Purple-fleshed Sweet Potato Research Articles

Characterization of volatile compounds profiles and identification of key volatile and odor-active compounds in 40 sweetpotato (Ipomoea Batatas L.) varieties

Sweetpotato with different flesh colors exhibits significant differences in flavor. Nevertheless, research on the identification of the key aromatic compounds in sweetpotato is scarce. Therefore, 40 primary sweetpotato varieties with different flesh colors were analyzed by HS-SPME/GC–MS to characterize the volatile compounds. A total of 121 volatile compounds were detected, with aldehydes, furans and terpenes being the most abundant components. Additionally, 35 compounds were identified as the key aromatic compounds by OAV > 1, of which 17 were found in all varieties and hence considered as the major components of sweetpotato aroma. Further analysis demonstrated that the yellow-fleshed sweetpotato had the strongest aroma, which was presumed due to the aldehydes like (E,E)-2,4-heptadienal, nonanal, (E,E)-2,4-decadienal,etc. that were produced during the degradation of unsaturated fatty acids. The unique sweety and floral aroma of orange-fleshed sweetpotato might be attributed to apocarotenoid volatiles (trans-beta-ionone, β-ionone, geranylacetone, etc.), the derivates of carotenoids. The purple-fleshed sweetpotato exhibited weak aroma with a significantly high terpenoids concentration. Overall, these findings may be the main reason for the different aromas of different colored sweetpotatoes and provides insights into sweetpotato aroma and a theoretical basis for improving sweetpotato aroma.

Effects of Steaming on Chemical Composition of Different Varieties of Purple-Fleshed Sweetpotato.

Purple-fleshed sweetpotatoes (PFSPs) are rich in anthocyanins and are one of the health foods of interest. In this study, the effects of steaming on the anthocyanin, starch, soluble sugar, volatile organic compounds (VOCs) and pasting properties of nine PFSPs from China were investigated. The anthocyanin content of raw PFSP ranged from 9 to 185 mg/100 g. The total starch content decreased and soluble sugar content increased in all purple potatoes after steaming. Among the nine PFSPs varieties, Guangshu20 showed the greatest decrease in starch content (30.61%) and the greatest increase in soluble sugar content (31.12%). The pasting properties affected the taste of the PFSPs, with Shuangpihuang having the lowest peak viscosity (720.33 cP) and Guangzishu12 having the highest peak viscosity (2501.67 cP). Correlation studies showed that the anthocyanin content and pasting properties were negatively correlated with most of the sensory indicators, whereas the soluble sugar content of steamed PFSPs was significantly positively correlated with sweetness. A total of 54 VOCs were identified in this study, and aldehydes and terpenoids were the major VOCs in PFSPs. This study provides a theoretical basis for the processing of different PFSP varieties.

Multi-trait selection for mean performance and stability in purple-fleshed sweet potato

Few purple-fleshed sweet potato (PFSP) cultivars are available for Brazilian growers, urging for the development of new and adapted cultivars. PFSP breeding programs should include multiple traits during the selection process to increase the chances of developing an adequate genotype, specially yield-related and quality-related traits. The objective was to select promising PFSP genotypes based on yield and tuberous-roots-related traits exploring genotype x environment interaction (GEI). Four experiments were carried out, in which 23 pre-selected PFSP genotypes were evaluated based on yield and quality traits, after screening among 2500 experimental genotypes. The first experiment adopted an augmented block design, with ‘Luiza’ interspersed as a control. From this first experiment, the 19 experimental genotypes with the best performance were selected for the following three experiments, which were conducted in a randomized block experimental design, with three replications each, including ‘Luiza’ as control. The best genotypes were selected in the first experiment using the multi-trait genotype-ideotype distance index (MGIDI). For the following experiments, the performance of the genotypes was assessed using deviance analysis, genotypic stability through weighted average of absolute scores (WAASB) index, and the multi-trait stability index (MTSI). In the first experiment, three factors were retained, being associated to commercial production of tuberous roots (‘K-104′, ‘K-25′ and ‘U1–29′), total production of tuberous roots (‘K-110′, ‘C-42′, ‘F-16′, and ‘U1–29′), and quality of tuberous roots (‘F-22′), respectively. Desired gains were observed for all traits. For the experiments II, III, and IV five factors were retained, being four related to quality of tuberous roots and one to yield components. The GEI was significant for yield-related traits and desired gains were observed for most traits. Due to high commercial tuberous root yield and low WAASB values, the genotypes ‘U1–29′, ‘K-98′, ‘F-22′, ‘K-57′, ‘C-36′, ‘U1–15′, ‘K-25′, and ‘U2–12′ were highly productive and stable. The genotypes selected by the MTSI index were ‘U1–15′, ‘U2–10′, ‘U1–29′, ‘K-98′, and ‘K-78′. The multi-trait selection enabled the identification of promising genotypes highlighting their strengths and weaknesses.

Proximate Composition, Health Benefits, and Food Applications in Bakery Products of Purple-Fleshed Sweet Potato (Ipomoea batatas L.) and Its By-Products: A Comprehensive Review.

Ipomoea batatas (L.) Lam is a dicotyledonous plant originally from tropical regions, with China and Spain acting as the main producers from outside and within the EU, respectively. The root, including only flesh, is the edible part, and the peel, leaves, stems, or shoots are considered by-products, which are generated due to being discarded in the field and during processing. Therefore, this study aimed to perform a comprehensive review of the nutritional value, phytochemical composition, and health-promoting activities of purple-fleshed sweet potato and its by-products, which lead to its potential applications in bakery products for the development of functional foods. The methodology is applied to the selected topic and is used to conduct the search, review abstracts and full texts, and discuss the results using different general databases. The studies suggested that purple-fleshed sweet potato parts are characterized by a high content of essential minerals and bioactive compounds, including anthocyanins belonging to the cyanidin or the peonidin type. The flesh and leaves are also high in phenolic compounds and carotenoids such as lutein and β-carotene. The high content of phenolic compounds and anthocyanins provides the purple-fleshed sweet potato with high antioxidant and anti-inflammatory power due to the modulation effect of the transcription factor Nrf2 and NF-kB translocation, which may lead to protection against hepatic and neurological disorders, among others. Furthermore, purple-fleshed sweet potato and its by-products can play a dual role in food applications due to its attractive color and wide range of biological activities which enhance its nutritional profile. As a result, it is essential to harness the potential of the purple-fleshed sweet potato and its by-products that are generated during its processing through an appropriate agro-industrial valorization system.

Yield performance and anthocyanin content of several purple-fleshed sweet potato clones grown in two locations in East Nusa Tenggara, Indonesia

Abstract. Arsa IGBA, Mau YS, Ndiwa ASS, Gandut YRY, Ishaq LF, Mahayasa INW. 2024. Yield performance and anthocyanin content of several purple-fleshed sweet potato clones grown in two locations in East Nusa Tenggara, Indonesia. Biodiversitas 25: 2276-2289. Several promising purple-fleshed sweet potato hybrid clones were identified to have high yield potential and, thus, can be evaluated for other superior traits and later be further processed for varietal registration and release. This study aimed to determine the tuber yield performance and anthocyanin content of several purple-fleshed sweet potato clones across two locations and to identify the best clones based on mean performance and stability. The study was conducted in the farmer's field in two different altitudes in West Timor, i.e., Mata Air Village, Kupang District (86 masl) and Netpala Village, Timor Tengah Selatan (TTS) District (1,090 masl) from April to September 2023. Six purple-fleshed sweet potato clones/varieties were assigned as treatment. The experiment was laid out in a complete block design in each location, and each treatment consisted of three replicates. Observed data included fresh storage root yield, number of storage roots per plant, storage root length, storage root tuber diameter, and tuber anthocyanin content. Observed data from the two trial locations were subjected to a combined ANOVA, cluster analysis, Principal Component Analysis (PCA), and GGE biplot analysis. The results showed that the genotype-by-location interaction effect was significant in all studied traits. Meanwhile, location or genotype significantly affected all traits except for the location, which did not significantly affect the anthocyanin content. The storage root yield ranged from ~19.95 t ha-1 to ~49.33 t ha-1, while the anthocyanin content ranged from ~28,64 mg/100 g to ~157,65 mg/100 g. The ranks of the tested genotypes based on the mean performance and stability are Undana UJ 7>Undana UJ 1>JPV-1>Antin 3>Undana UJ 6>Undana UJ 3 for storage root yield and JPV-1>Antin 3>Undana UJ 7>Undana UJ 6>Undana UJ 3>Undana UJ 1 for anthocyanin content.

Influence of Harvesting Stages on Phytonutrients and Antioxidant Properties of Leaves of Five Purple-Fleshed Sweet Potato (Ipomoea batatas) Genotypes.

Sweet potatoes (Ipomoea batatas) are highly profitable, contribute to food security, and their leaves rich in phytonutrients. This study examined the optimal leaf harvesting stage by harvesting newly formed leaves (leaves 1 to 5) to achieve the highest concentration of carotenoids, phenolic compounds, antioxidant properties and mineral content. Leaves of five purple-fleshed sweet potato genotypes '2019-11-2' and '2019-1-1', 'Purple-purple', and from the USA '08-21P' and '16-283P' were harvested based on tuber life cycle [vegetative 8 weeks after planting (VS-8WAP), tuber initiation (TIS-12WAP), and tuber maturation phases (TMS-16WAP)]. At the 8WAP stage, leaves of genotype '2019-11-2' had the highest concentrations of cyanidin-caffeoyl-sophoroside-glucoside (17.64 mg/kg), cyanidin-caffeoyl-feruloyl-sophoroside-glucoside (41.51 mg/kg), peonidin-caffeoyl-hydroxybenzoyl-sophoriside-glucoside (45.25 mg/kg), and peonidin caffeoyl-feruloyl-sophoriside-glucoside (24.47 mg/kg), as well as antioxidant scavenging activity. In contrast, 'Purple-purple' harvested at TIS-12WAP showed the highest concentration of caffeoylquinic acid derivatives. Zeaxanthin, lutein, all trans-β-carotene, and cis-β-carotene are the most abundant carotenoids in genotype '08-21P' at VS-8WAP. As a result, local genotypes '2019-11-2' harvested at 8WAP and 'Purple-purple' harvested at 12WAP are potential sources of anthocyanins and caffeoylquinic acid derivatives. Conversely, USA's genotype '08-21P' at the VS-8WAP stage is an excellent source of carotenoids. The leaves of USA's '08-21P' genotype and the local '2019-11-2' genotype at TMS-16WAP exhibited the highest content of Fe and Mn, respectively. The study identified the optimal leaf stage for consumption of leaves and for use as a functional ingredient.

Design, Optimization, and Modeling Study of Ultrasound-Assisted Extraction of Bioactive Compounds from Purple-Fleshed Sweet Potatoes.

This study focuses on optimizing the ultrasound-assisted extraction (UAE) of bioactive compounds from purple-fleshed sweet potatoes (PFSP) for potential use as natural colorants. Factors such as time, temperature, and solid-to-liquid ratio were varied using a Box-Behnken Design. The optimal conditions were determined as 75 min, 70 °C, and a 1:15 m/v solid-to-liquid ratio, resulting in 18.372 mg/100 g total anthocyanin (TA) and 151.160 mg GAE/100 g total phenolic content (TPC). The validation yielded 18.822 mg/100 g for total anthocyanin and 162.174 mg GAE/100 g for total phenolic content, showing a 7% difference from predictions. UAE significantly increased TA extraction by 81% and TPC by 93% compared with the conventional method, with a notable reduction in process time from 24 h to 75 min. Additionally, three kinetic models were tested to compare extraction mechanisms, confirming the efficiency of UAE for PFSP bioactive compound recovery. This study proposes the UAE technique as a highly effective means of extracting bioactive compounds from PFSP, offering promising applications across multiple industries.

Study of the drying process of the purple-fleshed sweet potato (Ipomoea batatas (L.) Lam) in spouted bed

This study aimed to study the drying of purple-fleshed sweet potato (PFSP) in a spouted bed and define the best drying conditions, producing flour and analyzing it using physical, chemical, and technological analyses. The best condition of the drying process was a feed load of 300 g PFSP and a drying temperature of 70°C. Flour with a moisture content of 3.95% and a low water activity was obtained, which had high carbohydrates, low fats, and a considerable amount of ashes and proteins. The sweet potato flour presented good solubility in water and milk and good absorption in water, oil, and milk, forming gel but not foam. PFSP flour is a good alternative for the use of its residues, avoiding the waste of raw material that has no commercial value and can be useful to incorporate in products such as porridges, creams, and sauces.

IbMYC2 Contributes to Salt and Drought Stress Tolerance via Modulating Anthocyanin Accumulation and ROS-Scavenging System in Sweet Potato.

Basic helix-loop-helix (bHLH) transcription factors extensively affect various physiological processes in plant metabolism, growth, and abiotic stress. However, the regulation mechanism of bHLH transcription factors in balancing anthocyanin biosynthesis and abiotic stress in sweet potato (Ipomoea batata (L.) Lam.) remains unclear. Previously, transcriptome analysis revealed the genes that were differentially expressed among the purple-fleshed sweet potato cultivar 'Jingshu 6' and its anthocyanin-rich mutant 'JS6-5'. Here, we selected one of these potential genes, IbMYC2, which belongs to the bHLH transcription factor family, for subsequent analyses. The expression of IbMYC2 in the JS6-5 storage roots is almost four-fold higher than Jingshu 6 and significantly induced by hydrogen peroxide (H2O2), methyl jasmonate (MeJA), NaCl, and polyethylene glycol (PEG)6000. Overexpression of IbMYC2 significantly enhances anthocyanin production and exhibits a certain antioxidant capacity, thereby improving salt and drought tolerance. In contrast, reducing IbMYC2 expression increases its susceptibility. Our data showed that IbMYC2 could elevate the expression of anthocyanin synthesis pathway genes by binding to IbCHI and IbDFR promoters. Additionally, overexpressing IbMYC2 activates genes encoding reactive oxygen species (ROS)-scavenging and proline synthesis enzymes under salt and drought conditions. Taken together, these results demonstrate that the IbMYC2 gene exercises a significant impact on crop quality and stress resistance.

Different regions and environments have critical roles on yield, main quality and industrialization of an industrial purple-fleshed sweetpotato (Ipomoea batatas L. (Lam.)) “Xuzishu8”

Purple-fleshed sweetpotato (PFSP) (Ipomoea batatas (L.) Lam), whose flesh is purple to dark purple, is a special variety type of sweetpotato, which has the characteristics of food crop, industrial crop and medicinal crop. The storage root (SR) of PFSP is rich in anthocyanins, starch, protein, soluble sugar, mineral elements, polyphenol, dietary fiber and so on, which has balanced and comprehensive nutritional value. And in recent years, its unique nutritional elements are increasingly known for their health functions. At present, there is no article on the characteristics and quality analysis of industrial xz8 variety. To explore the influence of different environments on the processing quality of xz8, we selected nine regions (Xuzhou, Jiawang, Pizhou, Xinyi, Peixian, Sihong, Yanchen, Xiangyang and Tianshui) to measure its yield and quality changes. The data demonstrated that xz8 has a very consistent high yield performance. In Tianshui, the anthocyanins, protein and minerals contents were significantly higher and yield also above average. Moreover, the variety with the lowest starch content exhibited the best taste. On the basis of the above results, it suggested that quite practicable to promote xz8 cultivation and suitable for processing in these areas. Thus, our present findings improve our understanding of xz8 variety and provide the basis for the industrial production of PFSP with strong prospects for success.

Aplicação de pó liofilizado de batata-doce de polpa roxa como ingrediente multifuncional em iogurte tipo Grego

ABSTRACT: Purple-fleshed sweet potato is a tuber rich in anthocyanins, which are phenolic pigments that confer color and present bioactive capacity. Moreover, its incorporation into dairy products can bring technological and functional benefits. Thus, this article evaluated the impact of the addition of lyophilized purple-fleshed sweet potato powder- LP (0% - Control, 2%, and 4%) on the physical, chemical, and technological characteristics of Greek yogurt. LP showed in vitro antioxidant and bioactive capacity by DPPH (20.64 ± 1.61 μmol TE g-1), FRAP (112.93 ± 4.38 μmol TE g-1), total phenolic content (103.66 ± 3.35 mg GAE g-1), and total anthocyanin content (51.10 ± 1.87 mg cyanidin 3-glucoside 100 g-1). Additionally, the assays demonstrated that the LP has 16.82 ± 0.63% of resistant starch. The fortification of Greek yogurt with LP reduced the syneresis, indicating that LP increased the water retention capacity. LP also inhibited the post-acidification process, increasing apparent viscosity, hardness, and gumminess, and promoting a stable pink coloration throughout the storage (P < 0.05). At the 4% level, the yogurt was firmer and showed greater chewiness, which is highly desirable for Greek yogurt. Therefore, the results suggested that lyophilized purple-fleshed sweet potato powder is a potential multifunctional natural ingredient.

The antioxidant property of home-cooked orange-fleshed and purple-fleshed sweet potato

One property inherent to sweet potato because of the presence of phytochemicas is its antioxidant property. As proven by researches, antioxidant property is affected by cooking. This study determined the effect of four home cooking methods: steaming, boiling, baking, and frying on the antioxidant property of orange-fleshed and purple-fleshed sweet potatoes. The antioxidant property of raw and cooked we measured samples for their Total Phenolic Content (TPC) using Folin-Ciocalteu assay and their antioxidant activity based on the EC50 value of the DPPH assay. The TPC of orange-fleshed sweet potato was significantly increased by boiling and steaming. Baking and frying decreased the TPC of the orange-fleshed. The TPC of the purple-fleshed variety was not affected by the cooking methods but compared to the orange-fleshed, the TPC of the purple variety is significantly higher in both the raw and cooked forms. Based on the result of the DPPH assay, cooking significantly affected the antioxidant activity of both varieties (p<0.05). Steaming gave the highest increase for both varieties. Boiling caused the lowest increase for the orange-fleshed but didn’t give a significant effect on the antioxidant activity of the purple-fleshed. Comparing the two varieties, the raw and cooked purple-fleshed sweet potato have better antioxidant activity based on DPPH assay except for the steamed samples wherein the antioxidant activity of steamed orange-fleshed sweet potato is significantly higher (p<0.05) than that of the purple variety. It can be concluded that steaming is the best cooking method for the two sweet potato varieties. Keywords: Anti-oxidant, cooking, sweet potato, total phenolic content.

Effect of cooking methods on metabolites of deep purple-fleshed sweetpotato.

The effects of different cooking methods on purple-fleshed sweetpotato (PFSP) metabolites were systematically explored, containing the changes of starch, soluble sugar, volatile organic compounds and non-target metabolites after steaming, boiling and baking. Compared to raw samples, the steamed samples showed the greatest changes in starch (degraded from 53.01% to 39.5%) and soluble sugar content (increased from 11.82% to 29.08%), while the baked samples showed insignificant changes in starch (51.06%). In total, 64 volatile organic compounds were identified in PFSP, with aldehydes decreasing and terpenes increasing after cooking. However, most of them were low in content and contributed weak aroma for PFSP. More importantly, 871 non-volatile metabolites were detected in PFSP, and 83.5% of which were well-preserved after cooking, while most of the changes were concentrated in phenylpropanoids, amino acids and carbohydrates. This study enriches the understanding of quality changes after PFSP cooking and helps consumers choose the right cooking method.

Yeast One-Hybrid Screening for Regulators of IbWD40 in Purple-Fleshed Sweet Potato (Ipomoea batatas [L] Lam.).

The transcription regulator IbWD40 is known to be involved in anthocyanin biosynthesis in purple-flesh sweet potato (Ipomoea batatas). However, little is known about the upstream transcription regulators on the promoter of IbWD40. Yeast one-hybrid screening was performed on the storage roots of purple-fleshed sweet potato to identity upstream transcription regulators on the promoter of IbWD40. Luciferase reporter assays and Yeast one-hybrid assays were used to verify these upstream binding proteins interacted with the promoter. Real-time PCR was used to analyze the gene expression of upstream transcription regulators, transcription factors, and structural genes involved in anthocyanin biosynthesis in different root stages of purple-fleshed and white-fleshed sweet potato. IbERF1, IbERF10, IbEBF2, IbPDC, IbPGP19, IbUR5GT, IbDRM, IbPPA and IbERF73 were identified as candidate binding proteins for the promoter of IbWD40. Furthermore, IbERF1, IbERF10 and IbERF73 were identified as upstream transcription regulators on the promoter of IbWD40 involved in anthocyanin biosynthesis. IbERF1, IbERF10 and IbERF73 were identified as transcription regulators on the promoter of IbWD40, which is involved in the regulation of anthocyanin biosynthesis in purple-fleshed sweet potato.

Suitability of Purple-Fleshed Sweet Potato Clones for Ingredients of Chinese Buns (Buns)

A form of tuber known as a sweet potato includes bioactive substances in addition to carbs, vitamins, minerals, and dietary fiber. Purple-fleshed sweet potatoes have been heavily marketed as functional foods due to their anthocyanin content. Different textures can be found in the three types and two clones of sweet potatoes used as a base for buns. In comparison to the other 3 kinds, the textures of RIS 10043-02 and MSU 10003-07 were harder, more cohesive, and chewier. The high values of hardness (5.78N), springiness (73.77%), and cohesiveness contributed to the high chewiness value of the buns manufactured from Antin 2 (257.52N) (0.63N). The L*, a*, and b* values of the generated buns decrease with increasing anthocyanin concentration in the raw material, and the panelists’ preferences for color also increase. For the four sensory evaluation criteria of the buns manufactured from five different sweet potato clones, the scores varied from 3.64 to 4.08. It seems that the MSU 10003-07 clone, followed by Antin 2 and Antin 3, was the panelists’ favorite bun.

Comparative elucidation on the phenolic fingerprint, sugars and antioxidant activity of white, orange and purple-fleshed sweet potatoes (Ipomoea batatas L.) as affected by different cooking methods

In this study, three cooking methods (baking, boiling, sous vide (SV)) were applied to Turkish sweet potatoes with three flesh colors (white, orange, purple) to examine the effects of the product color and cooking methods on the total phenolics, antioxidant activity, sugars, phenolic acids, and anthocyanins. LC-MS-MS was employed in the characterization of these compounds. It was observed that the product color and cooking method significantly affected the concentrations of bioactive compounds like polyphenols. Both the highest total phenolic content (11.36 mg/g) and antioxidant activity (DPPH (50.3 μM TE/g) and ABTS (63.53 μM TE/g)) were determined in the purple sweet potato cooked with the SV method. 10 phenolic acids were quantified in all samples which were in the highest amounts in the orange colored samples followed by the purple samples. Baking resulted in the highest total phenolic acids in all samples. 13 anthocyanins were detected in the purple-colored samples, while the SV cooking best preserved the anthocyanins. In sum, purple sweet potatoes cooked by SV are recommended for higher phenolic contents, antioxidant capacity and anthocyanins.

Yeast One-Hybrid Screening to Identify Transcription Factors for IbMYB1-4 in the Purple-Fleshed Sweet Potato (Ipomoea batatas [L.] Lam.).

IbMYB1 is a transcription factor involved in the biosynthesis of anthocyanin in the purple-fleshed sweet potato. So far, few studies have investigated transcription factors that are upstream of the promoter IbMYB1-4. In this study, a yeast one-hybrid screening aimed at identifying transcription factors upstream of the promoter IbMYB1-4 was performed in the storage roots of the purple-fleshed sweet potato, and IbPDC, IbERF1, and IbPGP19 were identified as upstream binding proteins for the promoter IbMYB1-4. A dual luciferase reporter assay, and yeast one-hybrid assays, were employed to confirm the interaction of these binding proteins with promoters. IbERF1 was found to be an upstream transcription factor for the promoter IbMYB1, and is implicated in the biosynthesis of anthocyanin in the purple-fleshed sweet potato. IbERF1 plays a major role in the biosynthesis of anthocyanin in the purple-fleshed sweet potato.

Polyploid GWAS reveals the basis of molecular marker development for complex breeding traits including starch content in the storage roots of sweet potato.

Given the importance of prioritizing genome-based breeding of sweet potato to enable the promotion of food and nutritional security for future human societies, here, we aimed to dissect the genetic basis of storage root starch content (SC) when associated with a complex set of breeding traits including dry matter (DM) rate, storage root fresh weight (SRFW), and anthocyanin (AN) content in a mapping population containing purple-fleshed sweet potato. A polyploid genome-wide association study (GWAS) was extensively exploited using 90,222 single-nucleotide polymorphisms (SNPs) obtained from a bi-parental 204 F1 population between 'Konaishin' (having high SC but no AN) and 'Akemurasaki' (having high AN content but moderate SC). Through the comparison of polyploid GWAS on the whole set of the 204 F1, 93 high-AN-containing F1, and 111 low-AN-containing F1 populations, a total of two (consists of six SNPs), two (14 SNPs), four (eight SNPs), and nine (214 SNPs) significantly associated signals were identified for the variations of SC, DM, SRFW, and the relative AN content, respectively. Of them, a novel signal associated with SC, which was most consistent in 2019 and 2020 in both the 204 F1 and 111 low-AN-containing F1 populations, was identified in homologous group 15. The five SNP markers associated with homologous group 15 could affect SC improvement with a degree of positive effect (~4.33) and screen high-starch-containing lines with higher efficiency (~68%). In a database search of 62 genes involved in starch metabolism, five genes including enzyme genes granule-bound starch synthase I (IbGBSSI), α-amylase 1D, α-amylase 1E, and α-amylase 3, and one transporter gene ATP/ADP-transporter were located on homologous group 15. In an extensive qRT-PCR of these genes using the storage roots harvested at 2, 3, and 4 months after field transplantation in 2022, IbGBSSI, which encodes the starch synthase isozyme that catalyzes the biosynthesis of amylose molecule, was most consistently elevated during starch accumulation in sweet potato. These results would enhance our understanding of the underlying genetic basis of a complex set of breeding traits in the starchy roots of sweet potato, and the molecular information, particularly for SC, would be a potential platform for molecular marker development for this trait.

Effect of Growth Stages on Anthocyanins and Polyphenols in the Root System of Sweet Potato.

The storage roots of purple-fleshed sweet potato contain a variety of anthocyanins and polyphenols. Little is known about changes in the total content and composition of anthocyanins and polyphenols in the early growth stages of the root system. In this study, we investigated the changes in anthocyanins and polyphenols in the root system of purple-fleshed sweet potato cultivars at 15, 30, 45, and 60 days after transplant (DAT). Unexpectedly, the highest percentage of acylated anthocyanins in three purple-fleshed cultivars among all growth stages was at 15 DAT. On the other hand, the total polyphenol content in the early growth stages of the root system increased rapidly toward 45 DAT, just before the beginning of storage root enlargement, and then decreased rapidly as the storage roots began to enlarge. These data indicate that the early growth stage of the root system is a critical time. This timing may present a strategy to maximize the accumulation of polyphenols with high antioxidant activity, as well as acylated anthocyanins, to protect against abiotic and biotic stresses.

Yeast One-Hybrid Screening for Transcription Factors of IbbHLH2 in Purple-Fleshed Sweet Potato.

The transcription factor IbbHLH2 has been identified as involved in the biosynthesis of anthocyanins in purple-flesh sweet potatoes. However, little is known about the upstream transcription regulators of the promoter of IbbHLH2 in terms of their involvement in anthocyanin biosynthesis. For this study, the transcription regulators of the promoter of IbbHLH2 were screened via yeast one-hybrid assays in purple-fleshed sweet potato storage roots. Seven proteins, namely IbERF1, IbERF10, IbEBF2, IbPDC, IbPGP19, IbUR5GT, and IbDRM, were screened as upstream binding proteins of the promoter of IbbHLH2. The interactions between the promoter and these upstream binding proteins were verified using dual-luciferase reporter and yeast two-hybrid assays. Furthermore, the gene expression levels of transcription regulators, transcription factors, and structural genes involved in the anthocyanin biosynthesis of different root stages of purple and white-fleshed sweet potatoes were analyzed via real-time PCR. The obtained results indicate that IbERF1 and IbERF10 are key transcription regulators of the promoter of IbbHLH2 and are involved in anthocyanin biosynthesis in purple-fleshed sweet potatoes.