Detection and seed transmission of viruses in faba bean germplasm

Faba bean (Vicia faba L.) and cowpea (Vigna unguiculata L.) are important pulse crops in India. Pests and diseases remain a major constraint to their production in farmers’ fields. Also, they are affected by seed-transmitted viruses, which reduce the yield and quality of these crops and are constraint for seed production. The present work deals with detection of seed-transmitted viruses in these crops by using different virus detection techniques viz. Infectivity Assay, Electron Microscopy (EM), Double Antibody Sandwich - Enzyme-linked Immunosorbent Assay (DASELISA) and Dot Immunobinding Assay (DIBA). Out of forty germplasm lines of faba bean subjected to growing-on test under controlled conditions, 38 lines showed symptoms of leaf rolling, mosaic, leaf narrowing and stunting of plants. Seed transmission based on symptoms ranged from 1–48%. The leaf samples showing virus-like symptoms were further tested using polyclonal antisera against Alfalfa mosaic virus (AMV), Broad bean stain virus (BBSV), Broad bean wilt virus (BBWV) and Pea seed-borne mosaic virus (PSbMV). BBWV and PSbMV were detected by DASELISA in leaf samples showing virus-like symptoms. The seed transmission of Broad bean wilt virus (BBWV) was found to be 10%. Blackeye cowpea mosaic virus (BlCMV) was successfully sap-transmitted in 22 cowpea seedlings out of 25 seedlings tested. EM of sap-inoculated cowpea leaves revealed the presence of flexuous particles of 750–950 nm indicating the presence of a Potyvirus and this was firther confirmed as Blackeye cowpea mosaic virus (BlCMV), a Potyvirus, using specific antisera to BlCMV by DIBA. These virus detection techniques have immense potential for quarantine processing of germplasm under exchange and in virus-free seed production and also for export which would be essential as per international obligations under WTO.