The effects of the repellents dodecanoic acid and polygodial on the acquisition of non-, semi- and persistent plant viruses by the aphid Myzus persicae

Few Myzus persicae settled on polygodial (1 g litre^-1) or dodecanoic acid (5 g litre^-1)-treated leaves and few nymphs were deposited. Polygodial decreased acquisition of the semi-persistent beet yellows virus and the non-persistent potato virus Y and dodecanoic acid that of the persistent potato leafroll and beet mild yellowing viruses, of beet yellows virus and of the bimodally-transmitted cauliflower mosaic virus. However dodecanoic acid increased the acquisition of potato virus Y.     

Metabolism of dodecyldimethylamine by Pseudomonas MA3

Pseudomonas MA3 was isolated from activated sludge on the basis of its capacity to use dodecyldimethylamine as a sole carbon (C) and energy source. Dodecylamine, dodecanal, dodecanoic acid and acetic acid also supported growth of Pseudomonas MA3. Dodecyldimethylamine-grown cells oxidized a wide range of alkylamine derivatives, dodecanal, dodecanoic acid and acetic acid. Degradation of the alkyl chain of dodecyldimethylamine by Pseudomonas MA3 appeared from the stoichiometric liberation of dimethylamine. A dehydrogenase catalysed the cleavage of the C_alkyl-N bond. The first intermediate of the proposed degradation pathway, dodecanal, accumulated in the presence of decanal used as a competitive inhibitor. The second intermediate,dodecanoic acid, was formed in the presence of acrylic acid during the degradation of dodecyldimethylamine. Dodecanal was converted into dodecanoic acid by a dehydrogenase and dodecanoic acid was then degraded via the oxidation pathway.     

The influence of primary infection date and establishment of vector populations on the spread of yellowing viruses in sugar beet

In three field experiments in 1985 and 1986, we studied the effect of the date of primary infection on the spread of beet yellows closterovirus (BYV) and beet mild yellowing luteovirus (BMW) from artificially inoculated sugar beet plants. Laboratory-reared vector aphids, Myzus persicae, were placed on these sources of virus. There was no substantial natural immigration of vectors or viruses. In two experiments, one with BMYV in 1985 and the other in BYV in 1986, populations of vector aphids remained low and there was little virus spread, i.e. c. 50 infected plants from one primarily infected source. The cause of this small amount of spread was the low number of vector aphids. In the third experiment, with BYV in 1986, large populations of M. persicae developed and there was substantial virus spread: c. 2000 infected plants in the plots which were inoculated before canopy closure. In later-inoculated plots in the same experiment, there was much less spread: c. 100 infected plants per virus source plant. Differences between fields in predator impact are implicated as the most probable factor causing differences in vector establishment and virus spread between these three experiments. Virus spread decreased with later inoculation in all three experiments. A mathematical model of virus spread incorporating results from our work has been used to calculate how the initial proportion of infected plants in a crop affects the final virus incidence. This model takes into account the effect of predation on the development of the aphid populations. The processes underlying the spread and its timing are discussed.     

Some effects of spraying with thiabendazole on the susceptibility of sugar beet to yellowing viruses and on their vector, Myzus persicae (Sulz.)

In a field experiment fewer sugar-beet plants became infected with aphid-transmitted yellowing viruses in plots that had been sprayed with solutions of thiabendazole lactate than in water-sprayed plots, after exposure to natural infestation with aphids. Subsequent glasshouse tests showed that foliar sprays of o·o1 % thiabendazole lactate in water significantly reduced the proportion of inoculated sugar-beet plants which became infected with beet yellows virus (BYV) or beet mild yellowing virus (BMYV) after inoculation with viruliferous Myzus persicae (Sulz.). This effect on virus transmission was not apparently due to a direct insecticidal action of thiabendazole, because adult aphids usually survived equally well on sprayed and unsprayed plants. Treatment of test plants with thiabendazole did not affect the transmission of beet mosaic virus to them by M. persicae. The fecundity of M. persicae was greatly reduced by transferring them to plants which had been sprayed with thiabendazole or by spraying them with thiabendazole before transfer to unsprayed plants. The fertility of adult Aphis fabae Scop, was also reduced by spraying with thiabendazole. The mechanisms whereby thiabendazole affected fecundity of aphids and transmission of viruses are not understood.     

Beet necrotic yellow vein virus coat protein-mediated protection in sugarbeet (Beta vulgaris L.) protoplasts

Transformed Beta vulgaris L. suspension cultures were obtained after cocultivation of sugarbeet cells with Agrobacterium tumefaciens harbouring a binary vector containing the coat protein gene of beet necrotic yellow vein virus inserted between the kanamycin resistance gene and a ß-glucuronidase reporter gene. Protoplasts were isolated both from untransformed cells, and from transformed cells expressing the viral coat protein, and both were then infected with beet necrotic yellow vein virus. Comparison of the levels of infectivity shows that the expression of the coat protein gene in sugarbeet protoplasts mediates high levels of protection against infection by beet necrotic yellow vein virus.Abbreviations TMV Tobacco Mosaic Virus - CP Coat Protein - BNYVV Beet Necrotic Yellow Vein Virus - ß-Glu ß-glucuronidase - MS Murashige and Skoog (1962) - PEG Polyethylene glycol - npt neomycin phosphotransferase - nos nopaline synthase - FITC fluoresceine isothiocyanate - IAA indole acetic acid - BAP benzyl amino purine - MES 2-[N-Morpholino]ethane sulfonic acid - IgG Immunoglobulin G - nt nucleotide     

The use of monoclonal antibodies to detect beet mild yellowing virus and beet western yellows virus in aphids

Information on infectivity of the aphids which invade sugar beet root crops each Spring is required for forecasting incidence and providing advice on control of virus yellows. Monoclonal antibodies, produced in the USA to barley yellow dwarf virus (BYDV) and in Canada to beet western yellows virus (BWYV), were used to distinguish between sugar-beet-infecting strains of the luteovirus beet mild yellowing virus (BMYV), and the non-beet-infecting strains of the closely-related BWYV in plant and aphid tissue. Totals of 773 immigrant winged Myzuspersicae and 124 Macrosiphum euphorbiae were caught in water traps in a crop of sugar beet between 25 April and 5 August 1990. Using the monoclonal antibodies and an amplified ELISA, 67%M. persicae and 19%M. euphorbiae were shown to contain BWYV; 8%M. persicae and 7%M. euphorbiae contained BMYV. In studies with live winged aphids collected from the same sugar beet field during May, 25 of 60 M. persicae and two of 13 M. euphorbiae transmitted BWYV to the indicator host plant Montia perfoliata; two M. persicae and two M. euphorbiae transmitted BMYV. In another study three of 65 M. persicae and one of three M. euphorbiae in which only BWYV was detected, transmitted this virus to sugar beet.     

The Beta vulgaris-derived resistance gene Rz2 confers broad-spectrum resistance against soilborne sugar beet-infecting viruses from different families by recognizing triple gene block protein 1

Sugar beet cultivation is dependent on an effective control of beet necrotic yellow vein virus (BNYVV, family Benyviridae), which causes tremendous economic losses in sugar production. As the virus is transmitted by a soilborne protist, the use of resistant cultivars is currently the only way to control the disease. The Rz2 gene product belongs to a family of proteins conferring resistance towards diverse pathogens in plants. These proteins contain coiled-coil and leucine-rich repeat domains. After artificial inoculation of homozygous Rz2 resistant sugar beet lines, BNYVV and beet soilborne mosaic virus (BSBMV, family Benyviridae) were not detected. Analysis of the expression of Rz2 in naturally infected plants indicated constitutive expression in the root system. In a transient assay, coexpression of Rz2 and the individual BNYVV-encoded proteins revealed that only the combination of Rz2 and triple gene block protein 1 (TGB1) resulted in a hypersensitive reaction (HR)-like response. Furthermore, HR was also triggered by the TGB1 homologues from BSBMV as well as from the more distantly related beet soilborne virus (family Virgaviridae). This is the first report of an R gene providing resistance across different plant virus families.     

Studies on beet western yellows virus in oilseed rape (Brassica napus ssp. oleifera) and sugar beet (Beta vulgaris)

Oilseed rape (Brassica napus L. ssp. oleifera) was studied as a potential overwintering host for the sugar-beet yellowing viruses, beet yellows virus (BYV) and beet mild yellowing virus (BMYV), and their principal vector, Myzus persicae. In spring 1982, plants infected with a virus which reacted positively in enzyme-linked immunosorbent assay (ELISA) with BMYV antibody globulin were found in oilseed-rape crops; none of the plants contained virus which reacted with BYV antibody globulin. This virus was subsequently identified as beet western yellows virus (BWYV). No leaf symptoms could be consistently associated with infection of oilseed rape, but the virus was reliably detected by sampling any leaf on an infected oilseed-rape plant. Some isolates from oilseed rape did infect sugar beet in glasshouse tests, but the proportions of inoculated plants which became infected were low. Apparently there is therefore little danger of much direct transmission of BWYV by M. persicae from oilseed rape to sugar beet in spring. BWYV was introduced to and spread within oilseed-rape crops in autumn by M. persicae, and autumn-sown oilseed rape proved to be a potentially important overwintering host for M. persicae. In a survey of 80 autumn-sown crops of oilseed rape in East Anglia, northern England and Scotland in spring 1983, 78 were shown to be extensively infected with BWYV. Experimental plots of oilseed rape with 100% BWYV-infection yielded approximately 13.4% less oil than plots with 18% virus infection, the result of a decrease in both seed yield and oil content.     

Occurrence of beet western yellows virus in sugar beet in Czechoslovakia

The beet western yellows virus (BWYV) was identified in sugar beet plants with leaf yellowing symptoms. When transmitted toSinapis alba L. the virus isolate caused severe symptoms of yellowing and violetting of the interveinal leaf tissue of this plant. By aphidsMyzus persicae (Sulz.) the virus isolate was transmitted toLactuca sativa L.,Raphanus sativus L. var.radicula Pers.,Baphanus sativus L. ssp.sativus L. ap., and toBrassica oleracea L. var.gemmifera DC. InLactuca sativa plants the virus induces a yellowing along with thickenning and brittleness of leaves and with mild dwarfing of the plants. InBaphanus sativus var.radicula andBaphanus sativus ssp.sativus plants it brings about a yellowing of the leaf margins with a change in consistency as was the case in lettuce, and inBrassica oleracea var.gemmifera it causes violet spots on the lower leaf sides. The transmission was proved in repeated experiments by a backtransmission to beet andSinapis alba and further transmission from beet toSinapis alba. The transmission of the virus isolate toVicia faba L.,Datura stramonium L., andPetunia hybrida hort. was unsuccessful. In the course of transmissions the isolate properties did not change. In its host range the virus resembles the Duffus’ strain 3 BWYV, isolated from beet in the U.S.A. This is the first characteristic of an Europian BWYV isolate, as obtained from naturally infected beet plants.     

The effect of plant age and infection with virus yellows on the survival of Myzus persicae on sugar beet

Survival of Myzus persicae confined in clip-cages on mature leaves of sugar beet declined as the plants aged. Death of aphids was often preceded by the appearance of a black deposit in the aphids' stomachs, which may have been the cause of death. Both the rate of death and the proportion of aphids dying with black deposits was significantly less when plants were infected with beet yellows virus or beet mild yellowing virus, by comparison with healthy plants. The implication of these phenomena on the onset of mature plant resistance is discussed.     

Aphids from mangold clamps and their importance as vectors of beet viruses

Mangold clamps are over-wintering sources of the aphid-transmitted beet mosaic, beet yellows and beet mild yellowing viruses, and of several species of aphid, three of the most common in clamps being Myzus persicae, Rhopalosiphoninus staphyleae tulipaellus and R. latysiphon. This study attempted to assess the relative importance of the different species in spreading viruses from clamps. Compared with M. persicae, R. s. tulipaellus and R. latysiphon are seldom trapped in flight, except near large infestations. Alatae of M. persicae and R. s. tulipaellus become common in clamps in April, but few fly below 15d? C., a temperature seldom reached in eastern England in early spring. Flight muscle autolysis, which occurs later in R. s. tulipaellus and R. latysiphon than in some aphid species, also probably prevents many alatae in clamps from flying. We confirmed the importance of clamps as sources of beet viruses, the percentage of infected plants decreasing with increasing distance from infested clamps. M. persicae is shown to be a better vector of beet viruses than the other clamp aphids, and is probably responsible for most virus spread from clamps. R. s. tulipaellus did not transmit beet mosaic virus, but it is a fairly efficient vector of beet yellows and beet mild yellowing viruses, and, although we did not find this species on sugar beet in the field, it probably spreads these viruses from clamps. R. latysiphon did not transmit any of the viruses, and the role of Macrosiphum euphorbiae, Aulacorthum solani and Myxus ascalonicus is probably small.     

Failure of British isolates of beet western yellows virus to infect potato

Potato cultivars were tested for susceptibility to two British isolates of beet western yellows virus originally obtained from sugar beet and oil seed rape. Neither isolate was transmitted by Myzus persicae to virus-free potato plants, either by itself or in association with potato leafroll virus.     

Nematode transmissibility of pseudo-recombinant isolates of tomato black ring virus

Pseudo-recombinant isolates of tomato black ring virus (TBRV), containing RNA-i of the potato bouquet serotype and RNA-2 of the beet ring-spot serotype, were transmitted by the nematode Longidorus elongatus, which also transmits the beet ringspot serotype but not the potato bouquet serotype. Transmissibility by L. elongatus was correlated with antigenic specificity of the virus particles, providing further evidence that nematode transmissibility depends on the structure of the virus coat protein. The distribution of genetic determinants for biological properties between the RNA-1 and RNA-2 of TBRV resembles that for raspberry ringspot virus.     

Characterization of Potyvirus Isolates from West African Yams (Dioscorea spp.)

In comparative studies on potyviruses from West African yams (Dioscorea spp.) the following isolates were used: Dioscorea greenbanding mosaic virus (DGMV) and a Nigerian yam virus (YV-N), both isolated from Dioscorea rotundata, and a beet mosaic virus isolate from D. alata (BtMV-Y) formerly designated Dioscorea alata ring mottle virus. Naturally infected D. alata containing very few particles of BtMV-Y, contained primarily particles of a second potyvirus (Dioscorea alata virus, DaV) which could not be transmitted but which was included in these studies wherever possible. The normal lengths of DGMV, YV-N, DaV, and BtMV-Y were 754, 772, 805, and 812 nm, respectively. All viruses induced cytplasmic inclusions of the pinwheel type and laminated aggregates. In addition, the nucleoli of BtMV-Y infected cells contained characteristic electron dense inclusions. The buoyant density of purified DGMV and BtMV-Y in CsCl was 1.336 g/cm³ and 1.321 g/cm³, respectively. The sedimention velocities (S_rel) of DGMV, YV-N, and BtMV-Y were 156, 158, and 162 Srespectively. In SDS-polyacrylamide gel electrophoresis the coat protein of purified DGMV and YV-N all migrated as a single band with an apparent molecular weight of 36 kd. Coat protein of purified DaV showed up to 5 bands with molecular weights of 36 to, 32 kd. Polypeptides of purified BtMV-Y had an estimated molecular weight of 35 kd but those from infected plant extracts had a molecular weight of 36 kd. DGMV, YV-N, and BtMV-Y particles contained a single nucleic acid with an apparent molecular weightof 3.2, 3.2, and 3.1 Md, respectively. Using λ-DNA digested with Hind III as a marker, the molecular weight of DGMV and BtMV-Y nucleic acid was calculated to be 3.6 Md ± 10%. The nucleic acid was determined to be single-stranded RNA by enzymatic digestion and by staining with acridine orange. In serological studies using immunoelectron microscopy (IEM), electro-blot immunoassay (EBIA), and enzyme-linked immunosorbent assay (ELISA), DGMV and YV-N were closely related. Strong serological reactions were also obtained in IEM and EBIA when DGMV and YV-N were tested with antiserum to yam mosaic virus (YMV). Antisera against DGMV, YV-N, and YMV also reacted strongly with DaV antigen. Serological reactions between these viruses and BtMV-Y were usually not found or were weak. A very close serological relationship could be detected between BtMV-Y and beet mosaic virus isolated from beet (BtMV); both isolates were also very similar in host range, symptomatology, and cytopathology.     

Effects of sucrose sprays and darkness on aphid colonization of sugar beet and on aphid transmission of yellowing viruses

In the glasshouse, adult, apterous Myzus persicae (Sulz.) and Aphis fabae Scop, settled better and deposited more larvae on sucrose-sprayed sugar-beet plants than on water-sprayed plants. M. persicae settled badly and deposited few larvae on plants that were kept in the dark before or after infestation. The effects of darkness on aphids were reduced by spraying the host plants with 10% solutions of sucrose before infestation. Viruliferous M. persicae transmitted beet yellows virus (BYV) and beet mild yellowing virus (BMYV) less efficiently to dark-treated plants than to those grown in normal daylight. Spraying sugar beet with sucrose before inoculation with viruliferous M. persicae increased the proportion of successful BYV transmissions but only when the plants were dark-treated. The effects of sucrose and darkness on settling and larviposition of aphids and on virus transmission may be related to changes in the concentration of carbohydrates, particularly sugars, in the leaves.     

Systemic resistance induced by Bacillus lipopeptides in Beta vulgaris reduces infection by the rhizomania disease vector Polymyxa betae

The control of rhizomania, one of the most important diseases of sugar beet caused by the Beet necrotic yellow vein virus, remains limited to varietal resistance. In this study, we investigated the putative action of Bacillus amylolequifaciens lipopeptides in achieving rhizomania biocontrol through the control of the virus vector Polymyxa betae. Some lipopeptides that are produced by bacteria, especially by plant growth-promoting rhizobacteria, have been found to induce systemic resistance in plants. We tested the impact of the elicitation of systemic resistance in sugar beet through lipopeptides on infection by P. betae. Lipopeptides were shown to effectively induce systemic resistance in both the roots and leaves of sugar beet, resulting in a significant reduction in P. betae infection. This article provides the first evidence that induced systemic resistance can reduce infection of sugar beet by P. betae.     

Beet curly top virus transmission by artificially fed and injected beet leafhoppers (Circulfer tenellus)

The transmission of beet curly top virus (BCTV) by leafhoppers, Circulifer tenellus, fed virus through Parafilm® membranes was compared with their transmission when injected with virus from phloem exudates of Amsinckia douglasiana. Virus uptake from ³²P-labelled test solutions and the resulting virus transmission, as measured by an infectivity index, varied widely. By contrast, insects injected with virus transmitted with similar efficiencies. If insects were fasted for 3, 5, or 7 h before a 6 h acquisition access period on test solutions, their ³²P, and presumably virus uptake, was greater than that of nonfasted insects and their variability in virus transmission decreased. The proportion of insects transmitting curly top virus, after fasting and given a 6 h acquisition access period, was similar to that of insects injected with virus. Maximum liquid uptake by the beet leafhopper occurred with a 12% sucrose solution.     

Effects on Myzus persicae (Sulz.) and transmission of beet yellows virus of applying certain trace elements to sugar beet

Applications of lithium chloride (LiCl), zinc sulphate (ZnSO₄) or nickel sulphate (NiSO₄) to the roots of sugar-beet plants in the glasshouse encouraged settling on the leaves of adult apterae from a clone of Myzus persicae (Sulz.); conversely, treatment with boric acid (H₂B₂O₇) inhibited aphid settling. Larviposition of M. persicae was increased by NiSO₄ and tin chloride (SnCl₂). Viruliferous M. persicae transmitted beet yellows virus (BYV) more efficiently to plants treated with LiCl or H₂B₂O₇ than to those treated with copper sulphate (CuSO₄), ZnSO₄ or SnCl₂. The sulphate and chloride anions of the applied chemicals appeared to have little effect on M. persicae and virus transmission. It is suggested that applications of trace elements to sugar beet affected M. persicae and virus transmission by changing the concentrations of trace elements in the aphids' diet and by altering the metabolism of the leaf tissues in the host plant.