Effects of Priestia aryabhattai Inoculation on Growth, Grain Production, and Oxidative Metabolism of Common Bean Under Contrasting Irrigation Regimes

Potential of Bacillus aryabhattai and Pseudomonas fluorescens for Promoting Plant Growth under Water Stress

Drought is one of the major abiotic stresses limiting productivity worldwide, highlighting the need for sustainable strategies to improve crop resilience under water-limited conditions. This study evaluated the effects of the plant growth-promoting bacteria Bacillus aryabhattai and Pseudomonas fluorescens, applied individually or in combination, on soybean growth under well-watered and water-deficit conditions. The experiment was conducted in a completely randomized design arranged in a 2 × 4 factorial scheme, consisting of two irrigation regimes (well-watered and water deficit) and four biological treatments (control, B. aryabhattai, P. fluorescens, and co-inoculation with both bacteria). Plant growth variables, including shoot and root length, root volume, fresh biomass, and dry biomass, were evaluated after the stress period. Under well-watered conditions, co-inoculation promoted the greatest fresh root biomass and consistently increased shoot biomass compared with the untreated control. Under water-deficit conditions, B. aryabhattai alone produced the highest fresh root biomass and root volume, demonstrating superior performance in promoting root development during drought stress. Although most variables did not differ significantly among treatments, inoculated plants consistently exhibited greater vegetative growth than non-inoculated plants. These findings demonstrate the potential of B. aryabhattai and P. fluorescens as plant growth-promoting bacteria capable of enhancing soybean development, with B. aryabhattai showing particular promise for improving plant performance under water-limited conditions.

Potential of Bacillus aryabhattai to Promote Plant Growth and Mitigate the Effects of Water Deficit

Water deficit is one of the main factors limiting soybean productivity, impairing plant growth and reducing crop yield potential. In this context, the use of plant growth-promoting rhizobacteria (PGPR) has emerged as a promising strategy to enhance plant tolerance to abiotic stresses and improve crop development. This study aimed to evaluate the effects of soybean seed inoculation with Bacillus aryabhattai on seed physiological performance during germination and plant growth under water-deficit conditions. Two experiments were conducted. In the first experiment, a completely randomized design was adopted in a factorial arrangement, evaluating seed inoculation (with or without aryabhattai) and water availability (with or without water deficit). Shoot and root length, as well as shoot and root fresh and dry biomass, were determined. In the second experiment, the seed physiological performance during germination of inoculated and non-inoculated seeds was evaluated by assessing seedling biomass accumulation. Seed inoculation significantly promoted shoot and root growth under both well-watered and water-deficit conditions. Inoculated plants subjected to water restriction exhibited greater length and biomass accumulation than non-inoculated plants, demonstrating enhanced tolerance to drought stress. In addition, inoculation increased shoot biomass accumulation during the seedling stage, indicating greater early vigor. Overall, the results demonstrate that Bacillus aryabhattai has considerable potential as a soybean seed inoculant, promoting plant growth and contributing to improved crop resilience under water-deficit conditions.

Comparative Efficacy of Seed and Soil Inoculation in Soybean Unveiling the Dominant Role of Soil Microbial Activity in Drought Mitigation

Drought stress severely negatively affects the growth and yield of soybean (Glycine max L.) by causing oxidative damage and suppressing physiological functions. While plant growth-promoting rhizobacteria (PGPR) alleviates these effects, the comparative effectiveness of different inoculation techniques has not been adequately investigated. This study investigated the physiological, biochemical, and soil microbiological responses of drought-stressed soybean (50% field capacity) to two Bradyrhizobium japonicum inoculation methods (conventional seed inoculation (A1) versus direct soil inoculation (A2)). Drought significantly reduced plant biomass, relative water content (RWC), and chlorophyll levels while aggravating markers of oxidative stress (H₂O₂, MDA, and electrolyte leakage). Both inoculation methods reduced drought-induced damage; however, soil inoculation (A2) showed significant superiority. Compared to uninoculated stressed plants, A2 treatment increased fresh and dry weight by 91.7% and 104.3%, respectively, while maximally suppressing lipid peroxidation and preserving cell membrane integrity. Moreover, soil inoculation profoundly increased rhizosphere microbial activity, increasing soil respiration (CO₂) and dehydrogenase activity (DHA) by 110.6% and 86.7%, respectively. In particular, Random Forest machine learning analysis identified soil DHA as the most critical determinant in predicting plant biomass under stress, far outweighing internal oxidative stress indicators. These findings suggest that direct soil inoculation optimizes rhizosphere enzymatic activity and offers a more robust agronomic strategy than seed inoculation for sustainable soybean cultivation in drought-prone regions.

Growth and Physiological Responses of Petunia to Chitosan and Arbuscular Mycorrhizal Fungi Under Sustained Water Content Reduction

Reducing irrigation inputs is essential for sustainable container crop production; however, the ability of biostimulants to mitigate the effects of deficit irrigation on ornamental crop quality and postharvest often may be crop-specific, product-specific, and application-specific. Two independent experiments were conducted to evaluate whether chitosan applied as a substrate amendment or arbuscular mycorrhizal fungi (AMF) applied during germination could improve growth, physiology, and postharvest performance of petunia ( Petunia milliflora ‘Picobella TM Pink’) under sustained water content reduction. Plants were grown under three container capacity (CC) treatments (100%, 70%, and 40%) combined with chitosan application timing (no application, week 1, or week 3) or AMF application (with or without). After production, plants were exposed to postharvest environments at 30 °C or 40 °C for 2 weeks. The growth index and canopy area decreased by 10% to 40% relative to plants grown at 100% CC under 70% and 40% CC; however, flower coverage percentage remained unaffected during production. Water use reduced by 20% at 70% CC and by up to 50% at 40% CC, while irrigation water use efficiency (IWUE) was maintained with all CC treatments. In the AMF experiment, plants grown at 40% CC with AMF exhibited the highest IWUE and increased root colonization under severe deficit irrigation. Photosynthetic pigment concentrations were generally maintained under deficit irrigation, whereas malondialdehyde concentrations temporarily increased at week 4 under 40% CC, indicating increased oxidative stress. Neither chitosan nor AMF consistently enhanced plant growth or reduced biochemical stress indicators under the evaluated conditions. Chitosan application timing strongly influenced plant responses, with week 3 applications reducing growth and increasing oxidative stress across CC treatments. During the postharvest evaluation, temperature was the primary factor affecting plant performance, with plants maintained at 40 °C exhibiting lower flower coverage and canopy area compared with plants maintained at 30 °C. The combination of deficit irrigation and chitosan application showed limited potential to improve postharvest heat tolerance, whereas AMF application did not improve postharvest performance. Overall, petunia demonstrated substantial tolerance to sustained deficit irrigation, and 70% CC appeared to be a practical strategy for reducing irrigation inputs while maintaining marketable crop quality.

Synergistic Effects of Vitreous Amendment and Mycorrhizal Fungi on Durum Wheat Water Stress Tolerance

Salicylic Acid Improves Morpho-Physiological Traits and Biomass of Kale under Drought Stress

Drought stress in agricultural land disrupts the physiological processes, growth, and yield of kale (Brassica oleracea L. var. acephala). This study evaluated the physiological responses, growth, and yield of kale treated with salicylic acid, a potential strategy to enhance plant tolerance to drought stress, in a greenhouse at the Department of Agriculture, Universitas Diponegoro, Semarang. A 4 × 4 factorial experiment was arranged in a Completely Randomized Design (CRD) with three replications. The first factor was drought level (100%, 80%, 60%, and 40% field capacity). The second factor was salicylic acid (SA) concentration 0, 0.75, 1.5, and 2.25 mM). The results indicated that physiological responses (chlorophyll a, chlorophyll b, total chlorophyll, relative water content, and electrolyte leakage) remained largely stable under moderate drought stress (60% FC), whereas plant growth parameters (plant height, leaf number, and leaf area) were reduced by 14.5–20.7% compared with the control (100% FC). At 40% FC, both physiological and growth responses were more severely affected; electrolyte leakage increased markedly, and plant height, leaf area, and dry biomass weight decreased by 24.4%, 47.2%, and 60.5%, respectively, compared with the control (P < 0.05). The best treatment was the application of 1.5 mM salicylic acid, which increased the relative water content by 4.13% and decreased the electrolyte leakage by 34.70% compared to untreated plants (P < 0.05). This concentration was likely more effective due to optimal stomatal regulation, increased antioxidant enzyme activity, and maintained membrane integrity, indicating that 1.5 mM SA has potential as a biostimulant to improve kale water status and membrane stability. However, field validation across locations and seasons is needed before recommending it for dryland farming.