High impacts of cultivar and home-cooking practice on the content of free myo-inositol, a bioavailable health-promoting cyclitol, in sweet potato.

Free myo-inositol is a bioavailable form of a cyclitol having various health-promoting activities. The impact of cultivar and home-cooking practice on the content of free myo-inositol in sweet potatoes (12 cultivars grown in 2 different locations) was studied. A GC-MS/MS method following in situ trimethylsilylation was established and validated to determine free myo-inositol. The established analytical method was sensitive, precise, and accurate. It was found that free myo-inositol content in sweet potato varied greatly (sevenfolds) with cultivar, ranging from 377.1 to 2628.3 mg/kg dw. A cultivar Poongwon-mi was found to be an exceptionally rich source of free myo-inositol (2628.3 mg/kg dw). Home-cooking practice markedly increased free myo-inositol content (maximum 240%). Baking showed the highest impact on the increase in free myo-inositol, followed by steaming, microwave cooking, and boiling, in decreasing order. This represents the first report of the remarkably high impact of cultivar and home-cooking practice on the free myo-inositol content in sweet potato. PRACTICAL APPLICATION: The free myo-inositol content in sweet potato varied greatly with the cultivars. Poongwon-mi contained a surprisingly high content of free myo-inositol. Home-cooking dramatically increased the free myo-inositol content.

Genome-wide association study to identify novel loci and genes for Fusarium root rot resistance in sweet potato using genotyping-by-sequencing.

Fusarium root rot, caused by Fusarium solani, is a major post-harvest disease in sweet potatoes (Ipomoea batatas (L.) Lam.). An effective strategy for controlling this disease is the development of resistant varieties. In this study, a genome-wide association study (GWAS) was conducted on 96 sweet potato genotypes to identify novel candidate loci and dissect the genetic basis of Fusarium root rot resistance. Genotyping was performed using genotyping-by-sequencing (GBS), and 44,255 SNPs were identified after filtering. The genotypes (n = 96) were evaluated through resistance tests in 2021 and 2022, separately and combined. The GWAS identified two significant SNP markers (LG3_22903756 and LG4_2449919) on chromosomes 3 and 4 associated with Fusarium root rot resistance, respectively. Lesion length showed significant differences between homozygous A and G alleles of LG3_22903756, which can potentially be used to develop molecular markers for selecting accessions resistant to Fusarium root rot. Expression analysis of 11 putative genes flanking the significant SNPs revealed the alteration in the expression of nine genes, indicating their possible involvement in Fusarium root rot resistance. The results of this study will aid in the marker-assisted selection and functional analysis of candidate genes for Fusarium root rot resistance in sweet potatoes.

Selection of flooding stress tolerant sweetpotato cultivars based on biochemical and phenotypic characterization.

Sweetpotato [Ipomoea batatas (L.) Lam] serves as a sustainable food source and ensures nutrition security in the face of climate change. Recently, farmers have developed increased interest in replacing rice with sweetpotato in paddy fields for higher income. However, sweetpotato is more susceptible to flooding stress than other abiotic stresses including drought and salinity. Here, we selected flooding tolerant sweetpotato cultivars based on biochemical characterization. Young seedlings of 33 sweetpotato cultivars were subjected to flooding stress for 20 days, and Yeonjami (YJM) was identified as the most flooding tolerant sweetpotato cultivar. Plant growth and biochemical characteristics of YJM were compared with those of Jeonmi (JM), a flooding sensitive sweetpotato cultivar. Under flooding stress, YJM showed higher content of chlorophyll and lower inhibition of plant height and fibrous root length than JM. Biochemical characterization revealed that although malondialdehyde and hydrogen peroxide contents were increased in fibrous roots of both cultivars, the amount of increase was 4-fold lower in YJM than in JM. Additionally, leaves of YJM showed higher ascorbate peroxidase activity than those of JM under flooding stress. Our results suggest that high membrane stability and antioxidant capacity are important flooding tolerance factors in sweetpotato. Furthermore, several flooding tolerance-related genes involved in starch and sucrose metabolism, fermentation, and cell wall loosening showed earlier induction and higher transcript levels in YJM leaves and fibrous roots than in JM tissues under flooding stress. Thus, phenotypic and biochemical characterization suggests that YJM could be used as a flooding tolerant sweetpotato cultivar.

Physicochemical Characteristics of Starch in Sweet Potato Cultivars Grown in Korea.

The objective of this study was to investigate the structural and physicochemical properties of starch from seven sweet potato cultivars (Shinyulmi, Sinjami, Hogammi, Jeonmi, Jinyulmi, Juhwangmi, and Pungwonmi). Jeonmi and Jinyulmi had amylose contents of 40.04% and 37.39%, respectively, whereas Juhwangmi and Pungwonmihad amylose contents of 30.95% and 32.37%, respectively. As a result of amylopectin polymerization, the seven cultivars were found to have high (>48%) contents of the degree of polymerization (DP) 13∼24 fraction, whereas the DP≥37 fraction content was <3.45%. The level of resistant starch was highest in Jeonmi (>30%) and lowest in Pungwonmi (<5%). The in vitro digestibility of Pungwonmi was greater than that of the other cultivars. Starch X-ray patterns did not differ among the cultivars. The results of this study provide useful information for the food industry regarding the application of sweet potato starches.

Comparative transcriptome profiling of tuberous roots of two sweetpotato lines with contrasting low temperature tolerance during storage.

Sweetpotato (Ipomoea batatas [L.] Lam) is considered an economically important crop worldwide and is used as a source of food, feed, and biomaterials. However, its origin in tropical regions makes it vulnerable to chilling injury during postharvest storage at low temperature. To gain further insight into the molecular mechanism of chilling response, we performed comparative transcriptome analysis of two sweetpotato lines, Xushu 15-1 and Xushu 15-4, with high and low cold storage ability, respectively. Tuberous roots of these lines were stored at 4 °C for 0, 2, and 6 weeks. RNA-Seq data of both lines were de novo assembled, producing 27,636 unigenes with a N50 value of 1204 bp. A total of 525 differentially expressed genes (DEGs) were identified and categorized into six clusters. Genes with higher expression in Xushu 15-1 than in Xushu 15-4 significantly increased in number over time during low temperature storage. Functional annotation of DEGs using KEGG enrichment analysis showed that these DEGs were involved in carbohydrate metabolism, ribosome, protein processing in endoplasmic reticulum, plant-pathogen interaction, and plant hormone signal transduction. Several key candidate genes involved in KEGG pathways were selected and discussed further. The results of this study enhance our understanding of the complex mechanisms involved in low temperature tolerance in sweetpotato during storage and provide a set of candidate genes for the development of new varieties with improved cold storage ability.

Intracellular Reactive Oxygen Species (ROS) Removal and Cytoprotection Effects of Sweet Potatoes of Various Flesh Colors and Their Polyphenols, Including Anthocyanin.

The flesh color of sweet potatoes varies based on the antioxidant pigments in the cultivar. In this study, the antioxidant characteristics of various flesh color sweet potato cultivars (Jinyulmi, Juhwangmi, Pungwonmi, and Sinjami) were investigated. The polyphenol contents were highest in the purple-fleshed cultivar, Sinjami (39, 68, and 71 µg gallic acid equivalent/g in distilled water, fermented ethanol, and ethanol extracts, respectively). The Sinjami cultivar contained 29 mg/100 g of anthocyanin, which is the major component resulting in increased concentrations of polyphenols. Using 2,2'-azinobis(3-ethylbenzothiazoline-6-sulphonic acid), 2,2-diphenyl-1-picrylhydrazyl, and ferric reducing ability of plasma assays, Sinjami showed greater antioxidant activity than the other cultivars. Additionally, the Sinjami extracts could recover cellular reactive oxygen species levels in tert-butyl hydroperoxide-stimulated HepG2 cells to a normal level. In conclusion, anthocyanin-enriched Sinjami has strong antioxidant activities and could improve health by suppressing oxidative damage.

Phylogenetic Placement and Morphological Characterization of Sclerotium rolfsii (Teleomorph: Athelia rolfsii) Associated with Blight Disease of Ipomoea batatas in Korea.

In this study, we aimed to characterize fungal samples from necrotic lesions on collar regions observed in different sweetpotato growing regions during 2015 and 2016 in Korea. Sclerotia appeared on the root zone soil surface, and white dense mycelia were observed. At the later stages of infection, mother roots quickly rotted, and large areas of the plants were destroyed. The disease occurrence was monitored at 45 and 84 farms, and 11.8% and 6.8% of the land areas were found to be infected in 2015 and 2016, respectively. Fungi were isolated from disease samples, and 36 strains were preserved. Based on the cultural and morphological characteristics of colonies, the isolates resembled the reference strain of Sclerotium rolfsii. Representative strains were identified as S. rolfsii (teleomorph: Athelia rolfsii) based on phylogenetic analysis of the internal transcribed spacer and large subunit genes along with morphological observations. To test the pathogenicity, sweetpotato storage roots were inoculated with different S. rolfsii strains. 'Yulmi' variety displayed the highest disease incidence, whereas 'Pungwonmi' resulted in the least. These findings suggested that morphological characteristics and molecular phylogenetic analysis were useful for identification of S. rolfsii.

Virus Incidence of Sweet Potato in Korea from 2011 to 2014.

A nationwide survey was performed to investigate the current incidence of viral diseases in Korean sweet potatoes for germplasm and growing fields from 2011 to 2014. A total of 83.8% of the germplasm in Korea was infected with viruses in 2011. Commercial cultivars that were used to supply growing fields were infected at a rate of 62.1% in 2012. Among surveyed viruses, the incidence of five Potyvirus species that infect sweet potato decreased between 2012 and 2013, and then increased again in 2014. Representatively, the incidence of Sweet potato feathery mottle virus (SPFMV) was 87.0% in 2012, 20.7% in 2013 and then increased to 35.3% in 2014. Unlike RNA viruses, DNA viruses were shown to decrease continuously. The incidence of Sweet potato leaf curl virus (SPLCV) was 5.5% in 2003, 59.5% in 2011, and 47.4% in 2012. It then decreased continuously year by year to 33.2% in 2013, and then 25.6% in 2014. While the infection rate of each virus species showed a tendency to decline, the virus infection status was more variable in 2013 and 2014. Nevertheless, the high rate of single infections and mixed infection combinations were more variable than the survey results from 2012. As shown in the results from 2013, the most prevalent virus infection was a single infection at 27.6%, with the highest rate of infection belonging to sweet potato symptomless virus-1 (SPSMV-1) (12.9%). Compared to 2013, infection combinations were more varied in 2014, with a total of 122 kinds of mixed infection.

Cryopreservation of garlic bulbil primordia by the droplet-vitrification procedure.

The droplet-vitrification protocol, a combination of droplet-freezing and solution-based vitrification was applied for cryopreserving garlic bulbil primordia. The highest survival and regeneration percentages of cryopreserved primordia (90.1 to 95.0 percent and 82.7 to 85.0 percent, respectively) were achieved after preculture for 2-4 days at 10 degree C on solid medium with 0.1 - 0.3 M sucrose, loading for 50 minutes in liquid medium with 2 M glycerol + 0.5 M sucrose, dehydration with PVS3 vitrification solution for 90-150 min, cooling primordia in 5 microl droplets of PVS3 vitrification solution placed on aluminum foil strips by dipping these strips in liquid nitrogen, warming them by plunging the foil strips into pre-heated (40 degree C) 0.8 M sucrose solution for 30 s and further incubation in the same solution for 30 minutes. The optimized droplet-vitrification protocol was successfully applied to bulbil primordia of five garlic varieties originating from various countries and to immature bulbils of two vegetatively propagated Allium species, with regeneration percentages ranging between 77.4 - 95.4 percent.

Skermanella aerolata sp. nov., isolated from air, and emended description of the genus Skermanella.

A light-pink-coloured bacterium, designated strain 5416T-32(T), was isolated from an air sample in Korea. Cells of the strain were strictly aerobic, Gram-negative, motile (single polar or subpolar flagellum) and rod-shaped. Optimal growth occurred at 25-30 degrees C and at pH 6.0-7.0. The major quinones were Q-10 and Q-8. The major fatty acids were C(18 : 1) omega 7c (53.8 %) and C(16 : 0) (15.9 %). The G+C content of the genomic DNA was 65.0 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain 5416T-32(T) was most closely related to Skermanella parooensis, with a similarity of 96.2 %, but relatively low sequence similarities (<92 %) were found with respect to other species with validly published names held in GenBank. Phenotypic and genotypic analyses indicated that strain 5416T-32(T) could not be assigned to any recognized species. Therefore strain 5416T-32(T) represents a novel species of the genus Skermanella, for which the name Skermanella aerolata sp. nov. is proposed. The type strain is 5416T-32(T) (=KACC 11604(T)=DSM 18479(T)).