اثر نانو دی اکسید سیلیسیم (SiO2-NP) بر عملکرد کمی و کیفی و اجزای عملکرد رقم‌های گندم (Triticum aestivum L.) تحت شرایط تنش خشکی آخر فصل

Introduction
Increasing temperatures and water deficit at the end of spring and early summer are very important challenges at the late-season growing season 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 present study was conducted to investigate the effect of Nano silicon (SiO2-NP) on the yield and yield components of two wheat varieties under late-season deficit stress.

Materials and methods
The experiment with three winter wheat cultivars was conducted in a split-plot design in a randomized complete block design with three replications. The main plots included four levels: non-water deficit stress with Nano silicon application, non-water deficit stress and non-Nano silicon application, water deficit stress with Nano silicon application, water deficit stress and non-Nano silicon application, and the subplots included three wheat cultivars, 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 69 of the BBCH scale). Nano silicon solution-spraying was carried out during two stages before flowering, spike emergence (stage 51 of the BBCH scale) and flowering initiation (stage 61 of the BBCH scale) at a concentration of 30 mg/L. The measured traits included the number of spikes per unit area, the number of spikelets per spike, the number of grains per spike, the weight of 1,000 grains, biological yield, grain yield, harvest index, leaf greenness index (SPAD), and grain protein percentage. Statistical analysis was performed using SAS software and graphs were drawn using Excel software.

Research findings
The effect of cultivar on the number of spikes per unit area was significant. Also, the number of spikelets per spike, the number of grains per spike, biological yield, harvest index, SPAD index, and grain protein percentage were affected by water deficit stress and Nano silicon. The interaction of stress and Nano silicon with cultivars was significant on the traits of 1000-grains weight and grain yield. The number of spikes per unit area in Alvand cultivar was significantly higher than Pishgam and Pishtaz cultivars. The traits that were affected by drought stress and Nano silicon showed a decrease during stress without Nano silicon application. In both water deficit stress and non-stress conditions, the application of Nano silicon increased the yield and yield components in all cultivars, but the effect of Nano silicon was greater in water deficit stress.

Conclusion
Water deficit stress at the grain filling period reduced grain yield of both wheat cultivars, but the reduction was greater in Alvand cultivar. The reason for the reduction was mainly related to the reduction in the number of grains per spike and 1000-grains weight under water deficit stress. Nano silicon foliar application was able to largely compensate for the reduction in yield accrued in terminal drought stress in all the studied cultivars, especially in Alvand cultivar.