Biofortification Techniques for Nutritional Improvement of Vegetable Crops: A Critical Narrative Review of Agronomic, Breeding and Genome-Based Approaches

Abstract

Background: Inadequate intakes of iodine, iron, zinc, selenium, folate and several vitamins remain widespread, and biofortification, the enrichment of edible plant parts with nutrients during crop growth, has become an established complement to supplementation and industrial fortification. Most biofortification research and policy has been built around cereals and pulses, whereas vegetables differ in portion size, water content, harvested organ, production system and consumption practice. Purpose and Scope: This critical narrative review appraises agronomic, breeding and biotechnological techniques used to biofortify vegetables, including potato and sweetpotato, and asks which techniques produce nutritionally meaningful, bioavailable, safe and deployable gains. Approach: Peer-reviewed literature published from January 2000 to July 2026 was identified through multidisciplinary and topic-specific scholarly sources, supplemented by citation searching and authoritative institutional documents, and was appraised for relevance, design, reporting basis, environmental replication and the level of nutritional evidence reached. Principal Findings: Agronomic enrichment with selenium and iodine is reliable in controlled and field conditions, but it operates within narrow safety margins and can alter other quality traits, while iron enrichment of vegetables through fertilisation is largely ineffective. Zinc responds to foliar and soil application in potato, although excessive doses reduce yield and may raise phytate. Conventional breeding has produced the strongest human evidence, notably for orange-fleshed sweetpotato and iron-dense potato, yet absorption studies show that higher concentration does not guarantee proportionally higher absorbed nutrient. Metabolic engineering and genome editing have generated striking gains in carotenoids, folate, anthocyanins, ascorbate, provitamin D3 and γ-aminobutyric acid in tomato, potato and lettuce, but few such lines have been tested for bioavailability, stability or agronomic performance across environments. Evidence for microbial and nanoscale enrichment remains largely confined to short-term controlled studies. Unresolved Questions: Major gaps concern portion-based reporting, post-harvest retention, human bioavailability, multi-nutrient stacking and cost-effectiveness outside staple systems. Implications: Technique choice should be matched to the nutrient, crop organ and delivery context rather than to technological novelty. Conclusion: Vegetable biofortification is technically feasible for several nutrients, but its public-health value remains demonstrated for only a small subset of crop–nutrient combinations.