The Coupling Effects of PGPR Inoculation and Foliar Spraying of Strigolactone in Mitigating the Negative Effect of Salt Stress in Wheat Plants: Insights from Phytochemical, Growth, and Yield Attributes

Salt stress has detrimental effects on wheat plants at several physiological, biochemical, and molecular levels. This stress leads to suppressed growth, reduced grain yield, and poor quality of harvested grains. However, two approaches have shown promise for improving wheat salt tolerance: using a synthetic strigolactone analog called GR24 and applying plant growth-promoting rhizobacteria (PGPR). GR24 plays a vital role in regulating plant growth and development and in defense against various stresses. Conversely, PGPR are beneficial bacteria that colonize the rhizosphere of plants and promote their growth through multiple mechanisms. In our study, we investigated the effects of salinity on the growth and yield traits of two different wheat cultivars and explored the combined role of PGPR and GR24 in mitigating the impact of salt stress. We created three different salinity levels using NaCl in pots (original, 5 dS m(-1), and 10 dS m(-1)) and inoculated wheat seeds with a salt-tolerant Bacillus velezensis UTB96 strain. In addition, we applied 10 mu M GR24 via foliar application during the pollination stage. Our observations showed that salt stress negatively affected wheat's growth, yield, and phytochemical properties compared to the control. However, both single and combined applications of PGPR and GR24 mitigated the adverse effects of salinity. The combined treatment had a more substantial impact than either alone in inducing and improving biochemical and ionic characteristics. These included decreasing Na+ content in both leaves and roots, and EL, H2O2, and MDA content in leaves while increasing K+ content in both leaves and roots, growth and yield-related traits, RWC, chlorophyll pigments, total protein, soluble sugar, starch, proline, GB, and antioxidant enzyme activity (APX, POX, and CAT) of leaves. In conclusion, integrating PGPR and GR24 can efficiently induce salt tolerance and improve plant growth under stressed conditions. This combined approach has the potential for broad applicability in supporting plant growth in the presence of salt stress.