Soybean mosaic virus (SMV) can cause serious yield losses in soybean. Soybean cultivar ‘RN‐9’ is resistant to 15 of 21 SMV strains. To well‐characterize this invaluable broad‐spectrum SMV‐resistance, populations (F1, F2 and F2:3) derived from resistant (R) × susceptible (S) and R × R crosses were tested for SMV‐SC18 resistance. Genetic analysis revealed that SC18 resistance in ‘RN‐9’ plus two elite SMV‐resistant genotypes (‘Qihuang No.1’ and ‘Kefeng No.1’) are controlled by independently single dominant genes. Linkage analysis showed that the resistance of ‘RN‐9’ to SMV strains SC10, SC14, SC15 and SC18 is controlled by more than one gene(s). Moreover, Rsc10‐r and Rsc18‐r were both positioned between the two simple sequence repeats markers Satt286 and Satt277, while Rsc14‐r was fine‐mapped in 136.8‐kb genomic region containing sixteen genes, flanked by BARCSOYSSR_06_0786 and BARCSOYSSR_06_0790 at genetic distances of 3.79 and 4.14 cM, respectively. Allelic sequence comparison showed that Cytochrome P450‐encoding genes (Glyma.06g176000 and Glyma.06g176100) likely confer the resistance to SC14 in ‘RN‐9’. Our results would facilitate the breeding of broad‐spectrum and durable SMV resistance in soybeans.

The resistance of different soybean varieties to the Chinese isolate of soybean mosaic virus SC3 was systematically studied. However, the resistance of different germplasm sources is still poorly understood. We constructed an infectious DNA clone of Chinese SMV isolate SC3 (pSC3) and modified it to allow the expression of yellow fluorescence protein (YFP)/ red fluorescence protein (RFP) during viral infection. By using the infection of pSC3-RFP, we can classify the resistance of different soybean cultivars to SMV-SC3 to the extreme resistance that restricts initial viral replication and the resistance that allows viral replication in the initially inoculated cells but restricts further movement. Also, we tracked the SMV-SC3 infection in susceptible cultivar Nannong 1138-2 (NN1138-2) and found that the seed transmission of SMV to the offspring plants can be tracked and recorded by imaging the virus-driven expression of YFP. Overall, we reveal new aspects of soybean resistance to SMV-SC3 and provide an essential tool to study the infection and transmission of SMV-SC3, which will help decipher the genes involved in SMV pathogenesis and host resistance.

The resistance of different soybean varieties to the Chinese isolate SC3 of soybean mosaic virus (SMV) was systematically studied. However, the resistance of different germplasm sources is still poorly understood. We constructed an infectious DNA clone of SMV-SC3 (pSC3) and modified it to allow the expression of yellow fluorescence protein (YFP)/ red fluorescence protein (RFP) during viral infection. By using the infection of pSC3-RFP, we can classify the resistance of different soybean cultivars to SMV-SC3 to the extreme resistance that restricts initial viral replication and the resistance that allows viral replication in the initially inoculated cells but restricts further movement. Also, we tracked the SMV-SC3 infection in susceptible cultivar Nannong 1138-2 (NN1138-2) and found that the seed transmission of SMV to the offspring plants can be tracked and recorded by imaging the virus-driven expression of YFP. Overall, we reveal new aspects of soybean resistance to SMV-SC3 and provide an essential tool to study the infection and transmission of SMV-SC3, which will help decipher the genes involved in SMV pathogenesis and host resistance.