Anthocyanin biosynthesis, quality, and yield in purple sweet potatoes: responses to different potassium fertilizer.

Purple sweet potato (PSP) (Ipomoea batatas (L.) Lam) is a nutrient-rich "K-favoring" crop. The reasonable application of potassium is an important means of improving the quality and yield of PSP. We designed four different forms of potassium fertilizer treatments: K₂SO₄, KCl, KH₂PO₄, and K₂HPO₄, and used qRT-PCR and HPLC techniques to explore their differences in anthocyanin synthesis, accumulation, quality, and yield in PSP tubers. Our findings indicate that potassium fertilizer treatment enhances the expression of structural genes such as CHI (chalcone--flavonone isomerase), F3H (naringenin,2-oxogluturate 3-dioxygenase-like), F3‧H (flavonoid 3'-monooxygenase), ANS (leucoanthocyanidin dioxygenase-like), DFR (dihydroflavonol 4-reductase-like), and CHS (chalcone synthase), which encode key enzymes of the anthocyanin metabolism pathway. This is achieved by stimulating the high levels of expression of the transcription factor MYB, which controls anthocyanin accumulation. Consequently, this leads to increased activities of key anthocyanin biosynthetic enzymes Phenylalanine ammonia lyase (PAL, EC 4.3.1.5), chalcone isomerase (CHI, EC 5.5.1.6), dihydroflavonol 4-reductase (DFR, EC 1.1.1.219), and UDP-galactose flavonoid 3-O-galactosyltransferase (UFGT, EC 2.4.1.234), thereby promoting the synthesis and accumulation of anthocyanins within PSP tubers. This ultimately improves tuber quality and yield. Analysis conducted through hierarchical clustering heat map, principal component analysis (PCA), and comprehensive evaluation revealed that PSP exhibits varying sensitivities to different forms of potassium fertilizer, with KCl treatment significantly enhancing anthocyanin production efficiency. Our results will provide a theoretical basis and data support for the rational selection of potassium fertilizer types for actual PSP production.