Silicon Improves Bacillus simplex Producing 1-Aminocyclopropane-1-Carboxylic Acid Deaminase Function in Order to Adjust Drought Stress in Wheat

Several mechanisms that plants utilize to cope with the effects of drought stress are mediated by ethylene. However, plants utilize several mechanisms to cope with the adverse effects of drought stress through ethylene. As the 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase can break ACC, the precursor of ethylene synthesis, the ACC deaminase-producing bacteria can be used to improve plant tolerance to drought stress. Silicon (Si) has beneficial effects on not only plant growth but also on environmental stresses such as drought stress. A field experiment was carried out to assess the effect of drought stress tolerant ACC deaminase-producing bacteria with and without the application of Si on the growth and yield of wheat under drought stress conditions. A novel bacteria strain, registered in the GenBank of BankIt with the Accession Number KT59926, Bacillus simplex UT1, was applied in this experiment. The main plots were three levels of irrigation (I) consisted of 7I level including all seven irrigation times as irrigation applied at stages of cultivation, seed germination, tillering, initial and mid-stem elongation, pre-flowering and grain-filling, five irrigation stages (5I), and three irrigation stages (3I). Sub-plots were randomly divided into four levels of treatments, including control treatment (no inoculation of bacteria, no Si application, and recommended nitrogen, phosphorus, potassium, and zinc fertilizers), the treatment of the application of B. simplex UT1, the treatment of the Si application as potassium silicate at the rate of 10 mg plant⁻¹, and the treatment of the combined application of B. simplex UT1 and silicon. The experiment was conducted as a randomized complete block design with four replicates (12 × 4 = 48 plots). Results indicated that the application of deficit irrigation increased the ethylene concentration of stems in all treatments, while the combined application of B. simplex UT1 and Si declined ethylene concentration. Irrigation saving (5I) decreased yield traits: grain yield (24.2%) and biological yield (26.2%), compared to the control irrigation level (7I). Combined application of B. simplex UT1 and Si decreased grain and biological yield by 12.4% and 11.5%, respectively. The application of the same treatment under the 3I level resulted in a greater increase in some yield traits including grain yield (16.1%) and biological yield (15.5%) compared to the control treatment. Significant differences in chlorophyll a, chlorophyll b, and solute conductance as affected by the combined inoculation of bacteria strain and application of Si were observed. Therefore, the combined applications of B. simplex UT1 and Si were effective in the alleviation of drought stress and enhancement of wheat production.