Influence of Endophytic Bacillus Bacteria on the Growth and Stress Tolerance of Spring Wheat and Soybean Seedlings

This study explores the potential of using endophytic bacteria from the genus Bacillus on monocotyledonous and dicotyledonous plants to enhance their drought tolerance. A comparison is made using parameters such as seed germination, root length, lipid peroxidation level, and the content of photosynthetic pigments and free proline. The experimental involves the simulation of a 30% drought on sand and the presowing treatment of spring wheat seeds (var. Yoldyz) and soybean seeds (var. Sultana) with the following strains of endophytic bacteria: Bacillus subtilis KS-55 AU, Bacillus cereus KS-56 AU, Bacillus pumilus KS-57 AU, Bacillus megaterium KS-58 AU, Bacillus cereus KS-59 AU, Bacillus megaterium KS-60 AU, and Bacillus pumilus KS-61 AU. The most efficient root growth stimulation is observed when bacteria titer is 1 × 10⁶ cells/mL; in the case of soybean, a 0.6-cm increase of this index is observed for seeds treated with Bacillus subtilis KS-55 AU and Bacillus megaterium KS-60 AU, whereas a 0.4-cm increase is observed for wheat seeds treated with Bacillus cereus KS-56 AU, Bacillus cereus KS-59 AU, and Bacillus pumilus KS-61 AU. For wheat, the Bacillus subtilis KS-55 AU strain demonstrates the most outstanding results compared to the control; its application causes a 30% increase in the germination rate, a 46% reduction in the lipid peroxidation level, a 148% increase in the content of free proline, and a 6% increase in the content of photosynthetic pigments. In the case of soybean, this strain provides a 40% increase in the germination rate, while the treatment with Bacillus cereus KS-59 AU reduces the lipid peroxidation level by 47% and increases the proline accumulation by 73%, and treatment with Bacillus pumilus KS-61 AU increases the total chlorophyll content by 141% compared to the control. Thus, the aforementioned strains of endophytic bacteria improve the growth and development of spring wheat and soybean seedlings and induce crop tolerance to the soil drought.