Role of Biostimulants in Wheat: Nutritional Quality and Resistance to Abiotic Stresses, a Systematic Review

Wheat is a major staple crop, and improving its productivity and grain quality is essential to meet rising global food demand. Biostimulants have attracted growing interest because they can enhance nutrient use efficiency, improve tolerance to environmental stresses, and support crop performance without acting as conventional fertilizers, yet a focused synthesis of their effects on wheat remains limited. Following a systematic search of Scopus and Web of Science (2000–2026), this review synthesizes 52 primary studies on microbial and non-microbial biostimulants in common and durum wheat, addressing grain yield, nutritional quality, and resilience to drought, salinity, heavy metals, and temperature extremes. Across studies, 88% reported significant positive effects and none reported a consistent negative effect; grain yield increases ranged from +6% to +123%, with parallel improvements in grain protein and micronutrient biofortification, notably zinc and iron. Microbial biostimulants, especially bacteria and microbial consortia, produced the largest but most variable gains, whereas non-microbial products gave more moderate and consistent responses. Benefits were greatest under low nitrogen, drought, and saline conditions and in nutrient-poor soils, and were modulated by wheat genotype and product dose. Biostimulants are promising tools for sustainable wheat production, though standardized field trials and reporting are still needed.