Using Mixed Cropping to Limit Seed Mottling Induced by Soybean Mosaic Virus. Harry Bottenberg, Postdoctoral Research Associate, University of Illinois and Illinois Natural History Survey, Champaign, IL 61820. Michael E. Irwin, Professor, University of Illinois and Illinois Natural History Survey, Champaign, IL 61820. Plant Dis. 76:304-306. Accepted for publication 24 October 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0304.

The spread of aphid-borne soybean mosaic potyvirus (SMV) from inoculated sources was studied in monocultures of soybean and additive mixtures with dwarf (cv. G522DR) or tall (cv. 102F) sorghum. SMV-induced seed mottling, averaged over rows outside the inoculated area, was 4.01% in the soybean monoculture, compared with 2.02 and 2.07% in plots with dwarf and tall sorghum, respectively. Seed mottling decreased rapidly with increasing distance from the inoculum source. Gradients were similar in different treatments, but the intercept was highest in the soybean monoculture. Mean soybean yield per plant was most severely reduced in the tall sorghum mixture, presumably due to competition effects. To minimize competition and protect soybean from aphid-borne virus spread, legumes might, in some circumstances, best be intercropped with cereals of similar height.