MONOCLONAL-ANTIBODIES FOR THE DETECTION AND DIFFERENTIATION OF FABA BEAN NECROTIC YELLOWS VIRUS ISOLATES

Murine monoclonal antibodies (MAbs) were produced for the detection of faba bean necrotic yellows virus (FBNYV), an isometric ssDNA virus be longing to a new, yet unnamed genus of plant viruses. A total of 19 FB NYV-specific MAbs were obtained from three fusion experiments and char acterised by determining their immunoglobulin types and titres as well as their corresponding epitopes. At least six distinct epitopes were revealed on FBNYV particles of different virus isolates. Only two MAbs reacted with SDS-dissociated FBNYV virions in triple antibody sandwic h (TAS)-ELISA and with viral capsid protein in Western blots. Almost a ll MAbs were more sensitive in detecting FBNYV in viruliferous aphids by TAS-ELISA than polyclonal anti-FBNYV IgG by double antibody sandwic h ELISA and permitted virus detection in individual aphids even follow ing short acquisition access feeding periods. Coat protein variation a mong FBNYV isolates and serological relatedness to taxonomically simil ar viruses was studied by determining the cross reactivity of these MA bs with several field isolates of FBNYV as well as with milk vetch dwa rf (MDV), banana bunchy top (BBTV), and subterranean clover stunt (SCS V) viruses. Whereas none of the MAbs reacted with BBTV, only one react ed with SCSV, indicating that FBNYV and SCSV share a common epitope. B y contrast, 16 of the 19 MAbs reacted with MDV, suggesting that FBNYV and MDV are serologically closely related and strains of the same viru s. When all 19 MAbs produced were tested against a total of 107 sample s of FBNYV collected during virus surveys in Egypt, Ethiopia, Jordan, Morocco and Syria, five MAbs showed differential reactions. While the majority of the samples reacted with all 19 MAbs, about 20% of the 107 FBNYV samples did not react with one and/or other of these five MAbs, permitting the differentiation of seven serotypes of FBNYV and sugges ting a considerable coat protein variation in FBNYV isolates from the countries surveyed. The MDV isolate from Japan and five FBNYV samples from Ethiopia appeared to be the least closely related to typical FBNY V isolates by not reacting with three and four, respectively, of the f ive differentiating Mabs.