Relationships Between Wheat Streak Mosaic Virus and Soilborne Wheat Mosaic Virus Infection, Disease Resistance, and Early Growth of Winter Wheat. H. J. Larsen, Agricultural Research Service, U.S. Department of Agriculture and Department of Plant Pathology, University of Nebraska, Lincoln 68583. M. K. Brakke, and W. G. Langenberg, Agricultural Research Service, U.S. Department of Agriculture and Department of Plant Pathology, University of Nebraska, Lincoln 68583. Plant Dis. 69:857-862. Accepted for publication 28 May 1985. 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, 1985. DOI: 10.1094/PD-69-857.

Hard red winter wheat cultivars resistant (Homestead and Newton) and highly susceptible (Scout-66) to field infection by soilborne wheat mosaic virus (SBWMV) were all susceptible to laboratory infection by SBWMV through sap inoculation of leaves and to root colonization by the SBWMV vector fungus, Polymyxa graminis. Effects of SBWMV infection on root growth were inversely related to resistance observed in the field, because Homestead and Newton were more severely affected than Scout-66. Shoot growth was unaffected for all cultivars, but secondary root growth of infected plants was reduced to 16% of control plant growth. In contrast, Homestead and Scout-66 inoculated with wheat streak mosaic virus (WSMV) had similar reductions in their root or shoot growth; shoot growth was less affected by WSMV infection than root growth, and primary root growth was less affected than secondary root growth. Resistance to Polymyxa zoospores carrying SBWMV or reduced movement of SBWMV within roots of cultivars resistant to SBWMV in the field are suggested as possible mechanisms of this resistance to SBWMV. Tolerance to the virus, resistance to the virus at the cellular level, and resistance to the vector fungus alone (without virus) are eliminated as possible mechanisms.

Keyword(s): field resistance, root and shoot dry weight, root volume and length.