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  • Author or Editor: L. Almási x
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Abstract  

A CAMAC system was installed for pulse height analysis and correction of counting losses due to the dead-time of a multichannel analyzer and the pulse pile-up. A computer program was developed to control the whole system, and to collect and store data in both conventional and cyclic measurement modes.

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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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Tomato spotted wilt virus (TSWV) is spread by Thrips tabaci tabaci nominate subspecies in the field under climatic conditions of Carpathian Basin. The overwintered females harbouring the pathogen proved to be the most important vector in the outbreak of epidemics in the tobacco growing district. Among the numerous host plants, the winter annual and the perennial weeds provide the survival of the pathogen. Infected weeds as Asclepias syriaca, Convolvulus arvensis grown in vineyards far from the tobacco fields and greenhouses indicate the wide spread of TSWV. Chickweed (Stellaria media) being a suitable host both for TSWV and the overwintering T. tabaci specimens constitutes the most dangerous source of epidemics. As a result of the common effect of the application of insecticides in accordance with the monitoring of T. tabaci, the centralized cultivation of the seedlings and the weed-free surroundings of the nurseries, the occurrence of TSWV was reduced to the minimum level in tobacco fields.

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