Constitutive Metabolomic Profiles Linked to Seasonal Climate Niche Adaptation and Resilience to Black Rot in Cabbage

Plants are dynamic chemical factories that produce diverse specialised metabolites essential for growth, defence, and environmental adaptation. Metabolomes, shaped by genetic architecture, enable plants to respond to abiotic and biotic pressures, including temperature fluctuations. In Brassica systems, warm and humid conditions favour black rot caused by Xanthomonas campestris pv. campestris (Xcc), whereas cooler temperatures reduce disease pressure, thus influencing seasonal cultivar deployment. In this study, we investigated whether the constitutive metabolomes of two commercially cultivated South African white cabbage (Brassica oleracea var. capitata f. alba) F1 hybrids reflect adaptation to contrasting seasonal niches and associated disease risk. 'Optima' exhibits intermediate resistance to Xcc, is heat-tolerant and cultivated during summer, whereas 'Superslam', which is more susceptible to Xcc, is grown under cooler late-season conditions when pathogen pressure is diminished. Their metabolomic profiles were characterised using untargeted ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS). Untargeted metabolomics coupled with multivariate chemometric analysis revealed clear metabolic divergence between the cultivars under controlled conditions. 'Optima' accumulated higher levels of amino acids and related intermediates, including phenylalanine, isoleucine, threonine and 2-oxobutanoate, suggesting enhanced nitrogen remobilisation, branched-chain amino acid biosynthesis, and photorespiratory activity associated with heat adaptation and metabolic flexibility. In contrast, 'Superslam' exhibited elevated levels of flavonoids and diverse glucosinolates, indicating reinforced phenylpropanoid metabolism and constitutive antioxidant capacity consistent with chilling adaptation. Pathway analysis highlighted significant modulation of phenylalanine metabolism, glycine-serine-threonine metabolism, glyoxylate and dicarboxylate metabolism, as well as glucosinolate biosynthesis. These findings reveal distinct constitutive metabolomic architectures associated with seasonal cultivation niches and reported differences in disease resilience. However, the proposed relationships remain correlative and require validation through controlled temperature treatments and pathogen challenge experiments.