The use of plant growth-promoting microorganisms is an effective agricultural practice to improve plant growth, especially under abiotic stress. In this study, the combined impact of three plant growth-promoting bacteria (PGPB) namely Brevibacterium halotolerans (Sd-6), Burkholderia cepacia (Art-7), Bacillus subtilis (Ldr-2) were tested with Trichoderma harzianum (Th) (possessing ACC deaminase producing activity) in Ocimum basilicum L. cv. Saumya to reduce drought-induced damages to the plants under different level of drought stress [i.e. wellwatered (100 %), moderate (60 %), severe (40 %)]. These PGPB strains, along with Th, were found to be tolerant against osmotic stress when tested in growth media containing different concentrations of polyethylene glycol (PEG 8000), and all were found to endure -0.99 MPa water potential. Compared to non-inoculated control, Th+Ldr-2 treatment improved fresh herb weight (62.45 %) and oil content (61.54 %) and higher photosynthetic rate under severe drought. Besides, in relation to control, the above treatment enhanced nutrient uptake, reduced ABA, ACC as well as ethylene levels and increased IAA content in addition to an increase in important constituents of essential oil, indicating better performance in terms of plant growth under drought. Higher RWC, decreased MDA, and reduced antioxidant activities in Th+Ldr-2 treated plants compared to non-inoculated control under drought support the mechanism of the microbes providing tolerance against drought. Colony forming unit of microbes and scanning electron microscopy (SEM) study support the effective colonisation behaviour of Th+Ldr-2, which protects plants against drought stress. A consortium of diverse microbes, found to improve plant growth under drought through increased nutrient uptake, reducing the levels of ACC and ABA, improving the content of IAA, antioxidant enzymes probably reducing the effect of drought stress and improving plant biomass could be a useful tool to reduce drought-induced losses in crop plants.

To investigate the synergistic effect of IAA and melatonin (MT) on three plants to alleviate the effects of salt damage on plants, we aim to determine the optimal concentrations of exogenous hormone treatments that improve salinity resistance for each species. In this experiment, three desert plants, Sarcozygium xanthoxylon, Nitraria tangutorum, and Ammopiptanthus mongolicus, which are common in Wuhai City, were used as plant materials. Two time periods (12 h,24 h) of exogenous hormone IAA (100 mu mol/L) and exogenous melatonin concentration (0, 100, 200, 300 mu mol/L) were used to treat the three desert plants in saline soil under different conditions of exogenous IAA and exogenous melatonin. The results indicate that under different concentrations of exogenous IAA and melatonin, the germination rate and vigor of the three desert plant species in saline-alkaline soil improved. However, as the concentration of melatonin increased, the germination rate and vigor of these desert plants were inhibited. Whereas, plant height, root length, leaf length, fresh weight, dry weight, and root vigor of the three desert plants were alleviated under different conditions of exogenous IAA and exogenous melatonin. under the action of two exogenous hormones, the low concentration of melatonin decreased their malondialdehyde content and increased their proline content. As melatonin levels increased, the activity of antioxidant enzymes also rose initially, followed by a subsequent decline. This study highlights the synergistic effects of two exogenous hormones on the critical role of cell osmomodulators and antioxidant enzyme activity in combating salinity damage in three desert plants.