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During recent months Agdia's testing services observed petunia samples exhibiting symptoms of tobamovirus infection. This virus group includes such well known problems as Tobacco Mosaic Virus and Tomato Mosaic Virus. The samples did not test positive for the usual tobamovirus found in Petunia, Tobacco Mosaic Virus, but several samples did give elevated optical density readings. An elevated reading could indicate any number of things, but one possibility is a cross-reaction with another, closely related virus.
The samples were retested using antisera to other tobamoviruses. The samples elicited a range of reactions to the combination of Tobacco Mosaic Virus - common strain (TMV-c), Tobacco Mosaic Virus non-specific antisera (TMV), and Tomato Mosaic Virus (ToMV) antisera.
As a direct result of these findings Agdia's Testing Services has been running, at no cost to our customers, these tests on known petunia samples. The following data summarizes the results from twenty-five positive samples, from many different customers. Table 1. Optical densities for selected positive petunia samples illustrating the three common types of reactions. Antisera TMV-c TMV ToMV Reaction type 1 0.004 0.384 0.026 2 0.039 0.114 1.198 3 1.319 2.105 2.393
It is not possible to draw any conclusions from these data as many events could explain them. Such explanations include, but are not limited to, several tobamoviruses being present or a new strain of a tobamovirus producing this range of reactions. One thing does seem certain, that caution should be used when dealing with these infections. It is not known whether the TMV resistance bred into many crops (especially vegetables) will hold against this problem.
In response to these findings, Agdia's testing services has changed both its Ornamental and Petunia screens to incorporate ToMV. A less frequently encountered virus was dropped from each screen, so that costs remain the same.