Seed and pollen transmission of <Emphasis Type="Italic">Apple latent spherical virus</Emphasis> in apple

To examine whether Apple latent spherical virus (ALSV) has spread among apple trees in an orchard, we surveyed 21 apple trees surrounding two ALSV-infected trees for virus infection using a double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). None of the 21 trees were infected, indicating that ALSV has not spread from the infected trees to the neighboring apple trees since it was first detected in 1984. We analyzed seed embryos and seedlings derived from infected trees and detected ALSV in 10 of 223 seed embryos (4.5%) and 10 of 227 seedlings (4.4%). From these results, we conclude that ALSV is seed-transmitted at a rate of ca. 4.5% in apple. We also analyzed seed embryos and seedlings from uninfected apple trees that were hand-pollinated with pollen from infected trees. We detected ALSV in only 1 of 260 seed embryos and in none of the 227 apple seedlings. This result indicated that the seed transmission rate via infected pollen is only 0–0.38%. In situ hybridization analysis of ALSV-infected apple flower buds showed that ALSV was present inside almost all pollen grains and in all ovary and ovule tissues, including the embryo sac and inner integument.     

Evaluation of Seed Transmission of Turnip yellow mosaic virus and Tobacco mosaic virus in Arabidopsis thaliana

ABSTRACT The mechanism of virus transmission through seed was studied in Arabidopsis thaliana infected with Turnip yellow mosaic virus (TYMV) and Tobacco mosaic virus (TMV). Serological and biological tests were conducted to identify the route by which the viruses reach the seed and subsequently are located in the seed. Both TYMV and TMV were detected in seed from infected plants, however only TYMV was seed-transmitted. This is the first report of transmission of TYMV in seed of A. thaliana. Estimating virus seed transmission by grow-out tests was more accurate than enzyme-linked immunosorbent assay due to the higher frequency of antigen in the seed coat than in the embryo. Virus in the seed coat did not lead to seedling infection. Thus, embryo invasion is necessary for seed transmission of TYMV in A. thaliana. Crosses between healthy and virus-infected plants indicated that TYMV from either the female or the male parent could invade the seed. Conversely, invasion from maternal tissue was the only route for TMV to invade the seed. Pollination of flowers on healthy A. thaliana with pollen from TYMV-infected plants did not result in systemic infection of healthy plants, despite TYMV being carried by pollen to the seed.     

Occurrence and transmission of sowbane mosaic virus in seed from naturally infected plants of spinach (Spinacia oleracea)

Sowbane mosaic virus was isolated as a single infectious component from seedlings and seeds from a seed-lot of spinach (Spinacia oleracea) propagated in Hungary, and was identified by experimental host-range, thermal-inactivation point, dilution end-point, electron microscopy and serology.Chenopodium quinoa was more susceptible and/or sensitive to infection thanC. amaranticolor and was a better indicator host, butC. amaranticolor is of diagnostic value. This is the first report on natural infection of spinach by the virus and on its natural seed-transmission in spinach. Growing-on tests on whole seeds and infectivity tests on separate embryos and seed-coats showed that over 30% of the seeds' embryos were infected and c. 80% of the seed-coats contained the virus. The incidence of infection in the spinach crop from which the seed was obtained must have been high.     

<Emphasis Type="Italic">Indian citrus ringspot virus:</Emphasis> localization of virus in seed tissues and evidence for lack of seed transmission

Indian citrus ringspot disease is an important viral disease in kinnow mandarin orchards where disease incidence up to 100% has been recorded. The disease is caused by Indian citrus ringspot virus (ICRSV), a positive sense flexuous RNA virus. The transmission of ICRSV is generally through budwood. Association of ICRSV with pollens of naturally infected flowers from cv. ‘Kinnow’ mandarins has been shown previously and this study demonstrates the presence of ICRSV in seed tissues. DAC-ELISA revealed the presence of virus in seed coats but not in embryo and endosperm of seeds collected from the fruits of ICRSV-infected Kinnow plants. Of the infected seed coats, 18% were found to harbor the virus. The seedlings in the grow-out test did not show any symptom for 2 years and the virus could not be detected in seedlings by DAC-ELISA and RT-PCR. The present study indicated that ICRSV could be localized in the testa of seeds but its transmission to progeny was not observed.     

Influence of the amount of blackgram mottle virus in different tissues on transmission through the seeds of Vigna mungo

Blackgram mottle virus (BMoV) was transmitted via up to 16% of seeds of different cultivars of blackgram, as determined by seedling symptom tests. The percentage of seed infection by BMoV as determined by EL1SA was even higher. Seed transmission was highest in cv. PLU-277 (15.9%), followed by cvs T-9 (11.8%), PLU-213 (7.0%) and UH-81-7 (1.3%). Seed transmission was correlated with the amount of virus present in the embryonic axis and later in primary leaves. The presence of virus in the testa alone did not result in its transmission through seeds. Virus concentration in different tissues varied; the mean amount of virus in the three cultivars was found to be 48–1234 ng per embryonic axis, 15–24 ng per cotyledon, and 12–20 ng per testa. The infection of primary leaves through the seed also resulted in systemic infection if the amount of virus in primary leaves exceeded 100 ng/100 mg of tissue. Close agreement was found between the percentage of seedlings with systemic infection and the percentage of seeds and embryonic axes containing more than 100 ng virus. The cultivars that resisted seed transmission contained relatively small amounts of the virus in embryonic axes.     

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 question of seed transmissibility of Plum pox virus

For many years, Plum pox virus (PPV) was considered to be transmissible by seed, increasing the fear of long-distance spread of the disease. In the late 1970s, it was claimed on the basis of biological transmission of the virus to herbaceous indicator plants and the development of serological diagnosis based on polyclonal antibodies, that PPV was seed-transmitted, with a different infection rate according to the plant species and part of the seed which was tested. In the 1990s, PPV was characterized into four different types, and specific monoclonal antibodies were produced for them. These new and more sensitive diagnostic techniques, together with RT-PCR with different sets of specific primers, were used to approach once again the problem of PPV transmission through seeds. The virus was detected in seed coats and cotyledons, but embryonic tissue and seedlings obtained from germinated seeds never showed symptoms, and gave negative results for PPV with both ELISA and PCR assays. No PPV isolate is currently recognized to be seed transmitted, so vertical transmission of PPV from infected mother plants to their progeny does not occur. Hypothetically, the only possibility of seed transmission would arise from a mutation in the helper component of the virus, associated with high susceptibility of the infected Prunus cultivar.     

Tomato spotted wilt virus in peanut tissue types and physiological effects related to disease incidence and severity*

Three peanut cultivars, Georgia Green, NC-V11, and ANorden, were grown using production practices that encouraged the development of Tomato spotted wilt virus (TSWV). The progression of TSWV infection was examined through the season using enzyme-linked immunosorbent assay (ELISA) tests on different tissue types [roots, leaves, pegs (pod attachment stem structures) and pods] and the effect of TSWV infection on physiological functions was examined at three harvest dates. Plants were classed into three severity categories: (i) no TSWV symptoms or previous positive ELISA tests; (ii) less than 50% of leaf tissue exhibiting TSWV symptoms; and (iii) greater than 50% of leaf tissue affected. TSWV showed a slow rate of infection at the beginning of the season and a greater percentage of infection of the roots than in the leaves. Photosynthesis was reduced in virus-affected infected plants by an average of 30% at the mid-season harvest and 51% at the late season harvest compared with virus-free plants across all three cultivars. Leaf tissue with symptoms had lower photosynthetic rates than healthy leaves. There were small differences among cultivars, with cv. ANorden maintaining higher average photosynthetic levels than cv. Georgia Green and higher transpirational levels than cv. NC-V11. The ability to maintain high assimilation physiology in the presence of the virus may help cultivars withstand TSWV infection and maintain final yields.     

Seed transmission of Melon necrotic spot virus and efficacy of seed-disinfection treatments

Rates of seed transmission of Melon necrotic spot virus (MNSV) were estimated in seedlings grown from commercial melon ( Cucumis melo ) cv. Galia F₁ seeds. Seedlings at the cotyledon stage and adult plants were assayed for MNSV by DAS-ELISA and RT-PCR. None of the seedling groups tested positive for MNSV by ELISA. The proportion of seedlings infected with MNSV was at least 7 and 8% in seed lots 05 and 06, respectively, as estimated from RT-PCR analysis of grouped seedlings. Fourteen and eight grouped samples (10 seedlings per group), of a total of 200 and 100 seedlings, respectively, grown from infected seeds were MNSV-positive in seed lots 05 and 06, respectively, corresponding to seed-to-seedling transmission rates of 11·3 and 14·8%, respectively. Several seed-disinfection treatments were evaluated for their ability to prevent seed transmission of MNSV. The results suggest that a treatment of 144 h at 70°C can be used to eradicate MNSV in melon seeds without hindering germination.     

A model system for plant-virus interaction—infectivity and seed transmission of <Emphasis Type="Italic">Cherry leaf roll virus</Emphasis> (CLRV) in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

The wide natural incidence of Cherry leaf roll virus (CLRV) in deciduous forest trees and nurseries in northern Europe is believed to have occurred, apart from occasional mechanical spread and transmission through grafting, mainly by seed transmission. The mode of the vertical transmission and its role in the epidemiology of the virus has not been investigated, basically due to the inconvenient host-pathogen combinations studied to date. With the aim of obtaining an appropriate system for identification of viral genes and products participating in infection processes and seed transmission of CLRV, we performed infection and seed transmissibility tests with CLRV in Arabidopsis thaliana plants. Two phylogenetically and serologically different CLRV isolates were tested. Both of them were found able to infect A. thaliana plants, exhibited clear symptoms of the infection and spread systemically in the plants. Infection of the seeds and of a remarkable number of seedlings generated from infected seeds was possible for two consecutive generations. These results, for first time, report seed transmission of CLRV in the model plant A. thaliana and allow the assumption to be made of embryo invasion during seed transmission. Furthermore, first indications are given that genetically diverse CLRV isolates exhibit different abilities for vertical transmission in A. thaliana. The CLRV-A. thaliana model system is suitable for investigating viral invasion of developing plant organs and meristematic tissue, a prerequisite for successful virus dissemination via vertical transmission through seed.     

Pathogenesis of Alfalfa mosaic virus in Soybean (Glycine max) and Expression of Chimeric Rabies Peptide in Virus-Infected Soybean Plants

ABSTRACT Infection of soybean (Glycine max) plants inoculated with particles of Alfalfa mosaic virus (AlMV) isolate 425 at 12 days after germination was monitored throughout the life cycle of the plant (vegetative growth, flowering, seed formation, and seed maturation) by western blot analysis of tissue samples. At 8 to 10 days after inoculation, the upper uninoculated leaves showed symptoms of virus infection and accumulation of viral coat protein (CP). Virus CP was detectable in leaves, stem, roots, seedpods, and seed coat up to 45 days postinoculation (dpi), but only in the seedpod and seed coat at 65 dpi. No virus accumulation was detected in embryos and cotyledons at any time during infection, and no seed transmission of virus was observed. Soybean plants inoculated with recombinant AlMV passaged from upper uninoculated leaves of infected plants showed accumulation of full-length chimeric AlMV CP containing rabies antigen in systemically infected leaves and seed coat. These results suggest the potential usefulness of plants and plant viruses as vehicles for producing proteins of biomedical importance in a safe and inexpensive manner. Moreover, even the soybean seed coat, treated as waste tissue during conventional processing for oil and other products, may be utilized for the expression of value-added proteins.     

大麦条纹花叶病毒(BSMV)在新疆的发生

 在新疆五家渠奇台黑芒小麦上分离到大麦条纹花叶病毒,致死温度60~65℃;体外存活期9~14天;稀释限点1:3000倍。人工接种可侵染禾本科植物,对接过种的非禾本科植物如灰藜、苋色藜、菠菜、甜菜、普通烟、心叶烟、枯斑三生烟、萹豆等不表现病状。用聚乙二醇沉淀和聚乙二醇沉淀、差速离心提取病毒,注入家兔体内,可形成相应的抗体,效价为1:128,1:1024,病毒颗粒为短棒状115~129×20毫微米。
初步观察,病株上的麦种带毒率与种子的饱满程度、品种、感病阶段有一定的相关性。病株上的花粉与健株母本杂交的种子不带毒。     

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.     

Epidemiology of dark leaf spot caused by Alternaria brassicicola and A. brassicae in organic seed production of cauliflower

In organic seed production of Brassica vegetables, infections by Alternaria brassicicola and A. brassicae can cause severe losses of yield and seed quality. Four field experiments with or without artificial inoculation with A. brassicicola were conducted in organically managed seed‐production crops of cauliflower cv. Opaal RZ in 2005 and 2006 in the Netherlands. The development of A. brassicicola and A. brassicae on pod tissues and developing seeds was followed and seed quality was assessed. Alternaria brassicicola was externally present on 1·2% of the seeds 14 days after flowering and observed internally within 4 weeks after flowering. In both seasons, seed colonization by the pathogen increased slowly until maturation but sharply increased during maturation. A similar pattern was found for the colonization of pod tissues by A. brassicicola as quantified by TaqMan‐PCR. The incidence of A. brassicicola on mature seeds reached 70–90%. Internal colonization was found for 62–80% of the seeds. External and internal seed colonization by A. brassicae was much lower, with incidences below 3%. The quality of harvested seeds was generally low, with less than 80% of seeds able to germinate. Seed quality was not affected by warm water treatments. It was concluded that A. brassicicola and A. brassicae have the potential to infect pods and seeds soon after flowering. For the production of high quality seeds, producers must prevent such early infections. Therefore, new control measures are needed for use in organic cropping systems.     

苜蓿花叶病毒ELISA检测方法的建立及其在大豆病毒调查和抗性资源鉴定中的应用

苜蓿花叶病毒(alfalfa mosaic virus, AMV)是一种世界性分布、宿主范围广、具有严重危害性的植物病毒,能引起大豆的严重病害。本研究利用原核表达的AMV CP蛋白制备的抗血清,建立了高效、准确的AMV间接ELISA检测方法,并应用于病害调查和抗性鉴定,结果表明制备的3份抗血清对重组蛋白和AMV感染的大豆植物粗提液的效价均达到256 000倍,血清特异性分析结果显示3份抗血清仅识别感染AMV的大豆叶片,不识别感染大豆花叶病毒(soybean mosaic virus, SMV)的大豆叶片。通过建立的AMV间接ELISA与常规RT-PCR同时对采集的50份疑似感染AMV的大豆样品进行检测,有46份样品检测结果一致,符合率达92%。利用建立的AMV ELISA方法和课题组已建立的SMV ELISA方法对吉林省大豆主产区的大豆样品进行病毒检测的结果表明,病毒检出率为38.30%,SMV的检出率达30.85%,AMV的检出率达17.06%,复合侵染率为9.61%。对接种AMV的40个大豆品种进行抗性鉴定,结果显示40份大豆全部感染AMV,但是病毒载量存在差异,部分品种表现出AM...     

Dynamics of wheat spindle streak mosaic bymovirus in winter wheat

The dynamics of wheat spindle streak mosaic bymovirus in winter wheat were studied during two crop cycles in a field site with a history of high virus incidence. Individual plants of two susceptible cultivars were sampled from autumn to spring and the presence of virus antigen in roots and leaves was determined by ELISA. Virus incidence was higher in cv. Frankenmuth than in cv. Augusta. During year one, incidence of viral antigen in roots remained very low for four months after sowing, and did not reach maximum levels until the following spring. During year two, incidence of viral antigen in roots rose to maximum levels in autumn, only three months after sowing. These results strongly suggested that root infection occurred in spring as well as in autumn. In both cultivars and in both years, we detected the virus in roots one month prior to its detection in leaves, suggesting that virus moves slowly from roots into leaves. Maximum incidence of virus in leaves occurred in spring of both years, coinciding with the period of symptom development. Typical symptoms (yellow streaks, spindles, and mosaic) were observed in year two, whereas only mild mosaic was observed in year one. Virus antigen was detected in nonsymptomatic leaves from two months after sowing through crop senescence. Because antigen could be detected in roots throughout the crop cycle, and zoosporangia and cystosori of the fungal vector could be detected one and two months, respectively, after sowing, it is possible that wheat spindle streak mosaic bymovirus is acquired and/or spread by the vector during the majority of the crop cycle.     

Rice Yellow Mottle Virus is Seed-borne but not Seed Transmitted in Rice Seeds

Seed transmission of two pathogroups of rice yellow mottle virus from Soudano-Sahelian areas of West Africa was studied in several rice genotypes. The virus was detected by enzyme-linked immunosorbent assay and the highly susceptible rice variety BG 90-2 was used for infectivity assays. In most of the rice genotypes studied (17 out of 21), rice yellow mottle virus was detected in all seed parts including glumella, endosperm and embryo at a rate ranging from 65 to 100%. Nevertheless, no seed-borne infection was found. Infectivity of the virus decreased throughout the process of seed formation suggesting inactivation of the virus as a result of seed maturation and desiccation. It was concluded that rice yellow mottle epidemics do not develop from seed-borne infections in rice seeds.     

Indian peanut clump virus (IPCV) infection on wheat and barley: symptoms, yield loss and transmission through seed

Wheat and barley crops were shown to be susceptible to Indian peanut clump virus (IPCV) under field conditions. In wheat, the Hyderabad isolate of IPCV (IPCV-H) induced symptoms resembling the rosette caused by soil-borne wheat mosaic virus, and these were apparent only three weeks after emergence. Early-infected plants were severely stunted and dark green, with chlorotic streaks on the youngest leaves, which turned necrotic as the plants aged; most of these plants died. Late-infected plants were also stunted and were conspicuous in the field because of their dark green appearance as a result of delayed maturity. The virus was detected by ELISA and nucleic acid hybridization in all plants with symptoms. These plants usually produced fewer tillers than healthy ones. Spikes were malformed, often did not emerge from the flag leaf, and they contained few, shrivelled seeds. Grain yield was decreased, on average, by 58%. In barley, IPCV-H caused severe stunting and general leaf chlorosis. As the plants aged, the leaves became necrotic and the few infected plants that reached maturity produced small spikes. IPCV-H antigens were detected by ELISA in every wheat seed from infected plants and the virus was transmitted through wheat seed at a frequency of 0.5–1.3%. Storage at 4°C for more than a year did not affect seed transmission frequency. The virus was detected in leaves and roots of seed-transmitted plants. Seed transmission was not detected in barley. The Durgapura isolate (IPCV-D) was detected in wheat crops (cv. RR-21) at 3 different locations in Rajasthan State, India. Infected plants showed reduced growth without any overt symptoms.     

Viruses and viroids of stone fruits in Syria

Field surveys were carried out in the main stone fruit-growing areas of Syria to evaluate the sanitary status of mother blocks, varietal collections and commercial orchards. The presence of virus and virus-like diseases was checked by enzyme-linked immunosorbent assay (ELISA), sap transmission to herbaceous hosts, testing on the woody indicators Prunus persica cv. GF 305 and Prunus serrulata cv. Kwanzan and dot-blot hybridization tests. A total of 1337 samples was tested by ELISA (444 apricot, 283 peach, 246 cherry, 222 almond and 142 plum). The overall mean infection rate was 13%, and the percentage infection level of single species was: peach 24%, cherry 16%, almond 13.5%, apricot 6%, plum 5%. The following viruses and viroids were detected: PNRSV, PDV, ACLSV, PPV, ApMV, PLMVd and HSVd ¹ .