature depression and its association with grain yield in six wheat cultivars under heat stress conditions and salicylic acid application

In order to evaluate canopy and organs temperature depression (TD) under heat stress conditions and the effects of plant morphology on organs temperature depression and their association with grain yield, two field experiments were conducted using six wheat cultivars (Behrang, Chamran, Kauz, Koohdasht, Karim and Montana) planted on three dates (early, optimum, late) in 2014-2015 and 2015 -2016 cropping seasons in Dashtestan, Bushehr, Iran. In addition, three concentrations of salicylic acid (0, 0.5 and 1 mM) were applied to alleviate the effects of heat stress.  Canopy and organs (flag leaf, peduncle and spike) temperature were measured by a hand-held infra-red thermometer (IRT). Also, some morphological traits in addition to yield components were measured. Results showed that the effects of cultivars and heat conditions were significant for most of the studied traits but salicylic acid application showed no significant effects. Under late sowing date, canopy and organs temperature depression were significantly higher than those at early and optimum sowing dates. No significant differences were found between early and optimum sowing dates for all temperature depressions. Among cultivars, Behrang had higher canopy temperature reduction (CTD), flag leaf temperature depression (FLTD) and peduncle temperature depression (PTD). Spike temperature depression (STD) was higher in Chamran and Kauz cultivars. Among plant organs, peduncle had higher temperature depression followed by flag leaf and spike. Canopy and organs temperature depression had positive correlation with stomatal conductance and grain yield. This research suggests that temperature depression can be used as an important criterion for the selection of stable genotypes under late sowing conditions. This is very helpful to improve wheat productivity under terminal heat stress resulting from late sowing conditions.