Sweetpotato, Ipomoea batatas (L.) Lam., is an important food crop worldwide.  Large scale evaluation of sweetpotato germplasm for genetic diversity is necessary to determine the genetic relationships between them and effectively use them in the genetic improvement.  In this study, the genetic diversity of 617 sweetpotato accessions, including 376 landraces and 162 bred varieties from China and 79 introduced varieties from 11 other countries, was assessed using 30 simple sequence repeat (SSR) primer pairs with high polymorphism.  Based on the population structure analysis, these sweetpotato accessions were divided into three groups, Group 1, Group 2 and Group 3, which included 228, 136 and 253 accessions, respectively.  Consistent results were obtained by phylogenic analysis and principal coordinate analysis (PCoA).  Of the three groups, Group 2 showed the highest level of genetic diversity and its accessions were mainly distributed in low-latitude regions.  The accessions from South China exhibited the highest level of genetic diversity, which supports the hypothesis that Fujian and Guangdong were the first regions where sweetpotato was introduced to China.  Analysis of molecular variance (AMOVA) indicated significant genetic differentiations between the different groups, but low levels of genetic differentiation existed between the different origins and accession types.  These results provide valuable information for the better utilization of these accessions in sweetpotato breeding.

Radopholus similis (Cobb 1893) Thorne (1949) is a destructive migratory endoparasitic plant nematode.  In this study, the pathogenic process of R. similis infection in Nicotiana benthamiana (tobacco) was studied using quartz sand culture in laboratory.  The results showed that R. similis mainly parasitised the root cortex, leading to cortical cell decomposition and tissue decay.  We optimised the inoculation conditions to establish a method for determining the pathogenicity of R. similis as follows: (1) a glass culture tube was filled with quartz sand (about 1/3 of the height) and sterilised twice; (2) 20-day-old N. benthamiana seedlings were transplanted into test tubes and cultivated for 10 days at (25±1)°C; (3) R. similis female nematodes were inoculated in the root rhizosphere at a rate of 150 nematodes per plant; (4) the number of nematodes, disease severity, and growth of the plant at 30 days post-inoculation (dpi) were determined.  The pathogenicity of eight R. similis populations from different hosts was determined, which proved the feasibility of this method.

Geranylgeranyl pyrophosphate synthase (GGPS) plays an important role in the biosynthesis of carotenoids.  In a previous study, the IbGGPS gene was isolated from a sweetpotato, Ipomoea batatas (L.) Lam., line Nongdafu 14 with high carotenoid contents, but its role and underlying mechanisms in carotenoid biosynthesis in sweetpotato were not investigated.  In the present study, the IbGGPS gene was introduced into a sweetpotato cv. Lizixiang and the contents of β-carotene, β-cryptoxanthin, zeaxanthin and lutein were significantly increased in the storage roots of the IbGGPS-overexpressing sweetpotato plants.  Further analysis showed that IbGGPS gene overexpression systematically up-regulated the genes involved in the glycolytic, 2-C-methyl-D-erythritol-4-phosphate (MEP) and carotenoid pathways, which increased the carotenoid contents in the transgenic plants.  These results indicate that the IbGGPS gene has the potential for use in improving the carotenoid contents in sweetpotato and other plants.

In the postharvest processing of tea leaves, withering is the first indispensable manufacturing process which produces the mellow, umami and sweet taste of white tea.  In this study, we aimed to determine the dynamic changes of the main metabolites and clarify the key differentially expressed genes (DEGs) involved in forming the characteristic taste of white tea during withering.  Phytochemical analyses revealed that the contents of total catechins and starch decreased continuously, whereas the contents of theaflavin, γ-aminobutyric acid (GABA), maltose, and soluble sugars increased significantly during withering (from 0–48 h).  Meanwhile, the elevation of α-amylase (AMY), β-amylase (BAM), total amylase, and glutamate decarboxylase (GAD) activities may be correlated with the accumulation of GABA and maltose.  By transcriptome sequencing, we detected 9 707, 15 921, 17 353, and 17 538 DEGs at 12, 24, 36, and 48 h of the withering process, respectively, compared with 0 h sample (fresh leaves).  The transcript levels of most of the DEGs involved in catechin biosynthesis were significantly inhibited, whereas those involved in catechin oxidation were significantly up-regulated, which could be correlated to a decrease in catechin content and an increase in theaflavin content.  The DEGs involved in GABA biosynthesis were considerably up-regulated, and the down-regulation of SPMS could reduce the competition for converting spermidine to GABA.  The up-regulation of the AMY and BAM genes could trigger starch degradation, resulting in the increase of soluble sugar content.  These results provide new insights into the importance of the withering process to the characteristic taste of white tea.

   The variant LM1 was previously obtained using embryogenic cell suspension cultures of sweetpotato variety Lizixiang by gamma-ray induced mutation, and then its characteristics were stably inherited through six clonal generations, thus this mutant was named LM1. In this study, systematic characterization of salt tolerance and Fusarium wilt resistance were performed between Lizixiang and mutant LM1. LM1 exhibited significantly higher salt tolerance compared to Lizixiang. The content of proline and activities of superoxide dismutase (SOD) and photosynthesis were significantly increased, while malonaldehyde (MDA) and H₂O₂ contents were significantly decreased compared to that of Lizixiang under salt stress. The inoculation test with Fusarium wilt showed that its Fusarium wilt resistance was also improved. The lignin, total phenolic, jasmonic acid (JA) contents and SOD activity were significantly higher, while H₂O₂ content was significantly lower in LM1 than that in Lizixiang. The expression level of salt stress-responsive and disease resistance-related genes was significantly higher in LM1 than that in Lizixiang under salt and Fusarium wilt stresses, respectively. This result provides a novel and valuable material for improving the salt tolerance and Fusarium wilt resistance of sweetpotato.

    A plastidic adenosine triphosphate (ATP)/adenosine diphosphate (ADP) transporter (AATP) is responsible for importing ATP from the cytosol into plastids. In dicotyledonous plants, increasing ATP supply is a potential way to facilitate anabolic synthesis in heterotrophic plastids. In this study, a gene encoding the AATP protein, named IbAATP, was isolated from sweetpotato (Ipomoea batatas (L.) Lam.). Transcripts of IbAATP were predominantly detected in the storage roots and leaves and were induced by exogenous sucrose and subjected to circadian rhythm. Transient expression of IbAATP in tobacco and onion epidermal cells revealed the plastidic localization of IbAATP. The overexpression of IbAATP in sweetpotato significantly increased the starch and amylose contents and led to enlarged starch granules. The IbAATP-overexpressing plants showed altered fine structure of amylopectin, which contained an increased proportion of chains with a degree of polymerization (DP) of 10–23 and a reduced number of chains with a DP of 5–9 and 24–40. In addition, starch from the transgenic plants exhibited different pasting properties. The transcript levels of starch biosynthetic genes, including IbAGP, IbGBSSI, IbSSI-IV, and IbSBE, were differentially regulated in the transgenic plants. These results revealed the explicit role of IbAATP in the starch biosynthesis of sweetpotato and indicated that this gene has the potential to be used to improve starch content and quality in sweetpotato and other plants.