Tuberous Roots Of Sweet Potato Research Articles

Comprehensive analysis of small RNA, transcriptome, and degradome sequencing: Mapping the miRNA-gene regulatory network for the development of sweet potato tuber roots.

As an important starch crop, sweet potato has significant practical importance for maintaining food security worldwide. This study identified differential expressed genes associated with the expansion of tuberous roots by comparing the transcriptome across tuberous roots at the initial period (initiated tuberous roots (ITRs), rapid expansion period (tuberous roots (TRs), fibrous roots (FRs) at the seedling stage, and fibrous roots at the adult stage (unexpanded FRs (UFRs)). sRNA-seq and degradome analyses were performed to reveal the role of miRNAs in tuberous root development in sweet potato. A total of 29,633 genes and 510 miRNAs were differential expressed among FRs, ITRs, TRs, and UFRs. Integrated analyses of these data revealed genes involved in metabolism, hormone response, and signal transduction that might participate in the induction of tuberous root formation, while genes involved in carbohydrate and energy metabolism that might participate in the tuberous root swelling. A joint analysis of miRNAs and DEGs related to tuber development revealed by degradome-seq identified twelve miRNA-target gene pairs involved in gene expression process, hormone response, and metabolism of secondary metabolites that might be key regulators of root tuber development in sweet potato. Moreover, the functions of many miRNA-target gene pairs involved in the initiation of root tuber were related to auxin signaling response, and an exogenous hormone treatment experiment was further performed. The results indicated that auxin treatment had the most significant effect on increasing sweet potato yield, suggesting a dominant role of the auxin pathway in the regulation of sweet potato tuberous root development. Additionally, two miRNA-target pairs, miR319-TCP4 and miR172-AP2, which were identified from the degradome, were verified via 5' RNA ligase-mediated rapid amplification of cDNA ends (RLR-RACE) and tobacco transient cotransformation tests, and their expression was impacted by auxin treatment, which further validated the reliability of our multiomics analysis results. Our research provides new insights into the role of miRNAs in sweet potato root tuber development.

Effects of ultrasound with slightly acid electrolytic water on storage of sweet potato: Physiological, nutritional, sensory and microstructural characteristics

Effects of ultrasound (US, 300, 400 and 500 W) combined with slightly acid electrolytic water (SAEW) at 25, 40 and 55 °C on physiological, nutritional, sensory and microstructural characteristics of sweet potato tuberous roots (TRs, Pushu 32) during 10, 30 and 60 d of storage were investigated, to explore a potential postharvest preservation technique for TRs. Sweet potato TRs by US500+SAEW50 exhibited the strongest PAL activity (10.63 U g−1) at 30 d of storage and SOD activity (83,707.42 U g−1) at 60 d of storage, suggesting the activation of strong defense system. Sweet potato TRs by US500+SAEW50 also showed integral cell walls, and presented the highest sensory acceptability (73.45). In addition, rotting rate of the TRs treated by US500+SAEW50 was reduced by 55% after 6 months of storage as compared to the untreated TRs in industrial application. Therefore, US500+SAEW50 could be a promising postharvest preservation technique for sweet potato TRs.

Hot air treatment alleviates chilling injury of sweet potato tuberous roots by regulating osmoregulatory substances and inducing antioxidant defense system

Sweet potato tuberous roots are susceptible to chilling injury (CI) when stored below 10 °C. In this study, we investigated the mitigating effects of hot air (HA) treatment on CI. Results showed that HA45°C-3h treatment delayed the CI and internal browning during cold storage. After HA45°C-3h treatment, the cells' structural integrity was maintained, malondialdehyde accumulation and ion leakage were inhibited. Additionally, the osmoregulatory substances, such as total soluble solids, proline were maintained, and soluble protein was enhanced. Higher activity of antioxidant enzymes including superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase, and the antioxidant substances including ascorbic acid, glutathione, total phenols, and flavonoids were observed in sweet potato tuberous roots treated by HA45°C-3h than untreated group. Our study suggested that HA45°C-3h treatment could reduce CI and maintain a better quality of sweet potato tuberous roots following cold storage.

Exploring the potential in postharvest preservation of sweet potato: 2-methylbutanoic acid, isobutyric acid, perillaldehyde and salicylaldehyde, to control Rhizopus stolonifer

Soft rot caused by Rhizopus stolonifer is one of the most destructive postharvest diseases inducing massive loss of sweet potato tuberous roots (TRs). Inhibitory effects of 2-methylbutanoic acid (2-ME), isobutyric acid (IS), perillaldehyde (PE) and salicylaldehyde (SA) against R. stolonifer was investigated, to explore their potential in postharvest preservation of sweet potato. The 2-ME, IS, PE and SA completely inhibited mycelial growth and spore germination, destroyed cell membrane integrity, and induced nucleic acids and proteins leakage of R. stolonifer. Compared to 2-ME and IS, SA caused the most severe ultrastructure damage to R. stolonifer, enhanced cell membrane permeability, reduced mitochondrial membrane potential, and induced more endogenous ROS production, followed by PE. In addition, SA better controlled R. stolonifer infection, decreased MDA content and increased disease-resistant enzyme activities in TRs during 15 d of storage. Therefore, SA might be a promising alternative to fungicides in postharvest preservation of sweet potato TRs.

Cyclic variable temperature conditioning induces the rapid sweetening of sweet potato tuberous roots by regulating the sucrose metabolism

This study aimed to investigate the influence of cyclic variable temperature conditioning (CVTC) on the rapid sweetening of sweet potato tuberous roots, as assessed through the analysis of sugar metabolism-related compounds and enzyme activities of tubers during storage. The results showed that CVTC effectively preserved the quality of sweet potato tuberous roots, leading to a significant elevation in soluble solids and soluble sugars. The CVTC group displayed sucrose and fructose levels that were 1.72 and 1.46 times higher, respectively, compared to the control group at the 8 d. Additionally, after storage, the activities of β-amylase, sucrose phosphate synthase (SPS), and sucrose synthase (SS) in the CVTC group were increased by 19.85 %, 60.74 %, and 82.48 %, respectively. Conversely, acid convertase (AI) activity showed inhibition of 64.72 %. In conclusion, implementing CVTC enhanced enzymatic activity in β-amylase, SPS, and SS, facilitating starch degradation and sucrose synthesis, which contributed to the overall improvement in the sweetness of sweet potato tubers.

Integrated metabolic and transcriptional analysis reveals the role of carotenoid cleavage dioxygenase 4 (IbCCD4) in carotenoid accumulation in sweetpotato tuberous roots

BackgroundPlant carotenoids are essential for human health, having wide uses in dietary supplements, food colorants, animal feed additives, and cosmetics. With the increasing demand for natural carotenoids, plant carotenoids have gained great interest in both academic and industry research worldwide. Orange-fleshed sweetpotato (Ipomoea batatas) enriched with carotenoids is an ideal feedstock for producing natural carotenoids. However, limited information is available regarding the molecular mechanism responsible for carotenoid metabolism in sweetpotato tuberous roots.ResultsIn this study, metabolic profiling of carotenoids and gene expression analysis were conducted at six tuberous root developmental stages of three sweetpotato varieties with different flesh colors. The correlations between the expression of carotenoid metabolic genes and carotenoid levels suggested that the carotenoid cleavage dioxygenase 4 (IbCCD4) and 9-cis-epoxycarotenoid cleavage dioxygenases 3 (IbNCED3) play important roles in the regulation of carotenoid contents in sweetpotato. Transgenic experiments confirmed that the total carotenoid content decreased in the tuberous roots of IbCCD4-overexpressing sweetpotato. In addition, IbCCD4 may be regulated by two stress-related transcription factors, IbWRKY20 and IbCBF2, implying that the carotenoid accumulation in sweeetpotato is possibly fine-tuned in responses to stress signals.ConclusionsA set of key genes were revealed to be responsible for carotenoid accumulation in sweetpotato, with IbCCD4 acts as a crucial player. Our findings provided new insights into carotenoid metabolism in sweetpotato tuberous roots and insinuated IbCCD4 to be a target gene in the development of new sweetpotato varieties with high carotenoid production.

Influence of Number of Buried Nodes and Sources of Potassium Fertilizers on Sweet Potato Growth and Yield in Dodoma, Tanzania.

Inadequate knowledge on appropriate number of nodes of sweet potato vines to be planted and sources of potassium fertilizer to be used are among major factors resulted into low sweet potato productivity in central part areas of Tanzania. This research aimed at evaluating the effects of four levels of nodes buried and three potash fertilizer sources on growth and yield of three sweet potato varieties. Split-split plot field experiment in complete randomized block design was conducted at Hombolo, Dodoma during 2013/2014 cropping season. Main plot were three sweet potato varieties, Kiegeya, Mataya, and Ukerewe. Sub plot were, four level of buried nodes, (two above ground), five buried nodes (three above ground), seven buried nodes (three above ground) and eight buried nodes (four above ground). The sub - subplot treatments were potash fertilizer sources i.e control no fertilizer used, Potassium chloride (KCl), Potassium nitrogen phosphate (NPK) and Farm yard manure (FYM). Results indicated that there were no significant effects on the yield among varieties used. The number of tubers increased significantly in fertilized plots compared to control. The lowest number of tuber roots (3 tubers) was from control treatment while the highest number of tuber roots (6) was from KCl treatment. The effect of potassium fertilizer sources on root yield were also significant, use of KCl resulted to highest yield (18.84 t ha-1), followed by NPK (17.51 t ha-1), FYM (11.33 t ha-1) and control treatment where no fertilizer applied (8.82 t ha-1). Plating of different number of nodes resulted into significant increase in yield where the highest yield of (15.91 t ha-1) was from eight buried nodes and lowest total yield (11.68 t ha-1) was from four buried nodes. Seven and eight buried nodes with KCl and NPK fertilizers appeared to be appropriate for optimum sweet potato growth, yield and tuberous root quality in the study area and are therefore recommended.

Long-Term Soil Drought Limits Starch Accumulation by Altering Sucrose Transport and Starch Synthesis in Sweet Potato Tuberous Root.

In this study, the influences of long-term soil drought with three levels [soil-relative water content (SRWC) (75 ± 5)%, as the control; SRWC (55 ± 5)%, mild drought; SRWC (45 ± 5)%, severe drought] were investigated on sucrose-starch metabolism in sweet potato tuberous roots (TRs) by pot experiment. Compared to the control, drought stress increased soluble sugar and sucrose content by 4-60% and 9-75%, respectively, but reduced starch accumulation by 30-66% through decreasing the starch accumulate rate in TRs. In the drought-treated TRs, the inhibition of sucrose decomposition was attributed to the reduced activities of acid invertase (AI) and alkaline invertase (AKI) and the IbA-INV3 expression, rather than sucrose synthase (SuSy), consequently leading to the increased sucrose content in TRs. In addition, starch synthesis was inhibited mainly by reducing ADP-glucose pyrophosphorylase (AGPase), granular starch synthase (GBSS) and starch branching enzyme (SBE) activities in TRs under drought stress, and AGPase was the rate-limiting enzyme. Furthermore, soil drought remarkably up-regulated the IbSWEET11, IbSWEET605, and IbSUT4 expressions in Jishu 26 TRs, while it down-regulated or had no significant differences in Xushu 32 and Ningzishu 1 TRs. These results suggested that the sucrose-loading capability in Jishu 26 TRs were stronger than that in Xushu 32 and Ningzishu 1 TRs. Moreover, IbA-INV3, IbAGPS1, IbAGPS2, IbGBSSI and IbSBEII play important roles in different drought-tolerant cultivars under drought stress.

Comprehensive Evaluation of Raw Eating Quality in 81 Sweet Potato (Ipomoea batatas (L.) Lam) Varieties.

The raw eating quality of sweet potato is complex. As consumers start paying more attention to the raw eating quality of tuberous roots in sweet potato, the evaluation of the raw eating quality of sweet potato is becoming an important issue. Therefore, we measured 16 quality indicators in 81 varieties of sweet potato. It was found that these 16 quality traits had different coefficients of variation (C.V.). Among them, the C.V. of fructose, glucose, and adhesiveness were the largest: 87.95%, 87.43% and 55.09%, respectively. The cluster analysis method was used to define six categories of the different tuberous roots of sweet potato. Group I, III, and IV had a stronger hardness and higher starch and cellulose content. Groups II, V, and VI were softer, with a high moisture and soluble sugar content. The principal component analysis method was used to comprehensively evaluate 16 quality indicators of 81 sweet potato varieties. It was found that Futian1, Taishu14, and Nanshu022 are good varieties in terms of raw eating quality. These varieties have low hardness, high adhesiveness in texture, high soluble sugar content, and low starch and cellulose. Future research should focus on improving the raw eating quality of sweet potato by reducing hardness, starch, and cellulose, while increasing adhesiveness, soluble sugar, and moisture content.

Effects of Foliar Application of Uniconazole on the Storage Quality of Tuberous Roots in Sweetpotato

Uniconazole (UCZ), as a plant growth regulator, has been extensively applied in sweetpotato (Ipomoea batatas (L.) Lam) to increase tuberous root yield and quality. It is usually used in the production of sweetpotato by foliar spray. The post-harvest storage stage is crucial for forming the quality of the sweetpotato’s tuberous root. Few studies have focused on the foliar spraying UCZ-affected storage quality of sweetpotato during pro-harvest storage. To examine the effects of foliar application of UCZ on the storage quality of tuberous root, this study mainly analyzed the influence of storage quality, with (K2 and K4) and without (K1 and K3) 100 mg·L−1 foliar spraying of UCZ, at a storage period of normal fertilizing treatments (K1 and K2) and rich fertilizing treatments (K3 and K4), on the storage quality of three representative sweetpotato varieties (Z13, Z33 and J26). Compared to the no-use UCZ treatments, the decay rate of K2 was the lowest for any storage time. The decay rate of all the varieties was 0.0% before 45 DAS. Only the decay rate of Z33 increased to 4.4% at 60 DAS (p < 0.05). The dry matter rate of K2 and K4 was still higher than that of K1 during 15–60 DAS in Z13 and J26 (p < 0.05). UCZ foliar spraying was higher than without treatment at 30–60 DAS. In Z33, the springiness of UCZ spraying was higher than no spraying treatments at 45–60 DAS. These results indicate that foliar spraying of UCZ had no effect on the storage quality of tuberous root decreasing sharply, and it sometimes kept the quality stable.

Integrated analysis of carotenoid metabolites and transcriptome identifies key genes controlling carotenoid compositions and content in sweetpotato tuberous roots (Ipomoea batatas L.)

Sweetpotato (Ipomoea batatas L.) with different depths of yellow color contains different compositions of carotenoids, which are beneficial for human health. In this study, we performed an integrated analysis of metabolomic and transcriptomic to identify key genes playing a major role in carotenoid coloration in sweetpotato tuberous roots. Herein, 14 carotenoids were identified in five sweetpotatoes. Orange-red and orange cultivars were dominated by β-carotene (385.33 μg/g and 85.07 μg/g), yellow cultivar had a high β-cryptoxanthin (11.23 μg/g), light-yellow cultivar was rich in zeaxanthin (5.12 μg/g), whereas lutein (3.34 μg/g) was the main carotenoid in white cultivar. Furthermore, 27 differentially expressed genes involved in carotenoid metabolism were identified based on comparative transcriptome. Weighted gene co-expression network analysis identified 15 transcription factors highly associated with carotenoid content in sweetpotatoes. These results provide valuable information for revealing the regulatory mechanism of carotenoid metabolism in different-colored sweetpotato tuberous roots.

Comparative transcriptome analysis of purple-fleshed sweet potato and its yellow-fleshed mutant provides insight into the transcription factors involved in anthocyanin biosynthesis in tuberous root.

In various plant species, many transcription factors (TFs), such as MYB, bHLH, and WD40, have been identified as regulators of anthocyanin biosynthesis in underground organs. However, the regulatory elements of anthocyanin biosynthesis in the tuberous roots of sweet potato have not been elucidated yet. Here, we selected the purple-fleshed sweet potato cultivar “Zhezi1” (ZZP) and its spontaneous yellow-fleshed mutant “Xinli” (XLY) to investigate the regulatory mechanism of the anthocyanin biosynthesis in the tuberous roots of sweet potato. By analyzing the IbMYB1 genotype in ZZP and XLY, we found that the IbMYB1-2, a MYB TF involved in anthocyanin biosynthesis, was missing in the XLY genome, which might lead to an extreme decrease in anthocyanins in XLY. A comparative transcriptome analysis of ZZP and XLY was conducted to find the TFs involved in anthocyanin biosynthesis in ZZP and XLY. The anthocyanin structural genes were significantly enriched among the differentially expressed genes. Moreover, one MYB activator (IbMYB1), one bHLH (IbbHLH2), three WRKY activator candidates (IbWRKY21, IbWRKY24, and IbWRKY44), and two MYB repressors (IbMYB27 and IbMYBx-ZZ) were highly expressed in ZZP accompanied with anthocyanin structural genes. We also tested the expression of these TFs in six purple- and two orange-fleshed sweet potato cultivars. Interestingly, most of these TFs were significantly positively correlated with anthocyanin contents in these cultivars. The function of the anthocyanin biosynthesis repression of IbMYB27 and IbMYBx-ZZ was verified through transient co-transformation with IbMYB1 into tobacco leaves. Further functional verification of the above TFs was conducted by Y2H, BiFC, and dual-luciferase assays. These tests showed that the MYB-bHLH-WD40/MYB-bHLH-WD40-WRKY complex activated the promoter of anthocyanin structural gene IbDFR and promoters for IbWRKY44, IbMYB27, and IbMYBx-ZZ, indicating reinforcement and feedback regulation to maintain the level of anthocyanin accumulation in the tuberous roots of purple-fleshed sweet potato. These results may provide new insights into the regulatory mechanism of anthocyanin biosynthesis and accumulation in underground organs of sweet potatoes.

Relationship between bud number in seed branches and yield aspects of sweet potato

ABSTRACT Planting sweet potato branches with the appropriate bud number and disposition, below and above ground, can favor vegetative growth and yield that better fit the marketable standards. This study aimed to explore the influence of the number of buds and their distribution ratio, above and below ground level, on the agronomic and marketable components of sweet potato tuberous roots. The experiment was carried out in a randomized complete block design with three replications. The treatments were arranged in a factorial scheme (3 x 5), with 2, 4, and 8 above-ground buds combined with 2, 4, 6, 8, and 10 below-ground buds. Branches from the UZBD 06 accession (Canadense standard) were used. Vegetative, productive, and marketable traits of roots were evaluated. The use of branches with a greater number of buds above and below ground increased shoot dry biomass. Planting seed branches with 8 buds above and 8 buds below ground provided a greater number and production of marketable roots. The use of 10 buried buds increased root number and yield in the 150-450 g marketable classes, which the consumer market values the most.

Overexpression of IbFAD8 Enhances the Low-Temperature Storage Ability and Alpha-Linolenic Acid Content of Sweetpotato Tuberous Roots.

Sweetpotato is an emerging food crop that ensures food and nutrition security in the face of climate change. Alpha-linoleic acid (ALA) is one of the key factors affecting plant stress tolerance and is also an essential nutrient in humans. In plants, fatty acid desaturase 8 (FAD8) synthesizes ALA from linoleic acid (LA). Previously, we identified the cold-induced IbFAD8 gene from RNA-seq of sweetpotato tuberous roots stored at low-temperature. In this study, we investigated the effect of IbFAD8 on the low-temperature storage ability and ALA content of the tuberous roots of sweetpotato. Transgenic sweetpotato plants overexpressing IbFAD8 (TF plants) exhibited increased cold and drought stress tolerance and enhanced heat stress susceptibility compared with non-transgenic (NT) plants. The ALA content of the tuberous roots of TF plants (0.19 g/100 g DW) was ca. 3.8-fold higher than that of NT plants (0.05 g/100 g DW), resulting in 8–9-fold increase in the ALA/LA ratio in TF plants. Furthermore, tuberous roots of TF plants showed better low-temperature storage ability compared with NT plants. These results indicate that IbFAD8 is a valuable candidate gene for increasing the ALA content, environmental stress tolerance, and low-temperature storage ability of sweetpotato tuberous roots via molecular breeding.

Bacillus velezensis T149-19 and Bacillus safensis T052-76 as Potential Biocontrol Agents against Foot Rot Disease in Sweet Potato

Sweet potato (Ipomoea batatas) tuberous roots are used for human consumption, animal feed, and many industrial products. However, the crop is susceptible to various pests and diseases, including foot rot disease caused by the phytopathogenic fungus Plenodomus destruens. Biological control of plant pathogens by Bacillus species is widely disseminated in agrosystems, but specific biological control agents against the foot rot disease-causing fungus are not yet available. Our previous studies showed that two Bacillus strains isolated from sweet potato roots—B. safensis T052-76 and B. velezensis T149-19—were able to inhibit P. destruens in vitro, but data from in vivo experiments using simultaneously the fungus and the bacteria were missing. In this study, both strains were shown to protect the plant from the disease and to mitigate the symptoms of foot rot disease in pot experiments. Total fungal community quantification using real-time PCR showed a significant decrease in the number of copies of the ITS gene when the bacteria were inoculated, compared to the control (with the fungus only). To determine the genes encoding antimicrobial substances likely to inhibit the fungus, their genomes were sequenced and annotated. Genes coding for mycosubtilin, bacillaene, macrolactin, bacillibactin, bacilysin, plantazolicin, plipastatin, dificidine, fengycin and surfactin were found in B. velezensis T149-19, while those coding for bacylisin, lichenysin, bacillibactin, fengycin and surfactin were found in B. safensis T052-76. Altogether, the data presented here contribute to advancing the knowledge for the use of these Bacillus strains as biocontrol products in sweet potato.

Exogenous progesterone alleviates chilling injury by upregulating IbAOX1 to mediate redox homeostasis and proline accumulation in postharvest sweetpotato tuberous root

This study aimed to elucidate the role of progesterone (PROG) in mitigating chilling injury (CI) in sweetpotato tuberous root and its relation to alternative oxidase (AOX). Root were pretreated by immersing them in 100 mM PROG or PROG-salicylhydroxamic acid (SHAM). The results showed that PROG effectively enhanced the transcription level of IbAOX1 and the activity of AOX, inhibited the formation of CI, and reduced membrane permeability, malonaldehyde levels, and the production of ROS compared with the control. PROG also enhanced the antioxidant protection system by maintaining higher activities of antioxidant enzymes and levels of ascorbic acid and total phenolics. PROG further induced the upregulation of Δ1-pyrroline-5-carboxylate synthetase and ornithine d-aminotransferase and the downregulation of proline dehydrogenase, which advanced the proline level. However, the abovementioned effects resulting from PROG treatment were weakened by SHAM. Therefore, PROG upregulated AOX to mediate the antioxidant system and proline accumulation, thereby alleviating CI in tuberous root. The strategy of PROG treatment combined with cold storage can potentially be used for cold-induced rapid sweetening and enhancing the antioxidant capacity of freshly harvested tuberous roots.

Molecular Mechanisms through Which Short-Term Cold Storage Improves the Nutritional Quality and Sensory Characteristics of Postharvest Sweet Potato Tuberous Roots: A Transcriptomic Study.

Sweet potato (Ipomoea batatas (L.) Lam.) is a commercially relevant food crop with high demand worldwide. This species belongs to the Convolvulaceae family and is native to tropical and subtropical regions. Storage temperature and time can adversely affect tuberous roots’ quality and nutritional profile. Therefore, this study evaluates the effect of storage parameters using physicochemical and transcriptome analyses. Freshly harvested tuberous roots (Xingxiang) were stored at 13 °C (control) or 5 °C (cold storage, CS) for 21 d. The results from chilling injury (CI) evaluation demonstrated that there was no significant difference in appearance, internal color, weight, and relative conductivity between tuberous roots stored at 13 and 5 °C for 14 d and indicated that short-term CS for 14 d promoted the accumulation of sucrose, chlorogenic acid, and amino acids with no CI symptoms development. This, in turn, improved sweetness, antioxidant capacity, and nutritional value of the tuberous roots. Transcriptome analyses revealed that several key genes associated with sucrose, chlorogenic acid, and amino acid biosynthesis were upregulated during short-term CS, including sucrose synthase, sucrose phosphate synthase, phenylalanine ammonia-lyase, 4-coumarate-CoA ligase, hydroxycinnamoyl-CoA quinate hydroxycinnamoyltransferase, serine hydroxymethyltransferase, alanine aminotransferase, arogenate dehydrogenase, and prephenate dehydratase. These results indicated that storage at 5 °C for 14 d could improve the nutritional quality and palatability of sweet potato tuberous roots without compromising their freshness.

Overexpression of IbLfp in sweetpotato enhances the low-temperature storage ability of tuberous roots

Sweetpotato (Ipomoea batatas [L.] Lam) is a prospective food crop that ensures food and nutrition security under the dynamic changes in global climate. Peroxidase (POD) is a multifunctional enzyme involved in diverse plant physiological processes, including stress tolerance and cell wall lignification. Although various POD genes were cloned and functionally characterized in sweetpotato, the role of POD in lignification and low-temperature storage ability of sweetpotato tuberous roots is yet to be investigated. In this study, we isolated the cold-induced lignin forming peroxidase (IbLfp) gene of sweetpotato, and analyzed its physiological functions. IbLfp showed more predominant expression in fibrous roots than in other tissues. Moreover, IbLfp expression was up-regulated in leaves and roots under cold stress, and was altered by other abiotic stresses. Tuberous roots of transgenic sweetpotato lines overexpressing IbLfp (LP lines) showed improved tolerance to low temperature, with lower malondialdehyde and hydrogen peroxide contents than non-transgenic sweetpotato plants under cold stress. The enhanced cold tolerance of LP lines could be attributed to the increased basal activity of POD, which is involved in reactive oxygen species (ROS) scavenging. Moreover, greater accumulation of lignin could also contribute to the enhanced cold tolerance of LP lines, as lignin acts as a protective barrier against invading pathogens, which is a secondary symptom of chilling injury in sweetpotato. Overall, the results of this study enhance our understanding of the function of POD in low-temperature storage of sweetpotato tuberous roots.

Contribution of ultrasound and conventional hot water to the inactivation of Rhizopus stolonifer in sweet potato

Effects of ultrasound (US, 100, 200, 300, 400, and 500 W) and hot water (HW, 25, 40, and 55 °C) treatment combination on Rhizopus stolonifer in sweet potato tuberous roots (TRs) were investigated. US (300, 400, and 500 W) simultaneous HW (55 °C) for 10 min significantly inhibited colony diameters (from 90 mm to 80.08, 65.60, and 6.00 mm) and spores germination (p < 0.05). US+HW treatment significantly increased the leakage of nucleic acids and proteins (p < 0.05). Scanning and transmission electron microscopy analyses showed that US+HW led to significant damage on the appearance and ultrastructure of R. stolonifer. These damages resulted in crumpled hyphae, thickened cell walls, disappeared membranous organelles, massive vacuolation of the cytoplasm. US500+HW55 treatment could lead to cell membrane permeability increase and mitochondrial membrane potential decrease of R. stolonifer. In addition, US500+HW55 controlled the R. stolonifer development in sweet potato TRs during 20 days of storage at 28 °C, suggesting that US500+HW55 effectively inhibited the infection of R. stolonifer. Therefore, US500+HW55 treatment could be an efficient alternative method for storing and preserving sweet potato TRs.

Response of Sweet Potato Storability with Different Pre-storage Treatments at Ambient Temperature

The storage of sweet potato tuberous roots in tropical countries is a major challenge to farmers and retailers due to unfavourable climatic conditions. In this study, the storage performance of sweet potato roots in an ambient condition was investigated over a 12-week duration. The three different pre-storage treatments used were ash, alkaline solution (1.5 mol dm-3) and Siam weed (Chromolaena odorata) extract – to evaluate their effects on weight loss, shrinkage, weevil damage and sprouting. The control comprised tubers with no pre-treatment. It was observed that weight loss increased linearly from the inception of storage while shrinkage became apparent only after two (2) weeks. The percentage shrinkage of the tuber pre-treated with Siam weed increased at decreasing rate from 8 WAP. Treatment of tuber with Siam weed extract provided significantly higher protection against weevil damage (p &gt; 0.05). After this, sprouting was initiated. By the 12th week, the Siam weed (Chromolaena odorata) extract treatment yielded better results. The Siam weed (Chromolaena odorata) treatment also recorded the lowest weight loss of 28% and lowest shrinkage of 2.8%. It also sustained less weevil damage at 33.5% compared with the other treatments. Sprouting was higher in the tuber without pre-storage treatment. The alkaline solution and ash treatments had varied degree of performance for all the indicators.&#x0D; Keywords: Sweet potato storability, Ambient condition, Pre-storage treatment, Chromolaena odorata