Papaya ringspot virus-type W (PRSV-W) is one of the most economically threatening viruses of cucurbits in Brazil. Premunization is one of the most effective PRSV control measures currently applied in squash and zucchini crops. PRSV-W-1, a mild and premunizing strain of PRSV has been successfully used to protect cucurbits against both the severe PRSV-W-C strain and other Brazilian PRSVs. To aid in understanding the mechanism by which PRSV-W-1 premunization operates, the complete genome sequences of PRSV-W-1 and PRSV-W-C were determined. PRSV-W-1 had a genome size of 10,332 nucleotides, whereas indels within the coat protein encoding gene meant that the genome size of PRSV-W-C was six nucleotides shorter than that of the mild strain. The genomes of the two strains shared 94.63% nucleotide sequence identity, with the 5' UTR and P1 being the most variable regions, and the coat protein and 3' UTR being the most conserved. Rigorous recombination analysis revealed that neither PRSV-W-1 nor PRSV-W-C was obviously recombinant, there was significant evidence that many other fully sequenced PRSV genomes were recombinant.

The nucleotide sequence of the genomic 3' terminal region (1,702 bases) of two Brazilian Bidens mosaic virus isolates (BiMV: BiMV-p and BiMV-b) was determined. BiMV-p and BiMV-b share 98% nucleotide sequence identity, and are most closely related to members of the potyvirus species: Sunflower chlorotic mottle virus (an isolate of Potato virus Y) and Potato virus Y. BiMV-p shares 88% capsid protein amino acid identity and 77% 3'UTR nucleotide sequence identity with SuCMoV an isolate of Sunflower chlorotic mottle virus. Phylogenetic analyses suggest the close evolutionary relationship of BiMV, SuCMoV and Potato virus Y (PVY), members of the PVY species. According to the analyses of capsid protein and 3'UTR sequences BiMV isolates must be regarded as a strain of Potato virus Y species, but their differences in host reactions and the phylogenetic distance suggest that they would be most likely better placed in a taxon between species and strains.

Two tospoviruses, Chrysanthemum stem necrosis virus (CSNV) and Zucchini lethal chlorosis virus (ZLCV), cause economical losses in several ornamental and vegetable crops in Brazil. The nucleocapsid gene and movement protein sequences had already been reported for both viruses, though the glycoprotein precursor gene sequence was not available. In this study, cDNA fragments (ca. 4 kb) of the M RNA 3' portion of CSNV (isolate Chry-1) and ZLCV (isolate 1038), including the complete glycoprotein precursor gene, partial NSm gene, and the entire intergenic and 3' untranslated regions, were cloned and sequenced. The sequences were assembled with the corresponding 5' region sequence (NSm gene and 5'UTR) of the same isolates to build up the complete sequence of the M RNA segment of both species. The M RNA of CSNV was 4,828 nucleotide-long, while of ZLCV 4,836 nucleotides. Both M RNA molecules comprised two ORFs in an ambisense arrangement. The vcRNA coded for the viral glycoprotein (Gn/Gc) precursor gene of CSNV and ZLCV (both with 127.5 kDa). Comparison of deduced amino acids of the CSNV and ZLCV glycoprotein precursor genes with those of other tospoviruses showed the highest identity with that of Tomato spotted wilt virus (86%) and with that of CSNV (82%), respectively. However, the nucleotide sequence of the intergenic and 3' untranslated regions of CSNV and ZLCV shared lower identities with other tospoviruses. The glycoprotein precursor gene is thought to be a good candidate as additional classification parameter for Tospovirus taxonomy. The presence of the RGD motif in both Gc proteins indicated that they are typical American tospoviruses, which was confirmed by phylogenetic analysis. The membrane topology of both glycoproteins is discussed.

A novel viral disease of melon, caused by Melon yellowing-associated virus (MYaV), has become one of the most serious problems for melon production in Brazil. Despite its importance, little is known about the genome sequence of the virus. In this study, the triple gene block genomic region including the 3 0 -end region of an isolate of MYaV was elucidated (ca. 3.1 kb). Sweet potato chlorotic fleck virus, a newly suggested carlavirus species, was the most closely related virus with 62% nucleotide identity. The presence of two heptanucleotide-motifs for subgenomic RNA synthesis was confirmed in this sequence.

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