Recent Outbreak of "Mal de Rio Cuarto" Virus on Corn in Argentina.

"Mal de Río Cuarto" (MRC) is the most important viral disease affecting corn in Argentina. Reovirus-like particles were observed in diseased plants (1,4) and were later serologically related to an isolate of maize rough dwarf virus (3), though this relationship was recently questioned (2). Based on estimates of the prevalence and severity of MRC and yield losses, government agencies, corn hybrid seed companies, and growers agreed that the worst epidemic in the country occurred during the 1996 to 1997 agricultural year. Approximately 300,000 ha of corn were affected by the disease and yield losses were estimated at $120 million. Affected areas included the central and southern Santa Fe, the central, northern, southeastern, and western Buenos Aires, and the eastern and southern (originally the endemic center of MRC in Río Cuarto County) parts of Córdoba. Virus infections were confirmed by double-antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) in root samples from each surveyed location, using an antiserum to MRC virus. The occurrence of MRC in non-endemic areas suggests an unusual phenological coincidence of high vector populations, abundant natural virus reservoirs, and susceptible stages in the crop. Most commercial hybrids surveyed were apparently susceptible to the virus, although some were tolerant. References: (1) O. E. Bradfute et al. Phytopathology 71:205, 1981. (2) C. Marzachi et al. Sem. Virol. 6:103, 1995. (3) R. G. Milne et al. Phytopathology 73:1290, 1983. (4) S. F. Nome et al. Phytopathol. Z. 101:7, 1981.