Here, ACC deaminase ACC Deaminase producing rhizobacteria, Priestia aryabhattai MD-85 (Accession no. PV155249.1) and Enterobacter cloacae MD-79 (Accession no. PV155250.1), were assessed for their potential to enhance water-deficit stress tolerance in muskmelon. Both strains produced ACC Deaminase and exhibited drought tolerance, with MD-79 showing 78.9 ± 7.6 µM α-ketobutyrate mg⁻¹ protein h⁻¹ at 18%-PEG, and MD-85 showing 68.4 ± 5.4 µM α-ketobutyrate mg⁻¹ protein h⁻¹ at 21%-PEG. Both strains produced multi-functional growth-promoting substances under PEG-induced stress, conferring their significant drought tolerance potential. Increasing water stress negatively impacted growth and physiological characteristics of soil-grown muskmelon plants. However, ACC Deaminase-producing strains, especially when applied in combination ( P. aryabhattai MD-85 + E. cloacae MD-79), effectively mitigated adverse effects of drought stress. For instance, under 3%-polyethylene glycol (PEG)-induced stress in muskmelon, co-inoculation (MD-79 + MD-85) enhanced root length (44.3%), shoot length (47.6%), root dry and fresh wight ratio (40.7%), leaf dry and fresh wight ratios (51.7%), total chlorophyll (41.5%), and carotenoids (38.8%). Further, bacterial consortia significantly ( p ≤ 0.05) enhanced chlorophyll colour index (56.7%), net photosynthetic rate (64.3%), F v/ F m (50.8%), stomatal conductance (64.3%) and relative water content (62.3%) in leaf tissues of 3%-PEG-stressed muskmelon. Single/combined bacterial inoculation lowered drought-induced oxidative stress markers in muskmelon. Moreover, bacterial partners strengthened antioxidant enzymes in water-deficit affected muskmelon. The 15%-PEG + MD-79 + MD-85 treatment exhibited greater increase in catalase (79.3%), ascorbate peroxidase (65.3%), peroxidase (55.7%), and superoxide dismutase (72%), activities over their respective untreated controls. Additionally, bacterial strains modulated ion homeostasis in PEG-stressed muskmelon roots, enhancing drought tolerance. Notably, combined inoculation synergistically enhanced drought tolerance compared to single-strain treatments. This study emphasizes the potential of ACC Deaminase-producing PGPR as a sustainable and long-term strategy to improve muskmelon resilience under water-deficit condition by modulating physiological, biochemical, and ionic responses. These findings underscore the use of PGPR in drought management to enhance crop productivity and stress tolerance.
Altaf et al. (Thu,) studied this question.