pathogens & hybridizing

Does anyone know if there is there any risk of contamination when using the pollen of either a virus or gall infected plant to the plant being used to carry the seed hip? Also would the resulting seed be infected? I know that in the case of orchids, clean seed can be produced from a virus infected plant if certain precautions are taken. I understand that all plants are different so can anyone expand on the information about roses in this respect?

Hi Fred:

It would be exceptionally rare if at all possible for pollen to transmit viruses or gall in roses. I would make crosses with free abandon, and without regard for the presence of those pathogens.

Jim Sproul

I agree with Jim on this one.


I would add one note of caution – while it is extremely unlikely that pollen will transmit a virus, and (as far as I know) impossible for pollen to transmit a gall problem, there is the chance that you could carry the virus from one plant to another on your hands. Whenever you handle a plant, you can get small amounts of stem fluids on you hands, which could concievably then infect another plant if you handle it directly afterwards. While the chance is small, and aphids are much much more likely to be the ones spreading a virus around, it never hurts to be cautious and give your hands a good washing after handling an infected plant.

Fred you did not give your zone. If you are in a non hot zone, I would say that from what has been reported in the literature, that you probably have a 1 to 2 percent chance of passing the infection to a seed if you use infected pollen. PNRSV (the main component of RMV in the U.S.) is a temperature sensitive virus. Because of this temperature sensitivity, in hot conditions PNRSV is probably only alive in the roots. The virus has been identified in rose pollen and has been transfered to indicator plants with the use of the infected pollen. Also rose hybridizers have reported that occasionally some of their seedlings are virused.

What I have found in the literature is available in the following link:


Fred, I would still not worry about it. Rose breeding does not have to be hard. I don’t worry about anything when I am making crosses - no hand washing or anything. I just wipe my finger off on my pants when selecting another pollen. Rose breeding is fun and easy when you get the hang of it! Enjoy.

Jim Sproul

Jim lives in Bakersfield, California. According to a computer search the high today in Bakersfield was 91 degrees.

You can make this as complicated and fraught with difficulty and stress as you want. Or not.

Work with clean plants whenever you can, but recognize that although some commercial growers have found virused seedlings in their work, the instances were VERY rare and contamination was considered to be a minor issue. If you can’t arrive at a mental state in which you enjoy your work, then perhaps you should re-assess why you are pursuing it. Some people proclaim annually that the sky will indeed fall, but I haven’t seen it happen yet :wink:



This has nothing to do with stress. It has to do with understanding your plants and nature. The more you understand of nature the more you can work with nature. If you understand that PNRSV is a temperature sensitive virus you are able to develop procedures specific to your area. It is like knowing whether you have to be concerned about downy mildew in your climate or whether in your climate you should bury the bud union at least 2 inches below ground. Should everyone take precautions against rust or should everyone ignor rust because it is not a problem in certain areas? Should everyone use the Minessota tip method? Should everyone ignor Rose Rosette Disease because certain areas of the country do not have it? One could go on and on.

Learning about roses has nothing to do with the sky is falling. For example the link below gives an interesting observation (to me). If others feel that that article causes them stress, that is their problem.

As an example of a great hybridizer/rosarian being interested in understanding his roses/nature, Ralph Moore did heat treatment experiments and found that the stripes in that particular rose was caused by a temperature sensitive virus.

By the way, the published values of PNRSV spread in roses (in non hot climates) all seem to be in the 1 to 2 % range.


Henry, you are right, it is really heating up in Bakersfield, but we are supposed to get a break in the heat for the next couple of days. I must clarify however, that most of my outdoor pollinations were done in April when we had temperatures here that were more characteristic of what northern climes are right now. Then in May, I moved my pollinations into the greenhouse (cooled with a pad/fan system), again taking advantage of cooler conditions.

I agree with Paul to use clean plants whenever you can. My only plant that I use that is clearly virus infected is ‘Geisha’. And I have used it and it’s seedlings extensively and have yet to find anything that looks like virus in any of the offspring.

Jim Sproul

Jim, I assume that you have not routinely had your seedlings virus tested.

Since you probably eliminate seedlings on the basic of vigor, mildew resistance, etc., you may have been eliminating the sickly virused few without realizing it. During most of the time that you kept any virused seedlings, in your temperature zone, obvious symptoms probably would not have been visible; and the pollen spread by bees (outside) to your other plants would of probably been clean plus of course there would of been no bee spread in your greenhouse. So, your lack of concern is probably applicable to “your” situation. The problem is that to recommend a similar action to someone without knowing their zone may not be the best advice for their conditions.

Perhaps our names should include our zones?

“Judith Singer: 9b”

Henry, your points are well taken. I did read your above referenced article. Clearly this issue (of virus transmission through pollen in roses) is not settled. Have you tried the experiment that you suggested in your last paragraph? I would be very interested in the results.

Rose breeding is lots of fun. It is the best hobby, in my opinion that anyone could take up. I will continue to encourage others to enjoy the hobby with the least amount of fuss as possible.

Rare events are rare events. I suspect that the estimated 1 to 2% transmission is an overestimation. Your experiment will help to shed more light on this question.

Fred, I stand by my earlier advice to you, “I would make crosses with free abandon, and without regard for the presence of those pathogens.”


Jim Sproul

Concerning whether I will undertake a virus transmission research project. I am retired. My hybridizing program and grandchildren are taking up all of the time that I have available. The Garden Rose Council is sponsoring research at U.C. Davis on the causes of observed RMV spread.

This is what the U.C. Davis rose virus cleaning document stated in November 2002 ( ):

“The Garden Rose Council (GRC) is a non-profit organization whose members account for more than 95 percent of U.S. garden rose production. The GRC mission is to support agricultural research and issues that will further the production of disease resistant roses in an environmentally sensitive manner. GRC support and funding has enabled FPMS to plant the new rose collection and improve the level of virus testing, and it supports research at FPMS on rose mosaic virus transmission and development of shoot tip culture methods for rose virus elimination.”

Are they still pursuing this investigation? As of 2004, yes. The following link gives the “Research Projects Funded for 2004”.

“Transmission of Rose Mosaic Viruses (continuing) Deborah A. Golino University of California, Davis; Plant Pathology Department Amount awarded: $12,500”


A preliminary report was given at a local rose society meeting:


Of particular interest is that the members reported: "The work was funded by an association of commercial rose producers, who were puzzled to find low (1 - 2%) but consistent emergence of virused plants in their supposedly clean blocks. "

Note the use of “low (1-2%) but consistent”.

Henry, this is a very fascinating area of research. And I say that sincerely. I’ve had the opportunity to attend a couple of the GRC meetings, including one where various RMV’s were discussed.

I think that the reference to “supposedly clean blocks” was made in a discussion of varieties that had been heat treated. They were surprised to see virus infected plants showing up again after they had been indexed at Davis. The 1 to 2% is not referring to the percentage of infected seed that one can expect from using pollen from a virus infected plant.

Also, the use of “low” in the article was a word selection made by the author. I would suggest that 1 to 2% is unacceptably high. I am sure that most commercial rose growers would be (were) disturbed by that high rate. But again, this is in reference to previously thought to be virus indexed clean stock, having nothing to do with seedlings.

Jim Sproul

Jim, interesting. Malcomn Manners made the following public statement concerning this point(see link below).

My literature search on the returning to cleaned stock is given at:

I would like to point out that the “meeting report” from Davis was not on virus returning to clean stock but about observed spread when using shears. Also, the All American Rose Grower who initially contacted me was interested because he found virus in his new seedlings and the British published study found 1 % infection in 2 batches of new seedlings (by a relatively insensitive method).

Perhaps you can use your membership in the GRC to get them to issue formal “progress reports” on their sponsored research.


I will attept to explain what I have interpreted as happening when a plant is exposed to a virus. Does everyone exposed to a cold virus get a cold - no. Years ago it was taught that plants did not have immune systems. That is not the case today - this link leads to an layman type article in this field:

I have a relative that got a virus from a lung transplant. It was explained that she was probably exposed to that virus many times but was able to fight it off. However, having a complete diseased lung provided more of the virus than the body could defend against. If you bud a modern rose to a virused understock, probably 100 % of the resulting plants will be virused. If an insect delivers a small amount of infected pollen or sap to a healthy rose will it be able to fight off the infection? We cannot answer that in advance; but it now appears that we can tell which roses have fought off a virus attack. As detection methods increased in sensitivity, it became possible to determine that the cells in some roses ( 17 % of the 160 roses tested) contain double stranded RNA particles (dsRNA)with molecular weights of about 1 megadalton. The particles are transmitted through both the ovules (100 %) and pollen (76 %). (Reference, Mary Kathryn Handley, PH.D. thesis, 1986, University of California, Davis, under the direction of Professor George Nyland.) At the time of the Thesis the meaning of the findings was not known.

It now appears that these may be footprints of previous viral infections. For example:

Authors: Kalai, M.; Van Loo, G.; Vanden Berghe, T.; Meeus, A.; Burm, W.; Saelens, X.; Vandenabeele, P.

Authors’ Address K.L. Ledeganckstraat 35, B-9000, Ghent, BelgiumK.L. Ledeganckstraat 35, B-9000, Ghent, Belgium

Title: Tipping the balance between necrosis and apoptosis in human and murine cells treated with interferon and dsRNA.

Published in: Cell Death and Differentiation, volumn 9, pages 981-994, (2002).

Abstract: “Interferons enhance the cellular antiviral response by inducing expression of protective proteins. Many of these proteins are activated by dsRNA, a typical by-product of viral infection. Here we…”

The following 2 very recent papers describe where the field is and where it expects to go in the near future. The first is the paper most applicable to explaining why all roses do not get infected (" This mechanism is conceived as a natural antiviral defense system in plants that is activated as a response to double-stranded RNA (dsRNA) formed during virus replication. ").

Title: RNA interference as a new biotechnological tool for the control of virus diseases in plants

Authors: Tenllado, Francisco; Llave, Cesar; Diaz-Ruiz, Jose Rarnn

Authors affiliation: Ctr Invest BiolDept Biol Plantas, CSIC, Ramiro Maeztu 9, Madrid, 28040, Spain.

Published in: Virus Research, volumn 102, pages 85-96, (June 2004).

Abstract: “RNA silencing occurs in a wide variety of organisms, including protozoa, fungi, plants and animals and involves recognition of a target RNA and initiation of a sequence-specific RNA degradation pathway in the cytoplasm. In the last few years, there have been considerable advances in our understanding of post-transcriptional gene silencing (PTGS). This mechanism is conceived as a natural antiviral defense system in plants that is activated as a response to double-stranded RNA (dsRNA) formed during virus replication. To develop new approaches for plant protection against virus diseases based on PTGS we have expanded previous findings on RNA interference (RNAi) in animals by Using dsRNA to specifically interfere with virus infection in plants. This approach differs from strategies based on transgenic expression of RNAs but still relies on PTGS as a means to achieve pathogen-derived resistance (PDR). Our findings suggest that exogenously supplied dsRNA could form the basis for the development of an environmentally safe. new biotechnological tool aimed at protecting crops against virus diseases. provided that some limitations of the current status of the approach Could be overcome.”

Title: RNA interference and mRNA silencing, 2004: How far will they reach?

Author: Pederson, Thoru

Author affiliation: Department of Biochemistry and Molecular Pharmacology and Program in Cell Dynamics, Medical School, University of Massachusetts, Worcester, MA, 01605, USA.

Published in: Molecular Biology of the Cell, volumn 15, pages 407-410, (2004).

Abstract: “The discoveries of RNA interference and RNA-mediated posttranscriptional gene silencing have opened an unanticipated new window on the regulation of gene expression as well as a facile and highly effective tool for knocking down gene expression in many organisms and cells. In addition, RNA interference and RNA silencing may conceivably be exploited for human therapeutics sometime in the future, possibly bringing greater clinical impact than have the so far disappointing antisense endeavors. This essay summarizes recent developments and offers some personalized perspectives, with emphasis on what we do not yet know.”


May I offer a suggestion? These technical posts would be much more user friendly to most of us if you could summarize them at the end with your own take on the information. The technical writing style is not easy to absorb and since it is often bulky, it discourages many of us from reading it at all, myself included. As I say, just a suggestion you might want to consider, thanks.


Good idea, Paul. It’s been 25 years since I left grad school and I wasn’t familiar with gene silencing. You can Google it and come up with a gaggle of articles. Interesting!

Thanks for all the advice. It is really nice to have this pool of informed members to turn to when in doubt about something. By the way I am in the Miami area USDA zone 11.