Effects of water-saving ridging and film-covering cultivation methods on fruit anthocyanin biosynthesis in apple fruit

Water-saving cultivation methods have been used for apple planting. However, the effect and mechanism of these treatments on apple fruit coloration remain unclear. Here, fruit quality determination, comprehensive metabolome, and gene expression analysis were carried out to elucidate the mechanism. In our research, compared with flat planting (BB), ridging (BD), film-covering (DB), and ridging plus film-covering (DD) could significantly improve the content of anthocyanin. Moreover, significant up-regulation of various flavonoids was found in apple fruits under BD, DB, and DD treatments via metabolomics, and 16 were significantly correlated with pericarp anthocyanin content. Cyanidin-3-O-glucoside was the significantly changed type of anthocyanidin in our study. Furthermore, partial MBW (MYB-bHLH-WD40) complex genes and the key enzyme genes CHS, F3H, ANS, and UFGT in the biosynthetic pathway of anthocyanin were significantly up-regulated under BD, DB, and DD treatments. In summary, the increased red color of apple fruits under different ridging and film-covering methods is due to the accumulation of cyanidin in its pericarp, and the MBW complex may play essential roles in leading to the accumulation of anthocyanins through CHS, F3H, ANS, and UFGT genes. These results provide a theoretical basis for identifying the best water-saving cultivation method for apples.