Henry... PNRVS experiment....

Hi Henry,

I’ve just read your article titled “Can North American rose hybridizers safely use pollen from PNRSV infected roses?” and in it you say “Another possible reason why some experiments have failed to detect the pollen spread of PNRSV is because PNRSV is a temperature sensitive pollen. There is a 1999 scientific study, see footnote (16) that the amount of PNRSV decreases as the temperature increases until it can no longer be detected in the above ground parts of the plant. This does not mean that PNRSV infected roses will cure themselves in southern climates as the virus in the roots is not killed. As the weather cools it appears that the virus returns to the above ground parts of the plants.”.

Sorry if this sounds daft but I was just wanting some clarification… When you say they return to the above ground parts of the plant do you mean it is previously killed in the above ground parts of the plant and parts of the plant that remain cool enough below the ground will play host to the virus and when temperature falls in above ground parts the virus can then reproduce and spread to reinfect these parts or are you saying that there appears to be a vertical migration of the virus that is driven by thermal gradients within the plant so that in hot whether the virus moves below the ground and in cooler weather it can spread to all parts of the plant? The reason I am wondering this is do you think it would be possible to cure plants showing clinical symptoms by placing them in pots and growing them in a controlled environment at temperatures above that condusive to the survival of the virus?

Link: home.neo.rr.com/kuska/rose%20virus%20and%20pollen.htm

Your first interpretation is correct. Heat is used to remove virus from roses. See the following link for a review:

Nornally continuous heat is used, but there are literature reports of killing the virus with alternate day/night (hot/cool) treatments. A example is given below:


Link: books.google.com/books?hl=en&lr=&id=KxnqzD1L36sC&oi=fnd&pg=PA187&dq=%22heat+treatment%22+pnrsv&ots=wwCk1w-Sps&sig=LweAHqAWuJAWiSb1YYR3-GV7eBw#PPA187,M1

20 days at 38 degrees Celcius is doable for the hobbyist too. I have a thermostat that goes to 40 degrees celcius and a heating element built into a large box I built for incubating chicken eggs. This can be sterilised and used to good effect for this purpose. It also has a clear perspex lid so I could mount my 6400K 105W hydroponics light over it too should the need arise. I’m not so much worried about the bought plants I’ve got that are showing RMV as they can be replaced easily but should any seedlings turn up with it that can’t be replaced then this might be a good alternative. Maybe a good way to ‘clean’ understock cuttings too. It might serve as a double edged sword and serve to both kill any PNRSV virus in cuttings and increase strike rate of cuttings in much the same way as bottom heat would.

Thanks very much for the explanation and links Henry.

Some time ago I read that the success rate is rather low. I believe it was Malcolm Manners who wrote on GardenWeb that they lost quite a few plants because of heat stress. However, maybe the hot/cool treatment combination may increase survival rate of the plants?


In terms of understock preparation or maybe even cleansing of bud material in a stent, low survival rate would be a bad thing but even if one worked (from a hobbyists point of view) clean material can then be propagated from that in more viable numbers.

Yes, certainly. I just meant to say that if you try it with a unique seedling and you have only one plant of it, the chance that it does not survive and you lose it entirely is considerable.


ahhhh - yes I agree. I think if one of my seedlings showed it I’d let it grow on in a pot until it was large and then try the heat treatment with multiple rootstocks and buds without killing the goose that laid the golden egg so-to-speak :slight_smile: