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  • Author or Editor: I. Tóbiás x
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Members of the family Closteroviridae have been traditionally defined as plant viruses with thread-like particles having messenger-sense single-stranded RNA, the largest genomes among RNA plant viruses. Individual virus species are distributed worldwide and some of them cause devastating crop losses. The natural host range usually narrow. Diseases symptoms are yellowing type or pitting and/or groowing of the woody cylinder. Infection systemic, but usually limited to the floem. Natural vectors are aphids, whiteflies, pseudococcids, coccids and mealybugs. Trans­mission is semipersistant. Closteroviruses contains 9-13 ORFs flanked by 5'- and 3'- untranslated regions with different length. The genome strategy is based on  polyprotein precessing, +1 ribosomal frame­shift and formation of subgenomic RNAs. Common features of closteroviruses that encode a homologue of HSP70 molecular chaperones found in all cells (HSP70h) and a duplicate (CPd) of the coat protein gene.

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Virus symptoms were observed on Hedge bindweed (Calystegia sepium) a well known plant in Hungary. In the literature there is no record of virus infection on Hedge bindweed, therefore, investigations were carried out to determine the causal agent. Sap from leaves showing virus-like symptoms was inoculated onto test plants inducing systemic infection on Nicotiana clevelandii, N. benthamiana, local lesions on Chenopodium quinoa and no infection on Datura stramonium and Cucumis sativus. Sap of N. clevelandii was examined by electron microscopy, showed the presence of long flexous particles. The biological and other properties of the virus have also been studied. Properties of particles in sap were as follows: TIP (thermal inactivation point): 78 °C, LIV (longevity in vitro): 26 days and DEP (dilution end point): log 10 minus 5. The size of coat protein is 36 kDa, and the genome consists of 7-8000 nt RNA. Double-stranded cDNA were produced using random hexanucleotide primers, cloned and sequenced. BLAST search of sequence databases revealed nucleotide sequence identity with carlaviruses. Further investigations are needed to decide whether the virus isolated from Hedge bindweed is a new carlavirus or a new strain of an existing carlavirus.

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Planococcus citri (Risso, 1813) and Planococcus ficus (Signoret, 1875) (Hemiptera: Pseudococcidae) are important polyphagous pests species. Their high degree of morphological similarity in male and larval stage makes them difficult to distinguish. The aim of the study was to find a simple and fast PCR-based method to separate these two mealybug species. Thanks to the use of a short DNA extraction method and species-specific primer pairs, P. citri and P. ficus can be distinguished at any developmental stages within three hours.

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The Fabaceae species Lathyrus tuberosus, Vicia species and Coronilla varia, all of which have an extended flowering period, provide the larvae food and shelter long enough for the pea thrips Kakothrips pisivorus to complete its development, and to have two generations yearly. Although flowers of pea cultivars also confer suitable conditions for egg laying, their flowering period is rather short. Therefore, the larvae are forced to move to developing pea pods in damaging numbers, resulting in the development of only one generation yearly on pea. However, specimens of K. pisivorus are able to colonize pea cultivars that have a similar phenology as Lathyrus tuberosus. Here we show that Hungarian pea thrips populations having either one or two generations are genetically identical.

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Maize dwarf mosaic is the most widespread virus disease affecting corn production in Hungary and Bulgaria. Samples from virus infected maize were collected from different part of Bulgaria and employed test plants, ELISA serological method and RT-PCR in order to identify the viral pathogen. Maize dwarf mosaic virus (MDMV) was detected in all tested samples. For further investigation three MDMV isolates were selected and cloned. Cloned cDNAs representing the coat protein gene of the virus have been sequenced. The coat protein genes of Bulgarian and Hungarian isolates of MDMV were compared. The nucleotide sequence identity and amino acid sequence similarity of the coat protein region varied from 88% to 99.1% and from 95.1% to 99.6%, respectively. The N-terminal region of coat protein was compared with other members SCMV subgroup and phylogenetic tree was constructed.

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Two wheat-infecting isolates of WDV-WDV-B and WDV-F- were collected in the field of Martonvásár and Nagykovácsi. The complete genomes were amplified by PCR, cloned into pBKS+ plasmid and sequenced. The nucleotide divergence in the total genome of the five isolates-WDV- Fra, WDV-Cz, WDV-Swe, WDV-B and WDV-F-originating from different part of Europe were found to be 0.44-1.69%. The four genes- MP, CP, RepA and Rep-and two non-coding region-LIR and SIR- were compared and a phylogenetic tree was constructed.

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Nucleotide and amino acid sequences of the helper component protease (HC-Pro) and the coat protein (CP) of two Hungarian Potato virus Y (PVY) isolates, differing in aphid transmissibility were determined. Isolate PVY-5 belongs to the common “O” strain (PVY O ), whereas isolates PVY-98 and PVY-111 belong to the “N” (PVY N ) and the PVY-NTN and PVY-H to the “NTN” (PVY NTN ) strains, respectively. The PVY-5 isolate varied significantly from the others in aphid transmission and in the ability to systemically infect potato plants. To elucidate whether these differences were due to mutations affecting known functional motifs, the corresponding cistrons of the two proteins were sequenced and aligned. Our analysis showed that none of the well-known motifs, responsible for aphid transmission in the two proteins had been affected. However, the defective isolate had two natural mutations in the HC-Pro in the vicinity of the PTK motif, and a number of mutations in the CP, distributed both in the N-terminus and the central region. As these two proteins are the only known viral participants in the aphid transmission mechanism, it is likely that some of the observed mutations might be involved in this process. Thus, our results indicate that other, previously unidentified sequences or factors may influence virus-vector interactions and transmission of PVY.

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Although Thrips tabaci is a well-known vector of Tomato spotted wilt virus (TSWV) it does not belong to the spreaders of this dangerous pathogen in North America. The possible explanation of the differences in its vector efficiency in Europe and in North America is rooted in the fact that out of the two subspecies of T. tabaci, i.e. T. tabaci tabaci and T. tabaci communis only the specimens of the latter were introduced from Europe into North America. To support our hypothesis we have used a molecular marker that detects intraspecific ribosomal DNA sequence variations between the two subspecies of T. tabaci.

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Zucchini yellow mosaic potyvirus (ZYMV)was isolated in Hungary from cucumber for the first time in 1995 and now it is widespread causing devastating epidemics in cucurbit crops. Four isolates were chosen from different cucurbit plants collected in 1995 and 1999 and mole- cular variability of N-terminal region of coat protein was studied.Hungarian isolates show lower molecular variability within themselves than with ZYMV isolates from other geographical origins.Hungarian isolates have amino acid sequences specific only to them that suggest common ancestor.

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Barley-infecting isolates of Wheat dwarf virus (WDV) were collected in the field in the vicinity of the cities Dunakiliti, Heves and Siófok, in Hungary. Viral genomic DNA was amplified by the rolling circle amplification technique, digested with Hind III, cloned into pBSK+ plasmid and sequenced. The clones were of the same size and showed above 99% identity to each other. Based on DNA sequences WDV-D01, WDV-H1 and WDV-H07 isolates showed high identity (94–99%) to isolates of WDV barley strain and Barley dwarf virus and lower identity to Oat dwarf virus (71% identity) and WDV wheat strains (85% identity).

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