Knowledge of genetic variations can provide clues into the molecular mechanisms regulating key crop traits. Sweet potato (Ipomoea batatas (L.) Lam.) is an important starch-producing crop, but little is known about the genetic variations in starch biosynthesis and sucrose metabolism genes. Here, we used high-throughput sequencing of pooled amplicons of target genes to identify sequence variations in 20 genes encoding key enzymes involved in starch biosynthesis and sucrose metabolism in 507 sweet potato germplasms. After filtering potential variations between gene copies within the genome, we identified 622 potential allelic single nucleotide polymorphisms (SNPs) and 85 insertions/deletions (InDels), including 50 non-synonymous SNPs (nsSNPs) and 12 frameshift InDels. Three nsSNPs were confirmed to be present in eight sweet potato varieties with various starch properties using cleaved amplified polymorphic sequence (CAPS) markers. Gene copy with loss of the fifth intron was detected in IbAGPb3 genes, and loss of multiple introns were observed in IbGBSS1-1 genes and various among germplasms based on intron length polymorphism (ILP) markers. Thus, we identified sequence variations between germplasms in 20 genes involved in starch biosynthesis and sucrose metabolism, and demonstrated the diversity in intron-loss alleles among sweet potato germplasms. These findings provide critical genetic information and useful molecular markers for revealing regulatory mechanism of starch properties.

Biochar and organic fertilizers are recommended for sustaining crop yield and sustainable agricultural development. However, the mechanisms of their combined application on the nutritional, flavor and eating quality and their optimal ratio remain unclear in sweet potatoes. Therefore, this field experiment employed four fertilization treatments: inorganic compound fertilizer (CF), organic fertilizer (OF), and biochar-based organic fertilizer containing 15% biochar (BOF15) or 30% biochar (BOF30). The results revealed that the OF, BOF15, and BOF30 treatments significantly ameliorated soil physical properties, elevated soil pH values and available nutrient contents compared with CF. They also increased sweet potato yield, regulated sucrose-metabolizing enzyme, and enhanced quality. Among them, the BOF15 treatment exhibited the most significant improvement. Compared with CF, BOF15 treatment increased the contents of starch, total soluble sugar, sucrose, and β-carotene by 23.16–31.82%. It also optimized texture by reducing hardness and chewiness while increasing springiness, elevated key volatile compounds (terpene and aldehyde), and received the highest sensory scores for mealiness, aroma, and sweetness. In conclusion, biochar combined with organic fertilizer synergistically improves soil properties and enhances sweet potato yield and quality, with BOF15 being the optimal treatment. This study provides support for optimizing fertilization strategies in high-quality sweet potato production.

Sustainable nutrient management in sweet potato requires matching fertilizer inputs with site-specific soil nutrient supply while maintaining productivity and processing quality. This study characterized site-specific NPK responses and identified fertilization regimes coordinating yield and starch content under contrasting soil nutrient backgrounds. To address this objective, a three-factor, five-level quadratic orthogonal rotatable composite design comprising 23 N–P–K experimental runs was conducted independently at two sites in Beibei and Youyang, Chongqing, China, using the starch-type sweet potato cultivar ‘Yushu 17’. The two sites differed markedly in initial soil nutrient status. Photosynthetic characteristics, nutrient accumulation, dry matter production and partitioning, fresh storage-root yield, and quality were measured. Quadratic regression models combined with a desirability function were used to characterize site-specific nutrient responses and optimize yield and starch content. The effects of N, P, and K differed markedly between sites. In Beibei, fresh storage-root yield was mainly affected by the linear effect of N, while P and K also had positive effects, and the P × K interaction was significant. In Youyang, yield was primarily regulated by the linear effect of K and showed a significant negative quadratic response to P. Photosynthetic performance; N, P, and K accumulation; total dry matter accumulation (TDMA); and root-to-top ratio (R/T) responded mainly to N in Beibei but were more sensitive to K in Youyang. Fresh storage-root yield was positively correlated with net photosynthetic rate, stomatal conductance, transpiration rate, chlorophyll content, leaf area index, nutrient accumulation, R/T, and TDMA, but negatively correlated with starch content, indicating a yield–starch trade-off. When yield was prioritized while starch content was maintained, the optimal N–P₂O₅–K₂O rates were 155.02–116.42–300.00 kg·ha⁻¹ in Beibei, predicting 42,800 kg·ha⁻¹ yield and 20.09% starch, and 153.34–75.00–282.90 kg·ha⁻¹ in Youyang, predicting 35,850 kg·ha⁻¹ yield and 24.92% starch. These site-specific optima provide a quantitative basis for more targeted fertilizer allocation while coordinating yield and starch content, thereby supporting sustainable nutrient management of starch-type sweet potato.