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The Effects of Temperature On The Durability Of Resistance Of Soybean To Soybean Mosaic Virus
Flora, Jonathan P.
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The objectives of this study were to determine the effects the temperature sensitivity of alleles of Rsv1 in soybean (Glycine max (L.) Merr.). Soybean cultivars carrying alleles of Rsv1 were exposed to several heat treatments designed to induce heat shock protein production prior to inoculation with soybean mosaic virus (SMV). The heat treatment methods were similar to those employed in the research with N gene-tobacco mosaic virus studies. The soybean cultivars used were Lee 69, York, Kwanggyo, Ogden and PI96983, carrying the Rsv, Rsv1-y, Rsv1-k, Rsv1-t, and Rsv1 allles of Rsv1, respectively, and were selected to provide a range of reactions to selected SMV pathotype groups. For example Rsv1-y and Rsv1-k give a necrotic response to SMV G4 and SMV G6, respectively, while both are resistant to SMV G1. To determine the durability of resistance under heat shock conditions, the symptoms were observed for changes in the phenotype of the resistance response. Immunological techniques were employed to determine the vascular movement and localization of the viral antigen in the plant. Heat treatments used were found to induce HSP but to have no effect on the resistance phenotype. A detached leaf assay was used to test the same Rsv1 alleles at constant high temperatures. Primary trifoliolate leaflets were removed and inoculated, then placed into a continuously lighted incubator at 20 C or 30 C. Leaf immunoprint assays were used to determine the localization of the viral antigen. The visible symptoms for necrotic lesions and veins were observed for necrotic phenotype-pathotype combinations but mosaic symptoms were not observed on detached leaves, as expected for inoculated leaves. The detached leaf assay confirmed that no change from the expected resistance response of the Rsv1 alleles occurred at 30 C. A breakdown of resistance to SMV at high temperature had been reported in soybean by Tu and Buzzell (1987). The resistance gene in which the high temperature breakdown occurred has been determined to be in Rsv3. Using cultivars and breeding lines carrying Rsv3 in a similar experiment was attempted in growth chambers. Preliminary results suggest that Rsv3 is temperature sensitive.
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