Differential regulation of the phenylpropanoid pathway highly contributes to the susceptibility of chilling-induced necrotic peel disorders in cold-stored hardy kiwifruit

Abstract

Fruit of hardy kiwifruit cultivars respond differently to chilling stress during cold storage. Therefore, this study aimed to evaluate the differential responses of fruit quality attributes, physiological disorders, and untargeted and targeted metabolites of two contrasting hardy kiwifruit cultivars, ‘Greenheart’ and ‘Daebo’ during cold storage. During cold storage, the ‘Daebo’ cultivar exhibited more severe symptoms of chilling injury, such as peel browning and peel pitting, compared to the ‘Greenheart’ cultivar. Untargeted and targeted metabolic analyses indicated that syringic acid, total phenolic compounds, total flavonoids, catechin, rutin, ferulic acid, quinic acid, citramalic acid, and isoquercitrin levels were higher in ‘Greenheart’ compared to ‘Daebo’ during cold storage. However, citric, isocitric, and threonic acids, gamma-aminobutyric acid, cysteine, β-alanine, titratable acidity, epicatechin, and proline were high in the ‘Daebo’ cultivar. Peel browning and pitting were positively correlated with soluble carbohydrates, organic acids, and amino acids but negatively correlated with individual phenolic compounds in ‘Daebo’ cultivar. The tricarboxylic acid cycle, glyoxylate and dicarboxylate metabolism, arginine and proline metabolism, biosynthesis of unsaturated fatty acids, arginine biosynthesis, and alanine, aspartate, and glutamate metabolism were upregulated in the ‘Daebo’ cultivar, whereas the phenylpropanoid pathway was upregulated in the ‘Greenheart’ cultivar. Our study showed that differentially upregulated pathways could lead to the contrasting development of necrotic peel disorders in these two hardy kiwifruit cultivars during cold storage. Our results suggest that the distinctive responses of metabolic analyses to chilling stress can contribute to susceptibility in chilling-induced necrotic peel disorders in cold-stored fruit of the ‘Daebo’ hardy kiwifruit cultivar.