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.

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.

Nitrogen is an important nutrient for plant development.  Nitrogen and carbon metabolisms are tightly linked to physiological functions in plants.  In this study, we found that the IbSnRK1 gene was induced by Ca(NO₃)₂.  Its overexpression enhanced nitrogen uptake and carbon assimilation in transgenic sweetpotato.  After Ca(¹⁵NO₃)₂ treatment, the 15N atom excess, 15N and total N content and nitrogen uptake efficiency (NUE) were significantly increased in the roots, stems, and leaves of transgenic plants compared with wild type (WT) and empty vector control (VC).  After Ca(NO₃)₂ treatment, the increased nitrate N content, nitrate reductase (NR) activity, free amino acid content, and soluble protein content were found in the roots or leaves of transgenic plants.  The photosynthesis and carbon assimilation were enhanced.  These results suggest that the IbSnRK1 gene play a important role in nitrogen uptake and carbon assimilation of sweetpotato.  This gene has the potential to be used for improving the yield and quality of sweetpotato.

Simple sequence repeat (SSR) markers have been shown to be a powerful tool for varieties identification in plants.  However, SSR fingerprinting of sweetpotato varieties has been a little reported.  In this study, a total of 1 294 SSR primer pairs, including 1 215 genomic-SSR and 79 expressed sequence tag (EST)-SSR primer pairs, were screened with sweetpotato varieties Zhengshu 20 and Luoxushu 8 and their 2 F₁ individuals randomly sampled, and 273 and 38 of them generated polymorphic bands, respectively.  Four genomic-SSR and 3 EST-SSR primer pairs, which showed good polymorphism, were selected to amplify 203 sweetpotato varieties and gave a total of 172 bands, 85 (49.42%) of which were polymorphic.  All of the 203 sweetpotato varieties showed unique fingerprint patterns, indicating the utility of SSR markers in variety identification of this crop.  Polymorphism information content (PIC) ranged from 0.5824 to 0.9322 with an average of 0.8176.  SSR-based genetic distances varied from 0.0118 to 0.6353 with an average of 0.3100 among these varieties.  Thus, these sweetpotato varieties exhibited high levels of genetic similarity and had distinct fingerprint profiles.  The SSR fingerprints of the 203 sweetpotato varieties have been successfully constructed.  The highly polymorphic SSR primer pairs developed in this study have the potential to be used as core primer pairs for variety identification, genetic diversity assessment and linkage map construction in sweetpotato and other plants.

Sweetpotato (Ipomoea batatas (L.) Lam.) breeding is challenging due to its genetic complexity. In the present study, interval mapping (IM) and multiple quantitative trait locus (QTL) model (MQM) analysis were used to identify QTLs for starch content with a mapping population consisting of 202 F1 individuals of a cross between Xushu 18, a cultivar susceptible to stem nematodes, with high yield and moderate starch, and Xu 781, which is resistant to stem nematodes, has low yield and high starch content. Six QTLs for starch content were mapped on six linkage groups of the Xu 781 map, explaining 9.1-38.8% of the variation. Especially, one of them, DMFN_4, accounted for 38.8% of starch content variation, which is the QTL that explains the highest phenotypic variation detected to date in sweetpotato. All of the six QTLs had a positive effect on the variation of the starch content, which indicated the inheritance derived from the parent Xu 781. Two QTLs for starch content were detected on two linkage groups of the Xushu 18 map, explaining 14.3 and 16.1% of the variation, respectively. They had a negative effect on the variation, indicating the inheritance derived from Xu 781. Seven of eight QTLs were co-localized with a single marker. This is the first report on the development of QTLs co-localized with a single marker in sweetpotato. These QTLs and their co-localized markers may be used in marker-assisted breeding for the starch content of sweetpotato.

Pharmacokinetics of cyadox (CYX) and its major metabolites in healthy swine was investigated in this paper. 1,4- Bisdesoxycyadox (BDCYX), cyadox-1-monoxide (CYX-1-O) and quinoxaline-2-carboxylic acid (QCA), three main metabolites of cyadox, were synthesized by College of Science, China Agricultural University. Cyadox (CYX) was administered to 8 healthy cross-bread swine intravenously (i.v.) and orally (p.o.) at a dosage of 1 mg kg-1 body weight and 40 mg kg-1 body weight respectively in a randomized crossover design test with 2-wk washout period. A sensitive high-performance liquid chromatography-tandem mass spectrometry (LC-ESI-MS/MS) method was developed for the determination of cyadox and its major metabolites in plasma. CYX and its major metabolites BDCYX, and CYX-1-O can be detected after intravenous administration of cyadox while CYX and its metabolites BDCYX, CYX-1-O and QCA can be detected after oral administration of CYX. Plasma concentration vs. time profiles of CYX and its major metabolites were analyzed by non-compartmental pharmacokinetic method. Following i.v. administration, the areas under the plasma concentration-time curve (AUC0- ) were (0.38±0.03) μg mL-1 h (CYX), (0.018±0.002) μg mL-1 h (BDCYX) and (0.17±0.02) μg mL-1 h (CYX-1-O), respectively. The terminal elimination half-lives (t1/2lz) were determined to be (0.93±0.07) h (CYX), (1.45±0.04) h (BDCYX), and (0.92±0.04) h (CYX-1-O), respectively. Steady-state distribution volume (Vss) of (2.14±0.11) L kg-1 and total body clearance (CL) of (2.84±0.19) L h-1 kg-1 were determined for CYX after i.v. dosing. The bioavailability (F) of CYX was 2.85% for oral administration. After single i.v. administration, peak plasma concentrations (Cmax) of (1.08±0.06) μg mL-1 (CYX), (0.0068± 0.0004) μg mL-1 (BDCYX) and (0.25±0.03) μg mL-1 (CYX-1-O) were observed at Tmax of 0.033 h (CYX), 1 h (BDCYX) and 0.033 h (CYX-1-O), respectively. The main pharmacokinetic parameters after p.o. administration were as follows: AUC0- were (0.42±0.04) μg mL-1 h (CYX), (1.38±0.14) μg mL-1 h (BDCYX), (0.59±0.02) μg mL-1 h (CYX-1-O) and (1.48±0.09) μg mL-1 h (QCA), respectively. t1/2lz were (4.77±0.33) h (CYX), (5.77±0.56) h (BDCYX), (4.12±0.28) h (CYX-1-O), and (8.51±0.39) h (QCA), respectively. After p.o. administration, Cmaxs of (0.033±0.002) μg mL-1 (CYX), (0.22±0.03) μg mL-1 (BDCYX), (0.089±0.005) μg mL-1 (CYX-1-O), and (0.17± 0.01) μg mL-1 (QCA) were observed at Tmax of (7.38±0.33) h (CYX), (7.25±0.31) h (BDCYX), (7.38±0.33) h (CYX-1-O), and (7.25±0.31) h (QCA), respectively. The results showed that CYX was slowly absorbed after oral administration and most of CYX was transformed to its metabolites in swine. The area under plasma concentration-time curve (AUC0- )of metabolites were higher than that of CYX after p.o. administration, and the elimination half-lives (t1/2lz) of QCA were longer than those of CYX, CYX-1-O, and BDCYX after oral administration.

Sequence-related amplification polymorphism (SRAP) markers closely linked to stem nematode resistance gene were developed in sweetpotato, Ipomoea batatas (L.) Lam. Using bulked segregant analysis (BSA), 200 SRAP primer combinations were screened with the resistant and susceptible bulked DNA from the 196 progenies of an F1 single-cross population of resistant parent Xu 781×susceptible parent Xushu 18, 77 of them showed polymorphic bands between resistant and susceptible DNA. Primer combinations detecting polymorphism between the two bulks were used to screen both parents and 10 individuals from each of the bulks. The results showed that primer combination A9B4 produced 3 specific bands in the resistant plants but not in the susceptible plants, suggesting that the markers, named Nsp1, Nsp2 and Nsp3, respectively, linked to a gene for stem nematode resistance. Primer combination A3B6 also produced a SRAP marker named Nsp4 linking to the resistance gene. Amplified analysis of the 196 F1 individuals indicated that the genetic distance between these markers and the resistance gene was 4.7, 4.7, 6.3, and 9.6 cM, respectively.

AFLP fingerprinting of the 98 main sweetpotato varieties planted in China has been constructed. Using 17 AFLP primer combinations which were selected from 1 208 primer combinations and generated the most amounts of polymorphic bands, AFLP analysis of the 98 main sweetpotato varieties gave a total of 410 clear polymorphic bands with an average of 24.12 polymorphic bands per primer combination. Each one of the 98 sweetpotato varieties could be clearly distinguished by EcoR I-cta/Mse I-ggc primer combination which generated the most polymorphic bands. AFLP-based genetic distance ranged from 0.0546 to 0.5709 with an average of 0.3799. The dendrogram based on AFLP markers indicated that sweetpotato varieties coming from the same regions or having same parents were clustered in the same groups. Analysis of molecular variance (AMOVA) revealed greater variations within regions (94.08%) than among regions (5.92%). Thus, the genetic variations mainly existed within regions, while the variations among regions were very low in the tested sweetpotato varieties. Significant genetic variations existed between “Northern” and “Southern” sweetpotato varieties when Yangtze River was used as the dividing line.