Biofertilizers in tropical and subtropical fruit crops: mechanisms, field evidence, and constraints in Asian orchard systems

This review works through 40 peer-reviewed studies published between 2015 and 2025 on biofertilizer use in mango, citrus, banana, and strawberry grown under tropical and subtropical Asian conditions, and it does so by cross examining each study as it is introduced rather than setting the critique apart from the findings. Synthetic fertilizers account for roughly 30–55% of variable production costs in these systems, which is reason enough for growers to look seriously at microbial alternatives, yet the trial evidence behind that interest is uneven. Reported yield gains range from 8% to 52% over unfertilized controls and from 5% to 31% over reduced-dose synthetic fertilizer treatments, though a meaningful share of these numbers come from assays, pot trials, or single-season designs whose reliability is questioned directly in the text alongside the results themselves. Consortium formulations that target nitrogen, phosphorus, and potassium limitations at once consistently outperform single-strain inoculants. Tropical storage instability, antagonism between biofertilizer strains and copper-based fungicides, and the multi-year lag before perennial crops respond remain the dominant practical constraints. Six research gaps are identified, and trial design standards suited to woody perennial horticultural systems are proposed, along with ten additional methodological references that sharpen the cross-examination of assay validity, trial duration, and scale-up representativeness.