No abstract

SUMMARY In host‐range studies, bean common mosaic virus strains (BCMV‐NL1, ‐NL3 and ‐NY 15) usually induced distinct systemic symptoms in susceptible bean cultivars and latent infection in several Vigna genotypes (except NY15 which gave mosaic symptoms in the latter), while blackeye cowpea mosaic virus (B1CMV‐W) caused distinct systemic symptoms in several Vigna genotypes and only weak systemic symptoms in a few bean genotypes only. Biologically, B1CMV‐W was closest to BCMV‐NY15 and less close to ‐NL1. When using antisera to the three BCMV strains and five strains of B1CMV (including a strain originally considered cowpea aphid‐borne mosaic virus CAMV‐Mor) in SDS‐immunodiffusion and ELISA, BCMV‐NL1 and ‐NY15 were found to be closely related to each other and to BICMV‐Fla, ‐NR and ‐W, and less closely to BICMV‐Ind and ‐Mor. Serological relationships of BCMV‐NL1 and ‐NY15 to BCMV‐ NL3 were more distant, which is in line with the biological distinction of NL3 in causing temperature‐independent necrosis in bean cultivars with the necrosis gene I. PAGE analysis of coat proteins revealed that the three strains of BCMV and B1 CMV‐W have similar but non‐identical molecular masses. Although molecular hybridisation may further elucidate quantitative relationships between potyvir‐uses, variation within and among the potyviruses may continue to pose problems in their classification and identification.

Earlier attempts to discriminate serologically strains NL1, NL3 and NY15 of bean common mosaic virus (BCMV) and strain W of blackeye cowpea mosaic virus (BlCMV) had been unsuccessful. Antibodies directed towards N-and C-, or N-terminal peptide regions of the coat proteins of the above strains enabled the distinction between BlCMV-W, BCMV-NY 15 and BCMV-NL3 in electroblot immunoassay and in ELISA. The distinction was better with antibodies directed towards N-termini than with those to N-and C-termini. Strain NL1 of BCMV cross-reacted with both BlCMV-W and BCMV-NY 15, but not with BCMV-NL3. Taxonomic implications of these findings are discussed.

The aphid transmissibility of seven Plum pox virus (P PV)

Plants of bean (Phaseolus vulgaris) inoculated first on one primary leaf with strain NY15 of bean common mosaic virus, as inducer, and after three days, on the opposite leaf, with the strain NL3 of bean black root virus, as challenger, did not show systemic necrosis characteristic of the latter strain. This interference phenomenon was studied by determining the amount, distribution and localization of both strains in the part of stem between primary leaves and first trifoliolate leaf in both challenge-inoculated and singly inoculated (control) plants. In dot-blot immunoassay, NL3 was detected seven days after its inoculation as challenger, whereas in control plants its presence was established on day four. Immunostained thick sections revealed a large accumulation of NL3 antigen on day eight in both phloem and cambium, but not yet in the xylem and cortex, contrasted with the controls. In immunogold-silver stained semi-thin sections, most of the NL3 label was present in the companion cells and other phloem parenchyma cells, while in the control plants this virus was also present in xylem vessels and xylem parenchyma cells. Inducer strain NY15 was abundantly present in practically all the cells, including xylem vessels, from day two after challenge inoculation onwards. It is concluded that inducer strain NY15 hampers transport of NL3 to, and its spread in, the stem and prevents the latter strain from exerting its deleterious influence on the water conducting elements.