Phenotypic Diversity in Maize Landraces: A Systematic Review of Global Patterns, Methodological Approaches, and Implications for Breeding

Background/Objective: Maize (Zea mays L.) is a globally important cereal crop widely cultivated for food, feed, fodder, biofuel production, and various industrial applications. Maize landraces represent a valuable source of genetic diversity that supports adaptationand resilience across diverse agroecological environments. However, evidence on phenotypic diversity based on agro-morphological traits in these landraces remains fragmented across regions and varying analytical approaches. This review synthesized global evidence on phenotypic variation, heritability patterns, experimental designs, statistical methods, and the extent of integration between phenotypic and molecular data. Methods: A systematic literature search was conducted in GoogleScholar, ScienceDirect, PubMed and AGRIS for studies published between 2000 and 2025 evaluating phenotypic diversity in maize landraces. The review followed PRISMA 2020 guidelines, and f50 studies from 30 countries met the eligibility criteria. Results: Substantial and structured phenotypic diversity was consistently reported across studies, with flowering time, plant architecture, and ear and kernel traits emerging as major contributors to landrace differentiation. Traits with moderate to high heritability were mainly morphological and phenological, suggesting relative genetic control and potential suitability for phenotypic selection. In contrast, grain yield showed greater environmental sensitivity and variable heritability, reflecting complex inheritance and genotype × environment interactions. Although molecular markers were incorporated in a some studies, integrative analyses linking phenotypic and genetic data remained limited. Conclusions: Phenotypic evaluation remains a reliable approach for characterizing maize landrace diversity. However, standardized methodologies, greater integration with molecular data and cross-environment validation are needed to strengthen inference and utilization in breeding and conservation. The review also provides recommendations for improving agro-morphological assessment in maize landraces.