Distribution and localization of bean common mosaic virus and bean black root virus in stems of doubly infected bean plants

Abstract

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.

Different forms of interference between two tobamoviruses in two different hosts

“…In Arabidopsis , TMGMV does not appear to prevent ORMV replication and accumulation, as the latter can replicate and accumulate in inoculated leaves. This phenomenon resembles the interference described in bean plants doubly infected with two different but closely related potyviruses (Khan et al ., 1994). In a similar way, TMGMV possibly does not allow ORMV to move from the inoculated leaf to the phloem, delaying (as in bean) or impairing the transport of the challenging virus from inoculated to uninoculated leaves.…”

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“…Such viral interactions may be antagonistic or synergistic [14]. Antagonism usually occurs when the co-infecting viruses are related, resulting in interference [15] or cross-protection [16,17]. Synergism normally occurs in mixed infections when the pair of viruses involved are unrelated, resulting in more severe disease symptoms than those produced by single infections [18-20].…”

Cowpea Reaction to Single and Mixed Viral Infection with Blackeye Cowpea Mosaic Virus and Cowpea Yellow Mosaic Virus

“…Antagonism has been found to usually occur when the co-infecting viruses are related, resulting in interference or cross-protection (Sakai et al,1983;Khan et al,1994). Synergisms on the other, occur when one virus enhances infection by a distinct or unrelated virus, which implies that protein(s) from one virus can enhance infection by another (Froissart et al, 2002).…”