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Resistance

Resistance to Soybean Mosaic Virus in Soybeans. S. M. Lim, Research plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, and also professor, Department of Plant Pathology, University of Illinois, Urbana 61801; Phytopathology 75:199-201. Accepted for publication 12 September 1984. 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/Phyto-75-199.

Soybean line SS74185 (PI 486.355), which was collected in Korea, was resistant to all previously known seven (G1- G7) strains of soybean mosaic virus (SMV) and to an unclassified SMV isolate, C14. Soybean line Suweon 97 (PI 483.084) previously identified as resistant to the seven strains was susceptible to isolate C14. PI 96983 was susceptible to strain G7 but was resistant to strains G1- G6 and isolate C14. Isolate C14 caused necrotic symptoms in susceptible soybeans and its pathogenicity was shown to be different from the seven strains previously described. The F₂ plants from crosses of the susceptible cultivars Williams 79 and Franklin with PI 483.084 segregated in a 3 resistant:1 susceptible ratio when inoculated with strains G2 or G7. The F₂ plants from cross PI 96983 x PI 483.084 inoculated with G7 also segregated in a 3 resistant:1 susceptible ratio indicating that resistance in PI 483.084 to these two SMV strains was conferred by a single dominant gene. The F₂ progenies of a cross (PI 483.084 x PI 486.355) that were inoculated with isolate C14 segregated in a 3 resistant:1 susceptible ratio indicating that resistance in PI 486.355 was conferred by a single dominant gene. The F₂ plants derived from all the possible crosses involving three resistant lines segregated in a 15 resistant:1 susceptible ratio when inoculated with SMV strains G2, G7, or isolate C14 as expected for dominant genes segregating independently. These results indicated that resistance in each of the three lines PI 96983, PI 483.084, and PI 486.355 was conferred by a different dominant gene. PI 96983 carries a dominant gene Rsv that conditions resistance to strains SMV-1 (G2) and SMV-1-B (G3). Genes in PI 483.084 and PI 486.355 cannot be assigned until further tests are performed to determine which of the genes are different from a newly identified gene Rsv₂ that confers resistance to all seven strains in soybean cultivar Raiden (PI 360.844). PI 360.844 plants inoculated with isolate C14 developed a severe necrotic symptom similar to the reaction of PI 483.084, indicating that resistance in PI 483.084 to all seven SMV strains was probably conditioned by the same gene, Rsv₂, and that the resistance gene in PI 486.355 was different from gene Rsv₂.