Caracterização parcial de um isolado do Turnip ringspot virus de rúcula no Paraná

Abstract

A virus associated with mosaic and leaf distortion on rocket plants (Brassicaceae) was isolated in Maringá, Paraná State, and idenfied as a comovirus based on indirect-Elisa and electronic microscopy. Comoviruses have positive-sense, single-stranded, bipartite RNA genomes designated RNA1 and RNA2 infecting predominantly Fabaceae. Turnip ringspot virus (TuRSV) is a Comovirus that infects Brassicaceae plants, reported only in the northern hemisphere, causing a variety of symptoms ranging from chlorotic spots and rings on leaves to complete chlorosis and death. In order to determine molecular properties of the Paraná isolate of TuRSV, fragments of viral RNAs were amplified by RT-PCR. After sequencing the amplified product of 917 bp from RNA1, an identity ranging from 86% to 88% was obtained with the amino acid sequences of RNA1 of other TuRSV isolates from the GenBank. The sequencing of the 168 bp product of RNA2 from Paraná isolate of TuRSV was amplified with specific primers for the Toledo-USA isolate of TuRSV, showing 97% of similarity with the amino acid sequence of RNA2 of this virus. The isolate of FuRSV from Paraná has a narrow host range, infecting Eruca sativa, Brassica rapa, Raphanus sativus, Nicotiana benthamiana and Chenopodium amaranticolor, differing from isolates B and M12 of TuRSV from Croatia and Russia, respectively, for not infecting white mostard (Brassica alba) and cauliflower (Brassica oleracea var. botrytis). There was no seed transmission of the virus by 283 seedlings from infected rocket plants. The thermal inactivation point of TuRSV-PR was 65°C, the dilution end point was 10-3, and the in vitro longevity was 28 days. The polyacrylamide gel electrophoresis of the purified virus revealed several bands, including the expected bands of 27 and 41 kDa, typical of Comovirus. This is the first report of the natural infection of TuRSV in rocket plants, and the occurrence of this virus in the southern hemisphere.