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TEMPERATURE EFFECTS ON VIRUS BEHAVIOR This page gives the information that I have collected from my own literature searches and from others posting on the internet. Please let me know if you feel anything is not clear or is not addressed at all as I am continually updating/modifying it as I get feedback. Bold print in quotes does not mean that the bold print appeared in the original; the bold print was added by me (H. Kuska) for emphasis. Information in pink indicates that a link is present for further information. Rose virus symptoms appear mainly in the spring and late fall. How does the scientific literature explain this? The following 4 papers discuss various aspects of this question. (The PNRSV literature will be mainly used as it it a common rose virus in the US.) PAPER 1)PNRSV infections in Peach have been reported to vary with the season (i.e. temperature). The following is the abstract of the published, refereed paper (please, keep in mind the reversal of our seasons with theirs). I have added bold print to indicate important sections. Their results are consistent with the casual observations that many have made that, in many roses, the symptoms are observable in the spring but disappear in the summer. This paper has been cited by 10 more recent papers according to Google Scholar.
END OF ABSTRACT Now, the question is: does PNRSV in roses have the same temperature behavior? Fortunately paper 2 appeared the next year. ------------------------------------------------------------------ Paper 2) This 2000 PNRSV in Roses published research paper by Moury et. al. is available free at the following web link: http://apsjournals.apsnet.org/doi/pdfplus/10.1094/PHYTO.2000.90.5.522 This paper has been cited by 15 more recent papers according to Google Scholar" Among other things, they studied the PNRSV Elisa readings on the hybrid tea rose Anna as a function of time of year. On December 8, 1998. The ratio of the absorbance of the infected leaves and the absorbance of the leaves of a healthy plant were (see Table 4, page 526) - 4.7 Same test on February 3, 1999 - ratio 7.8 Same test on March 31, 1999 - ratio 3.8 Same test on May 10, 1999 - ratio 18.9 Same test on July 15, 1999 - ratio 3.7 Same test on September 1, 1999 - all samples were ELISA negative - they could not detect the virus! Table 3, page 525 gives the percent of positive leaf samples
for the same 6 times. They are: 33.3%, 50.0%, 53.3%, 65.6%, 22.7%, and
0.0 %. (A less dramatic seasonal dependence (in a cooler climate) was reported by a later study in Poland. For your convenience: The average high temperature for Warsaw, Poland is 73.4 F June, 75.2 F July, and 73.4 F August.) Thus, the amount (concentration) of PNRSV in roses decreases as the temperature increases (and in at least one case, until it can no longer be detected). The obvious next question is: why would the virus concentration decrease with temperature? --------------------------------------------------- PAPER 3) The following study appears to be the critical study for explaining why plant virus infections have high concentration at lower temperatures but are attenuated at higher temperature. This 2003 paper has been already cited by 209 more recent papers (according to Google Scholar). The abstract contains the following: "Therefore, in cold, plants become more susceptible to viruses,.....". The Introduction contains the following: "Plant-virus 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 plant-virus interactions through the regulation of RNA silencing." (page 633 and 634)) In the Conclusion section (page 638), they state: 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). Here is a link that might be useful: Link to full paper ---------------------------------------------------------------------------- Paper 4) In addition to lower concentration with higher temperature papers, there is a published US study that reports that Tobacco Ringspot Virus (another of the viruses that together are called "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. 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 is familiar with Buck's crosses), and R.E. Ford Published in Phytopathology, volume 61, pages 45- 49, (1971). The back issues on the internet only go back to 1973 so I cannot give a computer link. I would expect that the "probability of infection of a rose" 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. ----------------------------------------------------------------------------------------- Summary Contrary to early "thinking" plants do have what could be called an immune system (natural defenses), it appears that we may have a combination of 2 interdependent effects as the temperature increases: 1) the plant's natural defenses are better able to overcome the virus as the temperature increases so the concentration of virus is decreased (or possibly even eliminated in the above ground parts of the rose in which certain types of spread could occur - use of pruners, branches touching, pollen spread by insects, seed transfer), and 2) the inherent infectivity of the virus may be weakened. -------------------------------------------------------------------------- Other points of interest Is this behavior limited to PNRSV? A 2005 paper ( that cited Paper 1) studied Apple Mosaic Virus (ApMV) in hazelnuts. (ApMV is one of the viruses grouped under the term Rose Mosaic Virus when found in roses). Of particular interest is the following quote (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 field of RNA silencing has advanced rapidly. The following link is to a paper that applies mathematics to the observed leaf infection patterns: http://www.biomedcentral.com/1752-0509/2/105 .The title is: "RNA silencing can explain chlorotic infection patterns on plant leaves" ------------------------------------------------------------- One of the easiest ways to catch up in a new (to the reader) field is to read recent Ph.D. Theses 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 will download a 2005 thesis titled:"Antiviral RNA silencing and viral counter defense in plants" I should warn you that it is a long download and took me 4 or 5 tries as my server kept timing out. The thesis also discusses why when a plant is infected by more than one virus the effect is more than the simple additive effect expected. Over the years there have been some comments in rose forums that people have observed that behavior. One example is at: http://www.uk.gardenweb.com/forums/load/roses/msg071057108109.html?16 "When you get severe virus symptoms more than one virus is found from analysis. Most virus strains are not obvious and little debilitating if alone. Combined they are very much deleterious." ---------------------------------------------------- The concept of cold weather affecting rose mosaic was around even before I started my literature search. The following is a 1988 document from the University of Illinois:http://web.aces.uiuc.edu/vista/pdf_pubs/632.pdf The following quotes are of particular interest (to me): "Usually, the higher temperatures and drier conditions of summer inhibit virus or virus like activity in the plant. As a result, rose plants that had symptoms of infection in the spring commonly resume normal or near-normal growth in summer. With a return of cooler temperatures in autumn, symptoms often reappear, depending on the variety of rose, the strain of the virus or other agent, and environmental conditions." AND "Studies show, however, that the concentration of the virus varies and that the virus is usually not uniformly distributed within the plant." ------------------------------------------------------------------ The behavior of the Rose Mosaic Virus "group" with temperature also appears in other State University type fact sheets: "Cool temperatures tend to favor virus multiplication and disease development within the rose plant.", see the University Of Arkansas fact sheet. AND The University Of Illinois has a web page about rose viruses: http://hyg.ipm.illinois.edu/pastpest/200113f.html Of particular interest is the following: "The heat of summer inhibits virus activity." -------------------------------------------------------------- The following recently posted University of California Cooperative Extension article recommends the following precautions against above ground spread: A University of California Davis -Ventura County link on rose Virus"In the meantime, you need to remember that viruses can be transmitted by pruning and cutting shears. Virus-infected plants should be pruned last and/or have their flowers harvested last. To be extra cautious, wipe your cutting shears with alcohol (rubbing alcohol is good) or a 10 percent bleach solution between plants." (In case you are not familiar with the Cooperative Extension program, the following was stated: "Extension is the other part of our name, Extension, indicates what we do. We extend research-based information from the University of California, other universities, and federal agencies, as well as our own local applied research." ---------------------------------------------------------------------------------------------------------------------------------------------- Other related links:
Go to Can North American rose hybridizers safely use pollen from PNRSV infected roses? Go to When was rose mosaic virus first observed? Go to Comments about rose mosaic virus returning to heat treated plants Go to Information
about Rose Rosette Disease (virus)
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