Caracteriza？？o de um isolado do Sugarcane mosaic virus que quebra a resistência de variedades comerciais de cana-de-a？úcar

viruses in the sugarcane mosaic virus (scmv, genus potyvirus, family potyviridae), subgroup cause mosaic in different botanical species in the subfamily panicoideae (family poaceae). however, only scmv and sorghum mosaic virus (srmv) naturally infect sugarcane. in brazil, scmv seems to be the only causal agent of mosaic in sugarcane. most sugarcane cultivars are believed to be resistant to mosaic, although new cases have been reported in the field. symptomatic samples, from several clones and cultivars, were collected in sugarcane crops. among these cultivars, rb72-454, one of the most grown in brazil, and considered resistant, showed plants with mosaic symptoms. samples were tested by das-elisa with antisera to scmv, johnsongrass mosaic virus (jgmv) and maize dwarf mosaic virus (mdmv), showing negative results. however, sorghum "rio" and "tx2786" showed mosaic symptoms when mechanically inoculated with the viral isolates, indicating infection by scmv. total rna was extracted and submitted to amplification with specific primers to scmv and srmv in rt-pcr. specific bands with ca. 880 bp were amplified with the scmv-specific primer pair, corroborating results from mechanical inoculation. pcr products were cloned and sequenced. one of the scmv isolates comprises a new and more severe strain capable of infecting rb72-454 and other tolerant cultivars in the field.