Sweetpotato Storage Roots Research Articles

Transcriptomic analyses of carvone inhibited sprouting in sweet potato (Ipomoea batatas (L.) Lam cv ‘Yan 25′) storage roots

Sprouting is an important postharvest problem in the transport and storage of sweet potato. This study investigated the effect of carvone fumigation on the development of sprouts in ‘Yan 25′ sweet potato storage roots and sprouts. The results showed that visible buds could be observed in untreated root after 4 d at 30 ℃, however no buds were found on carvone treated sweet potato, even after 14 d storage. The levels of β-amylase activity were lower in the carvone treated roots and were associated with higher starch content. Treatment of sweet potato sprouts with carvone severely damaged the sprouts after 24 h and finally turned black after 72 h treatment, resulting in higher MDA content. The transcriptomic analyses showed that the manipulation of auxin distribution, cytokinin metabolism, cell wall synthesis and cell wall loosening processes were associated with carvone inhibition of sprouting in sweet potato roots. Further transcriptomic analyses on sweet potato sprouts revealed a similar transcription profile except that the gibberellin metabolism was also affected in the sprouts by carvone treatment. The up-regulation of apoptosis related genes in carvone treated sprouts, included UDP-D-apiose/UDP-D-xylose synthase (UAXS), ACC oxidase (ACO), tonoplast intrinsic protein (TIP), respiratory burst oxidase (RBOH), senescence associated gene (SAG) which were correlated with the lethal effect of carvone on the sprout. Two conceptual models elucidating the molecular mechanism of carvone inhibited sprouting in sweet potato are proposed. The further elucidation of this mechanism will potentially lead to a theory to optimize the method in sprouting inhibition of sweet potato.

The Application of Nitrogen Source in Regulating Lignin Biosynthesis, Storage Root Development and Yield of Sweet Potato

The understanding of the effects of nitrogen sources on lignin synthesis in sweet potato during storage root formation is limited. In this study, we investigated the effects of different nitrogen source on sweet potato storage root formation and development, as well as lignin synthesis in potential storage roots. The sweet potato cultivars Shangshu 19 and Jixu 23 were used in field experiments in 2019 and 2020. Three treatments were tested: (a) no nitrogen fertilizer application (control); (b) 60 kg hm−2 ammonium nitrogen; and (c) 60 kg hm−2 amide nitrogen. The results indicate that during sweet potato storage root formation, ammonium nitrogen significantly enhanced root activity compared to that of the control. The ammonium nitrogen treatment promoted IbEXP1 and inhibited Ibkn1 and Ibkn2 expression during the early stages of storage root formation, then increased gibberellic acid and decreased zeatin riboside content, enhanced phenylalanine ammonia lyase and peroxidase activities, and promoted lignin synthesis in potential storage roots. The opposite effects of ammonium nitrogen treatment on gene expression, hormone contents, and enzyme activity were observed in the late stages of storage root formation. Relative to the control, the ammonium nitrogen treatment significantly increased the number of storage roots during canopy closure. The ammonium nitrogen treatment produced the highest storage root yield and number of storage roots per plant. These results indicated that the ammonium nitrogen can inhibit root lignin synthesis, then promote storage root formation and increase the yield of sweet potato.

Household Processing Methods and Their Impact on Bioactive Compounds and Antioxidant Activities of Sweetpotato Genotypes of Varying Storage Root Flesh Colours.

Sweetpotato storage roots, peeled and unpeeled, of varying flesh colours (white, cream, yellow, pale orange, deep orange, and purple) were spectrophotometrically evaluated for their bioactive compounds and antioxidant activities. Roots were boiled, steamed, baked, fried, or microwaved. The unpeeled roots had relatively higher (p < 0.001) bioactive compounds and antioxidant activities than the peeled ones. All cooking methods increased phenolic compounds, flavonoids, and tannins in all genotypes. Significant losses of total carotenoids occurred with all cooking methods (ranging from 24.18 to 172.76 µg/g in raw sweetpotatoes vs. 10.06 to 118.17 µg/g in cooked ones; p < 0.001), except the deep-orange-fleshed genotype, in which frying slightly increased carotenoids from 269.81 to 304.74 µg/g. Microwaving retained 69% vitamin C in the cream-fleshed one, the highest among the cooking methods. Anthocyanins decreased with baking and frying in the purple-fleshed one but increased with other methods; microwaving being highest at 13.9% (17.43 mg/g). While the 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid antioxidant activity decreased with all cooking techniques in some genotypes, ferricyanide-reducing antioxidant potential increased. The retention of bioactive compounds in sweetpotato storage roots depends on the processing method. Thus, to obtain the most health benefits, consumers should use different cooking methods but retain the peels.

Sweet Potato (Ipomoea batatas L.) Response to Incremental Application Rates of Potassium Fertilizer in Mississippi

Potassium (K) fertilization is a crucial component of sweet potato (Ipomoea batatas L.) production. The basis for K fertilizer recommendations in sweet potato production varies greatly and relies on studies conducted in the late 1950s–1970s. Changes in agronomic practices and increasing costs emphasize the need to revisit fertilizer recommendations. A field experiment was conducted to investigate the impact of seven different K fertilizer (K2O) application rates on sweet potato storage root yield, tissue K concentration, and economic implications in Mississippi. Incremental applications of K fertilizer did not influence sweet potato yield at any grade. Leaf tissue K concentration exhibited a quadratic trend in response to K fertilizer rate, with maximum leaf and root K content achieved at 269 and 404 kg·ha−1 K2O, respectively. Both the predicted K application rate for maximum yield and maximum profitability were the same, at 174 kg·ha−1 K2O. Accordingly, comparable sweet potato yields were achieved while applying substantially less fertilizer than the recommended rate. Further research is warranted to examine the impacts of only potassium fertilizer applications on soil characteristics and temporal trends in sweet potato potassium uptake, as well as refine fertilization recommendations for sweet potato production.

Changes in carbon allocation and subplastidal amyloplast structures of specialised Ipomoea batatas (sweet potato) storage root phenotypes

Vitamin A deficiency (VAD) in Low and Medium Income countries remains a major health concern. Ipomoea batatas, orange sweet potato (OSP), is one of the biofortification solutions being implemented by the World Health Organisation (WHO) to combat VAD. However, high provitamin A (β-carotene) content has been associated with a reduction in dry matter, reducing calorific value and having adverse effects on consumer traits. Both starch and carotenoid formation are located in amyloplasts and could potentially compete for the same precursors. Hence, five different sweet potato storage root phenotypes were characterized through spatial metabolomics and proteomics at the sub-plastidal level. The metabolite data suggested an indirect correlation of starch and carotenoids through the TCA cycle and pentose phosphate pathway. Furthermore, a change in lipid composition was observed to accommodate the storage of carotenoids in the hydrophilic environment of the amyloplast. The data suggests an alteration of cellular ultra-structures and perturbation of metabolism in high β-carotene producing sweet potato roots. This corroborates with previous gene expression analysis through biochemical analysis of sweet potato root tissue.

Isolation and characterization of IbAE7-like 1 gene encoding the cytosolic iron-sulfur cluster assembly pathway in response to skinning injury in sweetpotato

Abstract. Effendy J. 2022. Isolation and characterization of IbAE7-like 1 gene encoding the cytosolic iron-sulfur cluster assembly pathway in response to skinning injury in sweetpotato. Biodiversitas 23: 4223-4233. Skinning injury is a major constrain in postharvest loss in sweetpotato due to the loss of skin from the surface of the roots. ASYMMETRIC LEAVES1/2 ENHANCER7(AE7) is an important cytosolic iron-sulfur (Fe-S) protein assembly (CIA) pathway. A partial cDNAIbI51 encoding AE7-like 1 was isolated from a skinning injury cDNA library to evaluate its potential role in response to skinning injury. The open reading frameof IbAE7-like 1 consisted of 324 nucleotides and the deduced polypeptide sequences consistedof 108 amino acids with missing 46 amino acid residues at 5? end. The amino acid sequence ofIbAE7-like 1 shared 100% identity toAE7-like 1 previously identified in Ipomoea triloba and Ipomoea nil and 89.91-100% identity from other plants species. The findings indicated that AE7-like 1 was highly conserved in Ipomoea sp. In addition to similarity to AE7-like 1, IbAE7-like 1 also showed similarities to MIP18 (89.91-93.52%); DUF59 (91.67%); FAM96B (90.74%); and proteins with unknown function (90.74-91.67%). IbAE7-like 1 mRNA transcripts showed transient expression in response to skinning injury. The phylogenetic analysis classified IbAE7-like 1 into three main classes. This study revealed IbAE7-like 1 may play a key role in plant defense and wound repair to prevent DNA damage due to skinning injuryin storage roots of sweetpotato.

Optimum Nitrogen Application Promotes Sweetpotato Storage Root Initiation

Storage root formation of sweetpotato (Ipomoea batatas (L.) Lam) is a complex developmental process relating to the activity of cambium. Little information is available on the relationship between nitrogen (N) application levels and the initiation and development of sweetpotato storage roots (SRs). This study aims to examine how N application rates promoted/inhibited the formation and development of storage roots (SRs) for sweetpotato cultivar ‘Orleans’ during the first 8 weeks after planting. Cuttings were grown in coarse river sand culture supplied with modified Hoagland nutrient solution at four different rates (0 (N0), 50 (N50), 100 (N100) or 200 (N200) mg L−1) of N. The results showed that N100 treatment promoted the formation of primary and secondary cambium, resulting in a significant higher rate of SR formation between 21 and 56 days after transplanting (DAT). Due to the higher N demand after formation of SRs, N200 treatment displayed faster growth, higher N acquisition and the highest efficiency of N use after 35 DAT, but the SR formation rate and SR number per plant remained insignificantly lower than N100 when differentiation of adventitious root was mostly completed (49 DAT), suggesting irreversible an effect of N rate during SR initiation, which eventually affects SR number. The results suggested that the optimal substrate N level for sweetpotato SR initiation is lower than that for following SR growth, which should be considered in the fertilisation scheme.

Comparative full-length transcriptome analysis by Oxford Nanopore Technologies reveals genes involved in anthocyanin accumulation in storage roots of sweet potatoes (Ipomoea batatasL.).

BackgroundStorage roots of sweet potatoes (Ipomoea batatas L.) with different colors vary in anthocyanin content, indicating different economically agronomic trait. As the newest DNA/RNA sequencing technology, Oxford Nanopore Technologies (ONT) have been applied in rapid transcriptome sequencing for investigation of genes related to nutrient metabolism. At present, few reports concern full-length transcriptome analysis based on ONT for study on the molecular mechanism of anthocyanin accumulation leading to color change of tuberous roots of sweet potato cultivars.ResultsThe storage roots of purple-fleshed sweet potato (PFSP) and white-fleshed sweet potato (WFSP) at different developmental stages were subjected to anthocyanin content comparison by UV-visible spectroscopy as well as transcriptome analysis at ONT MinION platform. UV-visible spectrophotometric measurements demonstrated the anthocyanin content of PFSP was much higher than that of WFSP. ONT RNA-Seq results showed each sample generated average 2.75 GB clean data with Full-Length Percentage (FL%) over 70% and the length of N50 ranged from 1,192 to 1,395 bp, indicating reliable data for transcriptome analysis. Subsequent analysis illustrated intron retention was the most prominent splicing event present in the resulting transcripts. As compared PFSP with WFSP at the relative developmental stages with the highest (PH vs. WH) and the lowest (PL vs. WL) anthocyanin content, 282 and 216 genes were up-regulated and two and 11 genes were down-regulated respectively. The differential expression genes involved in flavonoid biosynthesis pathway include CCoAOMT, PpLDOX, DFR, Cytochrome P450, CHI, and CHS. The genes encoding oxygenase superfamily were significantly up-regulated when compared PFSP with WFSP at the relative developmental stages.ConclusionsComparative full-length transcriptome analysis based on ONT serves as an effective approach to detect the differences in anthocyanin accumulation in the storage roots of different sweet potato cultivars at transcript level, with noting that some key genes can now be closely related to flavonoids biosynthesis. This study helps to improve understanding of molecular mechanism for anthocyanin accumulation in sweet potatoes and also provides a theoretical basis for high-quality sweet potato breeding.

Comparative transcriptome profiling of sweetpotato storage roots during curing-mediated wound healing

Sweetpotato (Ipomoea batatas L. Lam) is an economically important crop that is cultivated for its storage roots. Storage roots provide a source of valuable nutrients, processed foods, animal feeds, and pigments. Sweetpotato storage roots spoil during post-harvest handling because of wounding, which makes them more susceptible to disease-causing microorganisms. Curing to promote wound healing is a common method to control microbial spoilage during post-harvest storage. However, molecular mechanisms underlying the process of curing in sweetpotato storage roots are unknown. To better understand the biology behind curing, the transcriptome of the sweetpotato cultivar, Pungwonmi, was studied using RNA-seq. Storage roots of sweetpotato were treated at 33 °C (Curing) and 13 °C (Control) for 3 days. RNA-seq data identified 78,781 unigenes and 3,366 differentially expressed genes by over log2 fold change (FC) > 2 and <−2. During curing, DEGs encoded genes related to drought/salt stress responses, phyto-hormones (e.g., auxin, ethylene and jasmonic acid), and proteolysis, were up-regulated, whereas those related to redox state, phyto-hormones (e.g., salicylic acid and brassinosteroids), and lignin and flavonoid biosynthesis were down-regulated. Additionally, among the candidate genes, DEGs encoded genes related to proteolysis and pathogen defense, such as protease inhibitors and lipid transfer proteins, were highly up-regulated during curing and storage. This study provides a valuable resource to further understand the molecular basis of curing-mediated wound healing in sweetpotato storage roots. Moreover, genes revealed in this work could present targets for the development of sweetpotato varieties with improved post-harvest storage characteristics.

Effects of Biochar, Poultry Manure and Their Mixture on Essential Nutrients of Sweet Potato Leaves and Storage Roots in Degraded Tropical Alfisols of Southwest Nigeria

ABSTRACT Essential nutrient concentrations in edible portions of crops can affect human health. Hence, field experiments were carried out for two growing seasons (2019 and 2020) at two degraded sites using a randomized complete block design in a factorial layout with three replications to evaluate the effects of biochar (B), poultry manure (PM), and their combined application on leaf nutrient concentrations and mineral composition of sweet potato. Each year, the experiment consisted of 4 × 3 factorial combinations of biochar (0, 10.0, 20.0, and 30.0 t ha−1) and poultry manure (0, 5.0 and 10.0 t ha−1). The results showed that the sole application of B and PM and their combined application, improved sweet potato leaf nutrient concentrations and mineral composition of sweet potato storage roots. In both years, there were significant interactions of B and PM (B × PM) on leaf nutrient concentrations and mineral composition of sweet potato that were determined, indicating the potential of B in enhancing PM use efficiency and improving better use of the nutrients in the PM. It was found that the highest dosage of combination of 30.0 t ha−1 B and 10.0 t ha−1 PM (B30+ PM10) gave the highest leaf nutrient concentrations and mineral composition of sweet potato at both sites. Lowest leaf nutrient concentrations and mineral composition was obtained for the control. The study indicated that B in combination with PM have the potential to improve sweet potato leaf nutrient concentrations and mineral composition of sweet potato storage roots for human health in severely degraded soils.

Effect of simulated synthetic auxin herbicide sprayer contamination in sweetpotato propagation beds

AbstractField studies were conducted to determine the effects of synthetic auxin herbicides at simulated exposure rates applied to ‘Covington’ sweetpotato propagation beds on the quality of nonrooted stem cuttings (slips). Treatments included diglycolamine salt of dicamba, 2,4-D choline plus nonionic surfactant (NIS), and 2,4-D choline plus glyphosate at 1/10, 1/33, or 1/66 of a 1X application rate (560 g ae ha−1 dicamba, 1,065 g ae ha−1 2,4-D choline, 1,130 g ae ha−1 glyphosate) applied at 2 or 4 wk after first slip harvest (WASH). Injury to sweetpotato 2 wk after treatment was greatest when herbicides were applied 2 WASH (21%) compared to 4 WASH (16%). More slip injury was caused by 2,4-D choline than by dicamba, and the addition of glyphosate did not increase injury over 2,4-D choline alone. Two weeks after the second application, sweetpotato slips were cut 2 cm above the soil surface and transplanted into production fields. In 2019, sweetpotato ground coverage 8 wk after transplanting was reduced 37% and 26% by the 1/10X rates of dicamba and 2,4-D choline plus NIS, respectively. Though dicamba caused less injury to propagation beds than 2,4-D choline with or without glyphosate, after transplanting, slips treated with 1/10X dicamba did not recover as quickly as those treated with 2,4-D choline. In 2020, sweetpotato ground coverage was 90% or greater for all treatments. Dicamba applied 2 WASH decreased marketable sweetpotato storage root yield by 59% compared to the nontreated check, whereas treatments including 2,4-D choline reduced marketable yield 22% to 29%. All herbicides applied at 4 WASH reduced marketable yield 31% to 36%. The addition of glyphosate to 2,4-D choline did not increase sweetpotato yield. Results indicate that caution should be taken when deciding whether to transplant sweetpotato slips that are suspected to have been exposed to dicamba or 2,4-D choline.

Early Nitrogen Applications Promote the Initiation of Sweetpotato Storage Roots

A number of published studies have focused on the effects of N application timing on sweetpotato yield. However, none of them examined the influence of the timing of N fertilisation on the initiation of storage roots (SRs), which largely determines the number of tubers per plant and substantially affect the yield. A pot experiment was conducted in sand culture to evaluate the influence of N application timing (N applied on the planting day, 3, 7 and 14 days after transplanting (DAT), denoted T1, T3, T7 and T14, respectively, and a no N applied control T0) on the plant acquisition of N and the initiation of SRs of &amp;lsquo;Orleans&amp;rsquo; cultivar. A previously-determined optimal N rate for the SR formation (Hoagland solution with 100mg/L N) in the experimental system was used. Rapid SR formation was found to require N during the first week after transplanting. No or late N application delayed the initiation of SRs and reduced the number of SRs. No or delayed N application inhibited the formation of regular vascular cambium (RVC) and anomalous cambium (AC) and led to an increase in lignification of stele cells leading to significantly higher proportion of lignified roots. By contrast, plants supplied with N within 7 DAT had a higher rate of SRs and lower rate of lignified roots. Also, earlier N application promoted total plant and root growth measured as higher biomass and storage root weight, as well as higher N accumulation in plants and higher nitrogen recovery efficiency (NRE). Results suggested that the SR formation required N during the first week after transplanting. Therefore, moderate N should be available in soil before or on planting day.

A cytochrome P450 superfamily gene, IbCYP82D47, increases carotenoid contents in transgenic sweet potato

The cytochrome P450 superfamily (CYP450) is one of the largest protein families in plants, and its members play diverse roles in primary and secondary metabolic biosynthesis. In this study, the CYP450 family gene IbCYP82D47 was cloned from the high carotenoid line HVB-3 of sweet potato (Ipomoea batatas). The IbCYP82D47 protein harbored two transmembrane domains and dynamically localized between plastid stroma and membrane. Overexpression of IbCYP82D47 not only increased total carotenoid, lutein, zeaxanthin and violaxanthin contents by 32.2–48.0%, 10.5–13.3%, 40.2–136% and 82.4–106%, respectively, but also increased the number of carotenoid globules in sweet potato storage roots. Furthermore, genes associated with the carotenoid biosynthesis (IbDXS, IbPSY, IbLCYE, IbBCH, IbZEP) were upregulated in transgenic sweet potato. In addition, IbCYP82D47 physically interacts with geranylgeranyl diphosphate synthase 12 (IbGGPPS12). Our findings suggest that IbCYP82D47 increases carotenoid contents by interacting with the carotenoid biosynthesis related protein IbGGPPS12, and influencing the expressions of carotenoid biosynthesis related genes in transgenic sweet potato.

Draft Genome Sequence of Diaporthe batatatis Causing Dry Rot Disease in Sweetpotato

Dry rot caused by Diaporthe batatatis leads to the serious decay of sweetpotato storage roots during postharvest storage, which can result in considerable economic loss. Genomic research of the pathogen could provide a basis for study and prevention of sweetpotato dry rot. Herein, we report a high-quality draft genome sequence of D. batatatis CRI 302-4 isolated from infected sweetpotato storage roots in Taizhou City, Zhejiang Province, China. The size of the genome was 54.38 Mb and consisted of 36 scaffolds with a G+C content of 50.56% and an N50 of 2,950,914 bp. The information provided in this genome sequence will be an invaluable resource for molecular genetic research and disease control in sweetpotato production.

Isolation and functional characterization of a glucose-6-phosphate/phosphate translocator (IbG6PPT1) from sweet potato (Ipomoea batatas (L.) Lam.)

Sweet potato (Ipomoea batatas (L.) Lam.) is a good source of carbohydrates, an excellent raw material for starch-based industries, and a strong candidate for biofuel production due to its high starch content. However, the molecular basis of starch biosynthesis and accumulation in sweet potato is still insufficiently understood. Glucose-6-phosphate/phosphate translocators (GPTs) mediate the import of glucose-6-phosphate (Glc6P) into plastids for starch synthesis. Here, we report the isolation of a GPT-encoding gene, IbG6PPT1, from sweet potato and the identification of two additional IbG6PPT1 gene copies in the sweet potato genome. IbG6PPT1 encodes a chloroplast membrane–localized GPT belonging to the GPT1 group and highly expressed in storage root of sweet potato. Heterologous expression of IbG6PPT1 resulted in increased starch content in the leaves, root tips, and seeds and soluble sugar in seeds of Arabidopsis thaliana, but a reduction in soluble sugar in the leaves. These findings suggested that IbG6PPT1 might play a critical role in the distribution of carbon sources in source and sink and the accumulation of carbohydrates in storage tissues and would be a good candidate gene for controlling critical starch properties in sweet potato.

Fungi Associated with Postharvest Diseases of Sweet Potato Storage Roots and In Vitro Antagonistic Assay of Trichodermaharzianum against the Diseases.

Sweet potato is the 11th most important food crop in the world and an excellent source of nutrition. Postharvest diseases were monitored in sweet potato storage roots collected from the local markets in Korea during 2021. Several diseases including Fusarium surface and root rot, charcoal rot, dry rot, and soft rot were observed in the postharvest sweet potatoes. A total of 68 fungal isolates were obtained from the diseased samples, and the isolates were grouped into 8 different fungal colony types. Based on multilocus phylogeny and morphological analysis of 17 representative isolates, the isolates were identified as Fusarium oxysporum, F. ipomoeae, F. solani, Penicillium citrinum, P. rotoruae, Aspergillus wentii, Mucor variicolumellatus (Mu. circinelloides species complex), and Macrophomina phaseolina. F. oxysporum was the predominant pathogen as this is the most common pathogen of sweet potato storage roots causing the surface rot disease, and M. phaseolina caused the most severe disease among the pathogens. Dual culture antagonistic assays were evaluated using Trichoderma harzianum strains CMML20–26 and CMML20–27. The results revealed that the two strains showed strong antifungal activity in different ranges against all tested pathogens. This study provides an understanding of diverse postharvest diseases in sweet potatoes and suggests potential biocontrol agents to manage the diseases. In addition, this is the first report of sweet potato storage root rot diseases caused by A. wentii, and P. rotoruae worldwide.

Role of AOX in low-temperature conditioning induced chilling tolerance in sweetpotato roots

Chilling injury is a significant postharvest physiological disorder in sweetpotatoes during storage. This study investigated the role of alternative oxidase (AOX) in low-temperature conditioning (LTC) induced chilling tolerance in sweetpotato storage roots. Roots were pre-treated with a LTC treatment (12°C for 5 days) or with salicylhydroxamic acid (SHAM, AOX inhibitor) combined with LTC, followed by storage at 4°C for 35 days. Results showed that LTC pre-treatment significantly lowered root chilling injury symptoms, suppressed malondialdehyde levels and the accumulation of reactive oxygen species. However, SHAM reduced the impact triggered by LTC and resulted in lower antioxidant enzyme activities and free proline content, reduced glutathione and adenosine triphosphate contents compared with LTC alone. The results from gene expression analysis showed that LTC-induced higher transcript level of IbAOX1a and IbAOX1b during storage at 4°C. However, SHAM suppressed the effect of LTC. SHAM treatment not only reduced AOX activity but also resulted in a lower AOX transcript and protein abundance, which might contribute to the lower AOX activity observed in the SHAM treated roots. These results suggest that AOX participates in LTC-induced chilling tolerance of sweetpotato storage roots.

Transcriptomic and Metabolic Profiling of High-Temperature Treated Storage Roots Reveals the Mechanism of Saccharification in Sweetpotato (Ipomoea batatas (L.) Lam.).

The saccharification of sweetpotato storage roots is a common phenomenon in the cooking process, which determines the edible quality of table use sweetpotato. In the present study, two high saccharified sweetpotato cultivars (Y25, Z13) and one low saccharified cultivar (X27) in two growth periods (S1, S2) were selected as materials to reveal the molecular mechanism of sweetpotato saccharification treated at high temperature by transcriptome sequencing and non-targeted metabolome determination. The results showed that the comprehensive taste score, sweetness, maltose content and starch change of X27 after steaming were significantly lower than those of Y25 and Z13. Through transcriptome sequencing analysis, 1918 and 1520 differentially expressed genes were obtained in the two periods of S1 and S2, respectively. Some saccharification-related transcription factors including MYB families, WRKY families, bHLH families and inhibitors were screened. Metabolic analysis showed that 162 differentially abundant metabolites related to carbohydrate metabolism were significantly enriched in starch and sucrose capitalization pathways. The correlation analysis between transcriptome and metabolome confirmed that the starch and sucrose metabolic pathways were significantly co-annotated, indicating that it is a vitally important metabolic pathway in the process of sweetpotato saccharification. The data obtained in this study can provide valuable resources for follow-up research on sweetpotato saccharification and will provide new insights and theoretical basis for table use sweetpotato breeding in the future.

Impact of nitrogen and green manure on yield and quality of sweet potato in sandy soil: A Brazilian case study

A field experiment was conducted to evaluate the effects of mineral N rates on the yield, morphological traits, quality, and mineral content of the storage roots of sweet potato grown after different green manure sources. Treatments included the application of N at four rates (0, 50, 100, and 200 kg ha−1) to sweet potato grown after the control (indigenous weeds) or the legumes showy crotalaria and velvet bean. PCA revealed that in the treatments with previous showy crotalaria cultivation, there was a low incidence of defects in the storage roots and the storage roots weighed more than they did in the control or in the velvet bean treatments. The current study also showed that legume cultivation only in the previous season was not enough to improve the yield and quality of sweet potato. Therefore, it is necessary to combine previous legume cultivation with the application of 100 or 200 kg N ha−1 in sweet potato to achieve higher levels of yield, quality, and mineral contents, such as Cu, Zn, K, Ca, and Mg, in storage roots. The current research has indicated that future studies should investigate whether the benefits of previous legume cultivation for sweet potato are restricted only to the current growing season.

Analysis of β-amylase gene (Amyβ) variation reveals allele association with low enzyme activity and increased firmness in cooked sweetpotato (Ipomoea batatas) from East Africa.

β-amylase is a thermostable enzyme that hydrolyses starch during cooking of sweetpotato (Ipomoea batatas) storage roots, thereby influencing eating quality. Its activity is known to vary amongst genotypes but the genetic diversity of the beta-amylase gene (Amyβ) is not well studied. Amyβ has a highly conserved region between exon V and VI, forming part of the enzyme's active site. To determine the gene diversity, a 2.3 kb fragment, including the conserved region of the Amyβ gene was sequenced from 25 sweetpotato genotypes. The effect of sequence variation on gene expression, enzyme activity, and firmness in cooked roots was determined. Six genotypes carrying several SNPs within exon V, linked with an AT or ATGATA insertion in intron V were unique and clustered together. The genotypes also shared an A336E substitution in the amino acid sequence, eight residues upstream of a substrate-binding Thr344. The genotypes carrying this allele exhibited low gene expression and low enzyme activity. Enzyme activity was negatively correlated with firmness (R = −0.42) in cooked roots. This is the first report of such an allele, associated with low enzyme activity. These results suggest that genetic variation within the AmyB locus can be utilized to develop markers for firmness in sweetpotato breeding.