CHARACTERIZATION AND SEROLOGY OF VIRUS-LIKE PARTICLES ASSOCIATED WITHFABA BEAN NECROTIC YELLOWS

A disease showing chlorosis, leaf rolling and stunting in Vicia faba a nd other legumes was observed in West Asia and North Africa during 198 7-1988. The putative causal agent could not be transmitted mechanicall y, but could be transmitted by aphids, most efficiently by Acyrthosiph on pisum, in the persistent manner. Further studies revealed isometric virus-like particles (VLPs) closely associated with the disease, alth ough their infectivity could not be demonstrated by membrane feeding. These particles, measuring c. 18 nm in diameter and containing a capsi d protein of about 22 kDa and ssDNA of about 1 kb, are hereafter desig nated faba bean necrotic yellows virus (FBNYV). A high proportion of c ircular nucleic acid molecules of about 0.9 kb were visualised by elec tron microscopy. Hybridisation analysis of cloned viral DNA suggests t hat the circular genome is larger than 1 kb and consists of several co mponents of similar size. An antiserum produced against FBNYV was used in ELISA, immunoelectron microscopy (IEM) and Western blot experiment s for virus detection in aphids and field samples and for serological comparison with other viruses. Weak heterologous reactions between FBN YV and subterranean clover stunt virus (SCSV) were detected in IEM, bu t could not be confirmed in ELISA or Western blots. No serological rel ationship to banana bunchy top virus (BBTV) was detected. Using a dire ct tissue blot immunoassay (TBIA), FBNYV was detected in vascular tiss ue of infected faba bean leaves and stems.