Resistance to Soybean Mosaic Virus in Soybeans

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Abstract
Soybean line SS74185 (PI 486.355), which was collected in Korea, was resistant to all previously known 7 (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 7 strains was susceptible to isolate C14. PI 966983 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 7 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 .times. PI 483.084 inoculated with G7 also segregated in a 3 resistant:1 susceptible ratio indicating that resistance in PI 483.084 to these 2 SMV strains was conferred by a single dominant gene. The F2 progenies of a cross (PI 483.084 .times. 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 3 resistant lines segregated in a 15 resistant:1 susceptible ratio when inoculated with SMV strains G2, 67, or isolate C14 as expected for dominant genes segregating independently. These results indicated that resistance in each of the 3 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 7 strains in soybean cv. 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 7 SMV strains was probably conditioned by the same gene. Rsv2, and that the resistance gene in PI 486.355 was different from gene Rsv2.