In the relay intercropping system of maize/sweet potato, the growth of the sweet potatoes is seriously limited by weak light stress in the early stage due to shade from maize plants. However, it is not clear how the weak light affects sweet potatoes and causes tuberous root loss. By setting two light intensity levels (weak light = 30% transmittance of normal light), this study evaluated the responses of two sweet potato cultivars with different tolerances to weak light in a field-based experiment and examined the divergence of gene expression related to light and photosynthesis in a pot-based experiment. The results showed that under weak light, the anatomic structure of functional leaves changed, and the leaf thickness decreased by 39.98% and 17.32% for Yuhongxinshu-4 and Wanshu-7, respectively. The ratio of S/R increased, and root length, root superficial area, and root volume all decreased. The photosynthetic enzyme rubisco was weakened, and the net photosynthetic rate (Pn) declined as well. The level of gene expression in Wanshu-7 was higher than that of Yuhongxinshu-4. The KEGG analysis showed that differentially expressed genes from the two cultivars under weak-light stress used the same enrichment pathway, mainly via glutathione metabolism and flavonoid biosynthesis. After full light levels were restored, the differentially expressed genes were all enriched in pathways such as photosynthesis, photosynthetic pigment synthesis, and carbon metabolism. These findings indicated that weak light changed the plant morphology, photosynthetic physiology and gene expression levels of sweet potatoes, which eventually caused losses in the tuberous root yield. The more light-sensitive cultivar (Wanshu-7) had stronger reactions to weak light. This study provides a theoretical basis and strategy for breeding low-light-tolerant varieties and improving relay intercropping production in sweet potatoes.

Seedling cultivation is the foremost part of sweet potato (Ipomoea batatas L. Lam) production. It is of great significance to reveal the effects of different temperatures on the nutrients of sweet potato storage roots and their relationship with the sprouting quality and to explore the appropriate temperature management for seedlings. In this study, we simulated the temperature differences during the sprouting and seedling period in the summer growing area of sweet potato in the Yangtze River Basin and set three constant temperatures (17 °C, 22 °C and 27 °C) and corresponding three-day/night variable temperatures (21/13 °C, 26/18 °C and 31/23 °C). Thus, we investigated the nutrients, amylase activity, endogenous hormones, and sprouting characteristics of storage roots during the sprouting and seedling period of three sweet potato cultivars with different starch contents. The results showed that with the increase in temperature, the starch and soluble protein (SP) contents in sweet potato storage roots decreased, and the total soluble sugar (TSS), reducing sugar (RS), and sucrose contents increased during the sprouting and seedling period. The amylase activity enhanced; the hormone (IAA) content increased, and the abscisic acid (ABA) content decreased, which, in turn, led to an earlier time of sprouting time (ST), emergence stage (ES), and full stand of seedling stage (FSS). Comparing at the same average temperature, the physiological metabolism and sprouting time and quality of sweet potato were better at variable temperatures than at constant temperatures, in which 31/23 °C was more conducive to the advancement of the ST of sweet potato. At the same time, it was more conducive to the improvement of the seedling cutting amount (SCA), seedling weight (SDW), and seedling number (SDN). The sprouting time and quality of different sweet potato cultivars differed, and cultivars with higher starch content were superior to those with lower starch content. The sucrose and starch contents at different sprouting stages of storage roots can be used as important indicators of the quality of sweet potato seedlings.

Sweet potato [Ipomoea batatas (L.) Lam.] is an important food and industrial crop. Its storage root is rich in starch, which is present in the form of granules and represents the principal storage carbohydrate in plants. Starch content is an important trait of sweet potato controlling the quality and yield of industrial products. Vacuolar invertase encoding gene Ibβfruct2 was supposed to be a key regulator of starch content in sweet potato, but its function and regulation were unclear. In this study, three Ibβfruct2 gene members were detected. Their promoters displayed differences in sequence, activity, and cis-regulatory elements and might interact with different transcription factors, indicating that the three Ibβfruct2 family members are governed by different regulatory mechanisms at the transcription level. Among them, we found that only Ibβfruct2-1 show a high expression level and promoter activity, and encodes a protein with invertase activity, and the conserved domains and three conserved motifs NDPNG, RDP, and WEC are critical to this activity. Only two and six amino acid residue variations were detected in sequences of proteins encoded by Ibβfruct2-2 and Ibβfruct2-3, respectively, compared with Ibβfruct2-1; although not within key motifs, these variations affected protein structure and affinities for the catalytic substrate, resulting in functional deficiency and low activity. Heterologous expression of Ibβfruct2-1 in Arabidopsis decreased starch content but increased glucose content in leaves, indicating Ibβfruct2-1 was a negative regulator of starch content. These findings represent an important advance in understanding the regulatory and functional divergence among duplicated genes in sweet potato, and provide critical information for functional studies and utilization of these genes in genetic improvement.

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.

To analyze the impact of intercropping, maize straw returning, plastic mulching, and different configurations on potato quality in southwest China, a three-factor split-plot field experiment was designed to investigate the effects of crop management practices on the starch physicochemical properties and textural properties for two potato cultivars (Mira and Huayu-5). Results indicated that intercropping, maize straw returning, and plastic mulching reduced tuber dry matter, total starch, and amylose content, thereby decreasing the hardness of steamed tubers. Plastic mulching and maize straw returning increased starch granule size, promoted thermal properties, improved pasting properties, and increased adhesiveness and cohesiveness. The potato/maize relay intercropping increased the thermal properties, pasting viscosities, adhesiveness, and cohesiveness, with stronger effects observed in Mira compared to Huayu-5. The combination of intercropping with plastic film mulching and straw returning reduces tuber hardness while enhancing tuber adhesiveness and cohesiveness.

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.