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ELISA DETECTION OF ILAR VIRUSES IN FRUIT TREES BY ANTISERA HAVING STRONG HETEROLOGOUS REACTIONS
PNRV is the ILAR virus commonly found in cherry.
PNRV and ApMV mixed infections are common in plum (Barbara et al., 1978). ApMV is the ILAR virus commonly found in apple.
PNRV and ApMV are distantly related serologically.
However, antisera specific to each virus are necessary for their routine detection in fruit trees because heterologous cross reactions of these two viruses are too weak for reliable determination (Casper, 1973).
In hop, an ILAR virus has been found that has a close serological relationship to both PNRV and ApMV. This hop virus can be easily detected with either PNRV or ApMV antiserum.
Because of the serologically intermediate position of this hop ILAR virus between PNRV and ApMV, it is likely that it will be possible to detect all three of these viruses with an antiserum against the hop ILAR virus.
Studies of this kind are currently in progress.
The particles of the hop ILAR virus are usually isometric but are occasionally elongated, resembling bacilliform particles Bacilliform-like particles also have been found in preparations of other ILAR viruses (Lister and Saksena, 1976). In polyacrylamide gel electrophoresis (PAGE) of crude sap from ApMV-infected cotyledons, the virus particles separate into two, and in some cases three, bands (Wolf and Casper, 1971) (figure 2). The particles in these bands react with homologous antisera and form widely spaced precipitin lines in the polyacrylamide gel after electrophoresis.
Homologous antigen-antibody systems of PNRV and ApMV each produce two distinct precipitin lines in PAGE. The hop ILAR virus produces one faint upper line and one distinct lower line in PAGE tests with either PNRV or ApMV antiserum.
So far, we have no explanation for this difference in behavior between the hop ILAR virus and PNRV and ApMV in PAGE.
Unlike the situation in plum, we have found that in hop PNRV, ApMV, and the hop ILAR virus are only found singly, never in mixed infections.
Using artificially prepared sap mixtures of two or of all three of these viruses to infect cucumber cotyledons, we found that PNRV and ApMV did not interfere with each other, i.e., both viruses continued to propagate in doubly infected cucumbers.
Some degree of interference appeared to occur when hop ILAR virus was used to coinoculate cucumbers with PNRV, ApMV, or both together.
In such cases the concentration of the hop ILAR virus did not rise as expected.
This preliminary investigation may explain why we could not find mixed infections of hop ILAR virus with PNRV and ApMV in hop, but it does not explain the absence of mixed infections of PNRV and ApMV in hop.