Sugarcane streak mosaic virus (SCSMV; genus Poacevirus, family Potyviridae) is a major causal agent of sugarcane mosaic disease in Asia. A survey of SCSMV was conducted in cultivated fields in Khuzestan province, southwestern Iran. Sixty-five sugarcane leaf samples showing mosaic symptoms were collected and investigated by RT-PCR. Almost one-fourth of the samples were found to be infected by SCSMV. To verify molecular variability, 12 SCSMV isolates were sequenced and analyzed by comparing partial NIb–CP gene sequences. The nucleotide identity among Iranian isolates was 83.1–99.8%, indicating high nucleotide variability, while amino acid identity was 95.2–100%, which suggesting selection for amino acid conservation. They shared nucleotide identities of 76.2–99.1% with those of other SCSMV isolates available in GenBank, the highest with isolates from Pakistan (PAK), India (IND671) and China (M117, KT257289). Further analysis was conducted based on complete CI coding region to gain more insight into the phylogenetic relationships of Iranian SCSMV compared to those from other Asian countries. Iranian isolates shared identities of 79.8–89.0% (nucleotide) and 94.8–98.6% (amino acid) with those from other geographical regions in the CI gene. The highest nucleotide identity of Iranian isolates was with isolates PAK (Pakistan), M121 (JQ975096, China) and IND671 (India), respectively. The phylogenetic trees (based on CI and NIb–CP) revealed the segregation of SCSMV isolates into two major divergent evolutionary lineages that reflect geographical origin of the isolates (with minor exception). Phylogenetic analyses grouped Iranian SCSMV isolates together with isolates from Pakistan, India and just one Chinese isolate in group II. Biological results showed that Iranian SCSMV isolates infect sugarcane, sorghum, maize and some wild grasses, causing mosaic symptoms on the leaves.
