That is interesting, Henry! Thank you! This is something I often wondered about at Sequoia. In the summer, those greenhouses were frequently 120 degrees F with 100% humidity. A number of their weaker older roses were grown in pots in hot greenhouses to push them to grow, and often were the source of propagating material for the variety. I wondered how possible it was that the new, soft cuttings of those plants grown in such heat and rooted under mist in the same heat, to be either cleaned of virus, or at least with reduced viral load. When you're dealing with a nearly extinct variety and all there is, is that one, weak plant, you use what you have. Ironically, the cutting grown plants of I. Zingari grew much better than the old plant of it at Rose Hills where all the material came from. Kim

There are a number of viruses that affect roses. Also, often there are different strains of each virus. Plus a rose can be infected by more than one virus. PNRSV which is considered by some/many as the most common rose virus in the U.S. is a temperature sensitive virus (its effects are more severe in lower temperature climates). This is explained by the rose's immune system being better able to fight the virus at high temperature. But remember there are more and less "strong" strains of even this one virus, PNRSV.

Taoseeker stated: "It would be interesting to compare a few old varieties with the heat treated ones." I am not sure if you are refering to what what I think you are. If you are interested in whether a virused but then heat treated plant does better or worse than one of the same variety that was never virused, this is my response. Plants are very complex, it is possible that the virus and / or the heat treatment may have affected other mechanisms (could be positive or negative). There are many types of examples but since a very recent (2009) example of the "expression of heat stress proteins" has been studied in a rose, I will present that example. The actual research paper is very technical. The paper is at the following link: http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=6203748 Rather than looking at the specific details most readers would probably benefit more from the following summary of the field: http://www.cspp.cn/Annual2009/upload/pub09.pdf Please notice the statement: "It is known that rapid heat hardening can be elicited by a brief exposure of cells to sub-lethal high temperature, which in turn provides protection from subsequent and more severe temperature." This does not "prove" that heat treated roses will have better heat resistance. Maybe a longer term of high temperature will result in other effects (positive or negative). I am presenting this to indicate that one cannot assume that other variables are being held constant. It is possible that effects may not show up till years later. Some "cured" polio victims are now finding that many years later problems related to the polio are appearing. -------------------------- The effects of a virus infection can be very unexpected. The following link discusses the observed effect of a virus on aphid population (not done on roses): http://www.springerlink.com/content/uw13564v21223876/ I have posted several times about my experince with a virused Culbert Grant from Pickering. Up to then my best Climber was Illusion. This new Culbert Grant bloomed and grew much better than Illusion all summer. I was very excited. That winter I received a letter from Pickering that it was virused and that they were pulling it off the market. That spring it was dead. Scientists at Cornell University surveyed approximately 2500 roses by visible assessment. They found that 166 had virus symptons: http://www.actahort.org/books/234/234_53.htm From the abstract, it does not appear that anything unusual was observed, but from the full paper a number of unexpected results were reported such as: "Total flower cut weight and total number of flower cuts with nonsymptomatic foliage was greater from PNRSV (severe) inoculated rose plants than from healthy control plants. The data revealed also that PNRSV (severe) and ApMV (severe) inoculated plants outyielded the PNRSV (mild) inoculated plants, which in turn outyielded the healthy tissue inoculated plants. These results were unexpected since reduced yields would be anticipated from virus infections." They then discuss some "maybes. one of these is: "Another speculation is that the initial stage of viral infection stimulates host metabolism by competing and utilizing the host ribonucleic acid polymerases for ita viral replication." i.e. The virus infection may be causing the rose to grow better. ----------------------------------------------- The following non rose paper may be of interest: http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=6203748 Explanation of the sympols: (VT) I assume that (VT) means heat treated since I found this using heat treatment as a key work. The abstract is not clear. (My literature search service says the full paper can be down loaded but when I try it states that it is too new and has not been uploaded yet.) (V) is virused infected. (VTR) is virused reinfected. Just to highlight one of the observations: "V plants produced big tubers that weighed more than those from VT plants."

The University of California, Davis plant virus group has been one of the active groups involved in rose virus detection and cleaning. A new technique called Next Generation Sequencing has recently appeared. The following paper by the Davis plant virus group compares the new method with the old. See: http://apsjournals.apsnet.org/doi/abs/10.1094/PHYTO-06-14-0165-R ---------------------------------------------------------------------- H.Kuska comment: The latest tool for virus identification seems to be next generation sequencing. The research paper below reports finding PNRSV in wild multiflora by what they call "deep sequencing".. "A bizarre virus-like symptom of a leaf rosette formed by dense small leaves on branches of wild roses (Rosa multiflora Thunb.), designated as ‘wild rose leaf rosette disease’ (WRLRD), was observed in China." "The assembly of siRNAs led to the reconstruction of the complete genomes of three known viruses, namely Apple stem grooving virus (ASGV), Blackberry chlorotic ringspot virus (BCRV) and Prunus necrotic ringspot virus (PNRSV), and of a novel virus provisionally named ‘rose leaf rosette-associated virus’ (RLRaV)." http://onlinelibrary.wiley.com/doi/10.1 ... ated=false H. Kuska comment: Although they call their procedure "Deep sequencing" it appears to be similar to "next generation sequencing" see below. ---------------------------------------------------------------------- - In the U.S. Professor Tzanetakis (whose research group was the first to identify Rose Rosette Virus) has recently published a paper on next generation sequencing. Title: "Development of a virus detection and discovery pipeline using next generation sequencing." Authors : Thien Ho , Ioannis E. Tzanetakis "The pipeline was used to process more than 30 samples resulting in the detection of all viruses known to infect the processed samples, the extension of the genomic sequences of others, and the discovery of several novel viruses. VirFind was tested by four external users with datasets from plants or insects, demonstrating its potential as a universal virus detection and discovery tool." http://www.sciencedirect.com/science/ar ... 2214004437