Alice,
Much like myself, I know that you have spent a few years researching this subject and know a good deal about it. We have certainly discussed it on more than a few occasions and both of us have contacted virologists, had them do virus testing on our cannas and attempt to give us their insight on the virus issues. Ideally we would like to have sound scientific information but I suspect there are no longer any pathologists living today that first observed the symptoms that canna virus produce. Chances are that when virus first infected cannas the field of virology did not exist. From a strictly scientific standpoint, our research on past virus issues must come from the "old" horticulture publications and scientific journals. Up until the past few years these publications were simply buried in a few libraries around the world (often written in the language of the publishing country). With the advent of high speed internet and the digitations of some of these historic publications we can now access a limited amount of this information.
I have spent a rather significant amount of time searching out as much of this canna related information as I can find. The best thing is a lot more information should continue to be available in the future. With the above noted and please dont hold me to specific dates, my findings go something like this.
The oldest reference to symptoms seen in canna cultivars was in the mid to late 1800Âs. This information as I recall did not reference the word "virus" but simply stated a leaf condition that could not be readily identified. Through the early 1900Âs, virus identification basically involved the elimination of all other potential causes. Not to scientific! Only with the advent of electron microscopy was a road open to actually see and identify the many virus species. I think that number exceeds over 2000 that effect just plants.
I think by the early 1900Âs identification was very subjective. We find in the 1950-1970Âs some limited references to isolated virus infection. This somewhat recent identification is speculative because the descriptions do not always match present data. For the most part we must jump forward to the mid 1980Âs - 1990Âs to find good scientific research beginning. This information remained hard to locate and it is only in the past five to six years has the canna industry begun to have information necessary to address the issue. The first scientific publication I have found was by Yamashita (in Japan) 1988 and followed closely by Lockhart in Acta Horticulturae 1988. Both of these publications deal with canna yellow mottle virus.
The end of my scientific research!
Philosophically speaking: Virus in canna may (or not) have been present in our species cannas growing in their native habit. Our specie canna likely had developed immunity to possible local native virus over thousands of years? Removing and exposing them to totally hostile environment they were not adapted to and exposing them to many other horticulture plants likely opened the door for a mutated virus to eventually infect our cannas. This likely occurred in the more hostile environments but who will ever know. It can be noted that all original scientific references are dated in climates not native to our cannas. Once a mutated body makes the jump to a new species it can certainly infect even cannas in their native area. Please note all these thoughts are speculative at best!
Regards,
Kent

Thanks Kent :-)
I have been curious to know if the three viruses that currently generally affect cannas occurred all along. The many historical cannas wiped off the face of the earth must have had something widely encompassing that caused their decline. The streaks virus possibly is a mutation of the mosaic.
On a note I have never liked, about 10-15 years back I heard horror rumors (I hope) of breeders injecting virus into non variegated cannas to "try" for more variegated varieties. Guess that thought will always haunt me )-;
Alice