Effect of foliar application of silicone on biochemical traits and yield of two wheat cultivars under late season drought stress conditions

Drought is always recognized as one of the most important limiting factors for wheat productivity particularly in arid and semi-arid regions (Debaeke and Abdellah, 2004). In such areas, the occurrence of water stress in vegetative and reproductive stages of plant development is inevitable, and low rainfall and poor distribution of rainfall are factors limiting the yield of winter cereals (Garcia del moral et al., 2003). Silicon is one of the many elements in the soil. As it is mostly considered as non-essential element for plant growth, much attention has not been paid yet to its biological role in plant. Recent studies have shown that it has beneficial effects on several plant species. Especially in the time of environmental stresses, with increasing activity of oxidative enzymes and increasing the content of osmolite plays an important role in the creation of resistance to live and non-polluting stresses in plants (Amiri et al., 2014). Gang et al. (2005) examined the effects of silicon on wheat under drought stress and found that silicon application increased the activity of peroxidase oxidizing enzymes, catalase and dismutase in comparison to drought treatments. Drought stress increased the amount of H2O2, while the use of silicon decreased the activity of peroxidase. The aim of this study was to investigate the effect of foliar application of Si on photosynthetic pigments, enzyme activity and grain yield of bread and durum wheat cultivars under late season drought stress conditions.

In order to investigate the effect of silicon application on biochemical traits and grain yield of wheat cultivars under late season drought stress conditions, a field experiment was carried out in the Research Station of College of Agriculture and Natural Resources of Darab, Fars Province as split factorial in a completely randomized block design with three replicates during 2017-2018 growing season. Soil sampling was carried out prior to the experiment at a depth of 0-30 cm in order to determine the physico-chemical characteristics of the experiment field. Experimental treatments consisted of drought stress in two levels included normal irrigation and drought stress at the end of flowering, silicone (Si) spraying at 0, 1, 2, and 3 mM which used at mid-flowering stage (ZGS code 65) (Zedokes et al., 1974) and two wheat cultivars (Chamran and Shabrang).Two weeks after drought stress, chlorophyll a, b, catalase, and peroxidase contents were measured. Also, at maturity, plants were harvested to determine the grain yield. Finally, analysis of variance (ANOVA) was performed using SAS v 9.4 and the means compared by LSD test at 1 % probability level.

Analysis of variance showed that the main effects including late season drought stress, cultivar and silicon, had significant effects on chlorophyll a and b contents, peroxidase and catalase enzymatic activity, and grain yield. Foliar application of 3 mM Si, increased chlorophyll a and b contents, 44 and 41%, respectively. Peroxidase and catalase enzymes increased by 7 and 8% in drought stress conditions, which increased by the addition of silicon in drought stress conditions at 3 mM level, and the activity of peroxidase and catalase enzymes was 52% and 35% respectively. In general, Chamran bread wheat cultivar with the yield of 7797 kg ha-1 had higher yield than Shabrang durum wheat cultivar (6220 kg ha-1), indicating the superiority and suitability of Chamran when plant exposed to drought stress. Finally, in Chamran cultivar foliar application of Si at 3 mM increased photosynthetic pigments, and peroxidase and catalase activity which caused 19.7% increase in grain yield compared to Shabrang.

It was concluded that when wheat cultivars exposed to drought stress, the amount of chlorophyll a and b, and grain yield decreased significantly while Si application at 3mM increased the photosynthetic pigments especially in bread wheat cultivar (Chamran). Overall, under drought stress conditions, foliar application of 3 mM Si at flowering stage of wheat caused a significant increase in catalase and peroxidase activity especially in Chamran which increased grain yield compared to durum wheat CV. Shabrang.