I do not want to leave the impression that findings of natural transmission of rose viruses is something new.

Tobacco streak ilarvirus was found by R. H. Converse and A. B. Bartlett naturally infecting roses in the U.S. (in 4 locations). They published a paper in Plant Disease Reporter, volumn 63, pages 441-444, (1979). They studied 21 wild rose plants from 17 Oregon, U.S.A. locations. 5 plants out of the 20 that were tested by agar-gel diffusion (1 plant was not tested) were found to have tobacco streak virus (often the "ilar" is dropped). The positive testing plants came from 4 of the 17 sites (2 positive out of 2 tested from one site; 1 out of 1 tested from another site; 1 out of 3 from another; and 1 out of 1 from another)."

The following is what appeared in a Google Scientific search:

"Occurrence of viruses in some wild Rubus and Rosa species in Oregon
RH Converse, AB Bartlett - Plant Disease Reporter (USA), 1979 - fao.org
... Personal Authors, Converse, RH; Bartlett, AB. Publication Date, (Jun 1979). AGRIS
Subj. ... Availability number, 7919311. Serial Title, Plant Disease Reporter (USA). ...
Cited by 10 - Related articles - Cached - Web Search - Library Search"

As you can see, it has been cited by 10 studies during the years that Google has abstracts for.
----------------------------------------
Another related point, some feel that viruses were not found in roses until the 1920s when grafting started.

See the link below:

Michaelg, in an earlier post you described the differences between your virused Elina and another Elina from Pickering in your garden that had never showed virus symptons(both mature plants, growing nearly side-by-side). Can you update that post?

Henry,

One Elina shows the watermark-type virus pattern every spring and occasionally later. It is on Dr. Huey and is 8-10 years old. The other, on multiflora, has never shown visible symptoms. It is two years younger, but became the larger plant probably in its second year and is now much bigger. It blooms, I'd say, three times as much.

The plants are about 12' apart in about the same sun but are in different soil, the symptomatic plant in heavier silt loam where some Dr. Huey plants have done well. Both plants have severe winter damage every year, but the symptomatic plant slightly moreso.

The symptomatic plant hasn't declined much (yet), but it hasn't improved with age either. It performs OK for the spot it's in, where there wouldn't be room for the Big Momma. The latter would grow from 3" stumps to 8' x 5' in a season except I take 12-18" deadheads later on.

My soil is pH 6.7 and seems fine for Dr. Huey.

It appears to me that the most extensive work on virus spread has to do with hops.

A full 2000 paper by Pethybridge et.al can be read in the link below. Note that they feel that "plant intertwining" is a contributer.

In a 2005 paper they changed the virus name from PNRSV to the closely related Apple Mosaic virus (ApMV). The abstract of this paper is at http://www.cababstractsplus.org/abstracts/Abstract.aspx?AcNo=20053143821

I have the full 2005 paper. Of interest is their efficiency of virus spread contributions (Table 4, page 141):

Pruning using scalpel blades contaminated after pruning virus-infected plants - 11%

Pruning using scalpel blades contaminated by dipping scalpel blades in inoculum -35%

Shoot contact simulated by fan - 60%

Shoot contact simulated by agitation - 23%

Root contact - 0%

Root grafting - 20%

----------------------------------------

Based on this investigation I feel that shoot contact (branches of nearby roses rubbing against each other) should be investigated. Of course, because I feel that PNRSV is a temperature sensitive virus, I feel that a northern University would provide the most unambigious results.

If Dr. Malcolm Manners issues a clear and concise statement about his knowledge on the subject of viruses in roses, I will take that to be the truth.

I feel that it is a matter of experience outweighing the virtues of sitting down and scouring the Web for any paper that might possibly support speculations on the spread of assorted viruses in woody plants, roses or otherwise. Dr. Manner is the authority on viruses in roses and for all practical purposes, it is his knowledge that should be viewed as the most constructive in guiding the average rose gardener through this touchy subject.

Paul Barden

Dr. Manners is the authority on viruses in roses

*** ABSOLUTELY!

Jeri

Concerning the Barden and Jennings comments. The following are links to what they are telling the general public concerning Rose Mosaic Virus:
http://www.goldcoastrose.org/shared/rosevirus.htm
http://paulbardenroses.com/main_december2002.html
Please compare the information presented with the information that I have presented in this thread.
In particular note: the statements about not hearing of any confirmed cases of natural root graft. On Paul Barden's page please also see the addendum link on the bottom.
Of course one could reply: ah they said "confirmed", no other research centers have duplicated the work. My reply would be that these web pages were written for the general public who in all probability would miss this distinction and assume that no scientific research on this topic had been done (reported) or in Paul's case that the work given in his addendum was all there was to it.
Is it possible that they were not aware of this research? On January 3, 2006 Ann Peck started a thread titled "Root to Root grafting as a source of rose virus transmission" which referred to the U. of California, Davis research. There were a number of follow up comments.
Since then, although I am not going to take the time to count the postings; I feel that the existence of this research has been discussed sufficiently in a number of forums so that anyone who has a web page on the subject should have been familiar with it and revised their information accordingly. i.e. Is it too much to expect that people who feel that there is a need to post accurate information about virus in roses (see Paul's statement at the beginning of his page on viruses in roses: "What rosarians need is factual information") would not keep their information reasonably up to date?
-----------------------------
To summarize the Davis information:
500 Rosa multiflora "Burr"plants were planted approximately 30 cm (11.8 inches) apart in rows (the distance between the rows was not given). Alternate plants were graft inoculated with 5 virus sources. Half were hedged with a gas-powered hedge trimmer four to six times during the growing season. In one year virus was detected in 10% of both the hedged and unhedged plants. After the second year, the number was 17 %; after the third year it was 31 %.

It is my opinion that Dr. Malcolm Manners has presented factual information that can be taken as current and truthful, and it is this information that I regard as the most relevant to discussion such as this one. The root grafting issue is not new and Dr. Manners and UC Davis have discussed the root grafting experiments and both have concluded that this factor does not represent a threat to the average rose grower under normal circumstances.

This is the last comment I will issue on this matter.

Respectfully,
Paul B.

I'm with Paul.
And may I add that I am very grateful for the time Dr. Manners spends (and will likely spend in the future) steering a clear path through all of this information.

Jeri

I find the use of the words "average rose grower" and "normal circumstances" interesting in the justification(if that was their intention?) for what was posted in Paul's, and Jeri's web sites.
I wonder what cooler temperature studies they used as the basis for the inclusion of those areas of the country (if they intended that normal circumstances included cooler areas than where they did their own studies.

I have received a communication (10/16/2007) from Deborah Golino that Davis had an experiment that was underway for 2 years (at that time) but had 1 or 2 more years to go concerning root-to-root grafting. She told me that I would be informed as to how the experiment turns out.

I suggest that the reader read the comments of the first author in Paul's addendum. Then please read the comment about that information at this site:
http://groups.google.com/group/rec.gardens.roses/msg/149feb9699983308?q=g:thl1339858437d&dq=&hl=en&lr=&ie=UTF-8&safe=off

I have investigated the "situation" concerning the 2 statements and prepared a web page on my findings:

http://home.roadrunner.com/~kuska/discussion_of_whether_virus_have.htm

If you look at the beginning of the thread you will see that I stated; "This virus is a temperature sensitive virus. In southern climates the risk of transmission is probably small as the virus will probably be mainly in the roots for much of the season. In Northern Virgina I would have some concern about spread."

Since then I have documented that there is published research that the detected PNRSV virus concentration in roses is season dependent (and even could not be detected in any of the leaves on September 1 in a 2000 well known study) and that similar variations of PNRSV in peach have been attributed to the temperature "This drop coincides with an increase in summer temperature and attenuates foliation symptoms caused by PNRSV."

In addition to lower concentration papers, there is a published U.S study that reports that Tobacco Ringspot Virus (see my post above about what viruses are part of the collective name "Rose Mosaic Virus") from infected Iowa roses has a temperature dependence to its ability to infect indicator plants. They do not present their data in a table but instead use a continuous line graph with dots indicating their actual data points(their Figure 5a). The graph is a smooth curve with 9 data points located right on the line (no obvious scatter to the fitted line). To convert their small graph into number results in approximate values - these are my approximations:

At 75.2 degrees F - leasons per leaf, about 161.
At 82.4 degrees F - leasons per leaf, about 158.
At 89.6 degrees F - leasons per leaf, about 152.
At 96.8 degrees F - leasons per leaf, about 148.
At 104 degrees F - leasons per leaf, about 141.

Please note this is not a concentration effect as the same collected sap was used ("For TIP studies, 0.2 ml of undiluted sap were placed in thin-walled test tubes (15 X 30 mm), heated 10 min, cooled immediately, and assayed on five cowpea plants." and that this amount of effect was noted after only 10 minutes at the stated temperature exposure. The graph continues until no lesions were observed at slightly less than 147 degrees F.

One could say: but there is only a 2 % decrease in infectivity from 75 deg to 97 degrees is this within experimental error?. My reply is that this observed effect is from a smooth fitted curve with the data points on the curve. To me the interesting question is: if that much infectivity was lost after only 10 minutes exposure, how much would be lost after time periods of hours/days/weeks?

They also studied the longevity of infectibility in vitro and obtained a smooth curve which went to zero at 72 hours (the study was done at a temperature of 77 degrees F). These results are complicated by their use of a mixture (1:2 sap/0.01 M phosphate buffer).

The article is:

Title: Isolation of Tobacco Ringspot Virus from Rose

Authors: G.L McDaniel, G. J. Buck (I assume that almost everyone on this forum is familar with Buck's croses), and R.E. Ford

Published in Phytopathology, volumn 61, pages 45- 49, (1971).

From my training, I would expect that the probability of infection of a rose occurring would depend on both the concentration of the virus in the sap AND on the infectivity of the sap due to the temperature that it was exposed to.

I've known Dr. Manners for a few years now, and I trust, completely, everything he has to say about roses. He has worked many, many long hours researching the rose virus problem, and it is because of his devotion to addressing the problem that I now own several wonderful, beautiful, virus free roses.

Sandy

I am assuming-and perhaps wrongly- that root to root grafting is most likely to happen when all the roses(or what ever)are identical clones as appears to be the case in this study-I assume this was done to increase the odds of root grafting and that what is meant by ordinary garden conditions is that you are unlikely to have closely planted rows of virused and unvirused clones of the same rose which is why this is not normally a problem in an ordinary garden? It would be prudent to remove a virused Hansa in a closely planted hedge of Hansa but it would not be as much of a threat in a mixed Rugosa hedge. Am I thinking correctly here?

patricia

Patrica, the other tests utilized 470 multiflora plants, 148 plants of Dr. Huey, and 98 plants of Sunflare. The multiflora and Dr. Huey were planted approximately 11.8 inches apart (it was not clear to me if they were mixed in the same row or in different rows). The Sunflare plants were planted 3.3 feet apart in rows. Roundup was applied to every other plant. The treated plants all died. About 50% of the multiflora plants showed roundup symptoms. 10 % of the Dr. Huey and 10% of the Sunflare plants showed symptoms.

I have warned that this may not be meaningful as the assumption that the roundup would not leave the treated plant, pass through the soil, and then be absorbed by the neighboring plant is not supported by recent research. See my 2007 post:

http://www.rosehybridizers.org/forum/message.php?topid=13673#13673

In 2007 I informed Deborah Golino of this problem.

Patricia, based on Dr. Manner's research, as well as that of UC Davis, you would not have to worry at all. I've removed roses that have tested positive for Rose Mosaic, but only because I am so fussy about how my roses look and perform for me. I was never worried about virus transmission. I am not a gardener that sterilizes my pruners between rose bushes that I am working on. My virus indexed roses didn't catch virus from roses that later showed to be infected. I like heritage roses, and there are many that have not been cleaned up yet. If you read Dr. Manner's posts above, you will see that you would not have to worry about a hedge.

I have also had Elisa testing done on virused roses at various times of the year here. Outside temperatures had absolutely no bearing on how my roses tested. We get below freezing here several times during the winter in North Central Florida, and we can get above 100 degrees in the summer. The rest of the year we have all sorts of variant temperatures. I have never had any of that influence a test result.

I'd hate to see people panic and start yanking roses out that are still giving them pleasure, virused or not.

Sandy

I recieved an answer from Dr Manners himself. I was not worried just wondering-enquiring minds...but thank you Sandy. I thought it might be like self grafting if all the plants are genetically identical but it turns out some plants are simply more likely to root graft than others- for instance there is a variety of Citrus that will root graft to any kind of Citrus around. I have two roses I know to have RMV(in a family of 600+)and I haven't done anything about them. It was interesting to me that my Mme Alfred Carrier which is virused suffered freeze damage in our recent Challanging winter and the one that is not virused had no damage at all(and it in a pot no less). I wont draw too much in the way of conclusions from one set of plants though. Interesting topic.

patricia

Patricia, virused roses definitely are weaker. I've seen that myself many times when infected roses just can't handle the Florida environmental stresses. But...I sure don't do as well whenever I have a virus either, like a cold or the flu. I always try to get virus free roses if I can, although I'm sure some of my old teas and such are infected and I just don't know it yet.

You're right, it is an interesting topic.

Wow, 600 roses! How do you keep up with all of them? If I'm fortunate enough to buy some land in the near future, I may wake up some morning and realize that I have 600 roses too.

Sandy

The only rose I have that I'm sure is virused (because it shows signs occasionally) is my climbing iceberg, which I got as a body bag from Home Depot. But except for it's black spot tendencies (which I think is an iceberg trait) it's fine. I rarely suffers frost damage and doesn't lose blooms like most of my roses did this freeze and the one in 2007. This year, for the first time in awhile, I do see some yellow patterns in the lower leaves. But the rose itself is fine. I am guessing that the cold wet weather we've been having is causing it to show the signs.

Another of the viruses that is part of the term Rose Mosaic virus is Apple Mosaic Virus (ApMV). This virus is also a temperature sensitive virus (not all viruses are). The link below is to a full paper concerning ApMV in Hazelnut. The reason for selecting it is because of their discussion of the temperature dependence, see page 157:

'ApMV, the member of ilarvirus group, is a labile virus, concentration of which can be negatively affected
by high temperatures (Matthews 1991, Zotto and Nome 1999), and whose disease symptoms are masked at such temperatures (Aramburu and Rovira 1998).'

The pictures (Figure 2, page 158) of infected leaves are also interesting (especially C).

Michaelg: I think it may have to do with our summer nights being so cool (and by our, I mean my particular little spot). Our warmest nights of the year are only somewhere in the 50s, and even the hottest part of the summer the nights still drop down to the low 50s, often the upper 40s. I know up around Asheville you have much cooler nights than the rest of the south (I seriously considered living up there just for that reason!), but unless you're up really high, are you as cool at night as we are?

Or maybe, the Elinas we have are just crappy ones.

--Ron

Ron, according to the weather.com monthly averages, your summer nights are definitely cooler, but summer days are the same. It's interesting that nighttime temperatures would make that much difference. But as Henry has been pointing out, RMV is more active in cool weather, so that could be a factor with yours. My symptomatic Elina is off to a very poor start this extra-cool spring, while the asymptomatic one is jumping out of the ground.

Of historical interest:

http://www.nature.com/icb/journal/v8/n2/pdf/icb19319a.pdf

Once again the title came through different?

The title for my last post should have been Rose Wilt - virus-like disease of unknown aetiology

I may have used brackets or quotes, maybe that is why the title was cut off.

Henry, give it a rest, please. We need Dr. Manners to stop by now and then.

Dr. Manner's has 2 web pages concerning RMV, see:

http://www.ars.org/About_Roses/disease_mosaic_virus.html

http://www.ars.org/About_Roses/disease_mosaic_effects.html

He used to have some at another site, but I cannot find then now.

Dr. Kuska
http://home.roadrunner.com/~kuska/

Hi Michael,

It's quite possible that the virus is more active or more destructive in cooler weather, and that's why our plants are such dogs (no offense to dogs out there!). I do like the flowers, so maybe I'll try to find a clean one to try sometime. In a way, I'm glad this thread came up, I've never seen anyone else's Elina, just heard about them (and then only about the flowers), so I had no idea it was ever a vigorous plant.

--Ron

Ron, Heirloom likely has a clean stock plant since they are careful about virus. They describe Elina as vigorous, but I don't know what the climate is like there.

The problem with Heirloom, in this respect, is that they have tended to take the fact of importation from England as proof of freedom from virus.
As I learned, from their plants, that is not necessarily so.

I'd ask, before ordering, if the stock was TESTED virus-free.

Jeri

I agree with Jeri. I would only take it as fact if they can testify that their stock of 'Elina' tested virus free.

If you have to purchase an Elina on a rootstock that may not be optimal for your area, try planting the plant on a angle with the bud line several inches below the ground. The rose can then decide whether it likes the understock roots or its own roots. The angle should be such that both areas of the plant are in the rooting zone.

Ron, I believe I have clean Elina. I got it (as a cutting )from a friend 7-8 years ago. It never showed any signs of virus. It ss very vigorous and blooms a lot. My friend send sample of his mother plant for testing 3 years ago and it can negative. His plant was own root and he doesn't remember from what nursery.
Ron, I can send you cuttings. Just send me e-mail with your address if you are interested.
Olga

Olga, will Elina live no spray in this area or does it require spraying please? I will tolerate defoliation as long as that does not kill it over winter.(I am assuming you are all talking about the HT).

Elina here will loose ~70-80% its leaves if grown no spray, but keeps blooming and doesn't have a lot of winter dieback.
If sprayed, it grows into 8x7 feet monster with ton of blooms. Very bushy, nice looking plant, no bare legs at all(when sprayed :)). The only thing I don't like about her is that thrips LOVE her. So first spring flush is usually destroyed by them.
Olga

Elina is one of the most blackspot-resistant HTs. Only 70-80% defoliation sounds about right for here as well.

I'm amazed that a rose can be described as "Blackspot resistant" when it is expected that it will lose 80% of its foliage to the disease! No wonder novices complain that growing roses is hard.

The blackspot resistant statement has to be taken in context. "one of the most blackspot-resistant HTs". "HT" is critical to the meaning.

Also, one has to consider the area of the poster. In "some" areas 70-80% may be unacceptable. The statement is clearly a relative statement to other hybrid teas in that area.

The only rose I have grown that consistently loses 70-80% of it's leaves to blackspot in a low blackspot pressure area is soleil d' or ... I classify it as a disaster rose

Relative or not, I consider a rose that loses 70% to 80% of its foliage as anything but "disease resistant.

Paul, in saying "only," I was sort of joking about HTs and about blackspot conditions in my area. But 'Elina' actually is the most resistant HT I have grown. I suspect it could be a no-spray rose in, say, Oklahoma. Here, when I tried not spraying, it was fine through the first flush but eventually lost 3/4 of the leaves. This is similar to how 'Old Blush' performs in Appalachia without fungicide.

There is no point to a rose that can not maintain it's leaves. I am always polite when I visit warm zone gardens and see canes and blooms but minimal leaves ... but lets face it a rose growing with blooms on sticks with no leaves to speak of is not worth a plugged nickel ... almost silly as these northern hardy azaleas. If my roses have no leaves it means they never made it through winter and are dead. In the end I take short, blooms and lots of leaves ... personal tastes I suspect.

Riku, I am with you on this. I don't like half naked (not to talk about fully naked)bushes. This is the main reason I mostly switched to oncebloomers. Repeat bloomers here in most cases require spraying or they will be half naked as the best case scenario. I tryied many roses based on peoples recommentaion that they can be grown no spray. But, as I learned, in many cases it means only that rose survives and blooms, but looses significant amount of its leaves. I want leaves too, otherwise it is not resistant and not a no spray in my opinion.
There are only a handful of repeater that qualify here for "no-spray/keeps leaves" category and I tried hundreds different roses, old and modern.
Olga

michaelg, are your 2 Elinas the same in blackspot resistance?

I think they are about the same in blackspot resistance. I normally spray with sulfur. I only tried not spraying once.

I see on another thread Kate in Kansas recommending Elina as a no-spray rose for that area.

When I said she only defoliates 70% in my climate, this is opposed to other HTs defoliating two or three times over.

There once was another link to the following manuscript that now appears on the ARS website: http://www.ars.org/About_Roses/disease_mosaic_effects.html

A major difference (to me) is that the old paper stated that the sample size was 10 clean plants.

In designing an experiment one normally calculates the number of samples required to obtain a result (in this case detection of diseased plants due to spread) so that the results of the experiment have a stated confidence level (95% is the common confidence level for non critical occurances). The link below takes you to an equation to use for "Detection of the presence of a disease (outbreak investigations, herd diagnosis, and certification of freedom from pathogens)". Please note, I have reported another set of statistical calculations in a previous thread. Those calculations gave higher number of plants required than the equations in this post. The earlier equation was useful for determing the experimental value of the % spread. The present equation determines the number required to detect the presence of a disease.

The equation is n=(log (1-C))/(log(1-P))

C is the Confidence Level desired (normally .95 is utilized) and P is the proporation of the sample that have the condition of interest (in our case 0.01 to detect 1% spread).

To detect this low rate of spread (1%), 298 plants would be required.

If the rate of spread was 4%, 74 plants would be needed to observe any presence of disease.

If the rate of spread was 10%, 28 plants would be required.

If the rate of spread was 30%, 8 plants would be needed.

If we make the assumption that studying 10 plants for 3 years is the same as studying 30 plants for one year, we see that this experiment was suitable for detecting any virus spread if the rate of spread was around 10% or higher.

Of course it does not address what the affect of temperature would be on similar experiments if done in cooler climates.

----------------------

In summary:

Thus, my interpretation of this paper regarding spread is that in the temperature conditions of Florida this experiment is ruling out rates of spread of about 10% or higher (with a 95% confidence level).

The following study appears to be the critical study for explaining why plant virus infections are observable at lower temperatures but are attenuated at higher temperature. This 2003 paper has been already cited by 131 more recent papers (according to Google Scholar).

--------------------------------------------------
The abstract is probably too technical for the average rose grower, but the introduction contains the following that may get the main point across better:

"Plantvirus interactions are strongly modified by environmental factors; especially by temperature. High temperature is frequently associated with attenuated symptoms (heat masking) and with low virus content of virus-infected plants (Johnson, 1922; Hull, 2002). In contrast, rapid spread of virus diseases and the development of severe symptoms are frequently associated with cold air temperature (Hine et al., 1970; Gerik et al., 1990). Harrison (1956) has speculated that the virus content of a plant represents an equilibrium between replication and degradation and that the activity of the virus degrading system increases with temperature. However, the underlying molecular mechanisms of these effects of temperature are still missing. We hypothesized that RNA silencing might be the postulated virus degradation system and temperature modifies plantvirus interactions through the regulation of RNA silencing." (page 633 and 634))

In the Conclusion section (page 638), they state:
"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 that statements in a reviewed published scientific paper have to be approved by the editor based on the comments of the manuscript provided to him/her by the reviewers (normally at least 3).

"A 5-acre garden on the University of California at Davis campus holds 400 of the most commercially important rose varieties. Researchers are maintaining these plants as samples that are tested and shown to be disease free. Some rose varieties can carry rose mosaic virus without showing symptoms. In the past, some rose stock has even failed to show disease symptoms in the temperate California climate, but has later shown rose mosaic symptoms after being shipped to the eastern United States.

"We do a bio assay of these plants by grafting a bud onto an indicator variety and growing it for two years to make sure symptoms do not show up," says Mike Cunningham, rose program manager at Foundation Plant Services. Cunningham made his remarks to rose experts from around the world as they toured highlights of California's floriculture industry following the recent Fourth International Symposium on Rose Research and Cultivation held in Santa Barbara, California, United States."

Title: Tracking three ilarviruses in stone fruit trees throughout the year by ELISA and tissue-printing hybridization.

Authors: Matic, S; Sanchez-Navarro, JA; Mandic, B; Myrta, A; and Pallas, V.

Published in: JOURNAL OF PLANT PATHOLOGY, volumn 90 (1), pages 137-141, (2008).

Abstract: "The presence of Prunus necrotic ringspot virus (PNRSV), Prune dwarf virus (PDV) and Apple mosaic virus (ApMV) was monitored throughout 2005 in stone fruit trees by ELISA and tissue printing hybridization. The highest detection rate for all three viruses was obtained in winter with both techniques. Detection was reliable also in spring and early summer, except for ApMV. However, neither technique was able to identify successfully all infected samples in one season. Overall, ELISA was more successful for PNRSV and PDV detection and tissue-printing hybridization for ApMV."

The following 2008 thread from Australia discusses the temperature dependence of rose virus. The message order is latest on top, oldest on bottom.

http://roseexchange.biz/roseexchange/discus/messages/2/10563.html?1219547808

Another link to a full paper in the reviewed scientific literature:

http://www.apsnet.org/phyto/PDFS/1978/Phyto68n07_1005.PDF

The following statement was made in this thread on April 29, 2009: "It has been demonstrated by natural root grafting at UC Davis, but then only on rootstock plants just a few inches from each other, in the nursery row, and then only on mutiflora."

In 2007 Golino et.al. at U.C. Davis published a paper on this subject. The abstract is at: http://www.actahort.org/books/751/751_26.htm

In the full paper, the following is stated (page 29-30): "Field Spread in Scion Cultivars
To test further for the occurrence of virus spread trials were conducted on over 300 plants each of three scion cultivars, Double Delight, Iceberg, and Queen
Elizabeth. Rooted cuttings were planted approximately 30 cm apart in rows in the field, grown for one year and alternate plants were graft-inoculated as described above with one of three virus accessions: 1) ROS98.36, 2) ROS98.27, and 3) ROS70.7, which were 1) a source of PNRSV that caused bright yellow chlorosis in the spring; 2) a source of ApMV, and 3) a source of a naturally-occurring mixed infection of ApMV and PNRSV, respectively. Plants were pruned yearly using shears that were cleaned between each plant by dipping in 10% bleach solution. Bushes were observed for symptoms periodically and ELISA tested for PNRSV and ApMV in the spring for two years. All non-inoculated plants that tested positive were re-sampled and tested to confirm the result."

In the conclusion section (page 221) the following was stated: "In scion varieties, transmission rates two years postinoculation ranged from 0 to 25% depending on virus and cultivar. Queen Elizabeth had the lowest percent infection of all the varieties at an average 5% for all three viruses; Iceberg had the highest for a scion cultivar at 13% average for the viruses (Table 4).
These differences correlate with the cultivars relative root vigor. It is possible that a larger, more vigorous root system would increase the chance of forming a root graft with an adjacent plant. R. multiflora has a more vigorous root system than all three scion cultivars tested and within the scions, Iceberg is more vigorous than Queen Elizabeth and Double Delight."
--------------------------------

I do not understand why someone would make the April 29 statement. Especially since on April 30, 2009 the same writer states: "If one actually looks up Golino's paper in Acta Horticulturae......."

-----------------------------------

Please also note that not all types of mechanical transmission were ruled out in the 2007 paper since the observed rate of spread was higher in the unpruned bushes than in the pruned bushes. In another PNRSV infected plant, hops, this is attributed, in part, to the branches of neighboring plants rubbing against each other. Golino et.al. acknowledge this as they state (page 220-221): "The possibility remains that spread occurred by mechanical transmission due to contact between the leaves of the closely spaced plants and experiments are underway to test that putative mechanism of spread."