Variation in Transmission Efficiency Among Barley yellow dwarf virus-RMV Isolates and Clones of the Normally Inefficient Aphid Vector, Rhopalosiphum padi

The RMV strain of Barley yellow dwarf virus (BYDV-RMV) is an unassigned member of the Luteoviridae that causes barley yellow dwarf in various cereal crops. The virus is most efficiently vectored by the aphid Rhopalosiphum maidis, but can also be vectored with varying efficiency by R. padi and Schizaphis graminum. Field collections of alate aphids migrating into the emerging winter wheat crop in the fall of 1994 in central New York identified a high proportion of R. padi transmitting BYDV-RMV. This prompted a comparison of the BYDV-RMV isolates and the R. padi populations found in the field with type virus and aphid species maintained in the laboratory. A majority of the field isolates of BYDV-RMV were similar to each other and to the type BYDV-RMV isolate in disease severity on oat and in transmission by the laboratory-maintained population of R. maidis and a field-collected population of R. maidis. However, several field populations of R. padi differed in their ability to transmit the various BYDV-RMV isolates. The transmission efficiency of the R. padi clones was increased if acquisition and inoculation feeding periods were allowed at higher temperatures. In addition, the transmission efficiency of BYDV-RMV was significantly influenced by the aphid that inoculated the virus source tissue. In general, BYDV-RMV transmission by R. padi was higher when R. padi was the aphid that inoculated the source tissue than when R. maidis was the inoculating aphid. The magnitude of the change varied among virus isolates and R. padi clones. These results indicate that, under certain environmental conditions, R. padi can play a significant role in the epidemiology of BYDV-RMV. This may be especially significant in regions where corn is a major source of virus and of aphids that can carry virus into a fall-planted wheat crop.     

The role of Poa annua in the epidemiology of barley yellow dwarf virus in autumn-sown cereals

Studies of cereal aphids and barley yellow dwarf virus (BYDV) from 1989 to 1992 revealed that Poa annua is an abundant weed of commercial winter barley crops during the summer months. P. annua was frequently infected with BYDV, and there were usually similarities with the BYDV infection of the surrounding barley crop. These P. annua weeds were often infested by cereal aphids both in July (pre-harvest) and in September (in cereal stubble fields). Poa -infested cereal stubbles may be major local sources of viruliferous aphids, increasing the risk of BYDV in nearby winter cereals. P. annua plays an important role in the epidemiology of S. avenae -transmitted BYDV.     

沙坡头地区豆科植物共生固氮资源初步研究

对沙坡头地区引进和野生的１９属５１种豆科植物的结瘤固氮状况进行了调查，除花生，三刺皂荚，铃铛刺３属３种外，其余４８种均能自然结瘤，种的结瘤率为９４．１％，其中２７种为Ａｌｌｅｎ文献中未记载的结瘤豆科植物。根瘤形态大多数圆形，棒状域指状，形态较为规则，白色黄色者居多，乙炔还原活力测定表明，２４．６％为无效根瘤，不同种豆科植物根瘤的乙炔还原活力相差不大，一般活力都较低，乙炔还原活力小于１μｍｏｌＣ２Ｈ     

12种药剂防治麦蚜及对天敌安全性田间试验

田间试验结果表明：吡虫啉30g/hm^2、啶虫脒11.5g/hm^2、辟蚜雾150g/hm^2、赛丹450g/hm^2对麦蚜防效高，药后7d的防效均在99％以上，且对捕食性天敌无害，可以作为综合防治麦蚜的药剂大面积推广应用。每hm^2喷液量为600kg。     

Occurrence of barley yellow dwarf virus in autumn-sown cereal crops in the United Kingdom in relation to field characteristics

The incidence of barley yellow dwarf virus and of its aphid vectors was surveyed in untreated parts of autumn-sown cereal crops, mainly wheat and barley, in the United Kingdom in 1995-8. The incidence of virus in the spring was related to the incidence of aphids in the preceding autumn. Both virus and aphid incidences could also be related to a range of crop and field characteristics, in particular sowing date, regions as defined by their geographical position, topography and climate, the proximity of the field to the sea, the extent of arable land in the vicinity of the field, and the aspect and size of the field. Proximity of cropped fields to setaside areas had no significant effect on either aphid or virus incidence.     

Increase in Zucchini yellow mosaic virus Symptom Severity in Tolerant Zucchini Cultivars Is Related to a Point Mutation in P3 Protein and Is Associated with a Loss of Relative Fitness on Susceptible Plants

ABSTRACT Zucchini yellow mosaic virus (ZYMV, Potyvirus) is a very damaging cucurbit virus worldwide. Interspecific crosses with resistant Cucurbita moschata have led to the release of "resistant" zucchini squash (C. pepo) F(1) hybrids. However, although the resistance is almost complete in C. moschata, the commercial C. pepo hybrids are only tolerant. ZYMV evolution toward increased aggressiveness on tolerant hybrids was observed in the field and was obtained experimentally. Sequence comparisons and recombination experiments revealed that a point mutation in the P3 protein of ZYMV was enough to induce tolerance breaking. Competition experiments were performed between quasi-isogenic wild-type, and aggressive variants of ZYMV distinguished by monoclonal antibodies. The aggressive mutants were more fit than wild-type strains in mixed infections of tolerant zucchini, but they presented a drastic fitness loss in mixed infections of susceptible zucchini or melon. Thus, the ability to induce severe symptoms in tolerant zucchini is related to a genetic load in susceptible zucchini, but also on other susceptible hosts. This represents the first quantitative study of the fitness cost associated with tolerance breaking for a plant virus. Thus, although easily broken, the tolerance might prove durable in some conditions if the aggressive variants are counterselected in susceptible crops.     

云南派姬小蜂对其寄主及寄主植物相关化学线索的行为反应

与寄主植物和寄主相关的化学线索在寄生蜂的寄主搜寻过程中起着重要作用。云南派姬小蜂Pediobius yunnanensis是松树钻蛀性害虫——微红梢斑螟Dioryctria rubella的蛹寄生蜂,为了探究该寄生蜂对其寄主和寄主植物相关化学线索的行为反应,本研究进行了一系列试验。利用Y形嗅觉仪,测定了该寄生蜂对不同处理的油松球果（含蛹球果、含空蛹壳的球果、幼虫为害的球果和健康球果）和松枝（含蛹松枝、幼虫为害的松枝、含蛹球果的系统枝、含蛹松枝的系统枝和健康松枝）以及幼虫虫粪（3龄幼虫虫粪、含蛹球果内的幼虫虫粪）挥发物的趋性行为;在开放场中,测定了老熟幼虫爬行痕迹对该寄生蜂搜索行为的影响;利用双选择试验,在培养皿中测定了该寄生蜂对微红梢斑螟茧或蛹浸提液的行为反应。结果显示,在嗅觉试验中,含蛹球果、含有空蛹壳的球果挥发物对寄生蜂有极显著的引诱作用,而幼虫为害的球果和健康球果对寄生蜂的行为无明显影响;该寄生蜂对含蛹松枝挥发物表现出明显的正趋性反应,而对幼虫为害的松枝、含蛹球果的系统枝、含蛹松枝的系统枝以及健康松枝则无趋性反应;寄生蜂对含蛹球果中的幼虫虫粪挥发物表现出偏爱性,而对3龄幼虫虫粪无明显反应;在开放场中,老熟幼虫的爬行痕迹对寄生蜂的搜索行为无显著影响;在培养皿中,微红梢斑螟茧的甲醇、二氯甲烷或正己烷浸提液以及蛹的二氯甲烷或正己烷浸提液,不仅能强烈地吸引该寄生蜂,还能明显延长其停留时间。该结果为揭示云南派姬小蜂寄主搜寻行为的化学调控机制以及微红梢斑螟的生物防治提供理论依据。     

1900-1949年关中地区旱涝灾害时空特征初探

本文将20世纪前半期关中地区40个县的旱涝灾害进行逐年、逐县统计分析。研究结果表明,50年间关中地区每年都有不同程度的旱灾或涝灾,灾害的发生具有阶段性和交替性特征;空间上总体呈现出“旱一片,涝一线”的成灾特点,但区域内部仍有差异。     

Generation and Molecular Mapping of a Sequence Characterized Amplified Region Marker Linked with the Bct Gene for Resistance to Beet curly top virus in Common Bean

ABSTRACT A random amplified polymorphic DNA (RAPD) marker directly linked (0.0 cM) with a resistance gene was identified in a snap bean recombinant inbred population (Moncayo x Primo) consisting of 94 F(5:7) recombinant inbred lines that had uniform segregation for disease reaction to Beet curly top virus (BCTV) across three field locations. Resistance was conditioned by a single dominant allele tentatively designated Bct. Seven hundred and fifty decamer primers were screened to obtain the linked RAPD marker that was then converted to a sequence characterized amplified region (SCAR) marker SAS8.1550. The SCAR mapped within a cluster of resistance genes on linkage group B7 of the core map. A survey of 103 BCTV-resistant and -susceptible snap and dry bean genotypes was conducted using SAS8.1550. Results showed that the SCAR would be highly useful for marker-assisted selection of Bct in snap and dry bean originating from the Andean gene pool. Marker-assisted selection for Bct will expedite the development of BCTV-resistant cultivars and minimize the need for cumbersome pathogen tests.     

The use of insecticides to control potato leafroll virus in seed-potato crops on the Golan Heights

Experiments were carried out in the laboratory and in the field for 3 years, in an attempt to protect seed-potato crops on the Golan Heights from potato leafroll virus (PLRV) by means of insecticides. The best results with spray compounds were obtained with pirimicarb (Pirimor), methamidophos (Tamaron) and ethiofencarb (Croneton); the commonly used and recommended aphicides oxydemetonmethyl (Metasystox R) and endosulfan (Thionex) were less efficient. The best results with granular insecticides were obtained with aldicarb (Temik) and ethiofencarb, while phorate (Thimet), carbofuran (CURATERR) and oxamyl (Vydate) were much less efficient. Dimethoate (Rogor) gave good results in the laboratory test, but was less efficient in the field trials. The flight of aphids in the Golan Heights is characterized by two close peaks: in May-June, and from late July to September. Potatoes are planted in early May, and hence crops need to be protected throughout almost the entire season. Weekly sprays using, in turn, pirimicarb, methamidophos and ethiofencarb, reduced PLRV incidence in seed-potato plots in 1977 from 33.4% (in the untreated controls) to 2.8%, thus ensuring their certification. A single pre-emergence treatment with aldicarb reduced PLRV incidence from 12.6% (in the untreated controls) to 1.8%; however, the best results (no infection) were obtained by the addition of weekly sprays, starting at the end of July, to a pre-emergence treatment with a granular insecticide.     

The characteristics of mineral oils in relation to their inhibitory activity on the aphid transmission of potato virus Y

In greenhouse trials paraffinic mineral oils, characterized by a viscosity gravity constant (VGC) of 0.790–0.819, and with viscosities between 12 and 30 cSt at 37°C (66–150 SUS) proved to have the best aphid transmission inhibiting activity of potato virus Y to red peppers. The activity decreased rapidly with decreasing viscosities but only slowly with increasing values.Effective oils are further characterized by an unsulfonated residue (USR) of 95–100, indicating the near or total absence of aromatic structures, which are inactive and known to be phytotoxic. The paraffine-pourpoint should be below 0°C, indicating that n-paraffines do not form a very important part of the oil, since they are also inactive. Naphthenic structures seem equally inert, their percentage in the oil depending on the origin of the crude oil, because they cannot be separated from the paraffinic structures by refining procedures.Mineral oils which one commercialize for agricultural practice normally have an USR above 95 and a paraffine-pourpoint below 0°C. Therefore, the information on the classification, based on a VGC value and on the viscosity, is already sufficient to allow an evaluation of those oils of their suitability as inhibitor of the virus transmission by aphids.Samenvatting In kasproeven bleken minerale paraffine oliën, gekenmerkt door een VGC (viscositeits-dichtheidsconstante) van 0.790–0.819 en een viscositeit tussen 12 en 30 cSt bij 37°C (66–150 SUS) de beste werking te bezitten tegen de overdracht van aardappelvirus Y naar paprika door bladluizen. De werking verminderde snel bij afnemende viscositeiten beneden 12 cSt, slechts langzaam bij toenemende waarden boven 30 cSt.De minerale olie met de meest gunstige eigenschappen met betrekking tot verhindering van de virusoverdracht wordt verder nog gekenmerkt door een USR (nier-sulfoneerbare rest) van 95–100. Dit betekent het geheel of bijna geheel afwezig zijn van aromatische verbindingen, die bekend zijn om hun fytotoxische eigenschappen en bovendien niet werkzaam zijn. Het stollingspunt moet bij voorkeur onder 0°C liggen wat betekent dat n-paraffinen geen al te belangrijk bestanddeel van de olie vormen, aangezien deze eveneens onwerkzaam zijn. Naphthenische structuren bleken ook onwerkzaam te zijn. Het gehalte hiervan in de oliefractie hangt echter van de herkomst van de ruwe olie of, omdat ze niet door raffineren van de paraffinestructuren kunnen worden gescheiden.Minerale oliën die aanbevolen worden voor landbouwkundige doeleinden, bezitten normalerwijze een USR boven 95 en een stollingspunt onder 0°C. Dit betekent dat informatie over de aard der oliën op grond van een VGC waarde en over de viscositeit voldoende is om dergelijke oliën te beoordelen op hun geschiktheid de virusoverdracht door bladluizen te kunnen verhinderen.     

The location of virus-like particles in the male gametophyte of birch, walnut and cherry naturally infected with cherry leaf roll virus and its relevance to vertical transmission of the virus

Virus-like particles (VLPs) in close-packed paracrystalline arrays were observed in cells forming the anther walls and in the sperm cell cytoplasm of immature pollen grains developing within cherry leaf roll virus (CLRV)-infected birch ( Betula pendula Roth.). VLPs within tubules, that were in some instances multiple and membrane bound, were also observed in anther cells and in pollen grains of CLRV-infected walnut ( Jugians regia L.). VLPs rarely coated the outer surfaces of developing grains. Washings from intact freshly collected pollen did not contain infective agents but pollen triturates were infectious after 12 months storage at-70°C. Purified CLRV (concentration 6·4 ng/ml) was readily detected by enzyme-linked immunosorbent assay (ELISA). CLRV-specific antigens (detected by ELISA) and VLPs (detected on grids coated with an antiserum prepared against CLRV) were readily removed by washing intact pollen grains from infected birch, walnut and cherry ( Prunus avium L. cv. F12/1). The antigen was less tenaciously held to the surfaces of anemophilous (birch and walnut) than entomophilous (cherry) pollen. Treatment of grains before ELISA testing with CLRV-specific γ globulin virtually eliminated the antigenicity of pollen washings whereas γ globulin from a pre-immune serum had no such effect. When anti-CLRV γ globulin-treated pollen grains were disrupted, CLRV-specific antigens were liberated. VLPs trapped on CLRV-antiserum coated grids to which pollen washings or extracts from disrupted grains had been applied were identified by decoration; a halo of antibody molecules enveloped VLPs treated with CLRV-antiserum but not those treated with antiserum prepared against poplar mosaic virus.     

西北干旱区农业生产对气候变化的响应评价初探——以黑河流域中段张掖市为例

由于气候变化的不确定性,对气候变化的响应评价比气候变化的影响研究更具现实意义。本文以张掖市为研究区域,将2000年作为基准年对农业生产对气候变化的脆弱性进行了评价。评价结果表明:肃南为最脆弱地区,甘州区属于中等脆弱地区,高台、民乐属于较不脆弱地区,临泽、山丹属于最不脆弱地区。在脆弱性评价的基础上提出了相应的适应性对策。对调整优化区域土地利用结构,促进区域生态、经济的可持续发展具有重要意义。     

The importance of the infected seed tuber and soil inoculum in transmitting Potato mop‐top virus to potato plants

Potato mop‐top virus (PMTV), the cause of spraing in potato tubers, is transmitted by Spongospora subterranea, the cause of powdery scab, and by planting infected seed tubers. This study was undertaken to determine the relative importance of these sources of infection in seed potato production in Scotland. The transmission of PMTV from tested seed tubers to daughter plants was examined over 2 years and six cultivars. The development of foliar symptoms varied with year and cultivar. Infection of daughter tubers derived from PMTV‐infected seed tubers was more prevalent on plants affected by foliar symptoms than those without symptoms. The rate of transmission of PMTV from infected seed tubers to daughter tubers ranged from 18 to 54%. Transmission was affected by cultivar and by origin of seed tubers used for a cultivar, but not by a cultivar's sensitivity to PMTV infection. The incidence of PMTV in daughter tubers of cv. Cara grown from seed potatoes from one source (common origin) by more than 25 seed producers was examined over two successive generations. The incidence of PMTV in daughter tubers was not correlated with that in the seed tubers but appeared to be strongly associated with soil inoculum. The incidence of PMTV was correlated with powdery scab in those crops in which both were present. There was some evidence from soil tests conducted in 2006 using a tomato bait plant and real‐time RT‐PCR that planting PMTV‐infected seed potatoes could increase the risk of introducing the virus into land not infested by PMTV.     

The Use of a GUS Transformant of Trichoderma Harzianum, Strain T3a, to Study Metabolic Activity in the Spermosphere and Rhizosphere Related to Biocontrol of Pythium Damping-off And Root Rot

The activity of Trichoderma harzianum in the spermosphere and rhizosphere of different plant species was studied by use of a beta-glucuronidase (GUS) transformant (strain T3a). Hereby, direct observation of micro-habitats supporting metabolic activity of T. harzianum is reported. Germination of conidia and mycelial growth were not supported by exudates from healthy roots of various ages. Instead, growth and activity of T. harzianum depended on access to dead organic substrates such as seed coats, decaying roots, and wounds, including those caused by infecting pathogens. A correlation between the GUS activity of T. harzianum and the biomass of Pythium ultimum in infected roots was established. On the basis of our observations, we suggest that the biocontrol ability of T. harzianum involves competition with the pathogen for substrates including the seed coat, and wounded or infected root tissue.     

The effect of DD and dazomet treatments on nematode populations at various depths in the soil and on the transmission of soil-borne tobacco rattle virus to gladiolus

The relation between log dosage of DD injected at 15 cm depth or of dazomet applied to the soil surface (all in November 1971) and probit mortality ofRotylenchus and trichodorids in the top 20 cm of a field on sandy soil was found to be linear. Dosage increase efficiencies of both chemicals against both nematode species were medium to high. Superficial application of dazomet was very effective against the nematodes that would have survived if only a low dosage of DD had been injected at 15 cm depth. Injection of 40 ml or 80 ml DD per m² at 15 cm depth killed all nematodes between 20 cm and 60 cm deep. Gladiolus planted in the spring of 1972 grew better, flowered earlier and produced more weight of corms on treated than on untreated plots. The poor growth on the untreated plots cannot be ascribed to direct damage by nematodes or to the effect of TRV transmitted to the plants by the viruliferous trichodorids occurring in these plots in high densities. Symptoms of TRV infection in plants grown in 1973 from the corms harvested in the 1972 experimental field showed that only DD treatments had reduced the rate of TRV transmission considerably. However, even the highest dosages of DD had only reduced it from 26% (on untreated plots) to about 8%. Most probably, this residual TRV infection was due to transmission by trichodorids that had survived in soil layers below 60 cm depth. Therefore, soil treatment with nematicides, cannot prevent TRV transmission to gladiolus sufficiently where viruliferous trichodorids occur at great depths, as is the case in many sandy soils having a low water table.     

The Role of the Bark Beetle, Hylastes ater (Coleoptera: Scolytidae), as a Sapstain Fungi Vector to Pinus radiata Seedlings: A Crisis for the New Zealand Forestry Industry?

The role of the bark beetle Hylastes ater in the re-establishment of Pinus radiata forest in New Zealand is discussed. H. ater was found to be a dominant factor in seedlings mortality in the first year following planting. However, seedling mortality is usually relatively low. In contrast, it was found the large numbers of seedlings were sub-lethally damaged by H. ater feeding attempts, particularly in high risk sites. High risk sites were identified as sites that were harvested during March and April (autumn) when the peak flight activity of H. ater occurred, and subsequently planted with P. radiata seedlings the following winter. H. ater was found to vector sapstain fungi to seedlings during feeding attempts, and a strong relationship between the severity of damage and presence of sapstain fungi was identified. The role of H. ater as a vector of these fungi and the potential implications to the New Zealand forest industry are discussed.