RECENT ADVANCES IN VIRUS PURIFICATION

In considering how best to approach a subject described as "recent advances" it was necessary to make some definitions rather arbitratily. How recent? For how long is an innovation new? I decided to consider three or four years as the lifetime of newness, and have not included much material older than that, except for a number of basic ideas that have recently been expanded upon. This decision, it rather soon turned out, was probably my second mistake, because a good bit of the most recent literature has not yet appeared in indexes or in abstract journals. Thus, there are probably articles I have overlooked; hopefully these do not include too many written by those of you who are here. Also, my subject seems sufficiently broad without saying much about virus characterization beyond the responses to the various techniques involved in purification.

In going over the recent literature one gets an impression, first, that there is little that is new. Centrifugation, clarification with organic solvents, or precipitation with polyethylene glycole are no longer new. A close look at the methods, however, showed that numerous modifications have been developed to meet specific problems presented by individual viruses. It is these modifications that I shall try to survey.

Perhaps a note of caution would be introduced; in many cases a particular buffer or reducing agent or solvent has been reported as being used. It is clear that the methods succeeds, but it is not always clear whether many variations were tried in selecting the method finally chosen.

I have not tried to limit my remarks to viruses found infecting ornamentals. The diversity of species among ornamental plants is so great that it may only be a matter of chance that a particular virus has not yet been reported in an ornamental.