Background and Aims: Alfalfa (Medicago sativa) is the most cultivated forage legume in Iran. Viruses belonging to the Luteoviridae family are among the important yellowing and stunting diseases in food and forage legume crops. Despite the important role of yellowing viruses, limited information is available on the occurrence of viruses from the family Luteoviridae in forage legume fields in Iran. In this study, a survey was conducted to detect Soybean dwarf virus (SbDV, from Luteoviridae family) in alfalfa fields in West Iran.
Materials and Methods: Twenty-one alfalfa fields were surveyed in the Lorestan province (West Iran) in 2011. Plants exhibiting symptoms of dwarfing, yellowing and reddening were collected and tested by tissue-blot immunoassay using monoclonal antibody 5G4. Thirty positive samples with 5G4 were further characterized by RT-PCR using total RNA and a pair of primers to amplify a 370 bp DNA fragment in the coding region of SbDV coat protein (CP) gene. The nucleotide sequence of PCR amplicons was determined and compared with the previously reported data.
Results: Forty-three out of the 127 (33.8 %) leaf samples reacted with antibody 5G4. A DNA fragment of the expected size was amplified in seven out of thirty (23.3%) symptomatic leaf samples, but not in healthy plants. Furthermore, a biological assay using grafting of Vicia faba induced interveinal yellows, one month after grafting and their infection with SbDV was confirmed by RT-PCR. Analysis of the sequences revealed the presence of 370 nucleotides of the SbDV partial coat protein gene. Phylogenetic analysis using the neighbor-joining (NJ) method clustered SbDV isolates into two main groups (D and Y), and SbDV-Irn1 and SbDV-Irn2 isolates fell into group D.
Conclusion: In Iran, the natural infection of SbDV has been reported from chickpea and lentil crops, but there was not any data about its occurrence on other crops and phylogenetic properties. Our results showed for the first time the occurrence of SbDV in alfalfa fields in West Iran using different biological and molecular approaches. Partial nucleotide sequence of CP gene of two Iranian SbDV isolates from alfalfa (Ir.Alf-D1 and Ir.Alf-D2) was determined and revealed that both isolates fell into the type D group of SbDV. The SbDV-D strain causes dwarfing and significant yield losses in a range of economically important food legume crops, so its occurrence in alfalfa fields should serve as an important warning to monitor its occurrence in respective food crops.