Effects of Deep Shading on Agronomic Traits, Coloration, and Antioxidant Properties in Sweetpotato Leaves

The vegetable sweetpotato (<i>Ipomoea batatas</i> L.) is a novel, specialized type, cultivated for its tender stems and leaves, which are rich in nutrients and bioactive compounds. To clarify its growth adaptation to weak light conditions often encountered during cultivation, this study examined the impact of 70% shading on 12 representative cultivars from 4 leaf color types. Agronomic traits, color, and nutritional and antioxidant properties were assessed in both young and mature leaves. Shading promoted leaf expansion, plant height, and vine length, but reduced stem thickness and dry-matter content. Leaf shape shifted from lobed to more cordate, with the foliage becoming darker green and lighter red due to elevated chlorophylls and reduced anthocyanins. Shading generally reduced soluble protein, sugar, cellulose, total phenols, flavonoids, and total antioxidant capacity. Antioxidant capacity correlated most strongly with soluble sugar and dry-matter content, followed by total phenols and flavonoids. Gene expression analysis of key light- and leaf color-related genes revealed up-regulation of chlorophyll genes and down-regulation of anthocyanin genes under shading, with light-responsive genes potentially affected by pigment feedback. These results elucidate the sweetpotato's adaptive responses to deep shading and provide valuable guidance for optimized cultivation and breeding of vegetable sweetpotato in light-limited environments.