Direct electron microscopy and serology with plant viruses in leaf material dried and stored over calciumchloride

Most of 43 viruses could easily be detected directly in 53 out of 66 leaf samples dried and stored over CaCl₂ for varying periods of time up to 20 1/2 years. Detection usually was with PTA pH 6.5, but alfalfa mosaic, cucumber mosaic and tomato aspermy viruses required PTA pH 3.0 to 4.0. Bean common mosaic, cowpea aphid-borne mosaic and cowpea mosaic viruses were also easily observed in newly dehydrated samples obtained for diagnosis from Morocco and Tanzania.Broad bean wilt virus, cowpea mosaic virus and cucumber mosaic virus were detected with agar gel-diffusion tests in dry leaf material ground in buffer. This serological assay demonstrated a high concentration of cucumber mosaic virus in leaf material dried over CaCl₂ 20 years ago. This paper further coroborates the value of the CaCl₂ method of dehydration and storage of plant viruses in leaf material.Samenvatting Zeer uiteenlopende plantevirussen kunnen goed worden bewaard in bladmateriaal van geïnfecteerde planten dat is gedroogd en bewaard boven CaCl₂. Bij rechtstreekse elektronenmicroscopische toetsing van 66 monsters met verschillende isolaten van 43 virussen konden in 53 monsters gemakkelijk virusdeeltjes worden waargenomen (Tabel 1 en Fig. 1 en 2). Meestal lukte dit met fosforwolfraamzuur pH 6,5 dat doorgaans voor in ruw plantesap voorkomende virussen wordt gebruikt. Bij luzernemozaïekvirus en komkommermozaïek virus gelukte dit alleen maar bij lagere pH (3,0 en 4,0). Ook het tomate-aspermievirus was dan veel gemakkelijker aantoombaar. Methylaminewolfraamzuur gaf geen beter resultaat.Draden van bonerolmozaïekvirus en van cowpea aphid-borne mosaic virus en bolletjes van cowpea mosaic virus waren snel waarneembaar in elektronenmicroscopische preparaten gemaakt van bladmateriaal van recent uit Marokko en Tanzania ontvangen monsters.Cowpea mosaic virus, tuinboneverwelkingsvirus en komkommermozaïekvirus konden eveneens gemakkelijk en snel serologisch worden aangetoond in met bufferoplossing vermalen droog blad van respectievelijk cowpea, erwt en tabak. Het laatstgenoemde, reeds 20 1/2 jaar geleden gedroogde bladmateriaal, bleek in vergelijking met pas geïnoculeerd vers blad van komkommer enChenopodium quinoa zelfs zeer veel serologisch actief virusmateriaal te bevatten (Fig. 3).De beschreven waarnemingen bevestigen nogmaals de waarde van de toegepaste methode van virusbewaring en tonen aan dat het mogelijk is vele virussen te herkennen in van elders ontvangen gedroogde bladmonsters, zonder het risico te lopen van virusontsnapping, zoals altijd aanwezig bij werk met toetsplanten in de kas.Guestworker from Istituto Sperimentale per la Patologia Vegetale, Rome, Italy, participating in the investigations from September 21 to December 21, 1977.     

Persistence of terbacil and trifluralin under different soil and climatic conditions

Soil samples were collected from forty-three field trials conducted on ten soil types to investigate the residual activity of terbacil and trifluralin at the end of the cropping season, approximately 6 months after application. The soil was bioassayed in a glasshouse using soya beans and German millet for terbacil and trifluralin respectively. At 1 kg/ha terbacil phytotoxic residues occurred in a majority of the trials, while at 2 kg/ha such a carry-over could be found in every case. Trifluralin doses of up to 1 kg/ha did not persist in toxic amounts in most soils, while application of 2 kg/ha showed residual activity in 74% of the trials and application of 4 kg/ha killed German millet in all instances. Results are also presented from the time-rate dissipation studies conducted on both herbicides by assaying soil samples collected at monthly intervals. Both organic matter and clay content of the trial sites affected the persistence of terbacil, while trifluralin residues were influenced only by the soil organic matter content. Trial sites receiving high rainfall showed considerably less residues of terbacil, but the persistence of trifluralin was not affected by rainfall to any appreciable extent.     

Persistence and mobility of chlorsulfuron and metsulfuron under different soil and climatic conditions

The persistence and mobility of chlorsulfuron and metsulfuron were studied in Italy at four field locations. Chlorsulfuron was applied pre-emer-gence to wheat at 15 and 30 g a.i. ha^?1 in the autumn of 1986 and metsulfuron early post-emergence at 8 g a.i. ha^?1 in the spring of 1987. Soil samples were taken periodically at each location for 1 year. Trials were conducted until 1989 at three locations. After the wheat harvest in 1989, chlorsulfuron and metsulfuron residues in the soil were measured by bioassay in plots that had been treated annually for 3 years and also in plots that had received single treatments. Chlorsulfuron at both application rates dissipated to levels below 0.3 g a.i. ha^?1 over 12 months at three locations while, at the fourth, which received only 250 mm rain during the study, significant levels of residues were still present after 15 months. The degradation of chlorsulfuron applied at 30 g a.i. ha^?1 followed first-order kinetics, with half-lives of 149, 70, 59 and 51 days at the four locations. Chlorsulfuron mobility was high at three locations while, in the silty clay soil of the fourth, the herbicide was confined to the upper 30 cm, despite the high rainfall. Metsulfuron applied in spring was detected only in the first soil sample collection. It was present in all sampled layers at one location but, in the others, was confined to the surface layer. There was no evidence of herbicide accumulation in the soil with repeated applications. Persistance et mobilité du chlorsulfuron et du met-sulfuron dans différents sols et sous différentes conditions climatiques La persistance et la mobilité du chorsulfuron et du metsulfuron au champ ont étéétudiées en Italie sur quatre sites. Le chlorsulfuron était appliqué en pré-levée sur le blé aux doses de matière active (m.a.) 15 et 30 g ha^?1à l'automne 1986 et le metsulfuron en post-levée précoce à la dose 8 g m.a. ha^?1 au printemps 1987. Des échantillons de sol étaient prélevés périodiquement sur chaque site pendant 1 an. Les essais ont été conduits jusqu'en 1989 sur trois des sites. En 1989, après la récolte du blé. les résidus de chlorsulfuron et de metsulfuron dans le sol ont été mesurés par des essais biologiques dans des parcelles qui avaient été traitées chaque année pendant 3 ans, ainsi que dans des parcelles qui n'avaient reçu qu'un seul traitement. Le chlorsulfuron aux deux doses disparaissait jusqu'à des niveaux inférieurs à 0.3 g m.a. ha^?1 en 12 mois sur trois des sites, alors que sur le quatrième, qui n'a reçu que 250 mm de précipitations pendant l'étude, des résidus étaient présents en quantité significative après 15 mois. La dégradation du chlorsulfuron appliquéà la dose 30 g m.a. ha^?1 suivait une cinétique du premier ordre, avec des demi-vies 149, 70, 59 et 51 j sur les quatre sites. La mobilité du chlorsulfuron était élevée sur trois des sites alors que sur le quatrième oú le sol était une argile limoneuse, l'herbicide était confiné aux 30 cm superficiels en dépit de précipitations élevées. Le metsulfuron appliqué au printemps n'était détecté que dans le premier prélèvement. Sur un des sites, il était présent dans toutes les couches, mais était confinéà la couche superficielle sur les autres sites. Après des applications répétées, aucune accumulation d'herbicide n'était observée dans le sol. Persistenz und Mobilität von Chlorsulfuron und Metsulfuron in verschiedenen Böden und bei unterschiedlicher Witterung Die Persistenz und Mobilität von Chlorsulfuron und Metsulfuron wurden in Italien an 4 Standorten unter Freilandbedingungen untersucht. Chlorsulfuron wurde im Herbst 1986 bei Weizen im Vorauflauf mit 15 und 30 g AS ha^?1 und Metsulfuron im Frühjahr 1987 im frühen Nachauflauf mit 8 g AS ha^?1 angewandt. Von jeder Versuchsfläche wurden über einen Zeitraum von 1 Jahr periodisch Bodenproben entnommen. Die Versuche wurden an 3 Standorten bis 1989 durchgeführt. Nach der Weizenernte 1989 wurden mit Biotests die Rückstände von Chlorsulfuron und Metsulfuron in den Böden mit jährlicher (über 3 Jahre) sowie mit einmaliger Behandlung bestimmt. Die Chlorsulfuron-Rückstände nahmen an 3 Standorten bei beiden Aufwandmengen nach 12 Monaten auf 0,3 g AS ha^?1 ab. Am 4. Standort, wo während der Untersuchung nur 250 mm Niederschlag gefallen waren, wurden nach 15 Monaten noch signifikante Rückstände gefunden. Der Abbau von Chlorsulfuron folgte an allen Standorten bei einer Aufwandmenge von 30 g AS ha^?1 einer Kinetik erster Ordnung mit Halbwertszeiten von 149, 70, 59 und 51 Tagen. Die Mobilität von Chlorsulfuron war an 3 Standorten hoch, während es in dem schluffigen Tonboden des 4. Standortes trotz hohen Niederschlags in den oberen 30 cm verblieb. Das im Frühjahr ausgebrachte Metsulfuron wurde nur in der 1. Bodenprobenserie gefunden. An einem Standort lagen in allen beprobten Bodenschichten Rückstände vor, doch sonst waren sie auf die oberste Bodenschicht beschränkt. Bei wiederholter Anwendung konnte keine Herbizidakkumulation im Boden festgestellt werden.     

Persistence of tebufenozide in aquatic ecosystems under laboratory and field conditions

The persistence and dissipation behaviour of tebufenozide, an ecdysone agonist, were investigated: (1) under laboratory conditions in aquatic models set up in glass aquaria, and (2) under field conditions in in-situ aquatic enclosures deployed in a mixed-wood boreal forest lake. Two models were set up in the laboratory study (Study I), which was conducted at constant conditions of temperature, water pH and photoperiod. In Model I, partitioning of tebufenozide from sediment, treated at a concentration of 1400 μg kg^-1, into untreated water was examined. The results showed that the chemical moved very little from the treated sediment into water. The concentration in sediment and water decreased gradually during the 90-day incubation period. Tebufenozide disappeared faster from the top layer of sediment than from the middle and bottom layers. The half-lives of disappearance were 64 days for the top layer but >90 days for the middle and bottom layers respectively. In Model II, partitioning from water, treated at a concentration of 350 μg litre^-1, into untreated sediment was investigated. The results showed that the chemical moved from treated water into sediment due to adsorption. Little vertical downward movement of the adsorbed residues from the top layer of sediment occurred into layers beneath. The adsorbed residues were also not released readily back into water. The concentration in water and sediment decreased gradually during the 90-day incubation period. The half-life of dissipation from water was 67 days. The field microcosm study (Study II), conducted under fluctuating conditions of temperature, water pH and photoperiod, involved application of tebufenozide onto aquatic enclosures at four concentrations of 0·05, 0·10, 0·26 and 0·5 mg litre^-1. This study also showed that the chemical moved downwards from the applied location and was adsorbed onto sediment. The chemical persisted longer in Study II than in Study I. Tebufenozide, being photo-labile, probably degraded faster after constant exposure to light in Study I than after exposure to fluctuating light in Study II. At 90 days after treatment in Study I, only about 55% of the applied material persisted in the sediment, and there was little accumulation. In Study II, the material not only persisted but also was accumulated in the sediment, since at 92 days post-treatment the residues were about 25 times higher than the applied concentration level. Residues in water also decreased more rapidly in Study I than in Study II, because the concentration at 90 days post-treatment was about 41% of the applied value. In Study II, however, about 65% of the applied chemical persisted in water at 92 days post-treatment. While the long persistence of tebufenozide in both the laboratory and field studies was attributable to its low vapour pressure, low water solubility, high octanol/water partition coefficient etc., the differences in the persistence characteristics observed in the two studies were due to the fluctuating environmental conditions and water pH encountered in the field study, compared with the constant environmental conditions and water pH utilized in the laboratory study. © 1997 SCI.     

Behaviour of ddt in three soils exposed to solar radiations under different conditions

Volatilization, mineralization, degradation and binding of soil-applied [¹⁴C]DDT were studied in three different soils from a tropical region of southern India subjected to solar irradiation and flooding for a period of 42 days. The soil types–red cotton soil, nursery soil and canal bank soil–differed in their organic carbon content, pH and texture. Under unflooded conditions, volatile losses were highest in the sandy canal bank soil. Flooding significantly enhanced volatilization, and this effect was maximal in the nursery soil, which had the highest organic carbon. The soils fully exposed to solar radiations in quartz tubes registered 1.5-1.8 times greater volatility. The volatilized organics contained appreciable quantities of DDE under both flooded and unflooded conditions. In addition, greater quantities of DDD volatilized from the flooded systems. The rate of formation of DDE was faster when soils were irradiated in quartz tubes. Mineralization remained minimal throughout the period of exposure and flooding the soil appeared to reduce further the [¹⁴C]carbon dioxide evolution. Canal bank soil exhibited the least mineralization and degradation. The data indicate that volatilization was significantly influenced by solar radiation and flooding to a much greater degree than by the differences in soil properties. Binding of DDT to soil was significantly increased by flooding the soil, thus leaving up to 33% of the initial DDT as bound residues in the nursery soil.     

Persistence of gamma-BHC and beta-BHC in Indian rice soils under flooded conditions

The relative persistence of [¹⁴C]-gamma-BHC and [¹⁴C]-beta-BHC in Indian rice soils under flooded conditions was studied. In alluvial, laterite and pokkali (acid sulphate, saline) soils, rapid degradation of both isomers occurred; in sandy and kari (acid sulphate, saline) soils, both isomers persisted even after 41 days of flooding. The rapid degradation of BHC isomers in the former three soils was related to highly negative redox potentials within 20 days of flooding in contrast to oxidised conditions in sandy and kari soils even after 41 days. During the degradation in the soils, beta-BHC showed longer lag than gamma-BHC. Results suggest that the degradation of beta-BHC commences at a potential lower than that required for gamma-BHC degradation. Greater decomposition of gamma-BHC occurred in rice straw-amended soils than in unamended soils when the insecticide was incorporated to the soils in an aqueous solution. Addition of BHC isomers to the soils in ethanol resulted in comparable rates of rapid decomposition in both rice straw-amended and unamended soils, since ethanol was as effective as rice straw in lowering the redox potentials of the soils favouring BHC decomposition in unamended soil as well.     

Persistence of pyrazosulfuron in rice-field and laboratory soil under Indian tropical conditions

BACKGROUND: Pyrazosulfuron ethyl, a new rice herbicide belonging to the sulfonylurea group, has recently been registered in India for weed control in rice crops. Many field experiments revealed the bioefficacy of this herbicide; however, no information is available on the persistence of this herbicide in paddy soil under Indian tropical conditions. Therefore, a field experiment was undertaken to investigate the fate of pyrazosulfuron ethyl in soil and water of rice fields. Persistence studies were also carried out under laboratory conditions in sterile and non‐sterile soil to evaluate the microbial contribution to degradation. RESULTS: High‐performance liquid chromatography (HPLC) of pyrazosulfuron ethyl gave a single sharp peak at 3.41 min. The instrument detection limit (IDL) for pyrazosulfuron ethyl by HPLC was 0.1 µg mL^?1, with a sensitivity of 2 ng. The estimated method detection limit (EMDL) was 0.001 µg mL^?1 and 0.002 µg g^?1 for water and soil respectively. Two applications at an interval of 10 days gave good weed control. The herbicide residues dissipated faster in water than in soil. In the present study, with a field‐soil pH of 8.2 and an organic matter content of 0.5%, the pyrazosulfuron ethyl residues dissipated with a half‐life of 5.4 and 0.9 days in soil and water respectively. Dissipation followed first‐order kinetics. Under laboratory conditions, degradation of pyrazosulfuron ethyl was faster in non‐sterile soil (t_1/2 = 9.7 days) than in sterile soil (t_1/2 = 16.9 days). CONCLUSION: Pyrazosulfuron ethyl is a short‐lived molecule, and it dissipated rapidly in field soil and water. The faster degradation of pyrazosulfuron in non‐sterile soil than in sterile soil indicated microbial degradation of this herbicide. Copyright © 2012 Society of Chemical Industry     

毛乌素沙地不同生境主要植物叶性状研究

叶性状与植物的生长对策及资源利用效率密切相关,能够反映植物对环境的适应策略.文中比较分析了毛乌素沙地不同生境中(固定沙地、半固定沙地和流动沙地)8种植物叶性状的差异及其相关关系.结果 表明:1)8种植物叶性状差异显著,流动沙地沙米(Agriophyllum squarrosum)具有较大的比叶面积(SLA)和较小的单位...     

The incubation period of beet yellowing viruses in sugar-beet under field conditions

In three years field trials, the incubation period, i.e. the time between infection and the appearance of symptoms, of beet yellows virus (BYV) and beet mild yellowing virus (BMYV) increased with later infection during the growing season. The incubation period of BYV, a closterovirus, increased from 3 weeks in young plants infected before canopy closure, to 9 weeks in old plants infected in August. The incubation period of BMYV, a luteovirus, increased from 4 to 5 weeks in young plants to 9 weeks in old plants. Symptoms were observed c. one week earlier on the inoculated leaves than on those infected systemically, except on young BYV-infected plants. On these plants, symptoms developed in 3 weeks on both leaf types.The incubation period decreased at increasing temperature, a fixed temperature sum being required for the development of symptoms on plants of a certain age. This temperature sum increased with plant age. Symptom development was related to leaf growth; the systemic symptoms appeared after the infected leaves attained their final size. Young, expanding leaves did not show symptoms. Thus the development of symptoms seems to be related to physiological conditions occurring only in full-grown leaves. A low rate of leaf expansion may constitute the underlying reason for the long incubation period of virus symptoms in old plants and at low temperatures.The incubation period was not substantially affected by: (1) the number ofMyzus persicae used to inoculate the plants, (2) the number of leaves inoculated, (3) the development stage of the inoculated leaf and (4) the source plant of BMYV, beet or shepherd's-purse,Capsella bursapastoris. The incubation period can be used to obtain rough estimates of the infection-date of individual plants, given the date on which symptoms appear.Samenvatting De incubatieperiode van het bietevergelingsvirus, BYV, en het zwakke-bietevergelings-virus, BMYV, nam toe naarmate suikerbieteplanten later in het seizoen geïnfecteerd werden. Jonge planten ontwikkelden BYV-symptomen na ongeveer 3 weken terwijl na gewassluiting de incubatieperiode geleidelijk toenam tot 9 weken. De incubatieperiode van BMYV nam toe van 4 à 5 weken na inoculatie in juni tot 9 weken na inoculatie in augustus. Geïnoculeerde bladeren ontwikkelden ongeveer een week eerder symptomen dan de systemisch geïnfecteerde bladeren, behalve bij jonge planten, geïnfecteerd met BYV, waar de symptomen zich op beide typen bladeren tegelijkertijd ontwikkelden.De incubatieperiode nam bij hogere temperatuur af en, afhankelijk van de leeftijd van de plant (aantal bladeren) was een bepaalde temperatuursom nodig voor de ontwikkeling van symptomen. Deze temperatuursom nam toe met de ouderdom van de plant. Van alle systemisch besmette bladeren, vertoonden de oudste, welke juist verschenen op het moment dat de plant werd geïnfecteerd, als eerste symptomen. Dit gebeurde zodra of kort nadat ze hun uiteindelijke grootte hadden bereikt. Groeiende bladeren vertoonden nooit vergelingssymptomen. De trage bladexpansie in oude planten en bij lage temperaturen is een mogelijke oorzaak van de lange incubatieperiode aan het einde van het seizoen.De incubatieperiode werd niet duidelijk beïnvloed door inoculatieomstandigheden, zoals (1) het aantal groene perzikluizen,Myzus persicae, dat werd gebruikt voor inoculatie, (2) het aantal geïnoculeerde bladeren, (3) de ouderdom van het geïnoculeerde blad, (4) de bronplant van BMYV, biet of herderstasje, of (5) de vector species. Omdat de incubatieperiode niet in belangrijke mate afhankelijk is van deze factoren kan bij kennis van de datum waarop symptomen verschenen de infectiedatum worden bepaald op basis van de incubatieperiode.     

Persistence and mobility of tebufenozide in forest litter and soil ecosystems under field and laboratory conditions

A field microcosm study was conducted to determine persistence of tebufenozide, an insect growth regulator, in sandy litter and soil. Litter and soil plots (c. 4·5 m² each) were sprayed with an aqueous suspension concentrate formulation of tebufenozide at rates of 35, 70 and 140 g AI ha^-1. Samples were collected at intervals up to 408 days after spraying, and analyzed for tebufenozide residues. The data were subjected to regression analysis and half-life (DT₅₀, the time required for 50% of the initial residues to disappear) values were computed. The DT₅₀ was c. 62 days for both substrates treated with the two lower dosage rates. At the highest dosage rate, the DT₅₀ was 115 days for the litter and c. 52 days for the soil, indicating irregular variations in persistence. Downward movement in soil occurred only in trace amounts, suggesting strong adsorption. Laboratory microcosm studies were conducted to investigate the relative importance of rainfall, exposure to light and volatilization on persistence. Vertical movement occurred in litter and soil (both sandy and clay types) during rainfall. The amount moved increased with the amount of rainfall, but decreased with the rain-free period. The larger the rain droplets, the greater the downward movement. When the rainwater could move laterally along the surface of the substrate (as would occur on a slope), more lateral movement than vertical movement of tebufenozide occurred. The photolysis study indicated that disappearance of tebufenozide was directly related to the duration of exposure to radiation and radiation intensity. Volatilization of tebufenozide depended upon the ambient temperature and the duration of air passing through the substrates. Nonetheless, the amount lost by volatilization was much lower than the amount lost after rainfall or exposure to radiation, thus indicating the greater influence of rainfall and sunlight on persistence. In the laboratory microcosm studies, more tebufenozide was lost from the sandy substrates than from the clay substrates. This behaviour was attributed to the greater adsorptive capacity of the clay substrates, thus providing a greater protection against downward mobility and loss due to radiation. © 1997 SCI     

室内条件下向日葵列当和弯管列当在三种不同寄主上寄生能力的比较

以向日葵列当Orobanche cumana Wallr.和弯管列当O.cernua Loefl.为研究对象,利用已有的室内寄生体系来研究两种列当在向日葵、烟草、番茄3种寄主上的寄生能力。结果表明,向日葵列当在室内条件下不仅能够寄生在向日葵上,同时也可以在烟草与番茄上寄生;但其寄生效率在上述不同的寄主之间存在显著差异,而在相同寄主的不同品系间没有差异。交互侵染的结果表明,在寄主番茄上,弯管列当平均每株寄生的瘤结数量为16.3个,向日葵列当只有2.5个;在寄主向日葵上,向日葵列当的平均寄生瘤结数量为25.2个,弯管列当为27.6个,预示着弯管列当在番茄上寄生效率均显著高于向日葵列当,而在寄主向日葵上,二者寄生效率差异不显著,均能高效寄生在向日葵根系上。上述研究结果将为向日葵列当和弯管列当发生严重地区作物轮作对象的选择提供理论依据。     

Weed suppression ability of three winter wheat varieties at different row spacing under organic farming conditions

For three seasons, six field trials were conducted in winter wheat ( Triticum aestivum ) at different sites in North Rhine-Westphalia, Germany. The aim was to evaluate the performance of three varieties, which differ in their shading behaviour, in suppressing weeds under organic farming (Ökologischer Landbau) conditions and grown at three row spacings. The experimental factors were cultivar, row width and row orientation. Key parameters of crop and weed development, including ground cover and biomass, were assessed at different growth stages and analysed with anova . Growth of the site-specific weed vegetation was significantly affected in five of six trials. Weed growth was reduced by cvs Astron and Pegassos compared with cv. Greif, and was lower at 12 cm compared with 24 cm row spacing. No effect of row orientation (East-West, North-South) on weed growth was observed. The more competitive cultivars Astron and Pegassos were taller than the less competitive cv. Greif and had higher ground cover and light interception, presumably induced by planophile leaf inclination and partly, in the case of cv. Astron, because of higher leaf area index (LAI). Narrow row spacing (12 cm), resulting in a more even spatial plant distribution, increased crop ground cover, LAI, dry matter and light interception. In two trials, the variety with planophile leaf inclination performed better at wider row spacing, suggesting that planophile wheat cultivars may be advantageous in wider row stands.     

Persistence of organochlorine insecticides on different substrates under different environmental conditions. I. The rates of loss of dieldrin and aldrin by volatilisation from glass surfaces

The losses of dieldrin and aldrin by volatilisation from crystalline deposits on glass surfaces in different environments were studied by using these insecticides labelled with the radioactive isotope ³⁶CL as a tracer. Volatilisation rates were very sensitive to changes in temperature and to a lesser extent to air movement, but not to change in relative humidity (the effect of which was measurable only on porous glass surfaces). All rates of loss from glass surfaces could be described mathematically in terms of single or double exponential equations, although many were better described by simple sigmoid (logistic) equations.     

Persistence and binding of DDT and gamma-HCH in a sandy loam soil under field conditions in Delhi,India

Persistence and binding capacity of [¹⁴C]p, p′-DDT and [¹⁴C]y-HCH were studied for one year in a sandy loam soil of Delhi, India, after surface treatment during monsoon, winter and summer seasons under field conditions. Both DDT and HCH dissipated more rapidly under the Indian subtropical climate than reported for temperate regions. In all three seasons, both insecticides dissipated most rapidly during the initial 60 days. However, in the final six months there was very little change in the residue levels. After one year, the final soil burden of DDT varied from 33 to 36% and of HCH from 14 to 15% of the initial concentrations in the different experiments. HCH bound more with the soil as, out of the total residues present after one year, more than 75% of HCH was in bound form compared with only 24% of DDT. The observed time for 50% initial dissipation of DDT ranged from 60 to 120 days, while in the case of HCH it varied from 30 to 45 days. However, the rate of loss of residues which persisted for more than 6 months was equivalent to a half-life of between 500 and 10000 days for DDT, and between 700 and 2000 days for HCH, thus illustrating the very long persistence of aged residues. Since degradation of both insecticides was apparently minimal, the data indicate that dissipation of DDT and HCH was largely due to volatilisation.     

Phytotoxic activity of pethoxamid in soil under different moisture conditions

The phytotoxic activity of soil-applied pethoxamid [2-chloro- N -(2-ethoxyethyl)- N -(2-methyl-1-phenyl-1-propanyl) acetamide], (TKC-94), on the plant growth of rice ( Oryza sativa cv. Kiyohatamochi ) seedlings as an assay plant in soil was investigated under different soil moisture conditions. The phytotoxic activity of pethoxamid mixed with soil on the shoot and root growth of rice seedlings was uppermost under the highest soil moisture condition and it decreased with declining soil moisture content, while the inhibition was greater on the root growth than the shoot growth. The amount of pethoxamid adsorbed on soil solid and the concentration of pethoxamid in soil water from soil applied with this herbicide were not influenced by the soil moisture content. In addition, the phytotoxic activity on the growth of rice seedlings in sea sand culture applied with the soil water from the herbicide-applied soil was not influenced by the soil moisture content. In the sea sand culture, the phytotoxic activity of pethoxamid was significantly reduced in negative water potential as the concentration of polyethylene glycol-6000 added to the water increased. It is suggested that the phytotoxic activity of pethoxamid in the soil primarily depends on the concentration in soil water, but the phytotoxic activity was affected by soil moisture through the effect on absorption of this herbicide by rice seedlings.     

单管多重RT-PCR同时检测大豆种子中三种检疫性植物病毒

我国大豆年进口量持续增长,快速、准确地检测进境大豆种子中可能携带的病原物是防止检疫性有害生物入境传播和扩散的有效手段。菜豆荚斑驳病毒(BPMV)、烟草环斑病毒(TRSV)和番茄环斑病毒(ToRSV)均是被大豆种子携带的检疫性有害生物。本研究建立了在单一PCR管中同时检测这3种检疫性植物病毒及大豆内源基因Bd-30K的多重RT-PCR方法。研究结果表明,所建立的多重RT-PCR方法具有较好的特异性和灵敏度,检测含BPMV、TRSV和ToRSV RNA的最低浓度分别为0.45、0.0093和0.004ng/μL,从大豆种子中同时检测3种病毒的最低RNA浓度为0.58ng/μL。     

Emergence of Chenopodium album and Stellaria media of different origins under different climatic conditions

Summary The emergence behaviour of weed species in relation to cultural and meteorological events was studied. Dissimilarities between populations in dormancy and germination ecology, between-year maturation conditions and seed quality and burial site climate all contribute to potentially unpredictable variability. Therefore, a weed emergence data set was produced for weed seeds of Stellaria media and Chenopodium album matured and collected from three populations (Italy, Sweden and UK). The seeds were collected in two consecutive seasons (1999 and 2000) and subsequently buried in the autumn of the same year of maturation in eight contrasting climatic locations throughout Europe and the USA. The experiment sought to explore and explain differences between the three populations in their emergence behaviour. Evidence was demonstrated of synchrony in the timing of the emergence of different populations of a species at a given burial site. The relative magnitudes of emergence from the three populations at a given burial site in a given year were generally similar across all the burial sites in the study. The resulting data set was also used to construct a simple weed emergence model, which was tested for its application to the range of different burial environments and populations. The study demonstrated the possibility of using a simple thermal time-based model to describe part of the emergence behaviour across different burial sites, seed populations and seasons, and a simple winter chilling relationship to adjust for the magnitude of the flush of emergence at a given burial site. This study demonstrates the possibility of developing robust generic models for simple predictions of emergence timing across populations.     

Retrospective estimation of the data of infection with beet yellowing viruses in sugar-beet under field conditions

Sugar-beet plants, infected with beet yellows virus (BYV, closterovirus group) or beet mild yellowing virus (BMYV, luteovirus group) develop symptoms on the inoculated leaves on which aphids infected the plant. Symptoms develop also on the systemically-infected leaves to which virus has been transported via the phloem. Systemic infection occurs in the leaves which have just, or not yet appeared at the moment of infection of the plant. All other, older leaves remain uninfected. The infection-date can be estimated by assessing the date of appearance of the oldest systemicallyinfected leaf of a plant. This approach was tested in the field and gave good results.Samenvatting Suikerbieteplanten die besmet zijn met het bietevergelingsvirus, BYV, of met het zwakke vergelingsvirus, BMYV, ontwikkelen symptomen op de geïnoculeerde bladeren, waarop infectieuze bladluizen virus hebben overgedragen, én op de systemisch besmette bladeren waarheen het virus vanuit de geïnoculeerde bladeren is getransporteerd via het vaatsysteem. Bladeren die op het moment van infectie nog niet verschenen zijn of vlak ervóór zijn verschenen, worden systemisch besmet, terwijl oudere bladeren gezond blijven. De infectiedatum kan worden bepaald door aan de hand van temperatuursommen de verschijningsdatum van het oudste systemisch besmette blad te berekenen. Deze methode bleek bij toetsing in het veld goed te voldoen.