Baldo Villeagas told me that researchers at UC Davis had found that when roses were planted very close together, as commercial propagators do, mosaic virus was sometimes transmitted from an infected plant to an uninfected plant. They determined that this occurred when the roots of two plants grew together allowing the virus to move from one plant to the other.
Jim, Harvey Davidson pointed this out in The American Rose Magazine, volumn 29, page 16, (1988). (Harvey Davidson is a northern California rose hybridizer (see http://www.rosehybridizers.org/winners.html )). He wrote in to object to Professors Manners’ November 1987 article in the same magazine in which Professor Manner’s had stated that Rose Mosaic is not contagious. Davidson cited 8 examples which included that he personally observed mosaic in his seedlings, he observed pruning spread in the plants in the direction that he normally pruned, Dr. Dennison Morey (who was at one time the head of the breeding program for Jackson and Perkins) stating that rose mosaic can be transferred through pollen, and Fred Edmunds, the owner of the firm “Roses By Fred Edmunds” is quoted that from his observations, he is convinced that rose mosaic is transmitted by cutting and budding tools and field machines and can also be transmitted through the soil. He also stated that Professor Robert Raabe, Plant Pathology, Univ. Of Calif., Berkeley (if you are not familar with his name, see http://groups.ucanr.org/cmgvideo/Robert_Raabe/ ) maintains that rose mosaic can be transmitted through root contact.
Wow, it is a wonder why aren’t all rose plants are not contaminated. I use a heavily virused ‘Queen Elizabeth’ with my thornlessness breeding, and got a very good number of seed with ‘77-361’. But in the past I haven’t seen symptoms of RMV in my ‘Queen Elizabeth’ pollen and hip seedlings, although I can say that if I allowed more time for my seedlings to live, maybe I can see those symptoms in a mature plant. One seedling I am absolutely keeping is not thornless, but exteamly disease free. The weather here in San Jose is rather stressful now to some of my seelings. Many of them got BS, but not this seedling. And my way of thinking is that if a seedling has the virus, it ought to show it now with the sudden cold rainy snapes during some nice warm weather.
I remember once reading on here that Ralph Moore once had a seedling (or few?) that showed symptoms of RMV, before he destoryed it. Does anyone have a statement about how it may had gotten it?