Bean common mosaic virus (BCMV; genus Potyvirus) has been recognized as a major constraint on bean production in Iran. BCMV and Bean common mosaic necrosis virus (BCMNV) have been reported from bean-growing regions of Iran (2,3), but no attempts were made to differentiate strains of BCMNV. During the early growing seasons of 2003 and 2004, 141 bean leaf samples suspected of BCMV infection were collected from the main bean-producing regions in Tehran Province (Varamin, Damavand, Boein Zahra, Hashtgerd, and Karaj). Symptoms included mild and severe mosaic, leaf curling, malformation, vein-banding, vein-clearing, mottle, and blister on the leaves. In addition, seeds of green bean and Chiti bean (300 each) were obtained from seed lots in Tabriz (East Azarbaijan) and Miyando-Âb (West Azarbaijan) and planted in the greenhouse. Emerging seedlings were subsequently screened for BCMV infection by ELISA and sodium dodecyl sulfate-Ouchterlony double diffusion test. Anti-BCMV polyclonal antisera used in this study included those raised specifically against NL-1, NL-3, NL-4, NL-6, NL-5, NL-8, and NY-15 strains. Seedborne viral infection on newly emerged seedlings varied (2 to 5%) depending on the province and bean cultivar. Seedborne symptoms were characterized as leaf curling, malformation, and necrosis. Among indicator plants used for host range determination, symptom characterization, and biological purification of BCMV, only Chenopodium quinoa, C. amaranticolor, and Phaseolus vulgaris L. cv. Red Kidney developed chlorotic local lesions in response to the BCMV inoculation. Further, P. vulgaris L. cvs. Bountiful, Red Kidney, and Stringless Green Refugee developed leaf mosaic and malformation as a systemic reaction to the inoculation. Of 172 isolates of BCMV investigated, seven representative strains, designated as A (37.2%), B (11%), C (9.3%), D (7.5%), E (12.2%), M (7.5%), and N (15.1%), were selected on the basis of symptom development on the indicator plants and serological tests with strain-specific polyclonal antisera. Thermal inactivation point, dilution end point, and longevity in vitro of the selected BCMNV strains were in the range of 60 to 65°C, -3-(-4), and 3 to 4 days, respectively. Pathogenicity groups of the selected strains were determined by symptom response (sensitive or resistance) at 26 and 32°C in the bean differential host range (1). The designated strains B and E from Tehran Province were assigned to standard strain NL-3 or pathotype VIa, strains A, C, and D from Tehran Province were assigned to standard strain NL-5 or pathotype VIb, and strains M and N from Azarbaijan Province were assigned to standard strain NL-8 or pathotype III. Western immunoblot analysis of viral capsid protein revealed that unlike NL-8, the BCMNV strains NL-3 and NL-5 had the apparent molecular mass of 32 kDa, which was slightly less than that of reference strain NL-8 (33 kDa), thus further confirming that these strains belong to serotype A of BCMV (e.g., BCMNV). Electron microscopy study showed that the virion particles were flexuous, filamentous, and unenveloped. To our knowledge, this is the first report of the differentiation of BCMNV strains from Iran.
References: (1) E. Drijfhout. Page 1 in: Agriculture Research Report 872. Centre for Agriculture 46 Publishing and Documentation. Wageningen, the Netherlands, 1978. (2) W. J. Kaiser and G. H. Mossahebi. Phytopathology 64:1209, 1974. (3) N. Shahraeen et al. Plant Dis. 89:1012, 2005.
