Genome-Wide Identification and Expression Analysis of the Starch Synthase Gene Family in Sweet Potato and Two of Its Closely Related Species.

The starch synthase (SS) plays important roles in regulating plant growth and development and responding to adversity stresses. Although the SS family has been studied in many crops, it has not been fully identified in sweet potato and its two related species. In the present study, eight SSs were identified from Ipomoea batatas (I. batata), Ipomoea trifida (I. trifida), and Ipomoea trlioba (I. trlioba), respectively. According to the phylogenetic relationships, they were divided into five subgroups. The protein properties, chromosomal location, phylogenetic relationships, gene structure, cis-elements in the promoter, and interaction network of these proteins were also analyzed; stress expression patterns were systematically analyzed; and real-time polymerase chain reaction (qRT-PCR) analysis was performed. Ipomoea batatas starch synthase (IbSSs) were highly expressed in tuber roots, especially Ipomoea batatas starch synthase 1 (IbSS1) and Ipomoea batatas starch synthase 6 (IbSS6), which may play an important role in root development and starch biosynthesis. At the same time, the SS genes respond to potassium deficiency, hormones, cold, heat, salt, and drought stress. This study offers fresh perspectives for enhancing knowledge about the roles of SSs and potential genes to enhance productivity, starch levels, and resistance to environmental stresses in sweet potatoes.

Effect of Cactus (Opuntia ficus-indica) and Acacia (Acacia seyal) Gums on the Pasting, Thermal, Textural, and Rheological Properties of Corn, Sweet Potato, and Turkish Bean Starches.

This study was planned to explore the locally available natural sources of gum hydrocolloids as a natural modifier of different starch properties. Corn (CS), sweet potato (SPS), and Turkish bean (TBS) starches were mixed with locally extracted native or acetylated cactus (CG) and acacia (AG) gums at 2 and 5% replacement levels. The binary mixtures (starch-gums) were prepared in water, freeze dried, ground to powder, and stored airtight. A rapid viscoanalyzer (RVA), differential scanning calorimeter (DSC), texture analyzer, and dynamic rheometer were used to explore their pasting, thermal, textural, and rheological properties. The presence of acetylated AG or CG increased the final viscosity (FV) in all three starches when compared to starch pastes containing native gums. Plain SPS dispersion had a higher pasting temperature (PT) than CS and TBS. The addition of AG or CG increased the PT of CS, SPS, and TBS. The thermograms revealed the overall enthalpy change of the starch and gum blends: TBS > SPS > CS. The peak temperature (Tp) of starches increased with increasing gum concentration from 2 to 5% for both AG and CG native and modified gums. When compared to the control gels, the addition of 2% CG, either native or modified, reduced the syneresis of starch gels. However, further addition (5% CG) increased the gels' syneresis. Furthermore, the syneresis for the first cycle on the fourth day was higher than the second cycle on the eighth day for all starches. The addition of native and acetylated CG reduced the hardness of starch gels at all concentrations tested. All of the starch dispersions had higher G' than G″ values, indicating that they were more elastic and less viscous with or without the gums. The apparent viscosity of all starch gels decreased as shear was increased, with profiles indicating time-dependent thixotropic behavior. All of the starch gels, with or without gums, showed a non-Newtonian shear thinning trend in the shear stress vs. shear rate graphs. The addition of acetylated CG gum to CS resulted in a higher activation energy (Ea) than the native counterparts and the control. More specifically, starch gels with a higher gum concentration (5%) provided greater Ea than their native counterparts.

Molecular Characterization and Target Prediction of Candidate miRNAs Related to Abiotic Stress Responses and/or Storage Root Development in Sweet Potato.

Sweet potato is a tuberous root crop with strong environmental stress resistance. It is beneficial to study its storage root formation and stress responses to identify sweet potato stress- and storage-root-thickening-related regulators. Here, six conserved miRNAs (miR156g, miR157d, miR158a-3p, miR161.1, miR167d and miR397a) and six novel miRNAs (novel 104, novel 120, novel 140, novel 214, novel 359 and novel 522) were isolated and characterized in sweet potato. Tissue-specific expression patterns suggested that miR156g, miR157d, miR158a-3p, miR167d, novel 359 and novel 522 exhibited high expression in fibrous roots or storage roots and were all upregulated in response to storage-root-related hormones (indole acetic acid, IAA; zeaxanthin, ZT; abscisic acid, ABA; and gibberellin, GAs). The expression of miR156g, miR158a-3p, miR167d, novel 120 and novel 214 was induced or reduced dramatically by salt, dehydration and cold or heat stresses. Moreover, these miRNAs were all upregulated by ABA, a crucial hormone modulator in regulating abiotic stresses. Additionally, the potential targets of the twelve miRNAs were predicted and analyzed. Above all, these results indicated that these miRNAs might play roles in storage root development and/or stress responses in sweet potato as well as provided valuable information for the further investigation of the roles of miRNA in storage root development and stress responses.

Drought, Low Nitrogen Stress, and Ultraviolet-B Radiation Effects on Growth, Development, and Physiology of Sweetpotato Cultivars during Early Season.

Drought, ultraviolet-B (UV-B), and nitrogen stress are significant constraints for sweetpotato productivity. Their impact on plant growth and development can be acute, resulting in low productivity. Identifying phenotypes that govern stress tolerance in sweetpotatoes is highly desirable to develop elite cultivars with better yield. Ten sweetpotato cultivars were grown under nonstress (100% replacement of evapotranspiration (ET)), drought-stress (50% replacement of ET), UV-B (10 kJ), and low-nitrogen (20% LN) conditions. Various shoot and root morphological, physiological, and gas-exchange traits were measured at the early stage of the crop growth to assess its performance and association with the storage root number. All three stress factors caused significant changes in the physiological and root- and shoot-related traits. Drought stress reduced most shoot developmental traits (29%) to maintain root growth. UV-B stress increased the accumulation of plant pigments and decreased the photosynthetic rate. Low-nitrogen treatment decreased shoot growth (11%) and increased the root traits (18%). The highly stable and productive cultivars under all four treatments were identified using multitrait stability index analysis and weighted average of absolute scores (WAASB) analyses. Further, based on the total stress response indices, 'Evangeline', 'O'Henry', and 'Beauregard B-14' were identified as vigorous under drought; 'Evangeline', 'Orleans', and 'Covington' under UV-B; and 'Bonita', 'Orleans', and 'Beauregard B-14' cultivars showed greater tolerance to low nitrogen. The cultivars 'Vardaman' and 'NC05-198' recorded a low tolerance index across stress treatments. This information could help determine which plant phenotypes are desirable under stress treatment for better productivity. The cultivars identified as tolerant, sensitive, and well-adapted within and across stress treatments can be used as source materials for abiotic stress tolerance breeding programs.

Effects of Variety and Growing Location on Physicochemical Properties of Starch from Sweet Potato Root Tuber.

Three sweet potato varieties with purple-, yellow-, and white-fleshed root tubers were planted in four growing locations. Starches were isolated from their root tubers, their physicochemical properties (size, iodine absorption, amylose content, crystalline structure, ordered degree, lamellar thickness, swelling power, water solubility, and pasting, thermal and digestion properties) were determined to investigate the effects of variety and growing location on starch properties in sweet potato. The results showed that granule size (D[4,3]) ranged from 12.1 to 18.2 µm, the iodine absorption parameters varied from 0.260 to 0.361 for OD620, from 0.243 to 0.326 for OD680 and from 1.128 to 1.252 for OD620/550, and amylose content varied from 16.4% to 21.2% among starches from three varieties and four growing locations. Starches exhibited C-type X-ray diffraction patterns, and had ordered degrees from 0.634 to 0.726 and lamellar thicknesses from 9.72 to 10.21 nm. Starches had significantly different swelling powers, water solubilities, pasting viscosities, and thermal properties. Native starches had rapidly digestible starch (RDS) from 2.2% to 10.9% and resistant starch (RS) from 58.2% to 89.1%, and gelatinized starches had RDS from 70.5% to 81.4% and RS from 10.8% to 23.3%. Two-way ANOVA analysis showed that starch physicochemical properties were affected significantly by variety, growing location, and their interaction in sweet potato.

Use of universal primers for the 18S ribosomal RNA gene and whole soil DNAs to reveal the taxonomic structures of soil nematodes by high-throughput amplicon sequencing.

Nematodes are abundant metazoans that play crucial roles in nutrient recycle in the pedosphere. Although high-throughput amplicon sequencing is a powerful tool for the taxonomic profiling of soil nematodes, polymerase chain reaction (PCR) primers for amplification of the 18S ribosomal RNA (SSU) gene and preparation of template DNAs have not been sufficiently evaluated. We investigated nematode community structure in copse soil using four nematode-specific (regions 1-4) and two universal (regions U1 and U2) primer sets for the SSU gene regions with two DNAs prepared from copse-derived mixed nematodes and whole soil. The major nematode-derived sequence variants (SVs) identified in each region was detected in both template DNAs. Order level taxonomy and feeding type of identified nematode-derived SVs were distantly related between the two DNA preparations, and the region U2 was closely related to region 4 in the non-metric multidimensional scaling (NMDS) based on Bray-Curtis dissimilarity. Thus, the universal primers for region U2 could be used to analyze soil nematode communities. We further applied this method to analyze the nematodes living in two sampling sites of a sweet potato-cultivated field, where the plants were differently growing. The structure of nematode-derived SVs from the two sites was distantly related in the principal coordinate analysis (PCoA) with weighted unifrac distances, suggesting their distinct soil environments. The resultant ecophysiological status of the nematode communities in the copse and field on the basis of feeding behavior and maturity indices was fairly consistent with those of the copse- and the cultivated house garden-derived nematodes in prior studies. These findings will be useful for the DNA metabarcoding of soil eukaryotes, including nematodes, using soil DNAs.

Genome-Wide Identification of ARF Transcription Factor Gene Family and Their Expression Analysis in Sweet Potato.

Auxin response factors (ARFs) are a family of transcription factors that play an important role of auxin regulation through their binding with auxin response elements. ARF genes are represented by a large multigene family in plants; however, to our knowledge, the ARF gene family has not been well studied and characterized in sweet potatoes. In this study, a total of 25 ARF genes were identified in Ipomea trifida. The identified ItrARF genes' conserved motifs, chromosomal locations, phylogenetic relationships, and their protein characteristics were systemically investigated using different bioinformatics tools. The expression patterns of ItfARF genes were analyzed within the storage roots and normal roots at an early stage of development. ItfARF16b and ItfARF16c were both highly expressed in the storage root, with minimal to no expression in the normal root. ItfARF6a and ItfARF10a exhibited higher expression in the normal root but not in the storage root. Subsequently, ItfARF1a, ItfARF2b, ItfARF3a, ItfARF6b, ItfARF8a, ItfARF8b, and ItfARF10b were expressed in both root types with moderate to high expression for each. All ten of these ARF genes and their prominent expression signify their importance within the development of each respective root type. This study provides comprehensive information regarding the ARF family in sweet potatoes, which will be useful for future research to discover further functional verification of these ItfARF genes.

Genome-Wide Identification and Expression Analysis of JAZ Family Involved in Hormone and Abiotic Stress in Sweet Potato and Its Two Diploid Relatives.

Jasmonate ZIM-domain (JAZ) proteins are key repressors of a jasmonic acid signaling pathway. They play essential roles in the regulation of plant growth and development, as well as environmental stress responses. However, this gene family has not been explored in sweet potato. In this study, we identified 14, 15, and 14 JAZs in cultivated hexaploid sweet potato (Ipomoea batatas, 2n = 6x = 90), and its two diploid relatives Ipomoea trifida (2n = 2x = 30) and Ipomoea triloba (2n = 2x = 30), respectively. These JAZs were divided into five subgroups according to their phylogenetic relationships with Arabidopsis. The protein physiological properties, chromosome localization, phylogenetic relationship, gene structure, promoter cis-elements, protein interaction network, and expression pattern of these 43 JAZs were systematically investigated. The results suggested that there was a differentiation between homologous JAZs, and each JAZ gene played different vital roles in growth and development, hormone crosstalk, and abiotic stress response between sweet potato and its two diploid relatives. Our work provided comprehensive comparison and understanding of the JAZ genes in sweet potato and its two diploid relatives, supplied a theoretical foundation for their functional study, and further facilitated the molecular breeding of sweet potato.

Effect of tebuconazole and trifloxystrobin on Ceratocystis fimbriata to control black rot of sweet potato: processes of reactive oxygen species generation and antioxidant defense responses.

Black rot, caused by Ceratocystis fimbriata, is one of the most destructive disease of sweet potato worldwide, resulting in significant yield losses. However, a proper management system can increase resistance to this disease. Therefore, this study investigated the potential of using tebuconazole (TEB) and trifloxystrobin (TRI) to improve the antioxidant defense systems in sweet potato as well as the inhibitory effects on the growth of and antioxidant activity in C. fimbriata. Four days after inoculating cut surfaces of sweet potato disks with C. fimbriata, disease development was reduced by different concentrations of TEB + TRI. Infection by C. fimbriata increased the levels of hydrogen peroxide (H2O2), malondialdehyde (MDA), and electrolyte leakage (EL), and the activity of lipoxygenase (LOX) by 138, 152, 73, and 282%, respectively, in sweet potato disks, relative to control. In the sweet potato disks, C. fimbriata reduced the antioxidant enzyme activities as well as the contents of ascorbate (AsA) and reduced glutathione (GSH) by 82 and 91%, respectively, compared with control. However, TEB + TRI reduced the oxidative damage in the C. fimbriata-inoculated sweet potato disks by enhancing the antioxidant defense systems. On the other hand, applying TEB + TRI increased the levels of H2O2, MDA, and EL, and increased the activity of LOX in C. fimbriata, in which the contents of AsA and GSH decreased, and therefore, inhibited the growth of C. fimbriata. These results suggest that TEB + TRI can significantly control black rot disease in sweet potato by inhibiting the growth of C. fimbriata.

Dynamic network biomarker analysis discovers IbNAC083 in the initiation and regulation of sweet potato root tuberization.

The initiation and development of storage roots (SRs) are intricately regulated by a transcriptional regulatory network. One key challenge is to accurately pinpoint the tipping point during the transition from pre-swelling to SRs and to identify the core regulators governing such a critical transition. To solve this problem, we performed a dynamic network biomarker (DNB) analysis of transcriptomic dynamics during root development in Ipomoea batatas (sweet potato). First, our analysis identified stage-specific expression patterns for a significant proportion (>9%) of the sweet potato genes and unraveled the chronology of events that happen at the early and later stages of root development. Then, the results showed that different root developmental stages can be depicted by co-expressed modules of sweet potato genes. Moreover, we identified the key components and transcriptional regulatory network that determine root development. Furthermore, through DNB analysis an early stage, with a root diameter of 3.5 mm, was identified as the critical period of SR swelling initiation, which is consistent with morphological and metabolic changes. In particular, we identified a NAM/ATAF/CUC (NAC) domain transcription factor, IbNAC083, as a core regulator of this initiation in the DNB-associated network. Further analyses and experiments showed that IbNAC083, along with its associated differentially expressed genes, induced dysfunction of metabolism processes, including the biosynthesis of lignin, flavonol and starch, thus leading to the transition to swelling roots.

Potassium Fertilization Stimulates Sucrose-to-Starch Conversion and Root Formation in Sweet Potato (Ipomoea batatas (L.) Lam.).

A field experiment was established to study sweet potato growth, starch dynamic accumulation, key enzymes and gene transcription in the sucrose-to-starch conversion and their relationships under six K2O rates using Ningzishu 1 (sensitive to low-K) and Xushu 32 (tolerant to low-K). The results indicated that K application significantly improved the biomass accumulation of plant and storage root, although treatments at high levels of K, i.e., 300-375 kg K2O ha-1, significantly decreased plant biomass and storage root yield. Compared with the no-K treatment, K application enhanced the biomass accumulation of plant and storage root by 3-47% and 13-45%, respectively, through promoting the biomass accumulation rate. Additionally, K application also enhanced the photosynthetic capacity of sweet potato. In this study, low stomatal conductance and net photosynthetic rate (Pn) accompanied with decreased intercellular CO2 concentration were observed in the no-K treatment at 35 DAT, indicating that Pn was reduced mainly due to stomatal limitation; at 55 DAT, reduced Pn in the no-K treatment was caused by non-stomatal factors. Compared with the no-K treatment, the content of sucrose, amylose and amylopectin decreased by 9-34%, 9-23% and 6-19%, respectively, but starch accumulation increased by 11-21% under K supply. The activities of sucrose synthetase (SuSy), adenosine-diphosphate-glucose pyrophosphorylase (AGPase), starch synthase (SSS) and the transcription of Susy, AGP, SSS34 and SSS67 were enhanced by K application and had positive relationships with starch accumulation. Therefore, K application promoted starch accumulation and storage root yield through regulating the activities and genes transcription of SuSy, AGPase and SSS in the sucrose-to-starch conversion.

Archaeological science meets Maori knowledge to model pre-Columbian sweet potato (Ipomoea batatas) dispersal to Polynesia's southernmost habitable margins.

Most scholars of the subject consider that a pre-Columbian transpacific transfer accounts for the historical role of American sweet potato Ipomoea batatas as the kumara staple of Indigenous New Zealand/Aotearoa Maori in cooler southwestern Polynesia. Archaeologists have recorded evidence of ancient Polynesian I. batatas cultivation from warmer parts of generally temperate-climate Aotearoa, while assuming that the archipelago's traditional Murihiku region in southern South Island/Te Waipounamu was too cold to grow and store live Polynesian crops, including relatively hardy kumara. However, archaeological pits in the form of seasonal Maori kumara stores (rua kumara) have been discovered unexpectedly at Purakaunui on eastern Murihuku's Otago coast, over 200 km south of the current Polynesian limit of record for premodern I. batatas production. Secure pit deposits that incorporate starch granules with I. batatas characteristics are radiocarbon-dated within the decadal range 1430-1460 CE at 95% probability in a Bayesian age model, about 150 years after Polynesians first settled Te Waipounamu. These archaeological data become relevant to a body of Maori oral history accounts and traditional knowledge (matauranga) concerning southern kumara, incorporating names, memories, landscape features and seemingly enigmatic references to an ancient Murihiku crop presence. Selected components of this lore are interpreted through comparative exegesis for correlation with archaeological science results in testable models of change. In a transfer and adaptation model, crop stores if not seasonal production technologies also were introduced from a warmer, agricultural Aotearoa region into dune microclimates of 15th-century coastal Otago to mitigate megafaunal loss, and perhaps to support Polynesia's southernmost residential chiefdom in its earliest phase. A crop loss model proposes that cooler seasonal temperatures of the post-1450 Little Ice Age and (or) political change constrained kumara supply and storage options in Murihiku. The loss model allows for the disappearance of kumara largely, but not entirely, as a traditional Otago crop presence in Maori social memory.

Integrated transcriptome, small RNA and degradome sequencing approaches proffer insights into chlorogenic acid biosynthesis in leafy sweet potato.

Leafy sweet potato is rich in total phenolics (TP) which play key roles in health protection, the chlorogenic acid (CGA) constitutes the major components of phenolic compounds in leafy sweet potato. Unfortunately, the mechanism of CGA biosynthesis in leafy sweet potato is unclear. To dissect the mechanisms of CGA biosynthesis, we performed transcriptome, small RNA (sRNA) and degradome sequencing of one low-CGA content and one high-CGA content genotype at two stages. A total of 2,333 common differentially expressed genes (DEGs) were identified, and the enriched DEGs were related to photosynthesis, starch and sucrose metabolism and phenylpropanoid biosynthesis. The functional genes, such as CCR, CCoAOMT and HCT in the CGA biosynthetic pathway were down-regulated, indicating that the way to lignin was altered, and two possible CGA biosynthetic routes were hypothesized. A total of 38 DE miRNAs were identified, and 1,799 targets were predicated for 38 DE miRNAs by using in silico approaches. The target genes were enriched in lignin and phenylpropanoid catabolic processes. Transcription factors (TFs) such as apetala2/ethylene response factor (AP2/ERF) and Squamosa promoter binding protein-like (SPL) predicated in silico were validated by degradome sequencing. Association analysis of the DE miRNAs and transcriptome datasets identified that miR156 family negatively targeted AP2/ERF and SPL. Six mRNAs and six miRNAs were validated by qRT-PCR, and the results showed that the expression levels of the mRNAs and miRNAs were consistent with the sequencing data. This study established comprehensive functional genomic resources for the CGA biosynthesis, and provided insights into the molecular mechanisms involving in this process. The results also enabled the first perceptions of the regulatory roles of mRNAs and miRNAs, and offered candidate genes for leafy sweet potato improvements.

Effects of water deficit on growth and performance of drip irrigated sweet potato varieties.

BACKGROUND: There are many scientific studies on performance of different sweet potato varieties under water deficits, however, no study on Koganesengan and Beniazuma varieties has been found in the literature. This study was aimed to investigate the effects of water deficit levels (control-WD0 , low-WD25 , medium-WD50 and high-WD75 water deficit levels) on growth, yield and quality parameters, water use efficiency and water-yield response factor values of these sweet potato varieties under drip irrigation. RESULTS: The seasonal water consumptions of varieties were calculated as 808 and 826 mm, respectively, under no water deficit. All of the growth (except average tuber length for Koganesengan) and yield parameters of both varieties were significantly affected by water deficit treatments. However, most of the quality parameters including total dry mater, starch, ß-carotene, ascorbic acid, protein, saccharose and glucose contents for both varieties; total ash, crude fiber and phenolic matter content for Beniazuma; and fructose content and antioxidant activity for Koganesengan variety had no response to water deficits at any level. Under high deficit and control, fresh and dry vine, tuber and total yields ranged from 4.80 to 14.54, 0.85 to 2.35, 1.59 to 10.97 and 6.40 to 25.52 t ha-1 for Koganesengan and 6.05 to 27.88, 0.99 to 4.09, 2.17 to 22.91 and 8.22 to 50.79 t ha-1 for Beniazuma, respectively. CONCLUSION: The results showed that Beniazuma variety is proportionally more sensitive to water deficit than Koganesengan. It can be concluded that both varieties can be grown in Mediterranean conditions by providing optimum irrigation applications. © 2020 Society of Chemical Industry.

Piriformospora indica colonization increases the growth, development, and herbivory resistance of sweet potato (Ipomoea batatas L.).

KEY MESSAGE: Piriformospora indica symbiosis promoted the growth and photosynthesis, and simultaneously enhanced the resistance against insect herbivory by regulating sporamin-dependent defense in sweet potato. Piriformospora indica (P. indica), a versatile endophytic fungus, promotes the growth and confers resistance against multiple stresses by root colonization in plant hosts. In this study, the effects of P. indica colonization on the growth, physiological change, and herbivore resistance of leaf-vegetable sweet potato cultivar were investigated. P. indica symbiosis significantly improved the biomass in both above- and under-ground parts of sweet potato plants. In comparison with the non-colonized plants, the content of photosynthetic pigments and the efficiency of photosynthesis were increased in P. indica-colonized sweet potato plants. Further investigation showed that the activity of catalase was enhanced in both leaves and roots of sweet potato plants after colonization, but ascorbate peroxidase, peroxidase, and superoxide dismutase were not enhanced. Furthermore, the interaction between P. indica and sweet potato plants also showed the biological function in jasmonic acid (JA)-mediated defense. The plants colonized by P. indica had greatly increased JA accumulation and defense gene expressions, including IbNAC1, IbbHLH3, IbpreproHypSys, and sporamin, leading to elevated trypsin inhibitory activity, which was consistent with a reduced Spodoptera litura performance when larvae fed on the leaves of P. indica-colonized sweet potato plants. The root symbiosis of P. indica is helpful for the plant promoting growth and development and has a strong function as resistance inducers against herbivore attack in sweet potato cultivation by regulating sporamin-dependent defense.

Identification of Shaker K+ channel family members in sweetpotato and functional exploration of IbAKT1.

The Shaker K+ channel family plays a vital role in potassium absorption and stress resistance in plants. However little information on the genes family is available about sweetpotato. In the present study, eleven sweetpotato Shaker K+ channel genes were identified and classified into five groups based on phylogenetic relationships, conserved motifs, and gene structure analyses. Based on synteny analysis, four duplicated gene pairs were identified, derived from both ancient and recent duplication, whereas only one resulted from tandem duplication events. Different expression pattern of Shaker K+ channel genes in roots of Xu32 and NZ1 resulted in different K+ deficiency tolerances, suggesting there is different mechanism of K+ uptake in sweetpotato cultivars with different K+-tolerance levels. Quantitative real-time PCR analysis revealed that the shaker K+ channel genes responded to drought and high salt stresses. Higher K+ influx under normal condition and lower K+ efflux under K+ deficiency stress were observed in IbAKT1 overexpressing transgenic roots than in adventitious roots, which indicated that IbAKT1 may play an important role in the regulation of K+ deficiency tolerance in sweetpotato. This is the first genome-wide analysis of Shaker K+ channel genes and the first functional analysis of IbAKT1 in sweetpotato. Our results provide valuable information on the gene structure, evolution, expression and functions of the Shaker K+ channel gene family in sweetpotato.

Changes in cell wall components and polysaccharide-degrading enzymes in relation to differences in texture during sweetpotato storage root growth.

Sweetpotato has special texture characteristics, which directly affect the eating quality and post-production processing quality of sweetpotato. To investigate the texture change mechanism of sweetpotato during the growth process, this study selected two varieties with significant differences in texture from 35 varieties. The storage roots were sampled at 50, 80, 110, and 140 days after planting. Measure the texture parameters, the cell wall composition content, cell wall-related enzyme activities and the expression of expansin genes of sweetpotato storage roots. The results show that the hardness, adhesiveness and chewiness parameters of 'Yushu No 10' were significantly lower than those of 'Mianfen No 1', they have significantly different texture properties. In terms of cell wall composition, the soluble pectin content of 'Yushu No 10' was more than twice that of 'Mianfen No 1', whereas the insoluble pectin content was lower than that of 'Mianfen No 1', with the cellulose content of 'Yushu No 10' being significantly higher than that of 'Mianfen No 1'. In terms of cell wall-related enzymes, 'Yushu No 10' hardness gumminess and chewiness had a significant correlation with hemicellulose activity, and 'Mianfen No 1' had insignificant correlation with four cell wall-related enzymes. Expansin genes were also expressed differently during the various stages of root tubers expansin. The expressions of IbEXP1, IbEXP2 and IbEXPL1 were significantly correlated with the changes in cell wall component content, and were related to the qualitative structure changes. The research conclusion shows that the texture changes during the growth of sweetpotato are related to cell wall composition, cell wall-related enzyme activity changes, and the expression of expansin genes. This study provides theoretical guidance for in-depth study of texture changes of sweetpotato, post-harvest processing and utilization and quality improvement of storage roots.

Leaf development and energy yield of hydroponic sweetpotato seedlings using single-node cutting as influenced by light intensity and LED spectrum.

Vine cuttings with six to eight unfolded leaves are utilized as is conventional in sweetpotato (Ipomoea batatas (L.) Lam.) seedling production. However, most vine cuttings wilt after transplanting into the field. Moreover, few researchers have examined the influence of photon flux density (PFD) provided by white or white plus red light-emitting diodes (LEDs) on sweetpotato plantlets. In this study, hydroponic sweetpotato (cv. Beniharuka) seedlings using single-node cutting were grown under 20 combinations of five levels of PFDs of 150, 200, 250, 300, and 350 µmol m-2 d-1 and four light qualities: white LEDs with a red light to blue light ratio (R:B ratio) of 0.9, white plus red LEDs with R:B ratios of 1.2 and 2.2, respectively, and fluorescent lamp with an R:B ratio of 1.8 as control, for 20 days under a controlled enviroment. Results showed that the number of newly developed leaves on hydroponic sweetpotato seedlings increased with time in a quadratic function, regardless of light quality. Fluorescent lamps led to greater numbers of new leaves on hydroponic sweetpotato seedlings compared with those grown under LEDs. Plant height, leaf area, and fresh and dry weights increased initially and then decreased with increasing daily light integral (DLI) in quadratic funcitons with a highest value under a PFD of 250 µmol m-2 d-1. However, no significant differences were observed in fresh and dry weights of hydroponic sweetpotato seedlings grown under PFDs of 200 and 250 µmol m-2 s-1. The quantum yield of photosystem II (ФPSII) decreased linearly as DLI increased from 8.6-20.2 mol m-2 d-1. Power consumptions based on fresh and dry weights were lowest in sweetpotato seedlings grown under a PFD of 200 µmol m-2 s-1 provided by white LEDs with an R:B ratio of 0.9. White LEDs also showed higher light energy use efficiency than white plus red LEDs. In summary, it is recommended that a PFD of 200 µmol m-2 s-1 with DLI at 11.5 mol m-2 d-1 provided by white LEDs with an R:B ratio of 0.9 is suitable for hydroponic sweetpotato (cv. Beniharuka) seedling production under a controlled environment.

Photosynthesis product allocation and yield in sweet potato with spraying exogenous hormones under drought stress.

This study investigated the alleviation effects of spraying phytohormones on the physiological characteristics and yield of sweet potato under drought stress during the early vine development and storage root bulking stage, respectively. The endogenous hormone contents, photosynthetic fluorescence indexes, photosynthetic products transfer allocation (based on 13C labeling method), and yield of sweet potato were studied by spraying water, 6-benzylaminopurine (6-BA), abscisic acid (ABA), and combined with the two exogenous hormones under artificial dry shed and dry pond. Results indicated that the yield was increased by spraying 6-BA or ABA separately in comparison with the control treatment under drought stress, and the alleviation effects of spraying 6-BA at the early stage were better than at the storage root bulking stage, while spraying ABA at the storage root bulking stage was better than at the early stage. The sweet potato yield increased when sprayed with 6-BA, especially at the early vine development stage, and sweet potato yield was further enhanced by the addition of ABA. When sprayed together, exogenous 6-BA and ABA increased plant shoot and storage root biomass, as well as leaf area and yield, at both stages. The combination of exogenous 6-BA and ABA also increased shoot 13C accumulation at the early vine development stage and storage root 13C accumulation at the storage root bulking stage, in comparison with 6-BA or ABA alone under drought stress. Spraying exogenous hormones under drought stress increased the endogenous hormone contents, enhanced carbon metabolism enzyme activities, improved the photosynthetic fluorescence characteristics of leaves, and regulated the source-sink balance, all of which alleviated the yield reduction caused by drought stress. Application of the combination of 6-AB and ABA yielded better results than that of the 6-BA or ABA alone.

Sequencing depth and genotype quality: accuracy and breeding operation considerations for genomic selection applications in autopolyploid crops.

KEY MESSAGE: Polypoid crop breeders can balance resources between density and sequencing depth, dosage information and fewer highly informative SNPs recommended, non-additive models and QTL advantages on prediction dependent on trait architecture. The autopolyploid nature of potato and sweetpotato ensures a wide range of meiotic configurations and linkage phases leading to complex gene-action and pose problems in genotype data quality and genomic selection analyses. We used a 315-progeny biparental F1 population of hexaploid sweetpotato and a diversity panel of 380 tetraploid potato, genotyped using different platforms to answer the following questions: (i) do polyploid crop breeders need to invest more for additional sequencing depth? (ii) how many markers are required to make selection decisions? (iii) does considering non-additive genetic effects improve predictive ability (PA)? (iv) does considering dosage or quantitative trait loci (QTL) offer significant improvement to PA? Our results show that only a small number of highly informative single nucleotide polymorphisms (SNPs; ≤ 1000) are adequate for prediction in the type of populations we analyzed. We also show that considering dosage information and models considering only additive effects had the best PA for most traits, while the comparative advantage of considering non-additive genetic effects and including known QTL in the predictive model depended on trait architecture. We conclude that genomic selection can help accelerate the rate of genetic gains in potato and sweetpotato. However, application of genomic selection should be considered as part of optimizing the entire breeding program. Additionally, since the predictions in the current study are based on single populations, further studies on the effects of haplotype structure and inheritance on PA should be studied in actual multi-generation breeding populations.