what is the significance of "widespread in roses affected by RRD"? It's just there? Makes RRD worse? Causes???

Can you find out more?

At first reading it appears to be a cofactor, i.e. it makes it easier for an RRV virus to take hold. For some reason the plant immune system seems to be less effective when more than one virus is present.

"In single infections BCRV induces mild symptoms in tea rose and is asymptomatic in blackberry (14) but may, as reported for other ilarviruses, act synergistically to cause severe disease or exacerbate disease symptoms."

And later:

"Although BCRV does not cause detrimental symptoms in single infections in the species tested (14), its presence in plants with raspberry mosaic and blackberry yellow vein diseases (15, 23), suggests that BCRV may be one of the contributing factors for disease development."
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There is a recent 2011 rose mosaic virus spread meeting abstract that appears to be saying that root to root transfer only occured when 2 viruses were present.

"All plants that became infected were potted with ApMV + PNRSV plants. Rose mosaic symptoms were observed only in plants with ApMV + PNRSV."

H.Kuska comment. The full paper for the above abstract has not yet appeared. It will be interesting to see their explanation for the observed results. My "guess" is that the presence of the 2 viruses "broke down" the newly infected plants immune system.

Here is a link that might be useful: link to 2011 abstract

Henry,
There are some plant pathologists who disagree with the concept of plant immune systems.

How would you interpret these papers if the plants had no immune systems but rather were just genetically limited?

Ann, can you give me some recent references to articles in which one or more plant pathologists disagree with the concept of plant immune systems. 30 years ago it was the norm to accept that plants did not have immune systems,

Here is a 2013 conference on the subject:

http://www.keystonesymposia.org/13D5

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H.Kuska comment: Genetically limited with respect to a plant virus would be (I assume) similar to the American Indians having no specific immune system defence against certain specific European viruses. i.e. It would be possible for a plant to have no immune system response to a specific virus, but to still have immune system responses responses against most viruses.

Here is a link that might be useful: link to 2013 conference

The following is from the discussion section of a published research paper:
Title: Co-infection of Soybean with Soybean mosaic virus and Alfalfa mosaic virus Results in Disease Synergism and Alteration in Accumulation Level of Both Viruses

by M. Malapi-Nelson, R.-H. Wen, B. H. Ownley, and M. R. Hajimorad, Department of Entomology and Plant Pathology, The University of Tennessee, Knoxville, TN 37996

Published in: Plant Disease / December 2009, pages 1259-1264)

"The underlying mechanisms of synergistic interaction of AMV with SMV and antagonistic interaction of SMV with AMV in soybean remain to be understood. Suppression of gene silencing activity of HC-Pro has been implicated as the underlying mechanism of synergism mediated by potyviruses (1,23,25,32). It is likely that a similar mechanism operates in the case of synergistic interaction between AMV and SMV. No suppression of gene silencing activity has been reported in the case of AMV (28), and this may account for symptom remission associated with AMV infection. Comparison of the level of accumulation of small interfering RNAs (SiRNA) (12) in plants infected with AMV alone with those of plants co-infected with SMV can reveal this possibility."

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H.Kuska comment. Although the words "immune system" do not appear, when they talk about "interfering RNAs" they are talking about the immune system.

Here is a link that might be useful: link to full paper cited above

Science can move rapidly. The abstract below was presented at the 2012 Petria -22nd International Conference on Virus and other transmissible diseases of Fruit Crops. Now that it is recognized that plants have an immune system against viruses (RNA Silencing) a logical next step is to use genetic engineering to add more RNA silencing molecular sequences. In the abstract below please note that they recognize that both low temperature and mixed virus infections can decrease the effectiveness of the plants natural immune system:
"Since it’s known that some abiotic - low temperature - and biotic stresses - mixed viral infection - could have a detrimental impact on RNA silencing-mediated viral resistances,"

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Title: Robust and Wide Spectrum RNA SIlencIng Mediated Resistance TO PLUM POX VIRUS

Authors: E. Di Nicola-negri(1), M. Tavazza(2), V. Ilardi(1)
(1)Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Centro di Ricerca per la Patologia Vegetale, Rome, Italy;
(2)ENEA CR Casaccia, Via Anguillarese, 301, 00123 Rome, Italy

Published in: Petria, Vol. 22 (3), 2012, 123-459,

Abstract:
"Plum pox virus (PPV) is a quarantine virus that causes sharka, one of the most important diseases of stone fruits worldwide. Seven PPV strains have been characterized, of which PPV-D, -M and Rec are the most important from an agroeconomical point of view. The best agricultural sustainable approach to prevent sharka disease consists in developing PPV-resistant plants. In this context we have
shown that Nicotiana benthamiana plants transformed with PPV-M sequences (PPVIsPaVe44), covering the 5’UTR region, P1 and HC-Pro genes and arranged to express self-complementary ‘hairpin’ RNAs, are immune to the homologous PPV-ISPaVe44. However, as the RNA silencing-mediated resistance operates in a sequence-specific fashion, transgenic plants harboring the four hairpin constructs were also challenged with viral isolates belonging to different PPV strains. All the transgenic plant lines were resistant to PPV-D, ��"M and Recc strains. Moreover, the transgenic plant line harboring the 5’ UTR/P1 sequence was also resistant to isolates of PPV-EA and PPV-C strains that are distantly related to ISPaVe44. Since it’s known that some abiotic - low temperature - and biotic stresses - mixed viral infection - could have a detrimental impact on RNA silencing-mediated viral resistances, 5’ UTR/P1 plants were challenged with PPV under different conditions. Transgenic plants were resistant to PPV infection both at high (30°C) and low temperature (15°C). Furthermore, no susceptibility to PPV-Was observed in 5’UTR/P1 plants previously inoculated with Potato virus Y (PVY), Cucumber mosaic virus (CMV) or Artichoke mottled crinkle virus (AMCV) suggesting that prior virus-mediated expression of HCPro (PVY), 2b (CMV) and P19 (AMCV) RNA silencing suppressors was not able to defeat PPV resistance. The overall data suggest that the 5’ UTR/P1 hairpin construct can be profitably used to confer resistance to the sharka disease in Prunus species."

The above is taken from a 338 page PDF document that gives the abstracts and/or full papers that were presented at that Conference.

Here is a link that might be useful: Link to 338 page PDF document (long download)

A very recent (October 2013) example of scientists utilizing gene silencing to lessen the effect of "a devastating synergistic disease complex" of multiple viruses.

From abstract: "Multiple infections of Sweet potato feathery mottle virus (SPFMV), Sweet potato chlorotic stunt virus (SPCSV), Sweet potato virus G (SPVG) and Sweet potato mild mottle virus (SPMMV) cause a devastating synergistic disease complex of sweet potato (Ipomoea batatas Lam.) in KwaZulu-Natal, South Africa. In order to address the problem of multiple virus infections and synergism, this study aimed to develop transgenic sweet potato (cv. Blesbok) plants with broad virus resistance. Coat protein gene segments of SPFMV, SPCSV, SPVG and SPMMV were used to induce gene silencing in transgenic sweet potato."

http://link.springer.com/article/10.1007/s11248-013-9759-7

Please note that gene silencing does not cure the plant, it only "Further analyses showed virus presence in the transgenic plants but all exhibited delayed and milder symptoms of leaf discoloration as compared with the untransformed plants."

Here is a link that might be useful: October 2013 link for above

I feel that one of the important contributions that we can make to the successful careers{{gwi:807}} of our children, grandchildren, nieces, nephews, etc. is to interest them in careers that will benefit society. Unfortunately, high school counselors are rarely "up" on the frontiers of science. With the assumption that you have instilled an interest in gardening, I recommend that you build on that by discussing/ guiding them to articles as to where plant science is "going" during their professional lifetimes. One "ripe" area is to improve the immune systems of food plants.
Perhaps this very recent review will be useful:

"In the battle between diseases and plants -- constant, changing and centuries old -- scientists and farmers usually arm themselves through classical breeding, crossing varieties in the hopes of eventually reaching disease resistance. With advances in DNA sequencing and genetics, however, they may soon have a more sophisticated weapon: disease-resistant seeds.

Basic research on the genetic gears of plant immune systems has advanced so much that scientists can now begin applying that knowledge, building healthier plants to decrease dependence on pesticides, water overuse and help agriculture in developing countries, according to a paper in this week's edition of the journal Science."

The full paper is at:
16 AUGUST 2013 VOL 341 SCIENCE www.sciencemag.org
(Subscription only)

Here is a link that might be useful: link for above

This post was edited by henry_kuska on Fri, Nov 22, 13 at 1:11