Genomics of Viral–Soybean Interactions

Virus infected soybean can be found in all soybean growing areas of the world. To date, over 67 viruses have been identified that are capable of replicating in the soybean plant. Twenty-seven of the 67 are currently a concern or have the potential to be a problem in soybean production systems (Tolin and Lacy 2004). The most prevalent viruses causing significant crop losses are made of single-stranded, positive-sense RNA from the Potyviridae and Comoviridae families, which this chapter will focus on. Soybean mosaic virus (SMV), which belongs to the Potyviridae, has been known to cause total crop loss (Kwon and Oh 1980) and occurs in all soybean growing areas of the world. Bean pod mottle virus (BPMV) is a member of the Comoviridae family and has increased its geographical distribution throughout the United States and poses a significant risk to soybean growers, particularly those in the North Central and Northern Great Plains states. Together the two viruses, BPMV and SMV, interact synergistically and drastically reduce yield and seed quality compared to each disease alone. Therefore, priority was placed on improving cultivar resistance often through utilization of molecular and genomic approaches. The most common method of controlling SMV in soybean is through development of resistant cultivars often carrying a single hypersensitive resistant (R) gene. However, recent reports of resistance-breaking (RB) stains in Japan and Korea (Choi et al. 2005; Koo et al. 2005; Saruta et al. 2005) shifted breeders and molecular biologists to incorporate durable forms of resistance into cultivars through gene pyramiding or transgenic methods. As SMV is seed borne, seed distribution processes such as those used in germplasm exchange programs, serve to spread the virus to different environments and other areas of the world. Disease management of BPMV through genetic resistance is not possible as no soybean cultivars with resistance to BPMV are commercially available. Only a few experimental transgenic lines conferring resistance against BPMV are available.