Soybean mosaic virus (SMV) causes mosaic symptoms in susceptible soybean [Glycine max (L.) Merr.] cultivars and stem-tip necrosis (STN) in some soybean cultivars carrying resistance genes. The objective of this study was to examine the effect of different temperature regimes on the expression of SMV-induced STN in soybean genotypes hemizygous for an SMV resistance gene. Three soybean genotypes, ‘Essex' (rsvrsv, mosaic response to SMV strains G1 and G7), V94-3971 (Rsv1Rsv1, resistant to G1 and necrotic to G7), and an heterozygous soybean genotype (Rsvrsv) derived from Essex × V94-3971, were inoculated with G1 and G7 and maintained in growth chambers with a 12-h photoperiod and constant temperatures of 25 and 33°C. V94-3971 was resistant to G1 and necrotic to G7 at 25°C. F1 plants hemizygous for the Rsv1 gene derived from Essex × V94-3971 were necrotic to both G1 and G7 at 25°C, indicating that the reaction of plants heterozygous for an SMV resistance gene expressed a necrotic symptom while plants in the homozygous state were resistant. However, the necrotic reaction in F1 plants derived from Essex × V94-3971 to G1 or G7 at 25°C changed to a mosaic response at 33°C. The necrotic reaction in V94-3971 to G7 at 25°C also changed to a mosaic reaction at 33°C, demonstrating that the necrotic reaction in both homozygous and heterozygous soybeans is temperature sensitive and shifts to a mosaic reaction at higher temperatures. The resistant reaction in V94-3971 to G1 was not changed at 33°C. Essex exhibited mosaic symptoms when infected with G1 or G7 at both temperatures tested. Research is in progress to investigate the response of hemizygous soybean genotypes to G1 and G7 at other temperatures.
See more of Crops Posters/Reception
See more of The ASA Southern Regional Branch (June 19-21, 2005)