Molecular detection and phylogenetic analysis of viruses causing mosaic symptoms in new sugarcane varieties in China

Seventy-seven mosaic leaf samples from new sugarcane varieties from national regional trials in Kaiyuan, Mile and Yuanjiang, Yunnan Province, China, were collected in 2015 and analyzed using reverse-transcription polymerase chain reaction (RT-PCR) to determine the pathogen causing mosaic symptoms in sugarcane. Three viruses, Sugarcane streak mosaic virus (SCSMV), Sorghum mosaic virus (SrMV) and Sugarcane mosaic virus (SCMV), were detected in 100, 27.3 and 1.3% of the samples respectively. Co-infection with SCSMV, SrMV and SCMV was also found for the first time in the new variety Qiantang 5. Nucleotide sequences of the coat protein (CP) gene of 48 SCSMV and 17 SrMV isolates were subsequently sequenced and analyzed with the CP gene sequences of SCSMV and SrMV reported in GenBank to perform phylogenetic analyses. Geographic differences were observed in the phylogenetic tree of SCSMV and all SCSMV isolates from China clustered into a single China group. Moreover, SCSMV isolates from different new varieties were distributed across all subgroups or clustered into an independent branch in the China group. SrMV isolates obtained in this study and those published in GenBank clustered into two groups and were distributed into different subgroups within these groups. Furthermore, the distribution of SrMV isolates from different new varieties overlapped in these different groups and subgroups, with no obvious geographic differences. These results provide a scientific basis for sugarcane mosaic or streak mosaic disease resistance breeding and effective control of this disease.