Pink Queen Elizabeth

General Discussion
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21

Hi Rob,

While I have no scientific studies to site, I have been particularly interested in RMV, and in the constellation of other viruses that mark up the foliage especially from an esthetic standpoint - I hate the way it looks and especially hate the thought of any of my own seedlings becoming contaminated. This is the main reason that early on in my rose breeding career, I decided to breed for an improved rootstock for my own use.

I was especially motivated to do this when several years ago, I discovered that some of my seedlings that were being evaluated by a grower were showing classic RMV changes. This was happening in a test block that was supposed to have been planted with virus indexed rootstock from UC Davis. When I questioned the person in charge of field production, he said that they had “mixed in” some of their own rootstock material because they didn’t have enough V.I. material. Needless to say, I stopped working with that company.

A few observations:

  1. Though it is true that older roses from the last century and many purchased roses may have virus, there are very few newly purchased roses from the more reputable companies that still have the classic RMV markings on them. I just do not see it. While it is true that RMV can go dormant (no outward appearances), it doesn’t go away year after year. From my observations these new roses from reputable companies do not have the classic RMV from years past.

  2. It is possible, however, that heat treatment has resulted in the existence of an attenuated RMV strain that may not produce outward signs in the foliage. This would be similar to the development of attenuated viruses that are used in live vaccines for humans. This is only conjecture on my part, but may explain why virus is still being detected in V.I. plants. If that is the case, then for practical purposes, the virus is not present - in the sense that it is not causing disease. The foliage is normal, so photosynthesis would not be impacted, and therefore vigor should also not be affected.

  3. I have used two obviously RMV infected roses in my breeding program: ‘Geisha’ and ‘Silverado’. Never have I seen the classic RMV markings in any of the resulting seedlings whether they were used as seed or pollen parents, though theoretically it should be possible. In fact, I have never seen RMV changes in any of my seedlings - not one (theoretically other parent plants purchased from commercial growers should/could be infected).

  4. Mini roses propagated exclusively through cuttings do not exhibit RMV changes - I have never seen it in this situation.

I share all of this to hopefully reduce the concern that you run a very high risk of producing virus infected seedlings. For those who may wish to argue this point, I am talking about RMV type viruses (and others that mark up the foliage). If you are careful to avoid grafting to non-seedling rootstock and your “possibly” infected parent plants are either grown in pots or if in the ground, away from your seedlings (to avoid root to root grafting), your risk is negligible.

Jim Sproul

22

I’d love to know what would happen if federal law forbid the sale of any virused plants within American borders.

I actually find it alarming that some of the body bag producers knowlingly sell the worst of the worst in terms of virus, and they do it at such a high volume that reaches anyone and their dog. I am guessing pride and grace dont work there, LOL.

I once interviewed for a very large wholesale company that I am not going to name =p They sold organic product as well. I inquired about their personal process and the female manager went on this extremely long, irate tangent about how much she hates the people that buy organic products. She then furthered her tangent on about how much she hates liberals while she used slurs against various culture groups. I was like x_X so… “My girlfriend has fibromyalgia so I grow her organic strawberry plants in containers every year. I like Seascape but she perfers Tribute.” I am not sure if the lady got the hint and I obvioulsy chose not to work there. I should have been more blunt and told her to go take human resource classes, lol. The point of the story is, though, is that these wholesalers that sell en masse tend to take on their own microculture. All they often begin to know is their isolated world of their perimeters of the company, the logistics within the company and whatever locale is near. Everything becomes about sell, sell, sell, sell on an articifical schedule within this little bubble of false reality that requires those working in it to forget themselves and the rest of the world. It seems so easy to forget right from wrong, as well as how various groups relate out and about. This lady is not exactly unique, although I was secretly curious as to which moron out in the world married her, haha. I was imagining some sniveling, passive-aggressive dunce.

I also wonder what would happen if big box stores were educated on how aesthetically displeasing virus is, and that it reflects directly on their image in terms of product quality. Even if a rose does not degenerate from a virus, a rose in and of itself is a product of aesthetic need or want. That is the nature of ornamental horticulture. So that basically means that these various people, that handle the product in some form of fashion, are selling faulty products. Regardless of any science or probability, it is wrong, especially without stated awareness of what someone is buying.

The obvious problem source is economic. ie. the value of the rose industry is far less than other indsutries, so less attention is paid towards it. I also always wondered if those that could help change the practice of wholesaling out random virus strains to Everywhere, USA is never questioned by someone such as the ARS is because no one wants to highlight a product known for aesthetic beauty as possibly… ugly.

I also wondered what would happen if the practice of body bag roses, as well as selling body bag type roses in a 2G full of sawdust and sand (seriously… what smuck thought of this?) force-grown in SW USA sun and then sold everywhere, ceased. The nice thing about the huge surge of KO/Flower Carpet sales in big box stores is the model for 8", 1G, 2G, 3G and 5G own-root plants. As much as I think grafting is an art that should not be forgotten, I am not sure that it has been helpful towards the success of the rose in our current world, except for maybe soils with nematodes.

lol maybe people should just be told to treat every rose just like every person – they may or may not have an STD, haha. Or is that asexually transmitted disease (ATD)? =/

23

Thank you for the link Henry. It’s much appreciated.

Jim,

Thanks for sharing your observations. My concern about my seedlings is less having read your posting. Thank you. I like your point about heat treatment and attenuated viruses. I was curious now, since it’s possible to selectively breed for black spot resistant varieties would it also be possible to selectively breed for RMV, or other viruses for that matter, resistant varieties so that grafting would not be as much of an issue? Or, are viruses a whole different ball game than the fungi?

24

Jim Sproul is in zone 9. Because of the temperature dependence of the immune system, his uninfected plants probably have very little chance of catching/substaining an infection (through above ground routes). I say “catching” because in the warmer summer months the above ground virus concentrations in his infected plants will be very low (or even zero in individual branches). I say “substaining” because even if a healthy bush picked up some virus in the cooler months, when the hot weather appeared the immune system should/may be able to overpower the virus. If this happens before some of the virus reached the shelter of the below ground parts of the plant, the plant may once again be virus free.

I have repeatably suggested that rose virus spread be studied in cooler climates.

25

Thank you Henry. This explains why I haven’t seen virus symptoms for years.

26

Hi Rob,

The attenuated virus idea would have to be tested. I just thought of it as a way to explain Kim’s observations. I do not see why it would not be possible, theoretically, to breed for virus resistant roses, however, it would probably be very expensive and a different kind of animal than breeding for roses with resistance/tolerance to fungal diseases!

Hi Henry,

Though I live in zone 9, nearly all of my observations of virus infected plants have been in this same zone - includes all of the older roses of the last century that I’ve observed around town with intense “ringspots” and bold “lightning flashes” across their foliage. Also the infected plants grown for evaluation noted above were in this same zone.

Though extreme heat might explain a non-sustained infection in a seed parent inoculated with virus infected pollen, it does not explain how seedlings coming from seeds harvested from virus infected plants are protected. The seeds are generally harvested when the weather has already begun to cool.

I should mention too, that the majority of my crosses are done while the weather is cool, during a time when extreme heat should not be a factor.

Please don’t get me wrong, I am in the camp of those who believe that there are many and varied rose viruses floating around. Several times on various threads I have stated my belief that stripes in roses are the result of either a virus or virus-like particle. What I am reporting and commenting on in this thread about RMV and other viruses that mark up the foliage, is that there has been a distinct and noticeable reduction in any evidence of their presence in the newer roses coming from reputable companies. Virus attenuation might be one explanation.

My second point is that while it is theoretically possible to transmit the RMV type viruses through pollen, it has rarely been reported, and I have never seen it. It is something that I wouldn’t worry too much about when doing rose breeding.

It would be interesting to hear the frequency of transmission of RMV type viral infections that you or others have observed via presumed pollen or root to root grafting.

Jim Sproul

27

Is this behavior equal among all species. Rosa rugosa, for example, is largely not grafted (cept like Grootendorsts and others) so it is not exactly an excellent guide but I had wondered if various rose families behaved differently, or were even resilient (ie. lower infection rate). I chose Rosa rugosa as an example because its both semi-polar and temperate, as well as from a different family than most, which means it shares an entirely different climate and history. Google images did not show anything with virus + rosa rugosa but that does not mean anything.

It is stated that some crop cultivar plant types have resistances to various viruses but I am unsure if that even translates to roses, especially since it is both new and non-native to them. However, I really do not know if various rose species throughout history ever had viruses without the aid of man – or not.

I think the idea of viruses in roses has a lot of unanswered questions. I am guessing it is because it is both a socially uncomfortable and anti-economic topic.

28

The following was stated: “Though extreme heat might explain a non-sustained infection in a seed parent inoculated with virus infected pollen, it does not explain how seedlings coming from seeds harvested from virus infected plants are protected. The seeds are generally harvested when the weather has already begun to cool.”

H.Kuska reply. Do you see virus symptoms in the Fall on the hip containing branches when the hips were harvested? If not, why are you assuming that the virus has returned to the above ground parts of the plant in sufficient numbers to overload the immune system in your climate?

One of the possible routes of spread that U. California Davis investigated for their 2007 paper is seed transmission.

The abstract is at: TRANSMISSION OF ROSE MOSAIC VIRUSES

They did not find any. Yet a famous hybridizer in Oregon, and 2 different scientists in England did find virused seedlings (in England it was in 2 different batches of multiflora and also in rugosa). What was different between these situations?

One obvious one is temperature. Has anything been published about whether temperature could be an important variable?

The following is from the 1994 review:

Title: SEED TRANSMISSION OF VIRUSES: Current Perspectives

Published in: Annu. Rev. Phytopathol. 1994. volumn 32, pages 363-386.

Authors:

Elisabeth Johansen, Danish Institute of Plant and Soil Science, 2800 Lyngby, Denmark

Michael C. Edwards, US Department of Agriculture, Agricultural Research Service, Northern Crop Science Laboratory, Fargo, North Dakota 58105-5677

Richard O. Hampton, US Department of Agriculture, Agricultural Research Service, Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331

The following is a quote from page 374 of the full review:

"The effect of temperature on seed transmission is well-documented (32, 49, 112). In alfalfa, rates of seed transmission were higher when plants were grown at 18

29

Regarding the idea that heat treated infected roses resulted in the formation of attenuated virus and that was what was being observed.

Of course, an attenuated virus could of resulted from fragment recombination; but a more severe virus could of also resulted. I would expect both extremes to be rare. Apparently the reoccurance of virus symptoms was rather frequent. One does not have to reach for such an improbable multiple occurance to explain what was observed. There are now many studies that have shown that the use of indicator plants and/or ELSIA resulted in a number of plants (usually in the 10% range) being declared clean that were actually still infected. The link below is one example. (The complete paper is available free.)

The next link is to a a paper that compares biological indexing, ELISA, and PCR for the detection of PNRSV in begonia after using heat indexing and chemotherapy on tissue cultured regenerated plants.

The full paper on page 242 states:

‘In biological indexing, i.e. local lesions on C. tetragonolba, only plants with strong signal in DAS-ELISA gave positive results.’ H.Kuska comment: in this case biological indexing was less sensitive then ELISA.

Please notice that the abstract reports that the new method, PCR, found that some (see percentages in the abstract) of the plants that ELISA reported as clean were actually infected.

The indexing method used when these historical problems (with rose viruses returning to heat treated stock) were encountered was first biological indexing and later biological indexing AND ELISA (both tests on each plant). From personal communication one of the major laboratories shifted to PCR testing several years ago.

Link: www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TC3-4CXMV4X-1&_user=10&_coverDate=01%2F01%2F2005&_rdoc=11&_fmt=high&_orig=browse&_srch=doc-info(%23toc%235159%232005%23998969997%23556186%23FLA%23display%23Volume)&_cdi=5159&_sort=d&_docanchor=&_c

30

Henry,

Regarding the rose growers that found virus in their seedlings, what virus did they think that they saw, and what were the symptoms? What was the relative prevalence of virus among their seedlings? Was it very common? Did they see the problem repeatedly? What did they do to eliminate the problem, or do they have to deal with it every year? Did those seedlings exhibit dwarfing like the fruit trees mentioned in your post?

Since roses are not the usual host for RMV, one might expect that transmission to roses is not very efficient. When looking back it seems that there was a definite point in time when RMV type viruses began to infect roses. This coincides with the time when risky grafting procedures were employed. It has been widely suggested as mentioned above that the index case occurred when someone attempted to graft material from an infected fruit tree onto a rose. Prior to that, I am unaware of any instances where biting insects or mites were capable of transmitting RMV type viruses to roses. For that matter, I am unaware of any instance where bees or other pollinators carried infected fruit tree pollen to roses that resulted in infections, and though perhaps less likely, I have never heard of root to root transmission of RMV type viruses from fruit trees to roses. If those other modalities were possible, RMV type viruses would have long ago been established in roses.

With the exception of direct grafting of infected tissue to uninflected roses, transmission of RMV type viruses appears to be very inefficient and rare. This would not be unexpected for roses since they are not the usual hosts for RMV type viruses.

Back to the question of dwarfing as a possible reason that virus infected seedlings aren’t being seen among rose seedlings because they are being culled early for nonvigor. I wouldn’t expect that dwarfing would be a uniform problem. I would expect some variability with some infected seedlings growing very well.

An observation that would support this expectation was my finding that RMV infected ‘Silverado’ cuttings rooted very well and had very good vigor. There is also excellent evidence of infected ‘Dr. Huey’ growing vigorously from cuttings.

Most observations about the effects of RMV type viruses on rose growth have been more subtle: perhaps lower flower production and subtle decreases in vigor. I don’t think that I am culling virus infected seedlings due to a dwarfing effect.

You asked about what evidence of RMV existed on the stems bearing hips from which seeds were extracted and planted. I don’t recall anything other than the effects that were present in the Spring. Absence of symptoms does not mean absence of virus in apparently clean sections of stems. I don’t think that the virus completely withdraws to underground structures during the heat of Summer. Cuttings taken from plants during the heat of Summer continue to carry the infection.

Grafting in Wasco, CA continues 1 to 2 months beyond my pollinations. If our heat is a factor in killing RMV type viruses in infected pollen, I wonder why heat wouldn’t be capable of eliminating virus from buds that are grafted high up for tree roses when grafting is done during a hotter part of the growing season.

I do not see RMV type viruses being much of a threat if one follows the suggestions that I have made above in my earlier post. It appears that the predominant, and perhaps only efficient way to transmit RMV type viruses to roses is through direct grafting of infected tissues onto uninflected roses. The exceptions appear to be quite rare.

Jim Sproul

31

The following was stated: “Since roses are not the usual host for RMV, one might expect that transmission to roses is not very efficient. When looking back it seems that there was a definite point in time when RMV type viruses began to infect roses. This coincides with the time when risky grafting procedures were employed. It has been widely suggested as mentioned above that the index case occurred when someone attempted to graft material from an infected fruit tree onto a rose. Prior to that, I am unaware of any instances where biting insects or mites were capable of transmitting RMV type viruses to roses. For that matter, I am unaware of any instance where bees or other pollinators carried infected fruit tree pollen to roses that resulted in infections, and though perhaps less likely, I have never heard of root to root transmission of RMV type viruses from fruit trees to roses. If those other modalities were possible, RMV type viruses would have long ago been established in roses.”

H.Kuska reply.

In addition to what I linked to earlier in this thread, maybe this will help convince the reader that PNRSV from roses did NOT have to only reach roses by transfer from other plants due to rose bud/other plant human experimentation as was “postulated” (apparently after the early literature was missed). Remember it even was found in wild roses.

There is evidence that the rose versions of PNRSV have measurable differences from the other plants’ PNRSV. (i.e. is not the same as PNRSV from many/most/all other plants.)

The following quote comes from the introduction of the recent paper whose link is:

http://www.up.poznan.pl/ptfit/pdf/PP40a/PP40_31-41.pdf

“Generally, received results have indicated that apricot,peach,plum and rose isolates are serologically different from cherry isolates and all fruit tree isolates significantly differ from those from rose and hop plants.”

Please note: “all fruit tree isolates significantly differ from those from rose and hop plants.”

In that paper’s Conclusion section they state (from their research): “Results presented in Table 2 indicated rather that rose isolates of PNRSV belonged to CH-9 serotype although they may have possessed less antigenic fractions than PNRSV isolates from fruit trees.”

In the following paper

http://www.springerlink.com/content/61n6chy7f3thb68a/

all of the rose PNRSV viruses (code names: Ring 13, Ring 25, and Ring 26) were grouped in classification I(pv32) (“Shown is the evaluation of the nucleotide sequences as described in the text. Horizontal distances are proportional to the number of changes.”) with only a few others close - also note there were even small differences between the 3 rose isolates.

There have been a number of papers pointing out the various differences between PNRSV of roses and other plants (including which will and which will not infect other species) which I have not included here as the first introduction statement summarized them (“Generally, received results have indicated …”).

To condense a response to the other “points” made in the last post. Roses have an immune system (of course in hybrids, one rose could have a more efficient immune system than another rose). The immune system has been shown to be temperature dependent - it works better at high temperature. PNRSV (one of the viruses that collectively are called RMV has been studied extensively both in roses and in other plants. The same temperature dependence is found. Also PNRSV and other members of the RMV group have a number of strains with different strengths. At one extreme is the death of most of the ApMV infected roses in the fourth year of the Florida spread experiment. At the other extreme is the PNRSV infected rose Anna in a French experiment that was observed to be cleaned by simply taking cuttings in a hot summer month.

Yes, there are observations of a particular infected rose doing very well in a northern climate. Was this due to a better than average immune systen or a lower than average virus strength (or combination) one cannot say without doing a scientific study. There also have been many, many experiences of virused roses only living about 4 or 5 years in northern gardens. Why did some survive and many die?

In my first virus response in this thread I stated:

" In cool climates there would appear to be about a 2 per cent chance of virus transfer through seeds. See link below. In hot climates, probably no transfer.

http://home.roadrunner.com/~kuska/rose%20virus%20and%20pollen.htm"

Please notice the “In hot climates, probably no transfer.”

Concerning damaged seedlings. Even in the hot summers Davis experiment where they reported no seed spread they stated: “In seedling transmission tests, all of 651 seedlings from seven virus infected scion varieties ELISA tested negative for PNRSV and ApMV. Ten other seedlings had distorted strap leaves, were chlorotic and/or had other foliar abnormalities; the abnormalities were not typical of RMD symptoms. Most of these 10 plants died before they could be tested. Herbaceaous host tests using cucumber on three of these plants were negative for virus. We suspect that the odd appearance of these plants was due to genetic weakness rather than a result of virus infection.”

H. Kuska comment: A Herbaceaous host test is not considered a sensitive test. Since there was not a “blank” consisting of the same type of seedlings (but virus free), one cannot say if there was something else in their makeup that resulted in these weak seedlings. Also we do not know what percentage of seedlings would be weak or not even germinate in a cool climate situation where the virus would be more active.

To further look at the subject of whether a hybridizer can expect problems when using infected mothers or infected fathers, the following paper should be useful. This paper reports that seeds of apricot exhibit something like a hypersensitive response when attacked by PNRSV. This defense (to quote from the abstract) “would inactivate PNRSV during seed formation and/or the storage period or even during seed germination. Those results can explain the decrease in seed germination and the low transmission of PNRSV by seeds in apricot trees.”.

http://www.ingentaconnect.com/content/mksg/ppl/2007/00000131/00000002/art00013

32

Hi Henry,

In looking over the information that you have provided, I do not find compelling evidence that RMV type viruses are spread efficiently or to any important degree between roses by other than mechanical means through grafting. It seems that if there is transmission via pollen, the infected seedlings either die or do not develop. In any case, they do not appear to present the rose breeder any difficulty or concern (if they do in fact exist to any significant degree).

The examples cited of the discovery of virus infected seedlings by rose hybridizers do not indicate whether these were confirmed by ELISA or PCR. You do not seem critical of these reports, while you seem to criticize other experiments for lacking sufficient controls when RMV is not found.

What have your personal observations been regarding RMV? How often do you see it in your seedlings? What do you do to avoid producing RMV infected seedlings? How much do you worry about it?

From my observations, I am not concerned about RMV being an important problem to the rose breeder (except where mentioned - I do not advise grafting unique desirable seedlings to non-seedling rootstock).

Jim Sproul

33

One reason that more viruses do not get transferred from seedlings is that heavily virused plants don’t set seed as well. However I would expect more viruses to be transferred from seed or pollen parents. Maybe we just select seedlings that do not show signs of viruses but in reality they are virused.

This past year I bought Cornelia virused indexed but it has shown signs of being virused the whole year. Hopefully the seedlings come out well. I used it heavily as a seed parent. I only did a few crosses as a pollen parent only on females I had more than one plant of. Just using one of the plants just in case it did transfer viruses via the pollen.

This thread has been very interesting.

34

To me, trying to hybridize and having seedlings not develop or die is a problem worth trying to understand. Having roses die after about 5 years is a problem worth trying to understand. Having viruses return to heat treated roses is a problem worth trying to understand. Having reports of slow virus spread is a problem worth trying to understand. I have examined the literature in an attempt to see what is happening as the “common” printed explanations concerning rose virus behavior were not consistent with what scientific reading I had done and what others told me. The present knowledge is that roses have a temperature dependent immune system. I recommend cool climate research to see whether northern gardeners will have more/different virus problems than predicted by the up to now hot climate U.S. scientific studies (for example, since there was a scientific report of 2% infected seedlings, in a cooler climate, using the old low sensitivity methods, what percentage will be found with the new much more sensitive modern methods?

The viruses that infect roses also infect weeds and plants like Lilly and Begonia. Of course in hot climates we now understand that the immune system is doing a relatively good job protecting the roses so probably the southern rose gardener will not have to be concerned about these possible sources of virus infection. What about a northern rose gardener where the roses are not able to fight back to the same degree? I feel we need cool climate research.

See these links for weed examples:

35

This is so weird. My rheumatologist ordered some specialized version of the ELISA for me lol. I still havent coughed up the few hundred bucks for it though. Fun times… :slight_smile:

Henry,

Do you believe all rose species to be equal regarding how they mediate viral infections (or the possibility of). I am curious as to a lot of things. For example, I’d love to know if various species operate differently depending on the environment they are in. Also, I am curious as to which species possibly may have totally different variations in how the interact/react. It also makes me curious about the genus Rosa as a whole and how it is similar/different in the above regard to its close relations such as Fragaria, Potentilla, Mollis, Rubus, etc. The biggest factor for us human folk is obviously food production. 2 of the above are among the main sources of food types. I know some virus types can wipe out food crops. Potentilla would also be interesting /worthwhile since P. fruiticosa is one of the very few sources of reblooming color for both the cold and arid (extreme climate types) that is mass produced with ease. Most of them are labeled wrong because of both cultivar similarity and the sheer numbers reproduced asexually. Virus in something like that could easily spread like wildfire, and even possibly to its relations. In other words, I am curious as to how everything relates globally to roses and viral infections.

36

The question was asked: “Do you believe all rose species to be equal regarding how they mediate viral infections (or the possibility of).”

H.Kuska reply. The original published article Low temperature inhibits RNA silencing-mediated defence by the control of siRNA generation - PMC stated “We find that siRNA-mediated RNA silencing is temperature dependent in three dicot species, thus inefficient siRNA generation at low temperature is probably a universal feature of higher plants.”

Please note “probably a universal feature”.

Cornell researchers reported SYMPTOMATOLOGY AND OCCURRENCE OF APPLE MOSAIC AND PRUNUS NECROTIC RINGSPOT VIRUSES ON ROSE IN NEW YORK

that one of the roses, Nearly Wild, using their infection method did not become infected (I have put my virus literature in storage in preparation for a Florida move, so I cannot describe their method). Of course if you bud graft an infected rootstock to even that rose; it’s immune system will be overcome (infected commercial versions of that rose (probably budded) have been reported).

Also the rose Anna may have a better than normal immune system (or the PNRSV was weaker than normal). Moury et. al. http://apsjournals.apsnet.org/doi/abs/10.1094/PHYTO.2000.90.5.522

I “think” that I have read articles that claim to find other virus defence mechanisms that their particular studied plant had; but my old memory is not good enough to draw the information out of my head. I also think that I have read about groups trying to use gene splicing to increase a plant’s virus defense.

I feel that plants and their ability to fight off viruses is an interesting field. If one is interested, I suggest starting with a recent PhD. Thesis in the field. Each thesis normally has an historical section at the beginning which covers the pertinent literature with much more detail than is allowed in a published, reviewed paper. This link http://edepot.wur.nl/121792

will download a 2005 thesis titled:

“Antiviral RNA silencing and viral counter defense in plants” (you may also be able to reach it by putting the title, with quotes, into Google).

I should warn you that it is a long download and took me 4 or 5 tries as my server kept timing out.

37

Hi Henry,

Asking questions and seeking the answers are marks of a good scientist. I think that you have done an excellent job scouring the literature to find information to help answer the questions that you pose. I agree with you that it doesn’t all add up yet, that there are still unanswered questions, that the evidence is conflicting.

My purpose in this discussion is to encourage the enjoyment of rose breeding. I wouldn’t want new rose breeders to worry too much about RMV type viruses being an important factor in their new hobby. They haven’t been an important obstacle for me over the 20 years that I have been breeding roses (with the exception of my mentioning the instance where some of my seedlings were grafted onto virus infected rootstock by one of the commercial growers).

I understand that there may be different experiences among northern rose breeders, but even then, I suspect that the absolute effect of RMV type viruses on a breeding program would be small. You are right that the question has not been answered. It would be interesting to conduct controlled experiments to get a better handle on the degree to which the rose immune system is challenged by cooler climates, and whether there is a greater impact there with respect to RMV type viruses.

Jim Sproul

38

Yes, I join Jim in thanking you for sharing such a great breadth of information and research, Henry. While many questions do remain unsatisfied, many others now make a whole lot more sense. Thank you!

39

This information is not directly related to hybridizing but hopefully will be of some interest particularly in showing your children/nieces/nephews what kind of job opportunities will be available to individuals trained in the plant sciences. Soon after the plant immune ststem was understood, scientists found that viruses produced compounds to fight the plant’s defense molecules. This research report is one result of this increase in understanding.

Some quotes from the link below:

"For this study, Scholthof said, only one gene of the virus – called P19 – was used because it is the one that suppresses RNA silencing.

RNA silencing is a fairly recently discovered defense that plants use against viruses," he explained. "During this silencing, short strands of RNA serve as signals to alert the plant that a virus is attempting to infect so that all of its tissues start mobilizing to defend.

The elegance is that the P19 protein forms counter-defense units that are each composed of two protein molecules which form a sort of caliper to measure and capture signal molecules, thereby suppressing the defense to the virus which can infect a plant."

…

"Scholthof said the process of expressing foreign genes in plants is common in research, but there also is an important practical use.

It also is used in biotechnology to produce beneficial proteins for medical and veterinary applications," he noted. “By developing this new P19, we have ‘tamed’ a suppressor because it still works to suppress but does not induce severe disease symptoms in the plant.”

Link: www.physorg.com/news/2010-11-virus-component-gene.html