Morphotype-Specific Metabolomic Signatures and Trait Associations in 32 Accessions of underutilized African Strychnos spinosa (Monkey Orange) fruit

Monkey orange (Strychnos spinosa Lam.) is an underutilised indigenous fruit of the Loganiaceae family with considerable nutritional and phytochemical potential; however, its intraspecific morphological and metabolomic diversity remains poorly characterised. This study integrated morphological characterisation, physicochemical analysis, phytochemical quantification, antioxidant assays, and untargeted ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) metabolomics to characterise 32 S. spinosa fruit accessions and elucidate morphotype-specific compositional signatures and trait–metabolite associations. Multivariate analysis resolved three distinct morphotype groups with differentiated physicochemical and metabolomic profiles. Large pyriform fruits (1103-1328 g) were characterised by elevated carotenoid content (632.50 mg β-carotene/100 g) and lipid-enriched metabolomic profiles dominated by putatively annotated phosphatidylcholines. Small, roundish purple fruits exhibited comparatively high titratable acidity (1.20-1.83%) and total phenolic content (3.72 mg GAE/g), accompanied by strong antioxidant activity (DPPH: 1.82 μmol TE/g), with total phenolic content positively correlated with DPPH antioxidant activity (r = 0.65). Smooth green fruits displayed a comparatively balanced total soluble solids (14-16 °Brix) and titratable acidity (1.50-1.80%) profile together with diverse metabolite features. Principal component analysis further differentiated the accessions, with separation along PC1 associated predominantly with features putatively annotated as phosphatidylcholines at mass-to-charge ratios (m/z) 596.40125 and 814.56787 and a triterpenoid-related feature at m/z 377.19971. PC2, accounting for 21.7% of the variance, provided additional discrimination, with features at m/z 550.39569 and 586.37256 contributing positively to group separation. Overall, phosphatidylcholine-related features were important discriminants between purple- and green-fruited accessions, whereas the triterpenoid-related feature contributed to differentiation of Group 3. Accessions exhibiting favourable combinations of morphological, physicochemical, antioxidant, and metabolomic traits, particularly PRR-dGRO and GRP-GEO accessions and folded-leaf morphotypes, represent promising candidates for germplasm selection, domestication, breeding, and development of value-added functional food products. These findings provide new evidence of substantial intraspecific phenotypic and chemical diversity within S. spinosa and establish a trait–metabolite framework for selecting superior germplasm for future utilisation and improvement programmes.