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Sugarcane Mosaic Virus and Maize Dwarf Mosaic Virus in Mixed Infections of Sugarcane and Other Grasses. A. G. Gillaspie, Jr., Research Plant Pathologist, Southern Region, Agricultural Research Service, U.S. Department of Agriculture, Houma, Louisiana 70360, Current address of senior author: Applied Plant Pathology Laboratory, Agricultural Research Center-West, Beltsville, Maryland 20705; H. Koike, Research Plant Pathologist, Southern Region, Agricultural Research Service, U.S. Department of Agriculture, Houma, Louisiana 70360. Phytopathology 63:1300-1307. Accepted for publication 12 April 1973. DOI: 10.1094/Phyto-63-1300.

Johnsongrass, itchgrass, and sugarcane were inoculated with one or more strains of sugarcane mosaic virus (SCMV) before, during, or after inoculation with maize dwarf mosaic virus strain A (MDMV). Inoculum from doubly inoculated itchgrass infected johnsongrass and ‘Rio’ sorghum, but the symptoms on Rio were milder than those of MDMV alone and distinct from those of SCMV alone. Inocula from simultaneously inoculated itchgrass were serially passaged through johnsongrass or Rio. When tested on Rio, symptoms from the johnsongrass series appeared to be MDMV, whereas those from the Rio series appeared to be variants of SCMV. The symptoms became stabilized after three serial passages through Rio, and further passages through other hosts, johnsongrass, itchgrass, or sugarcane (‘Chunnee’) did not change the symptom expression on Rio. These mixtures could be mistaken for new strains of MDMV. The mixtures could be separated biologically by passage through sugarcane (‘Louisiana Striped’) which yielded only SCMV, and physically, by purification methods detrimental to one component. When in a stabilized mixture, SCMV could multiply in johnsongrass, which is highly resistant to SCMV alone.