Agrophysiological barley traits associated with flag leaf temperature and canopy light interception under salinity of irrigation water and zinc foliar application

To understand the agrophysiological barley associated with flag leaf temperature and canopy light interception under salinity and zinc foliar application (ZnFA), a field experiment was conducted in a strip-plot design with three replications in Isfahan, Iran. Saline irrigation water in three levels [2 (low), 10 (moderate) and 18 (high) dS m-1] were applied as vertical factors. Three barley genotypes [‘Morocco’ (salt-sensitive), ‘Nosrat’ (semi-salt-tolerant) and ‘Khatam’ (salt-tolerant)] were arranged within the vertical factors. The horizontal factors were four ZnFA [Nano-ZnO, Zn-EDTA, simultaneous applications of (Nano-ZnO + Zn-EDTA), and water (control)]. With increasing  salinity, light interception (LI), maximal efficiency of PSII (Fv/Fm), chlorophyll content (SPAD), relative water content (RWC),  number of spike (NS), kernel number per spike (KNS), thousand-kernel weight (TKW), and grain yield (GY) decreased, but electrolyte leakage (EL), flag leaf temperature (FLT) and proline  increased. Nano-ZnO had the highest EL and the lowest FLT, RWC, NS and KNS. Zn-EDTA application provided the highest LI, RWC, TKW and GY, and the lowest proline. Minus zinc application (check) had minimum LI, Fv/Fm, SPAD and GY. The tolerant genotype had maximum LI, proline, SPAD, RWC, KNS and GY, and minimum FLT, EL, NS and TKW. Overall, it was concluded that Zn-EDTA can be as a proper tool for increasing barley yield under salinity stress conditions. Likewise, this study has highlighted the close relationships existing between GY with, TKW (r= 0.89**), KNS (r= 0.46**), RWC (0.45**), NS (r= 0.36**), FLT (r= -0.32**), EL (r= -0.21**), and SPAD (r= 0.20**). These findings indicated that these physiological traits could be key factors, tools for screening, and provide useful information about stress tolerance mechanisms, which could be useful to plant breeders for selecting and developing salt-tolerant genotypes.