短波紫外线处理对紫背天葵采后贮藏品质的影响

为了减少紫背天葵的采后损失,提高其贮藏品质,采用不同辐照剂量的短波紫外线(UV-C)对采后紫背天葵进行处理,研究短波紫外线对紫背天葵采后品质及活性氧代谢相关酶的影响。结果表明,UV-C处理可以有效降低紫背天葵的失重率和菌落总数,延缓维生素C、叶绿素以及L*值的下降,减少总酚和黄酮的损失,抑制丙二醛(MDA)的积累,能较好地保证紫背天葵的感官品质和营养价值,同时显著提高超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)等活性氧代谢相关酶的活性,其中5 k J·m~(-2)UV-C处理效果优于1、3 k J·m~(-2)UV-C处理组。本研究中UV-C处理能有效地提高紫背天葵的采后品质,其在采后紫背天葵贮藏保鲜中具有潜在的应用价值。     

短波紫外线照射对鸡腿菇保鲜的影响（简报）

为寻求适应分散的小规模生产食用菌的保鲜技术,以鸡腿菇为试验材料,研究了短波紫外线（UV-C）照射对鸡腿菇低温（4℃）和常温（20℃）贮藏保鲜的影响。研究结果表明,UV-C照射处理能够显著延长鸡腿菇的保鲜时间,鸡腿菇在4℃贮藏时的保鲜时间由处理前的6～7 d延长至10～11 d,在常温下的保鲜时间由2 d延长至4 d以上。UV-C照射能够抑制鸡腿菇在贮藏期间的后熟作用,降低多酚氧化酶（PPO）活性,从而降低鸡腿菇的呼吸强度,减小细胞膜透性,延缓褐变反应,尤其能有效地抑制菌柄伸长,从而延长鸡腿菇的保鲜时间。UV-C的照射时间越长,抑制后熟生长、降低PPO活性的作用越明显,但带给鸡腿菇的损伤（如褐变、呼吸增强等）越强烈,因此UV-C的照射时间不宜过长。     

采后UV-C辐照对马铃薯干腐病的抑制效应及相关酶活性的影响

为探讨不同辐照剂量的短波紫外线(UV-C)处理对马铃薯干腐病的抑制作用及相关酶活性的影响,以贮藏期间的马铃薯块茎为材料,经剂量为0、5、15、25、35、45 kJ·m-2的UV-C辐照,研究分析经损伤接菌后马铃薯块茎干腐病病斑及相关防御性酶[过氧化氢酶(CAT)、过氧化物酶(POD)、苯丙氨酸解氨酶(PAL)、丙二醛(MDA)]的变化情况。结果表明,损伤接菌后的马铃薯块茎,经剂量5~45 kJ·m~(-2)的UV-C辐照处理,块茎中MDA、PAL活性均显著降低,POD活性显著升高;剂量5 kJ·m~(-2)的辐照处理可显著提高损伤接菌后的马铃薯块茎中CAT活性;剂量5~45 kJ·m~(-2)的辐照处理均可有效抑制马铃薯块茎病斑直径的扩散,其中以35 kJ·m~(-2)处理效果最佳。本研究证实UV-C辐照有助于提高贮藏期间马铃薯块茎对于干腐病的抗性,为利用UV-C这种新型环保的马铃薯贮藏方法提供了理论参考。     

不同环丙烯类乙烯抑制剂对苹果常温贮藏保鲜效果的影响

为了研究不同支链长度的3种环丙烯类乙烯抑制剂处理对寒富苹果常温贮藏效果的影响,分别采用0.75μL/L1-MCP(1-甲基环丙烯),2μL/L1-PentCP(1-pentylcclopropene,1-戊基环丙烯)和0.5μL/L1-OCP(1-octylcyclopropene,1-辛基环丙烯)在常温条件下,熏蒸处理寒富苹果20h,以不处理为对照,处理后装入厚度0.02mm保鲜袋于常温下贮藏(20℃)。结果表明:1-MCP和1-PentCP处理能较好地抑制寒富苹果贮藏过程中的呼吸强度和乙烯释放量,各处理呼吸高峰时间较对照晚出现了4d,各处理对乙烯释放高峰出现的时间延迟了8d,较好地保持了果实贮藏期间的硬度,延缓了果实固形物含量和丙二醛含量的上升速度。这2个处理还在一定程度上延缓了细胞膜保护酶过氧化物酶、超氧化物歧化酶和过氧化氢酶的活性变化。而1-OCP处理却促进了寒富苹果果实贮藏期间的丙二醛含量的上升,进而导致在贮藏后期出现了一定的伤害作用。研究结果表明,1-MCP和1-PentCP处理可以抑制寒富苹果的生理代谢,保持果实品质和降低膜脂伤害程度,从而延缓寒富苹果采后的成熟衰老进程。     

短波紫外线处理对采后香菇褐变的影响

为了控制采后香菇在贮藏过程中的褐变并提高其贮藏品质,本试验采用不同剂量(2、4、6和8 kJ·m^-2) 短波紫外线(UV-C)对新鲜香菇进行预处理,研究不同剂量UV-C处理对香菇色泽、总酚含量、多酚氧化酶(PPO)活性、过氧化物酶(POD)活性、超氧化物歧化酶(SOD)活性、过氧化氢酶(CAT)活性、苯丙氨酸解氨酶(PAL)活性、可溶性蛋白含量、还原糖含量、游离氨基酸含量以及香菇表面微生物的影响。结果表明,UV-C处理延缓了香菇色泽的下降,保持了较高的总酚含量,并且有利于POD、SOD、CAT和PAL活性维持在较高水平,抑制了PPO活性,同时可以保持较高的还原糖和可溶性蛋白含量,在一定程度上延缓了蛋白质的降解,而且可以有效抑制微生物的生长,其中4 kJ·m^-2 UV-C处理效果最佳。综上所述,UV-C处理可以有效地抑制香菇褐变,延长其贮藏期。本研究结果为香菇的贮藏保鲜提供了理论依据。     

热激和山梨酸钾处理对猕猴桃果实灰霉病的抑制效应

为了探究热激和山梨酸钾对离体灰霉菌(Botrytis cinerea)及猕猴桃果实采后灰霉病的抑制效应,用48℃热水(Hot Water Treatment,HT)和5 g/L山梨酸钾溶液(Potassium Sorbate,PS)及二者复合(PS+HT)分别处理离体灰霉菌和接种过灰葡萄孢霉的猕猴桃果实。离体试验以不添加山梨酸钾的马铃薯葡萄糖琼脂培养基(Potato Dextrose Agar,PDA)培养不加热处理的灰霉菌悬液为对照,结果表明与对照相比,PS和PS+HT处理均能显著抑制离体灰霉菌菌丝生长(P<0.05)。损伤接种试验以常温即18℃下清水浸泡接种灰霉菌的猕猴桃果实为对照,浸泡后果实分别贮藏在0℃和24℃,结果表明在2种温度贮藏条件下,上述处理均可以显著诱导提高多酚氧化酶、过氧化物酶、几丁质酶和β-1,3-葡聚糖酶活性(P<0.05),从而抑制果实病斑扩散,显著降低果实发病指数(P<0.05)。其中复合处理抑菌效果最佳,而PS、HT单一处理的果实病斑直径在贮藏后期与对照差异不显著(P>0.05)。此外,为了进一步探究上述处理是否对猕猴桃果实冷藏品质产生影响,将对照及不同处理组果实在0℃下贮藏90 d,每10 d测定品质相关指标。结果表明,与对照相比,PS+HT复合处理延缓了可滴定酸和维生素C含量的下降,并且显著降低了果实失重率和腐烂率(P<0.05),提高了猕猴桃果实耐贮性,对延缓猕猴桃果实衰老和减轻采后腐烂衰败具有重要的意义。     

伞形花内酯处理对采后徐香猕猴桃果实灰霉病抗的影响

为探讨伞形花内酯处理对猕猴桃果实采后灰霉病的控制效应,本试验研究了伞形花内酯对灰霉菌孢子和生长的影响,以及对美味猕猴桃徐香损伤接种灰霉菌后果实病害发展、抗病相关酶活性和抗性物质的影响。结果表明,离体条件下,0.5和1.0 mg·mL^-1伞形花内酯能够显著抑制灰霉菌孢子的萌发和生长;0.5 和1.0 mg·mL^-1伞形花内酯处理能够抑制损伤接种灰霉菌猕猴桃果实病斑的扩张,显著提高果肉几丁质酶(CHT)、β-1,3 葡聚糖酶(GLU)、苯丙氨酸解氨酶(PAL)、4-香豆酰辅酶A连接酶(4CL)、过氧化物酶(POD)和多酚氧化酶(PPO)的活性,提高果实贮藏后期总酚、类黄酮和木质素的含量,因而诱导了猕猴桃采后果实对灰霉病的抗性。本研究为应用外源伞形花内酯控制猕猴桃采后果实灰霉病害提供了理论依据。     

葡萄籽提取物对采后猕猴桃青霉病的抑制效果与机理

为探讨葡萄籽提取物(GSE)对采后猕猴桃接种青霉菌后青霉病的防治效果,本试验以贵长猕猴桃为试材,通过测定猕猴桃果实发病率、病斑直径以及与果实抗病相关物质的含量和防御相关酶的活性,研究GSE对采后猕猴桃果实青霉菌的作用效果。结果表明,GSE处理延迟了猕猴桃在损伤接种扩展青霉(Penicillium expansum)后果实发病率的上升,抑制了果实病斑直径的扩大。同时,GSE处理极显著提高了猕猴桃果实总酚和总类黄酮含量,降低了膜降解标志性代谢产物丙二醛(MDA)含量以及脂氧合酶(LOX)活性,提高了猕猴桃果实几丁质酶(CHI)、β-1,3葡聚糖酶(GLU)和过氧化物酶(POD)活性。接种扩展青霉后,接种前期GSE处理显著提高了果实的多酚氧化酶(PPO)活性,接种后期GSE处理显著提高了苯丙氨酸氨解酶(PAL)活性。综上,GSE处理通过激活抗氧化防御代谢从而提高了猕猴桃果实对青霉病的抗性。本研究为利用GSE防治青霉病研究提供了理论指导和技术参考。     

甜樱桃采后热空气处理抑制青霉病的工艺优化

为确定热空气处理控制采后甜樱桃果实青霉病的最优条件,采用响应曲面法研究了不同温度-时间的热空气处理对甜樱桃采后青霉病的抑菌效果和果实品质的影响。甜樱桃果实采后用不同温度热空气(40~48℃)和不同处理时间(60~180 min)处理后,接种青霉菌在20℃、相对湿度90%~95%的条件下贮藏5 d,贮藏结束后测定果实的病斑直径、硬度、抗坏血酸含量和固酸比,建立了4个响应值的二次多项数学模型,分析了拟合程度,并利用模型的响应面对甜樱桃的抗病性和果实品质进行了探讨。结果表明,热空气处理控制采后甜樱桃果实青霉病的较优条件为热处理温度为44℃、热处理时间为114 min,该条件显著(P0.05)抑制了甜樱桃采后青霉病的扩展,与对照组相比,热处理较好的保持了甜樱桃果实品质,显著(P0.05)减缓了硬度、抗坏血酸含量和固酸比的下降,为热空气处理在甜樱桃贮藏保鲜中的应用提供理论依据。     

壳聚糖及UV-C处理对长山药冷害和品质的影响

为探讨壳聚糖及UV-C处理对贮藏过程中长山药冷害和品质的影响,以长山药为试验材料,采用不同浓度的壳聚糖及不同剂量的UV-C照射处理长山药块茎,对比分析长山药的冷害指数、可溶性固形物、丙二醛(MDA)、相对电导率、抗氧化酶类活性等指标的变化。结果表明,维持长山药块茎品质的壳聚糖最佳浓度为1.0%,UV-C最佳照射剂量为6 KJ·m^-2。此条件下,壳聚糖、UV-C、壳聚糖+UV-C处理都能有效降低长山药块茎的冷害指数,抑制其MDA含量和相对电导率的升高,保护膜结构的完整性,显著降低了多酚氧化酶(PPO)活性,还可以保持较高的可溶性固形物含量和过氧化物酶(POD)活性,说明这3种处理均可控制长山药冷害的发生,延长块茎的贮藏期,其中以壳聚糖+UV-C处理效果最佳。本研究结果为减缓采后长山药冷害提供了一定的理论依据。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.