Effect of nano-TiO2 foliar application on ear weight and some of biochemical characteristics of sweet corn (Zea mays var saccharata) under water deficit stress

Introduction Drought is one of the most important causes of decline in agricultural productivity worldwide (Kamanga et al., 2018). TiO2 is one of the materials that nowadays, its properties have been reported to reduce environmental impact (Rosi and Kalyanasudaram, 2018). TiO2 with increasing Activity of Ps II Light Reduction, activity of chloroplast photophosphorylation, rubisco enzyme, nitratreduktase enzyme activity, catalasea and peroxidase and improving the content of some essential elements in plant tissues, increases the yield of different products (Khater, 2015). Also, by reducing free oxygen radical and malondialdehyde and increasing the antioxidant enzymes reduces the negative effects of stress (Zheng, 2007).In the study of the effect of nano-TiO2 spraying on some of the agronomy characteristics in wheat, 0.02% nano-TiO2 foliar application under drought stress conditions compared to non-foliar application was increased seed yield by 23% (jaberzadeh et al., 2010). Considering that a large part of cultivated land in Iran has semi-arid climatic conditions and because of its special geographical position, in most parts of it, important abiotic stress such as drought, salinity and temperature, decrease the yield and, in some cases, also has led to failure in agriculture, therefore, achieving the highest yield with the least possible water consumption in the shortest time with the use of nano-compounds such as TiO2  against breeding methods that are often long-term and cost-intensive, it seems necessary that the present research also aims to achieve goals such as evaluating and identifying important physiological traits of sweet ear weight under water deficit stress and application of the above compound.   Material and Methods In order to investigate the effects of water deficit stress and nano-TiO2 foliar application on ear weight and some of biochemical characteristics in sweet corn plant, an experiment was conducted in split plot form based on RCBD in three replications at the Research Station of the Islamic Azad University, Tabriz Branch, during growing seasons of 2017. Treatments were water deficit stress in three levels contained: 50, 75 and 100% filed capacity (FC) as well as the nano-TiO2 foliar application in four levels contains: non application (control), 0.01, 0.03 and 0.05%. Field capacity was determined from the pressure plate machine. TiO2 foliar application on the shoot was performed three times during the growing season and in the stages of 8-10 leaf, tasseling and grain filling. Irrigation is done according to the needs of the canopy and depending on the weather conditions of the area and from 8-10 leaves stage, regarding irrigation intervals, treatments were applied. Peroxidase enzyme activity by Hemeda and Klein method (1990), malondialdehyde  according to the Heath and Packer method (1968), amount of Soluble carbohydrates by phenol-sulfuric acid method (Dubios et al., 1956), and amount of leaves proline according to the Bates et al., (1973) method were measured. The ear weight was calculated in gm-2. Analysis of variance, and mean comparison with MSTAT-C software were used. The means of the treatments were compared using the Duncan’s test at P< 0.05 and Charts are plotted by the EXCEL program. Results and discussion The analysis of varianceshowed that the TiO2 foliar application on peroxidase and interaction effect between TiO2 foliar application and water deficit stress on malondialdehyde, soluble carbohydrates, proline and Ear weight was significant (p< 0.01). According to this study, the concentration of 0.01% of TiO2 foliar application, increased the activity of peroxidase enzyme, but the important point is that with increasing TiO2 concentration, the activity of this enzyme decreased. Since the increase in peroxidase activity is related to the rate of peroxidation of membranes, reducing malondialdehyde levels in treated plants indicates that the activity level of peroxidase activity is sufficient to collect active oxygen species to prevent damage to the membrane. 0.01% of TiO2 foliar application under conditions of 50% moisture content increased the amount of soluble carbohydrates and proline, which was reduced by increasing the amount of this compound and increasing the available moisture content. 0/01% TiO2 foliar application under full irrigation conditions with an average of 744 gm-2 and no irrigation at 50% moisture content with an average of 457 gm-2 had the lowest grain yield, which showed a decrease of 38.5% that compared with 0.03% nano- TiO2 in the same irrigation and 0.01% nano- TiO2 in 75% moisture content was not significantly different. The results of this study showed that TiO2 foliar application increased the activity of peroxidase enzyme, soluble carbohydrates, proline and decreased malondialdehyde enzyme activity under water deficit stress in sweet corn. Furthermore, the nano-TiO2 also increased the ear weight in all treatments, which indicates the positive effects of this composition on the plant. According to the research objectives, the use of nano- TiO2 in order to increase yield under minimum water use conditions can be a good alternative to breeding methods that are often long-term and cost-effective