Blackspot book link

See:

Link: books.google.com/books?hl=en&lr=&id=dz3oAyhaGtAC&oi=fnd&pg=PA277&dq=Partial+resistance+to+black+spot+disease+in+diploid+and+tetraploid+roses:+general+combining+ability+and+implications+for+breeding+and+selection+&ots=XeN21eEsRk&sig=-tqinpg4f1PpmIxT

Using the “Find it in a library” link on the left side of the page, I was dismayed to find that there are only five copies in libraries withiin 500 miles of my zipcode.

I’ll try to get Interlibrary Loan to get it for me, but that’s not a lot of options.

(It’s interesting that Wiley continues to price their scientific books for libraries and not individuals. By that, I mean that they price them so that they break even and/or make a profit based solely on sales to libraries.)

This is a nice resource summarizing the literature of disease resistance breeding in roses especially focusing on black spot resistance as that is what most of the work has been done with. This is Vance’s literature review for this Ph.D. thesis that him and Stan added a bit more to on other diseases to publish as this nice chapter in Plant Breeding Reviews.

Sincerely,

David

That is a great article. David, it was nice to see your name in there.

I am wondering if blackspot resistance is ever recessive. For example, is it even worth using hybrids of Knockout that are blackspot prone. Once resistance is lost, is it lost forever?

Recessiveness would be seen in a single gene encoded trait where it was only one of 2 alleles in a diploid. Self seedlings could be resistant in 1/4 progeny that got two copies of teh resistance. For a tetraploid, recessive is a bit more relative, depending whether the “opposite” allele is strongly dominant so that one copy overcomes 3, or weak so only 2 overcomes 2. In the tetraploid case, it might be hard to select many resistant forms, fewer than 1/6.

With a multigene trait there is no dominant/recessive, but only relative blending. So if the blackspot resistance is “horizontal”, made up of many small resistances, a seedling showing some disease could yield seedlings having more resistance than it did. But not a very big fraction would be that way. So you’d need a strong selection. Better to breed resistant x resistant and keep trying to add further resistances, to different strains of the

disease.

Thanks Larry. Your explanation makes a lot of sense.

One example that I have that does not fit the mold is a cross between Midnight Blue x (Fourth of July x Basye Legacy). Both Midnight Blue and (Fourth of July x Basye Legacy) are quite blackspot prone in my garden, but this particular hybrid is far more resistant that either. At first I thought that Bayse Legacy has some recessive blackspot genes. Bayse Legacy is entirely blackspot free.

What is more likely is that Midnight Blue passed on resistance genes for certain strains of blackspot, and the other hybrid passed on resistance genes for different strains. I guess I will never know for sure.

Shane

Hi Shane!

That is a great explaination of stacking or pyramiding resistance genes/alleles. We can sometimes get offspring from more susceptible parents that are relatively resistant in our garden depending on what races we have and if we can accumulate resistance factors (like locks on doors) that will keep all our races out. In the end though, if we rely only on race-specific resistance, we are bound to get a race that comes in contact with our rose that can overtake it. Horizontal resistance that depends primarily on multiple genes (the explanation may be a bit too simplified as there can be some genes that have a moderate effect relative to adding all little effects) is what will likely be more durable or predictable in the long run and what we want to aim for.

In Santa Barbara in 2005 at those rose meetings, Dr. Andy Roberts presented some research regarding black spot resistance and challenges with characterized races in populations of Rosa rugosa where he suspects there was a resistance factor that may have been recessive. He didn’t get that sub topic into his abstract before the meetings and as far as I know yet hasn’t published on it. It was really interesting as Rdr1 and Rdr3 (rose disease resistance and then gene number) both have dominant alleles conferring resistance and it seems in general single gene resistance is dominant.

Take Care,

David

David,

As always, thanks for your input. Your posts are always so informational and helpful.

Shane