Search

In sweet potato, rational nitrogen (N) assimilation and distribution are conducive to inhibiting vine overgrowth. Nitrate (NO3-) is the main N form absorbed by roots, and cultivar is an important factor affecting N utilization. Herein, a hydroponic experiment was conducted that included four NO3- concentrations of 0 (N0), 4 (N1), 8 (N2) and 16 (N3) mmol L-1 with two cultivars of Jishu26 (J26, N-sensitive) and Xushu32 (X32, N-tolerant). For J26, with increasing NO3- concentrations, the root length and root surface area significantly decreased. However, no significant differences were observed in these parameters for X32. Higher NO3- concentrations upregulated the expression levels of the genes that encode nitrate reductase (NR2), nitrite reductase (NiR2) and nitrate transporter (NRT1.1) in roots for both cultivars. The trends in the activities of NR and NiR were subject to regulation of NR2 and NiR2 transcription, respectively. For both cultivars, N2 increased the N accumulated in leaves, growth points and roots. For J26, N3 further increased the N accumulation in these organs. Under higher NO3- nutrition, compared with X32, J26 exhibited higher expression levels of the NiR2, NR2 and NRT1.1 genes, a higher influx NO3- rate in roots, and higher activities of NR and NiR in leaves and roots. Conclusively, the regulated effects of NO3- supplies on root growth and NO3- utilization were more significant for J26. Under high NO3- conditions, J26 exhibited higher capacities of NO3- absorption and distributed more N in leaves and in growth points, which may contribute to higher growth potential in shoots and more easily cause vine overgrowth. [ABSTRACT FROM AUTHOR]

In recent years, sweet potato has been cultivated not only in marginal lands but also in fertile plains in northern China. The fertile nitrogen (N)‐rich soil may inhibit storage root formation. Cultivars with different N tolerances and split application of reduced N rates should be considered. To investigate the effects of N on the N utilization, root differentiation, and storage root formation of cultivars with different N tolerances, the cultivars Jishu26 (J26) and Xushu32 (X32) were treated with three N levels supplied by urea: 0 (N0), 200 (N1) and 400 mg kg−1 (N2). With increasing N rates, "X32" absorbed less N in plants and distributed more N to developing storage roots than "J26." The storage root development of "J26" was sensitive to both N1 and N2, while that of "X32" was only sensitive to N2. High N nutrition upregulated the expression of certain genes during storage root formation, such as PAL, CHI, F3H, C4H, 4CL, CAD, α‐amylase, and β‐amylase. Under N1 and N2, "X32" led to an increased sugar supply in sink organs and downregulated the expression of genes related to lignin and flavonoid synthesis, which promoted the C flux toward starch metabolism, thus reducing lignification and promoting starch accumulation during storage root formation. These results provide evidence for the effects of N on the C distribution in different metabolic pathways by regulating the expression of related key genes. N‐tolerant cultivars are suitable in fertile plain areas because of the earlier formation of storage roots under high N conditions. [ABSTRACT FROM AUTHOR]

Sweetpotato leaf curl virus (SPLCV) causes leaf curl symptoms in sweetpotato [Ipomoea batatas (L.) Lam]. These symptoms disappear under high temperature. Previous studies have shown that SPCLV reduces storage root yield in sweetpotato. However, knowledge of SPLCV's effect on root quality is limited. In this study, we surveyed the effect of SPLCV on storage root yield and quality in edible sweetpotato. Quantitative real‐time reverse transcriptase–polymerase chain reaction and leaf paraffin section results showed that the SPLCV mRNA level and the distribution density of spongy mesophyll cells in SPLCV‐infected plants were significantly higher than in healthy control plants (CK). Leaf net photosynthetic rate, vine length, and storage root yield were reduced in SPLCV‐infected plants during the growing period, and the shoot/root ratio was significantly increased compared with CK. Additionally, root abscisic acid, auxin, and zeatin riboside contents under SPLCV infection were higher than the CK, whereas root gibberellic acid content was lower. Root dry matter, starch, and carotenoid contents were lower in the infected plants than in the CK. Moreover, SPLCV‐infected plants showed reduced expression of starch and carotenoid metabolitic genes, such as ADP‐glucose pyrophosphorylase‐ß, granule‐bound starch synthase I, starch branching enzyme I and II, and carotenoid isomerase, and increased expression of α‐amylase, ß‐carotene hydroxylase, and zeaxanthin epoxidase. These results suggest that sweetpotato infected by SPLCV had decreased storage root yield and decreased starch and carotenoid contents through reducing photosynthetic capacity, regulating starch and carotenoid degradation, and changing endogenous hormone contents. Therefore, effective management should be taken to prevent SPLCV epidemics during sweetpotato production. [ABSTRACT FROM AUTHOR]

To examine the effects of uniconazole (UCZ) on the distribution and transport of photosynthate in sweetpotatoes, three spraying levels of UCZ, 0 (control), 50 and 100 mg L−1, were exposed to an experimental field cultivated with Jishu26 ('J26ʹ) and Xushu32 ('X32ʹ) varieties. Compared to control, the distribution of carbon-13 (13C) was significantly higher in the tuberous roots of both varieties treated with UCZ. In addition, UCZ treatments promoted a desirable top-to-base sucrose gradient and significant greater declines in the top-to-bottom amino acid and potassium ion (K+) gradients along the stem. Higher tuberous root yields were found in the UCZ-treated 'J26ʹ and 'X32ʹ. In comparison to 50 mg L−1 UCZ, 'J26ʹ treated with 100 mg L−1 UCZ exhibited significantly higher distribution ratio of 13C in tuberous root, and reductions in the top-to-bottom amino acid and K+ gradients along the stems at 105 and 150 days after planting. Furthermore, 100 mg L−1 of UCZ application exhibited a significantly higher tuberous root yield. For 'X32ʹ, the two concentrations of UCZ demonstrated no significant differences in these parameters. A reasonable distribution structure of photosynthates that responsible for high yields is associated with the desirable sucrose, ammonia nitrogen (N) or K+ gradient along the stems caused by UCZ application. [ABSTRACT FROM AUTHOR]

In recent years, the sweet potato cultivar Jishu 25 has exhibited good characteristics for starch processing in northern China. The storage root dry matter yields of this cultivar can exceed one ton per mu (1/15 of a hectare) at nitrogen (N) rates of 60–90 kg ha-1 based on soil nutrient content. However, the effect of N fertilizer on the physicochemical properties of starches isolated from this cultivar has not been reported. In order to evaluate these effects, three different N rates, 0 (control, N0), 75 (N1), and 150 kg ha-1 (N2), were selected for a field experiment in 2017. The results showed that N1 exhibited the highest storage root yield and starch yield. Compared to the control group, N fertilizer significantly increased the total starch content while no significant difference was found in these between the N1 and N2 groups. The amylose (AM) content was highest in the N2 group and lowest in the N0 group. In addition, N fertilizer exhibited no significant effects on the values of [D(v, 0.9)], D [4, 3] and D [3, 2]. Compared to the control group, N1 demonstrated significantly higher setback viscosity (SV), while N2 showed significantly higher peak viscosity (PV), cold paste viscosity (CPV) and SV. However, there were no significant differences in the hot paste viscosity (HPV), peak time and pasting temperature between the N1 and N2 groups. For the thermal properties of starch, there were no significant differences in peak temperature (Tp), conclusion temperature (Tc) or gelatinization enthalpy (ΔH) between the N1 and N2 groups. Overall, for the starch samples of cultivar Jishu 25, N fertilizer exerts significant effects on the starch content, AM content and viscosity properties but little effect on the particle size distribution and ΔH. 75 kg N ha-1 can easily lead to substantial planting benefits from the high storage root yield, dry matter yield and total starch content of this cultivar. [ABSTRACT FROM AUTHOR]

To characterize the differences in photosynthate distribution and transport between nitrogen(N)-tolerant and N-susceptible sweetpotato cultivars under different N conditions, three N levels, including 0 (N0), 120 (N120), and 240 kg ha−1 (N240), were used in field experiments with the Jishu26 (J26) and Xushu32 (X32) cultivars in 2015 and 2016. The results from both years revealed that high N application reduced the tuberous root yield, the tuber/vine rate of carbon-13 (13C), and top-to-base (three equal segments of stem divided from the fifth opened leaf of the shoot tip to the main stem, defined as the top, middle, and base parts, respectively) gradients such as sucrose, ammonia N and potassium along the stem. ‘J26’ showed a higher yield than ‘X32’ under N0 but lower yield than ‘X32’ under N120 and N240. It also exhibited a higher 13C distribution to tuberous roots compared with that of ‘X32’ under N0, and the opposite trend was observed under N120 and N240. Under N0, ‘J26’ showed a steep top-to-base amino acid gradient and a significantly lower top-to-base sucrose increase along the stem in the late growth stage. Under N120 and N240, ‘X32’ exhibited a greater top-to-base decrease in the ammonia N along the stem during the main growth stages, a steep top-to-base sucrose gradient along the stem in the early growth stage, and a lower top-to-base sucrose increase along the stem in the middle and late growth stages. The formation of a reasonable photosynthate distribution structure attributed to high yield was related to a desirable sucrose, ammonia N or K+ gradient downward along the stem. These results might help provide farmers with sweetpotato cultivars using less or no N fertilizer in soils of different fertility and enhance the knowledge of yield-related physiology. [ABSTRACT FROM AUTHOR]

• The abundance of ureC gene was significantly correlated with NH 4 +-N concentration. • The abundance of AOA amoA gene was moderately correlated with NH 4 +-N concentration. • The abundance of AOB amoA gene was moderately correlated with NH 4 +-N concentration. • The abundance of nirK gene was moderately correlated with NO 3 −-N concentration. In this article, the changes in the functional marker genes associated with nitrogen biological transformation during the organic-inorganic co-composting process with adding biochar or not were studied. Results showed that the addition of biochar increased the abundance of ureC , AOA amoA and AOB amoA gene while decreased the abundance of nirK gene. The addition of 10% biochar by weight ratio was better for the optimization of nitrogen biological transformation process. The correlation analysis showed that the ureC gene was highly correlated with NH 4 +-N concentration while the AOA amoA and AOB amoA genes were moderately correlated with NH 4 +-N concentration. Similarly, the nirK gene was moderately correlated with NO 3 −-N concentration. This work would contribute to understanding the mechanisms underlying in the nitrogen bio-transformation further at the molecular level during organic-inorganic co-composting. [ABSTRACT FROM AUTHOR]