Detection, Understanding and Controlof Soybean Mosaic Virus

Encapsulated in the viral particle is the viral genome which is a linear, positive-sense, single-stranded RNA molecule.The thermal inactivation point (10 min) of particles is 55 to 60°C.(Bos, 1972).The decimal exponent (DEX) of the dilution end point (DEP) is 10 -3 ～10 -5 , and the longevity in vitro (LIV) is 2～5 days at 25°C (Hill, 1999).SMV is relatively stable at pH 6.0 and loses infectivity at pH values higher than 9 or lower than 4 (Galvez, 1963).The cylindrical, pinwheel-shaped inclusions formed by the viral CI protein, a characteristic cellular phenotype for potyvirus infection, are often found in the cytoplasm of infected cells (A.Wag, unpublished). Host range and symptomsIn comparison with other potyviruses, SMV has a relatively narrow host range.It infects six plant families, i.e., Fabaceae (also Leguminosa), Amaranthaceae, Chenopodiaceae, Passifloraceae, Schropulariaceae and Solanaceae, but mostly the Leguminosae including soybean and its wild relatives (Galvez, 1963;Hill, 1999).The symptoms induced by SMV depend on host genotype, virus strain, plant age at infection, and environment.In SMV-infected soybeans, symptoms commonly observed include rugosity, dark green vein banding and light green interveinal areas, stunting, leaf curling and seed coat mottling, male sterility, flower deformation, less pubescent, necrosis, sometimes necrotic local lesions, systemic necrosis and bud blight (ICTVdB Management, 2006).Some of these SMV symptoms may be masked at temperatures above 30°C (Hill, 1999). TransmissionUp to 30% or more of the seeds from SMV-infected soybean plants carry SMV depending on cultivar and time of infection before flowering (Bos, 1992).SMV-infected seeds are the primary inoculum source, though weeds and other plants may also serve as a reservoir of SMV.Further spread within and among soybean fields is through the activity of more than 32 different aphid species of 15 different genera in a non-persistent manner (Cho and Goodman, 1982;Arif and Hassan, 2002;Steinlage et al., 2002).Some aphid species are Acyrthosiphom pisum, Aphis craccivora, A. fabae, A. glycine, A gossypii, Myzus persicae, Rhopalosiphum maidis and R. padi.In addition, SMV can be efficiently sap-transmitted with or without the use of abrasives. StrainsNumerous SMV isolates have been reported worldwide.In the United States, at least 98 isolates of SMV have been documented (Cho and Goodman, 1979, 1982, 1983).Based on their differential reactions in two susceptible, i.e., Clark and Rampage, and six resistant soybean cultivars including Buffalo, Davis, Kwangyo, Marshall, Ogden and York, SMV isolates were classified into seven distinct strain groups, G1 through G7 (Cho and Goodman, 1979).Later, two more groups, G7A and C14 were added (Buzzell and Tu, 1984;Lim, 1985).Similarly, five strains (A to E) have been identified in Japan (Takahashi et al., 1963;Takahashi et al., 1980).In Canada, a necrotic strain, SMV-N, and a number of G2 isolates were identified (Tu and Buzzell, 1987;Gagarinova et al., 2008a;Viel et al., 2009).But SMV-N shares high sequence similarity with the G2 group and is thus considered a G2 isolate (Gagarinova et al., 2008b).In South Korea, SMV was also monitored by pathotype.All the SMV G strains, including G1 through G7, SMV-N, G5H, G7a and G7H, have been found (Seo et al., 2009), but dominant www.intechopen.com

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