I have been thinking about this for weeks now: years ago a friend told me that when breeding Rabbits, sometimes a desirable trait would skip a generation, so that just because a trait appears to have vanished from a population, that doesn’t mean it can’t be recovered in a subsequent generation. So, I wonder, is this commonly true with roses as well? I mean, if I create a cross using two highly disease free roses, and yet the seedlings don’t have that same resistance, should I abandon that group, or select a couple of the better ones and cross them with each other, or backcross to one of the parents to recapture resistance? My instincts tell me that yes, this ought to be worthwhile, and yet I am also inclined to abandon a line of breeding if a group of seedlings appears to have lost a trait I deem essential to the line.
What are your experiences with such things? (Perhaps this should become an RHA newsletter discussion topic, hint, hint?)
Paul B.
There was a post a while ago that I can not seem to find about R. rugosa blackspot resistance. I think it was posted by Henry who is always finding these interesting papers. But in it the paper showed that Scabrosa resistance was reccessive which is different then some of the dominate type of resistance we see out there. So in this case it would skip a generation.
Another possibility that comes to mind is if the resistance is due to vertical or horizontal resistance. If it is the lock and key resistance maybe it is just not there anymore or that your two plants have different types of resistance and now what resistance they do have is no longer strong enough.
If the resistance is due to the overall genotype and not one gene, maybe the cross threw the delinquent balance that was found in the parents off.
Those are just some theories I can think of. Right now all I got is some theories and ideas. Most of them have been pilfered from Henry and David and from the scientific papers that are posted on here from time to time.
So with the above in mind. Mind you right now I am not that knowledgeable. But I would first ask myself what type of resistance do I think I am dealing with and why that particular type broke down and if any of these seedlings are worth the effort.
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If it is lock and key type I would probably backcross to the original parent or something with a similar background.
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If I got two lock and key type coming from the two different parents I would backcross to the one that I think has the better overall resistance and the better track record of resistance. Hopefully this will double up or triple up the gene that I want. Making it easier for the next generation to get this gene passed down to it. Ideally you would want four copies but breeding this far with genes I think it would be very easy to lose a lot of other characteristics one was aiming for. Anyways if one had 3 copies of the gene in a tetraploid and that gene was dominate it would transfer to every seedling at least one copy unless you got some weird gene splitting or a copy of a whole chromosome left out.
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If it is not lock and key resistance I would evaluate the best seedlings and figure out which ones had the best resistance and overall vigor. If I had enough seedlings to choose from and I considered it worth the effort I would pick the 4 best seedlings and inter-mate them randomly together. This should restore some of the balance of the genes that create not total resistance but good overall resistance at least in some of the seedlings. You could also mate these seedlings with something else with this type of resistance.
Like I said right now these are just theories in my head. I am beginning to work on them but some one else out there probably has a better answer or idea. Hopefully this helps out.
Oh too be a little clearer. The one type of resistance I would chose a back cross because it depends on one gene and the number of copies of that gene. With the other type of resistance I would continue to move forward looking at the overall plant characteristics while also taking a look at which ones handled disease best and had the most vigor and hope that by randomly crossing them together I could weed out some of the bad genes and simultaneously restore the delinquent balance that produced the resistance.
The first type of breeding can be seen in the work done with some of the Canadian disease resistant roses like William Baffin and John Davis. The second type of breeding a good example would be Buck and his work. Some of his hybrids have lock and key resistance but overall they depend on the overall genotype. I do think both types are important to breed for. I however lean towards the second type but it would be the harder route to go.
On rugosas which is probably not what your talking about I believe as Jadea does that some of the resistance does come from the thickness of the petal, I also think in whicurana that some of the resistance is due to the shiny leaves but again these are theories. Certainly the shiny leaves break down in many hybrid teas so maybe this theory is not worth its weight in salt. Also Henry on the article that I mentioned above why do you think the induced scabrosa lacked resistance, I am still pondering this? The only thing I can think is that it lost a chromosome or a mutation occurred in the tetraploid version?
Selfing such a cross, to me, seems like taking the available genes and continually re-shuffling them until the desired combination comes out. Question would be how patient can you be waiting for it to happen. You aren’t adding any new genes so with any luck the ones for disease resistance were successfully passed on in the first place and it would only be a matter of time until they recombined. There is no guarantee, however, that they were passed on. Breeding them among themselves should widen the net I would expect. I have beenthinking about this myself and was thinking I would choose one to be the seed parent and I would keep as many of the seedlings as I could and then put every one of the seedings back to the one seed parent.
Having bred hundreds and hundreds of rabbits and knowing their coat colour genetics inside and out… recessive genes were always popping back up one or more generations down the track. There was an myth going around rabbit circles that a recessive could remain hidden for up to 11 generations before re-showing its head… I don’t believe I ever had a gene lie hidden for that long, because I was always trying to pair unknown rabbits up with rabbits whose complement of recessive coat colour genes was the largest (my long term goal was to make aabbccddee rabbits; i.e. entirely recessive so that they could be used to test mate any rabbit to reveal recessives). Pity there wasn’t some kind of rose equivalent that you could use to test mate to see just what genes were lying dormant in the genome.