A genetic shift in the virus strains that cause mosaic in Louisiana sugarcane

Leaf samples from 693 sugarcane plants showing mosaic symptoms were collected in 2001, 2002, and 2003 at 12 locations within the Louisiana sugarcane industry. Virus isolates associated with the diseased plants were identified using reverse-transcriptase polymerase chain reaction (RT-PCR) to distinguish between Sugarcane mosaic virus (SCMV) and Sorghum mosaic virus (SrMV). No SCMV strain was associated with any diseased plant collected during the survey. RT-PCR-based restriction fragment length polymorphism (RFLP) analysis showed that SrMV strains 1, H, and M were associated with 67, 10, and 2% of the plants with mosaic symptoms, respectively. In previous surveys conducted between 1978 and 1995, over 90% of the plants sampled were infected with SrMV strain H. The remaining plants mostly were infected with SrMV strain 1, except for an occasional sample with SrMV strain M. RT-PCR showed that approximately 13% of the samples collected between 2001 and 2003 were infected with SrMV, but the RFLP banding pattern did not match any described strain. Twelve plants were co-infected by two SrMV strains and two plants by three SrMV strains. No RT-PCR product was produced by either the SCMV- or the SrMV-specific RT-PCR primer set for 8% of the plants showing mosaic symptoms, suggesting that another virus may cause sugarcane mosaic in Louisiana.