There was a 4 year Specialty Crop Research Initiative (SCRI) grant through the USDA that funded Rose Rosette Research. One of the things it funded was replicated field plantings. Thankfully we are one year in a new 4 year grant continuing the work (there were a few years in between these two grants without funding, unfortunately). Below is a link to the paper that came out in the journal Pathogens recently from the field plantings during the first grant. Roses like ‘Chuckles’, ‘Morden Blush’, and some others did not show symptoms and did not test positive for the virus in these multiyear trials where there was high RRD pressure. Roses that seem to have a good degree of resistance seem for the most part to be derived from the Cinnamomeae section members native to the US (Carolinae has been merged with Cinnamomeae) and also R. rugosa in that same section from Asia. It is great that ‘Chuckles’ has resistance too (strong dose of R. setigera- US Synstylae member). Hopefully the continued research on the virus, mite vector, and resistance mechanisms in these and other roses will help us better manage/control this destructive and generally lethal disease.
I honestly WANT to believe there may be actual “resistant”, perhaps even “immune” types, but with the serendipitous nature of wind spread, how can anyone be sure the mites just weren’t blown into those particular plants? Perhaps if they could be deliberately inoculated with the disease and THEN remain negative for it…
Actually, this study was designed to reduce (as far as possible) the chances of random landing/infection caused by the eriophyid mite vector; they used randomized block plantings with three replications each. Field resistance encompasses resistance to the vector and/or the virus, while deliberate inoculation would only involve resistance to the virus, even if the otherwise virus-susceptible rose might never become infected by the mite under natural conditions.
The resistance noted anecdotally relatively early on in the RRV “pandemic” among species of Sect. Rosa (formerly Sect. Cinnamomeae*) and R. setigera does seem to have held up pretty well under scientific scrutiny, at least in terms of field resistance. I have never seen RRD occur on R. setigera or any of its near hybrids, nor any of the Sect. Rosa species (or their close hybrids) that I’ve grown.
*Section Rosa, formerly Sect. Cinnamomeae–the type species of the genus has been designated as R. majalis [R. cinnamomea] after a proposal accepted at the 2005 International Botanical Congress in Vienna, and it follows under the international rules of nomenclature that the type section of the genus must bear the same name as the genus.
It would be pretty interesting to see a study conducted starting with a functionally female R. setigera being crossed with a highly susceptible cultivar or species selection, and seedlings backcrossed to the same susceptible cultivar/species for multiple generations to better understand the heritability of genetic resistance from R. setigera. While breeding with some of the other potential sources of resistance (R. rugosa or other members of Sect. Rosa) also has merit, using R. setigera would probably be the easiest route to create new modern cultivars with naturally derived resistance.
Thank you Stefan for the nomenclature information. It makes sense that Cinnamomeae should be Rosa with R. majalis (R. cinnamomea) being the first rose described by Linnaeus. The paper linked below describes Gallicanae as section Rosa for some reason. https://www.public.asu.edu/~camartin/plants/Plant%20html%20files/Wisseman%20and%20Ritz%202005.pdf
I am suspicious too Kim about escapes in a planting relying on natural infection. Dr. Mark Windham’s passion and hard work to clip parts of brooms 2 to 4 times per season on every plant eases my mind that it would be hard for a rose to escape. In some of his talks I remember him saying brooms have 40x or more the amount of mites than normal parts of the plants. They love the crevices the broom provides to feed, hide, and multiply.
That is a great idea Stefan about looking at inheritance of RRD resistance out of R. setigera. I made a number of crosses with a few different female R. setigera plants and polyanthas/Candy Oh! Vivid Red. They are the FA series in Maddie’s Thesis. https://oaktrust.library.tamu.edu/bitstream/handle/1969.1/192819/SHIRES-DISSERTATION-2020.pdf?sequence=1
A number were susceptible. I made the crosses and propagated the genotypes to send to Texas as part of the in kind donation needed by stakeholders to justify the USDA SCRI grant. Unfortunately, Maddie likely didn’t get the pedigrees of these plants and likely wasn’t made known of their origin. I didn’t know at least some of the plants went to her until I read her thesis.
Patrick Debello as part of his research grafted RRD infected pieces onto ‘Chuckles’ and at least as long as he followed the plants he didn’t detect transmission. Hopefully the RRD tolerance/resistance holds up for the roses highlighted in the recent Pathogens paper. I’m excited for the continued research being done to more quickly and reliably test for resistance in cultivars and to also come up with a quick and reliable diagnostic test for growers, etc. to know if suspicious roses are positive.
I think that it’s commonly assumed that Rosa gallica is the type of the genus, but the acceptance of the 1992 conservation proposal by Jarvis et al. was recorded officially in Appendix III of the Shenzhen Code of the ICN. If you visit the link below, it links to a searchable database at the National Museum of Natural History, where you can search for Rosa to find the decision:
Once you get there, you’ll read the following: " Rosa L., Sp. Pl.: 491. 1 Mai 1753 [Ros. / Ros.]. Typus: R. cinnamomea L., nom. cons. (etiam vide) (typ. cons.)."
It’s great to know that resistance from R. setigera is not necessarily present in F1 seedlings! There must be so much more to learn.