Plant growth-promoting fungi (PGPF) are a diverse group of non-pathogenic fungi that benefit host plants through multiple mechanisms. With the growing global emphasis on sustainable agriculture, research has increasingly focused on understanding fungal ecology and its role in enhancing plant growth and development. PGPF contributes significantly by facilitating nutrient acquisition, solubilizing minerals, producing growth hormones, and transferring essential elements from the soil to plants. PGPF have been proposed as biofertilizers, bio-stimulants, and/or biocontrol agents for a variety of plant species in earlier research findings. Modern biotechnological tools can help uncover plant-PGPF interactions, facilitating the development of crop-specific bioinoculants. This review critically evaluates PGPF as drivers of sustainable agriculture by bridging mechanistic insights with field-level applications. Unlike previous descriptive reviews, this study integrates nutrient acquisition, stress resilience mechanisms, and real-world efficacy under varying environmental conditions. We highlight the role of PGPF in climate-resilient cropping systems and circular bioeconomy frameworks, including waste valorization and biofertilizer development. Furthermore, we identify key limitations such as host specificity, environmental variability, and scalability challenges. Finally, future research directions including omics-driven inoculant design and microbiome engineering are proposed. This review provides a novel, integrative perspective on the application of PGPF in sustainable agriculture.
Sunflower (Helianthus annuus L.) is an important food, oil and bioenergy crop frequently affected by drought stress. Plant growth-promoting bacteria (PGPB) can enhance plant growth and resilience to water deficit. However, their efficiency often diminishes over time under prolonged stress due to reduced bacterial survival. This study investigated whether encapsulated forms of Bacillus subtilis, with and without humic acid supplementation, improves bacterial viability and photosynthetic performance of a drought-sensitive sunflower variety under water deficiency. Seedlings were grown in a greenhouse, with water deficit imposed at 30% field capacity for 29 days. Treatments included solution (B) or encapsulated forms (alginate beads alone (EB) or supplemented with humic acid (HEB)) under well-watered (W) and drought (D) conditions. Encapsulation, particularly with humic acid, increased bacterial viability, mitigating damage to photosynthetic reaction centers as reflected by subsequent morphophysiological measurements. Under drought, all PGPB treatments enhanced plant height (BD: 15.2%, HEBD: 14.6%, EBD: 6.1% vs. D), above-ground biomass (HEBD and BD significantly higher), Gsw (EBD: 3-fold, HEBD: 10-fold vs. D), ΦPSII (HEBD: 10%, BD: 4% vs. D), ETR (HEBD: 31% vs. D), and ChlF indices like PIABS (BD: 95%, HEBD: 81%, EBD: 53% vs. D). Stable encapsulation without premature release, especially with humic acid, sustained bacterial viability and prolonged benefits by protecting the bacteria against stress, improving root interactions and photosynthetic resilience. These findings demonstrate that encapsulation, particularly with humic acid, optimizes PGPB delivery and sustains physiological benefits under drought, highlighting its strong potential as a strategy for sustainable agriculture in semi-arid regions.
