The effect of foliar application of nano- and bulk silicon dioxide particles on grain yield and redistribution of dry matter in wheat under drought stress

Under water shortage, applying and adjusting of some elements concentration such assilicon (Si) can be used as a strategy to reducethe negative effects of stress on wheat(Triticum aestivum L.) growth and enhanced plant compatibility.Some of the studies showed that exogenousSi application increased crop resistance to environmental stresses such as drought (Ahmed et al., 2011; Maghsoudi and Emam, 2016). Likewise, macro and micro nano fertilizers application caused an increase in crop yield. Therefore, this study aimed to investigate the effect of foliar application of nano and bulk Si dioxide particles on yield and yield components of wheat and also to determine the contribution of different sources in grain yield formation. In order to investigate the effect of foliar application of silicon on yield and redistribution of wheat dry matter under drought stress conditions, a field experiment was conducted as split plots based on a randomized complete block design with four replications at Ramin Agriculture and Natural Resources University of Khuzestan. Drought stress periods included three levels of normal irrigation (full irrigation throughout growing season or control), drought stress from stem elongation to flowering and drought stress from flowering to maturity were considered as main plot and foliar application of silicon dioxide levels in seven levels including non-foliar application (control), application of nano and bulk particles of silicon dioxide in concentrations of 50, 100 and 150 mg L-1 were considered as subplots. Data analysis was performed using SAS software and GLM procedure, and means comparison was carried out using a protected LSD method at a 5% probability level. Drought stress from stem elongation to flowering reduced the number of fertile tillers, number of spikelets per spike and number of seeds per spike, thereby reducing seed yield by about 35% compared to full irrigation conditions. Drought stress in the grain filling period resulted in a 10% reduction in wheat 1000-grains weight. Silica foliar application slightly reduced the effect of drought stress on grain yield.Wheat grain yield was significantly higher than other spraying treatments with the application of concentration of 100 mg L-1 of nano silicon particles (61.71 g m-2) and 150 mg L-1 of bulk silicon particles (572.73 g m-2). The efficiency of redistribution of dry matter in drought stress conditions from stem elongation to flowering (18.46%) was significantly higher than non stress conditions (14.07%) or stress induced from flowering stage to end of growth period (13.75%) Regardless of Silica foliar application treatments, redistribution of dry matter under full irrigation conditions was about 11% less than that of drought stress. The highest percentage of redistribution of dry matter from wheat grain yield was related to foliar application with concentration of 100 mg L-1 of bulk silicon particles under drought stress from flowering to the end of the growth period.
The contribution of current photosynthesis in grain filling in non-stress conditions (458.68 g m-2) was significantly higher than drought stress conditions from flowering stage to end of growth period (399.68 g m-2) and for this was also significantly more than that of the stress conditions from the stem elongation to flowering (261.98 g m-2). The contribution of current photosynthesis in grain filling in spray treatment with a concentration of 100 mg L-1 of nano silicon dioxide was the maximum (451.25 g m-2) and in control treatment was at least (311.11 g m-2).
It seems that nano silicon particles application caused an increase in plant tolerance to drought stress due toincreasing water balance, photosynthetic efficiency, and seedling growth (Hattori et al., 2005). In general, the present study showed that the presence of silicon and especially nano particles in drought stress has a significant role in improving yield and grain yield components of wheat as well as redistribution of dry matter. It seems that in order to reduce the negative effect of moisture stress during wheat growth season and increase grain yield and dry matter redistribution, application of 100 mg L-1of nanosilica particles is recommended.