Effect of Temperature on the Expression of SMV- Induced Necrosis in Soybean Carrying Homozygous and Heterozygous Alleles.

Expression of symptoms caused by Soybean mosaic virus (SMV) is dependent on host genotype, SMV strains, and temperature. The objective of this research was to investigate the effect of different temperature regime on SMV symptom expression conditioned by different resistance genes. The F1 seeds resulted from crossing Essex (rsv) and set of differential genotypes for identification of SMV strains including V94-3971 (Rsv1), V262 (Rsv1-n), V229 (Rsv3), V97-9-003 (Rsv4), and PI 96983 (Rsv1) were grown in the pots in the greenhouse. The F1 plants were inoculated with G1 or G7 at the unifoliate stage and were transferred into the growth chambers with temperature set at 28, 29, 30, 31, 32, 33, or 37⁰C. Virus was detected by enzyme- linked immunosorbent assay (ELISA). The results revealed that SMV-inoculated plants carrying Rsv3 and Rsv4 remained symptomless in homozygous and heterozygous states at all temperature settings. Threshold temperatures for symptom shifting from stem tip necrosis (STN) to mosaic were 30⁰C for V94-3971,  33⁰C for PI 96983 and V262 in homozygous state, respectively. In heterozygous state, threshold temperature for symptom shifting from STN to mosaic was 30⁰C for (V94-3971× Essex) F1, 32⁰C for (V262× Essex) F1, and 30⁰C for (Essex × PI 96983) F1. Incomplete STN was observed as a mixture of necrosis and mosaic symptoms in heterozygous state in (V262× Essex) F1 and (V94-3973× Essex) F1. Resistant reactions were not affected by temperature changes, whereas high temperature appears to prohibit virus replication and movement in both heterogeneous and homogenous state