The effect of SiO2 nanoparticles on quantitative and qualitative yield and yield components of winter wheat (Triticum aestivum L.) varieties under late season water deficit stress conditions

Introduction
Increasing temperatures and water deficit at the end of spring and early summer are very important challenges at the late-season growing period of winter wheat varieties in temperate and cold regions. Considering the economic importance of wheat, it seems necessary to use appropriate strategies to optimize the wheat production system under terminal drought stress. In this regard, cultivating high-yielding and terminal drought-resistant varieties in combination with growth regulators can be effective. The objective of the present study was to investigate the effect of nanosilicon (SiO₂-NP) on yield and yield components of three winter wheat varieties under late-season water deficit stress conditions.

Materials and methods
The experiment was conducted with three winter wheat varieties based on split-plot in a randomized complete block design with three replications at the research field of Bu-Ali Sina University, Hamedan, Iran, in 2021-2022. The main factor was in four levels, including no-water stress with nanosilicon application, no-water stress and no-nanosilicon application, water deficit stress with nanosilicon application, and water deficit stress and no-nanosilicon application, and the subfactor was three winter wheat varieties, including Alvand, Pishgam and Pishtaz. Water deficit stress was applied at the end of the growing season by stopping irrigation at the end of flowering stage (code 69 in BBCH scale). Nanosilicon foliar application at a concentration of 30 mg/L was performed in two stages, before flowering and spike emergence (code 51 in BBCH scale) and flowering initiation (code 61 in BBCH scale). The measured traits in this study included the number of spikes per unit area, number of spikelets per spike, number of grains per spike, 1000-grain weight, grain yield, biological yield, harvest index, leaf greenness index (SPAD), and grain protein content. Statistical analyses was performed using SAS software and graphs were drawn using Excel software.

Research findings
The results of the analysis of variance showed that the effect of water deficit stress and nanosilicon was significant on all measured traits, except for the number of spikes per unit area. The differences between the studied wheat varieties were also significant in terms of the number of spikes per unit area, grain yield, biological yield and harvest index, but was insignificant in term of other measured traits. However, the interaction of stress and nanosilicon × variety was significant only on two traits, 1000-grain weight and grain yield. The results of comparison of means revealed that the number of spikes per unit area in Alvand variety was significantly higher than two varieties, Pishgam and Pishtaz. Also, the traits that were affected by water deficit stress and nanosilicon, showed a decrease during water stress without nanosilicon application. The results showed that in both non-stress and water deficit stress conditions, the application of nanosilicon increased grain yield and yield components in all three wheat varieties compared to its non-application. However, the effect of nanosilicon was greater in water deficit stress, so that the grain yield of three varieties Alvand, Pishgam and Pishtaz increased by 18.03, 8.05 and 9.22 percent, respectively, with the application of nanosilicon compared to the non-application of nanosilicon under water deficit conditions. The highest grain yield (6275.7 kg.ha^-1) was obtained with the application of nanosilicon in Alvand variety under non-water stress conditions, and the lowest grain yield (5185 kg.ha^-1) was observed in Pishtaz variety under water deficit stress conditions without the application of nanosilicon.

Conclusion
Water deficit stress at the end of flowering stage and the beginning of grain filling period reduced grain yield of the studied three wheat cultivars, but the yield reduction was greater in Alvand variety than in the two other varieties. The reason for this reduction was mainly related to the reduction in the number of grains per spike and 1000-grain weight under water deficit stress conditions. Nanosilicon foliar application largely compensated for the yield reduction caused by late season water deficit stress in all three studied varieties, especially in Alvand variety.