Rapid identification of viruses causing sugarcane mosaic by direct sequencing of RT-PCR products from crude extracts: a method for large scale virus surveys.

Sugarcane mosaic virus (SCMV) and sorghum mosaic virus (SrMV) diversity studies are important to characterize virus populations in sugarcane producing areas, enabling (i) identification of shifts in predominant strains, (ii) detecting associations of strains with specific varieties, and (iii) possibly exposing the appearance of new strains which may affect the performance of varieties in a region. Recent studies have shown significant sequence variability within SCMV populations around the world, indicating that isolate identification would be best achieved by direct analysis of sequence data. Because virus sequence-based studies that require the characterization of large numbers of isolates may be impractical using standard sample preparation and processing methodology, a simple protocol that yields quality sequence information, requiring neither viral RNA purification nor cloning of RT-PCR products was developed. Rapid virus release extracts are obtained by submerging a portion of leaf tissue into an extraction buffer, followed by a brief incubation at 95 degrees C. An aliquot of the extract is pipetted into an RT-PCR amplification mix for the detection of SCMV and the SrMV coat protein gene fragments. RT-PCR fragments are sequenced directly using oligonucleotide primers similar to the RT-PCR primers, yielding sequence information of an adequate quality. This rapid, cost effective protocol is practical for large scale virus diversity and evolutionary studies.