First Report of Sugarcane mosaic virus Infecting Columbus Grass (Sorghum almum) in the United States.

Mosaic symptoms in sorghum can be caused by several potyviruses (family Potyviridae), includingSorghum mosaic virus and Sugarcane mosaic virus (SCMV). Both are responsible for global economic losses in sorghum, maize, and sugarcane. During spring 2015, in a patch of Columbus grass (Sorghum almum) growing near a sugarcane field at Canal Point in Florida, patterns of contrasting shades of green were observed on leaves of several plants. Ten of these plants with mosaic-looking symptoms were collected for further investigation. Partial virus purification was performed with 20 g of leaves from one plant, and filamentous virus particles (~750 nm long) were observed by transmission electron microscopy (TEM). This preparation was used for immunosorbent electron microscopy (ISEM) with Maize dwarf mosaic virus (MDMV) antibody A and MDMV antibody B, which react with SCMV (Pirone 1972). Maize dwarf mosaic virus B antibody trapped and decorated virus particles, but the serological reaction with the MDMV A antibody was not readily observed. Five of the 10 plants with mosaic symptoms all tested positive by ELISA using a broad-spectrum potyvirus antibody (Agdia, Elkhart, IN). These plants also reacted in ELISA with SCMV-specific antibodies (Agdia). Total RNA was extracted from leaves of all 10 S. almum plants using RNeasy Plant mini Kit (Qiagen, Hilden, Germany) and used as a template for RT-PCR. Poaceae potyvirus-specific primer pair oligo 1n (ATGGTHTGGTGYATHGARAAYGG) and oligo 2n (TGCTGCKGCYTTCATYTG) (Marie-Jeanne et al. 2000) produced the expected 327-bp amplicon in all 10 samples. Five amplicons were sequenced revealing 93 to 95% nucleotide identity with SCMV isolates in GenBank (BLASTn). Additional cDNA was generated from two plants using primer M4T (GTTTTCCCAGTCACGAC-(T)15), and PCR amplified using universal primers Poty S (GGNAAYAAYAGYGGNCARCC) and M4 (GTTTTCCCAGTCACGAC) (Chen et al. 2001) yielding an approximately 1.8-kb product. The products were cloned into pGEM-T Easy Vector System (Promega, Madison, Wisconsin), and complete sequences were determined for three cloned fragments. These 1.8-kb sequences were most similar to isolates of SCMV and had 92% identity to GenBank Accession No. U57356 (SCMV strain D from sugarcane) at the nucleotide level, and 81% similarity to Accession No. CAX36842 (SCMV from Saccharum officinarum) at the amino acid level. TEM, ISEM, ELISA, RT-PCR, and sequence analysis from multiple plants confirmed the presence of SCMV in S. almum exhibiting mosaic symptoms in Florida. SCMV has been previously reported to infect S. almum in Australia (Teakle and Grylls 1973), but to our knowledge, this is the first report in the United States. This federal and state noxious weed is widely distributed in sugarcane-growing areas in Florida where sugarcane also occasionally exhibits mosaic symptoms. It may be an alternative host for SCMV. The relationship between SCMV strains occurring in S. almum and strains infecting sugarcane requires investigation to determine the importance of S. almum in the epidemiology and management of SCMV in sugarcane. © 2016, American Phytopathological Society. All rights reserved.