Association of a Geminivirus with a Leaf Curl Disease of Sunn Hemp (Crotalaria juncea) in India

Natural occurrence of a geminivirus causing severe leaf curl disease on sunn hemp (Crotalaria juncea) was recorded in India. The association of a geminivirus with the disease was demonstrated by whitefly transmission tests and polymerase chain reaction (PCR) amplification of DNA fragments of expected sizes with three pairs of degenerate geminivirus primers. The PCR-amplified viral DNA fragments were further characterized by Southern hybridization with a geminivirus probe consisting of the cloned coat protein (CP) gene of Indian tomato leaf curl virus (ITLCV). Restriction fragment length polymorphism analysis of a PCR-amplified CP fragment revealed that the geminivirus from sunn hemp was different than ITLCV.     

猪屎豆种子脂溶性成分及其抗氧化活性研究

运用气相色谱-质谱联用技术(GC-MS)对猪屎豆种子中脂溶性成分进行分析,应用色谱峰面积归一化法定量分析各成分的相对百分含量,共分离鉴定出37个化合物,占其总量的70.52%。同时采用清除DPPH自由基能力的方法对猪屎豆种子中的脂溶性成分进行抗氧化活性测定,结果显示一定的抗氧化活性,其IC50为560.3μg/mL。     

赤霉素对猪屎豆和黄葵种子萌发的影响的初步研究

使用不同浓度的赤霉素GA3浸泡猪屎豆和黄葵种子,研究对种子萌发的影响。结果表明：200 mg/L的GA3处理对猪屎豆的催芽效果最好,而100 mg/L的GA3处理对黄葵的催芽效果最好;GA3浸种催芽对种子的发芽势和发芽率有一定的促进作用,种子发芽率、发芽势有提高,但效果不显著。GA3的浓度过低或者过高,对种子发芽率的影响不明显。     

Application of low‐phosphorus‐containing legume residues reduces extractable phosphorus in a tropical Ultisol

Application of legume green manure (GM) is suggested to be effective in increasing the availability of native soil phosphorus (P) and the dissolution and utilization of phosphate rock (PR)‐P by food crops. Experiments were conducted to study the dynamics of extractable P (P extracted by Bray‐1‐extracting solution) of an Ultisol amended with or without GM residues of contrasting P concentrations in the absence of growing plants. In two separate experiments, GM residues of Aschynomene afraspera (a flood‐tolerant legume) and of Crotalaria micans (upland) with varying P concentrations were added to an acidic soil amended with PR‐P or triple superphosphate (TSP) in plastic bottles. Soil moisture was brought to field capacity of the soil in the upland experiment and saturated with distilled water in the lowland setup. This was done to simulate aerobic upland and anaerobic lowland soil conditions in the relevant plastic bottles. Only P concentration of the residues added varied, while lignin and C : N ratios were similar. A temperature of 25°C was maintained throughout the experiment. Changes in soil extractable Bray‐1‐P were measured at the end of the incubation period (60 or 80 d). In the aerobic soils, extractable P in the combined PR+GM or TSP+GM treatments was significantly lower than in the PR‐ or TSP‐ treated soils. The amendment with GM residues alone significantly increased Bray‐1‐P over the unamended control in the case of the inorganic P‐fertilized GM residues. The trend in extractable P was similar in the soils incubated under anaerobic conditions. However, in the case of PR, concentrations of P extracted by Bray‐1 solution did not significantly change in the presence or absence of GM. The results suggest that the incorporation of GM residues with low P concentration does not lead to a net P release in upland or lowland soils. These results have implications for nutrient cycling in farming systems in W Africa as most of the soils are poor and very low in available P.     

Isotopic fractionation during N2 fixation by four tropical legumes

To quantify the contribution of biological nitrogen fixation (BNF) to legume crops using the ¹⁵N natural abundance technique, it is necessary to determine the ¹⁵N abundance of the N derived from BNF—the B value. In this study, we used a technique to determine B whereby both legume and non-N₂-fixing reference plants were grown under the same conditions in two similar soils, one artificially labelled with ¹⁵N, and the other not. The proportion of N derived from BNF (%Ndfa) was determined from the plants grown in the ¹⁵N-labelled soil and it was assumed that the %Ndfa values of the legumes grown in the two soils were the same, hence the B value of the legumes could be calculated. The legumes used were velvet bean (Mucuna pruriens), sunnhemp (Crotalaria juncea), groundnut (Arachis hypogaea) and soybean (Glycine max) inoculated, or not, with different strains of rhizobium. The values of %Ndfa were all over 89%, and all the legumes grown in unlabelled soil showed negative δ¹⁵N values even though the plant-available N in this soil was found to be approximately +6.0‰. The B values for the shoot tissue (B_s) were calculated and ranged from approximately −1.4‰ for inoculated sunnhemp and groundnut to −2.4 and −4.5‰ for soybean inoculated with Bradyrhizobium japonicum strain CPAC 7 and Bradyrhizobium elkanii strain 29W, respectively. The B (B_wp) values for the whole plants including roots, nodules and the original seed N were still significantly different between the soybean plants inoculated with CPAC 7 (−1.33‰) and 29W (−2.25‰). In a parallel experiment conducted in monoxenic culture using the same soybean variety and Bradyrhizobium strains, the plants accumulated less N from BNF and the values were less negative, but still significantly different for soybean inoculated with the two different Bradyrhizobium strains. The results suggest that the technique utilized in this study to determine B with legume plants grown in soil in the open air, yields B values that are more appropriate for use under field conditions.     

Maize Yields as Affected by Short- and Long-Term Improved Fallows: A Comparative Analysis in the Asian Humid Tropics

Improved short‐ or long‐term fallows are considered suitable low external input technologies for maintaining productivity and sustainability of tropical smallholder upland cropping units, although comparisons on the benefits of this technology are not widely reported. A field study evaluated the impact of improved short (6 months) and long‐term fallow (18 months) using Crotalaria juncea and Tithonia diversifolia, in relation to a natural fallow of the same durations, on the productivity of maize (Zea mays), the most important upland cereal in tropical Asia, over a minor season. The use of improved fallows, especially Tithonia, increased maize yields over the Crotalaria or natural fallow. While the overall yields of maize after a long fallow were greater, the beneficial impact of the green manures was significantly higher in the short fallows. The causal factors for this trend, including biomass production of the improved fallows and possible impact on soils, along with the greater benefits of short‐term fallows for increasing maize yields in the tropics due to lower requirements of unproductive time are presented.     

响铃草黄酮提取物体外抗菌活性研究

为探讨响铃草黄酮提取物的体外抗菌活性.采用乙醇索氏抽提、大孔树脂纯化的方法获得响铃草黄酮提取物,通过打孔扩散法和最低抑菌浓度法(MIC)检测其对4种人体常见致病菌生长的影响.结果表明:响铃草黄酮提取物对供试菌具有不同程度的抑制作用,对金黄色葡萄球菌的抑制效果最好,对大肠杆菌的抑制作用不明显.响铃草黄酮提取物总黄酮含量为38.51%,该提取物对金黄色葡萄球菌、绿脓杆菌、藤黄微球菌、大肠杆菌的抑菌圈分别为36 mm、11 mm、9 mm和0 mm,对金黄色葡萄球菌、绿脓杆菌、藤黄微球菌最低抑菌浓度分别为6.25 mg/mL、25 mg/mL,50 mg/mL.用乙醇索氏抽提、大孔树脂纯化的方法提纯响铃草总黄酮简便可行.     

Seasonal nitrogen dynamics in lowland rice cropping systems in inland valleys of northern Ghana

Farmers in the inland valleys of northern Ghana are challenged with nitrogen (N) deficiency as a major production constraint of rainfed lowland rice (Oryza sativa L.). With extremely low use of external inputs, there is a need to efficiently use the systems' internal resources such as native soil N. Largest soil nitrate‐N losses are expected to occur during the transition between the dry and wet season (DWT) when the soil aeration status changes from aerobic to anaerobic conditions. Technical options avoiding the build‐up of nitrate are expected to reduce N losses and may thus enhance the yield of rice. A field study in the moist savanna zone of Ghana assessed the in situ mineralization of native soil N, the contribution of nitrate to the valley bottom by sub‐surface flow from adjacent slopes, and the effects of crop and land management options during DWT on seasonal soil N_min dynamics and the yield of lowland rice. Large amounts of nitrate accumulated during DWT with a peak of 58 kg ha⁻¹ in lowland soils, of which 32 kg ha⁻¹ were contributed from the adjacent upland slope. Most of this nitrate disappeared at the onset of the wet season, possibly by leaching and denitrification upon soil flooding. While the incorporation of rice straw (temporary immobilization of soil N in the microbial biomass) had little effect on soil N conservation, growing a crop during DWT conserved 22–27 kg of soil N ha⁻¹ in the biomass and Crotalaria juncea supplied an additional 43 kg N ha⁻¹ from biological N₂ fixation. Farmers' practice of bare fallow during DWT resulted in the lowest rice grain yield that increased from 1.3 (2.2) to 3.9 t ha⁻¹ in case of the transition‐season legume. Growing a pre‐rice legume during DWT appears a promising option to manage N and increase lowland rice yields in the inland valleys of northern Ghana.     

猪屎豆抗氧化活性成分的提取及活性测定体系的优化

[目的]研究猪屎豆（Crotalaria mucronata Desv.）乙醇提取物的抗氧化活性。[方法]采用超声波辅助乙醇提取法提取猪屎豆抗氧化活性成分,用H2O2-鲁米诺化学发光体系测定清除羟自由基（·OH）的效率。并对测定体系进行优化。[结果]在料液比为3.6∶1,乙醇体积分数为70%,提取时间为30min,提取温度为80℃,猪屎豆乙醇提取物对·OH的清除效果最佳。清除率测定体系中,H2O2浓度为0.60%和Luminol浓度为1.00×10-4mol/L时测定结果较准确。[结论]猪屎豆乙醇提取物对·OH有很好的清除作用。     

Summer cover crop impacts on soil percolation and nitrogen leaching from a winter corn field

The impacts of a leguminous summer cover crop (sunn hemp; Crotalaria juncea) on nitrogen leaching from a corn (Zea mays L.) field was evaluated by direct measurements of soil water content and nitrogen balance components, complemented by direct and inverse modeling as an exploratory tool to better understand water flow and nitrogen balances in the soil. Water and nitrogen inputs and outputs were measured during winter corn production in an experimental field located in the south Miami-Dade basin in southern Florida (USA). Data from the last two seasons (2001-2002 and 2002-2003) of a 4-year study are presented. The field was divided into six 0.13 ha plots. One-half of the plots were rotated with sunn hemp (CC plots) during the summer while the remaining plots were kept fallow (NC plots). Sweet corn management was uniform on all plots and followed grower recommended practices. A numerical model (WAVE) for describing water and agrochemical movement in the soil was used to simulate water and nitrogen balances in both types of plots during the corn seasons. The hydrodynamic component of WAVE was calibrated with soil water data collected continuously at three depths, which resulted in accurate soil water content predictions (coefficients of efficiency of 0.85 and 0.91 for CC and NC plots, respectively). Measured components of the nitrogen balance (corn yields, estimated nitrogen uptake, and soil organic nitrogen) were used to positively assess the quality of the nitrogen simulation results. Results of the modeled water balance indicate that using sunn hemp as a cover crop improved the soil physical conditions (increase in soil water retention) and subsequently enhanced actual crop evapotranspiration and reduced soil drainage. However, nitrogen simulation results suggest that, although corn nitrogen uptake and yields were slightly higher in the CC plots than in the NC plots, there were net increases of soil N content that resulted in increased N leaching to the shallow aquifer. Therefore, the use of sunn hemp as cover crop should be coupled with reductions in N fertilizer applied to the winter crop to account for the net increase in soil N content.