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Strains of Sorghum Mosaic Virus Causing Sugarcane Mosaic in Louisiana. M. P. GRISHAM, Sugarcane Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Houma, Louisiana 70361. Plant Dis. 78:729-732. Accepted for publication 7 April 1994. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1994. DOI: 10.1094/PD-78-0729.

The viruses found causing sugarcane mosaic in Louisiana during 1978-1988, 1990, and 1992 were strains H, I, and M of sorghum mosaic virus. The percentages of plant samples that were infected with the three strains within the three production areas of the sugarcane belt were determined (because approximately 4% of all plants sampled were infected by more than one strain, incidences totaled more than 100%). In the Bayou Lafourche area, strain H was found in 99% of infected plants, strain I in 1%, and strain M in 2%; in the Mississippi River area, strain H was found in 98% of infected plants, strain I in 1%, and strain M in 2%; and in the Bayou Teche area, strain H was found in 90% of infected plants, strain I in 12%, and strain M in 5%. Strains were identified annually by inoculating differential host plants (sugarcane cultivars CP 31-294 and CP 31-588, sweet sorghum cultivar Rio, and johnsongrass) with leaf juice from diseased sugarcane plants. The highest incidence of strain I (12-31% of samples assayed) occurred in the Bayou Teche area during 1978-1982. The subsequent decline in incidence of strain I in this area corresponded with the decline of cultivar NCo 310. Strain M appeared intermittently at low levels in all areas, but in 1987 and 1988 in the Bayou Teche area, strain M appeared in 17 and 13%, respectively, of the samples—most often those of the cultivar CP 79-318