Miscellaneous Information About Rose Mosaic Virus

     This page gives the information that I have collected from my own literature searches and from others posting on the internet. Please let me know if you feel anything is not clear or is not addressed at all as I am continually updating/modifying it as I get feedback.  

    Bold print in quotes does not mean that the bold print appeared in the original; the bold print was added by me (H. Kuska) for emphasis.

     As background material the term "rose mosaic virus" means different things to different people. Here is a literature comment:

Title: Roses: virus and virus-like diseases.
Author: Lisa-V
Published in: Colture-Protette. 1998, 27: 5 Supplement, 35-38; 14 ref.
Language of article: Italian
Abstract: "Notes are given on the viruses and virus-like diseases that are known to affect roses around the world. The most common and widespread virus disease is rose mosaic, associated especially with prunus necrotic ringspot ilarvirus (PNRSV), apple mosaic ilarvirus (ApMV), arabis mosaic nepovirus (ArMV) and strawberry latent ringspot nepovirus (SLRV), but also with tobacco ringspot nepovirus, tobacco streak ilarvius and tomato ringspot nepovirus. Tobacco mosaic tobamovirus and an unidentified closterovirus are found sporadically. The virus-like diseases of unknown aetiology include rose ring pattern, rose flower break, rose streak, rose rosette (or rose witches' broom), rose leaf curl, rose spring dwarf and rose wilt. Other disorders are caused by hormonal imbalances or other types of incompatibility between the graft and the rootstock of unknown aetiology, such as rose bud proliferation, rose dieback (or rose stunt) and frisure. Techniques for diagnosing viruses in roses and methods for their control are described." (The actual articles are copyrighted. This is why one will only see the abstract on public forums.)

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     TEMPERATURE EFFECTS ON VIRUS CONCENTRATION

   There is a 1999 scientific study that the amount of PNRSV (the main RMV component in the U.S.) decreases as the temperature increases until it can no longer be detected.  This does not mean that PNRSV infected roses will cure themselves in southern climates as the virus in the roots is not killed.  As the weather cools it appears that the virus returns to the above ground parts of the plants.   

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Strength, Virility of the Virus

As indicated above, RMV is a group of viruses. Even within a single type of virus, there are often more than one strain. The strains differ in their effect (strength, virility). The ApMV strain that Malcolm Manners used in his Florida experiment killed the roses after 3 years even in the heat of Florida: ( "During the fourth year, most of the ApMV-infected bushes died.")

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Ability of the Variety to Resist RMV

     One variety of rose may have a different ability to defend itself against a given virus than another variety of rose; and even the general health of the individual plant may affect its ability to resist a virus.

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     Thus, someone may make the statement that he/she had a certain variety that had RMV for many years with no observable negative effects; unless you have the same variety, grown under the same garden conditions; and it is infected with the same strain of the same type of virus and you live in the same temperature zone, his/her experience is not strictly applicable to your situation.

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                                                                                              Does RMV Spread Naturally?

     I have seen a number of comments where someone states that 5 or 8 years after they purchased a bush that it displayed RMV symptoms. Someone then replies along the line "It did not spread to it; it always had it".

     I also have read statements along the line: someone had a bush that performed well for several years and then declined or winter died for no apparent reason.

     Are these cases of plants catching RMV? Since we do not have home ELSIA kits, we do not know. One person  can no more claim that these were "all" cases of RMV spread then can another  who states that since a homeowner cannot prove that the bush was not virused when it was purchased that there are "no" cases where it did catch it by spreading. This simply is not a disease that the homeowner can say for certain does or does not spread. We have to rely on 1) published scientific studies, 2) RMV found occurring naturally in roses,  3) in progress scientific studies and 4) the observations of hybridizers who have reported virus in never grafted seedlings.

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 1) Published Scientific Studies and 2) RMV found occurring naturally in roses

     Natural occurrence has been reported in a published widely available scientific refereed journal (bold face was added by Henry Kuska for emphases):
J. B Sweet, Long Ashton Research Station, University of Bristol, United Kingdom. Journal of Horticultural Science, volumn 55, pages 103-111, (1980) - he states: "Two plants from a batch of about 200 Rosa multiflora seedling rootstocks with mosaic symptoms on their leaves induced PNRSV-type  symptoms in the woody indicatore, whereas four symptomless plants did not."

 My (Henry Kuska) comment: PNRSV is considered to be the main American form of Rose Mosaic Virus.

     Note, there are no grafts in these plants; they are seedlings. In Sweet's conclusion section, the following appears: "in this study only PNRSV was detected naturally infecting roses." This statement had to be approved by both the journal editor and the referees.

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     In a 1962 American Rose Annual article the following is stated: "L.C. Cochran found two roses in California naturally infected with the virus of peach ring spot." (Peach ring spot is another name for PNRSV, the main component of RMV in the U.S.).
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3) In progress Scientific Study

      The two links below address  the U. Cal. Davis Natural Spread of RMV Ongoing Investigation:

http://www.rdrop.com/~paul/tom_virus.html

and

http://www.goldcoastrose.org/pdf/clean-stock.pdf

     This is what the U.C. Davis rose virus cleaning document states (the goldcoastrose link above):
"The viruses that cause rose mosaic disease are most commonly spread through propagation procedures such as budding an infected scion onto a healthy understock, or a healthy scion to an infected understock. Disease symptoms are not always obvious, which is why the use of virus-tested planting stock is advantageous. There is some evidence that rose mosaic spreads in commercial rose plantings. UC researchers are presently looking for possible explanations."
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4) Hybridizers that have reported finding RMV infected seedlings

     Ping Lim, an All American Rose winning hybridizer, stated in rec.gardens.roses that he has observed virused seedlings from virused parents.

     He is not the first hybridizer to report that some of his seedlings were virused. Harvey Davidson reported in 1988 (Davidson, H., The American Rose Magazine, volumn 29, March, page 16, (1988))  that some of his seedlings were virused and that he had heard, in a recent lecture, Dr. Dennison Morey state that rose mosaic can be transferred through pollen.  Dr. Morey was at one time the head of the breeding program for Jackson and Perkins.

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     In the April 1994 issue of the "American Rose" George R. Barse writes "Rose Mosaic virus disease is supposedly spread primarily through using infected propagation stock, although pollen is considered an occasional means - and who knows what future investigation will reveal." The article closes with the following "To insure against mis-quoting the USDA, this article was sent to and approved by the participants in the meeting prior to publication."

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     I have learned that in science it is always good to check what scientists not in our "sphere of influence" have to say about a subject).  Here are 3 such reports:

1) The following is from the Royal Botanical Garden, Sydney (bold face was added by Henry Kuska for emphases).
"Rose mosaic virus: Symptoms include yellowing of leaves, blotching etc. but are most often observed as a mosaic pattern of yellowing that looks like an oak leaf pattern. Infected plants may have some mottling and distortion of flowers, although there is a viral disease, rose flower break, reported to be different to rose mosaic virus which causes these symptoms. In most cases the initial effects of the virus are not significant but build up over a period of time to produce effects that can become quite considerable. There are only two effective strategies to control these diseases. The first is to ensure that the roses that are purchased come from a reputable producer who can guarantee that the roses are free of virus (i.e.. certified). The second and most important is to ensure that there are very stringent hygiene procedures in place to minimize the spread of the virus from plant to plant. Sterilization of cutting implements between plants is essential. These viruses do not spread by insects or any other vector."

AND

2) Master Gardeners' Manual states the following:

"1. Rose Mosaic VirusRose mosaic virus occurs worldwide. The symptoms are highly variable depending on the variety and the environment, however chlorotic bands or rings, vein clearing, and general mosaics are common. Symptom development on only a portion of a plant is common. Infected plants have decreased vigor, poor flower production, and are more susceptible to winterkill. The virus is transmitted through vegetative propagation and pollen. There is no control for a plant infected with the virus. Infected plants should be removed and destroyed."

AND

3) 2002 European and Mediterranean Plant Protection Report.

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     You may want to compare what one poster has called "an unsatisfying air of "Don't worry, be happy" surrounding the occurrence of rose mosaic virus" of some American rose mosaic information articles with what has been published about virus occurrence in Dahlias.

     For many gardeners, roses are a $15-$20 a bush plus much time investment with only a limited amount of garden space available.  Baldo Villigas RMV information states that "Some pathologists suspect that mosaic may be pollen transmitted which could prompt removal if other roses in the garden are valuable and not already infected." This is a very balanced answer.  

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     Oregon State University (one of the first universities to investigate RMV) has changed its stance from "no spread" to the following:

    U. C. Davis recently (2006) presented a paper on virus spread in roses (see Golino's abstract).  They apparently find  root grafting and contaminated pruning equipment as causes but in their (relatively hot) climate find no pollen or seed transmission. 

     In a 2005 paper they reported: "Over the course of one year, approximately 10% of the healthy plants became infected. After two years, rate of virus spread ranged from 0% to 48% to depending on virus strain and rose variety. Mechanical hedging did not increase the rate of spread in these trials, implying that another mechanism, possibly root grafting, was responsible."  

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Conclusion

     There is enough evidence to dismiss the concept that spread is not occurring as the "no spread" group has advocated. Of course, there may not be spread in hot climates, but we now know that is because PNRSV is a temperature dependent virus.

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Other related links:

Go to Can North American rose hybridizers safely use pollen from PNRSV infected roses?

Go to When was rose mosaic virus first observed?

Go to Comments about rose mosaic virus returning to heat treated plants

Go to Information about Rose Rosette Disease (virus)

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