Effects of Intercropping with Solanum nigrum on the Quality and Cadmium Accumulation of Grape Berries in Cadmium-Contaminated Soil

To improve berry quality and reduce cadmium (Cd) accumulation in berries, ‘Summer Black’ grapevines were intercropped with the Cd hyperaccumulator Solanum nigrum in Cd-contaminated soil; the effects of this intercropping system on berry quality and Cd accumulation were investigated over a single season, and sampling was performed from the onset of berry coloration to ripening. Intercropping with S. nigrum increased single fruit weight as well as longitudinal and transverse diameters of berries, which were increased by 7.34%, 5.43%, and 6.25%, respectively, at maturity compared with monoculture. Intercropping with S. nigrum also increased total color difference, accelerated berry coloration, and enhanced the contents of total anthocyanins and other phenolic compounds in grape berries. Meanwhile, intercropping with S. nigrum increased the contents of soluble solids, total soluble sugars, and vitamin C, while reducing the titratable acidity and Cd. At maturity, intercropping with S. nigrum increased the contents of soluble solids and total soluble sugars by 7.88% and 3.60%, respectively, and reduced Cd content by 15.22% compared with monoculture. These preliminary results suggest that intercropping with S. nigrum can improve berry quality and reduce Cd accumulation in grapes grown in Cd-contaminated soil.