I have to imagine this topic has already been touched upon several times here but I wasn’t able to find anything via the search function. Does a fireblight resistant rootstock pass that quality on to a variety that is grafted to it?
Fireblight resistant rootstocks convey some resistance to scions.
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One of the reasons that the Old Home x Farmingdale rootstocks are in use for pears is because of their fireblight resistance.
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This is just my opinion with no data to support it. I think that the resistant roots offers some FB protection in that the root system is likely to survive when the grafted variety is attacked by blight. It might even offer a faster recovery when the top is partially damaged. I hope it provides the top some immunity but I’m skeptical that it does. Just my opinions.
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I too agree that a fireblight resistant rootstock offers some resistance for the scion. I say this with proof. A friend of mine ordered an apple variety for his commercial orchard. I forget what the variety was but very susceptible to fireblight. His supplier did not have enough available on the fireblight resistant rootstock he wanted so he planted 2 rows on M26 and the next 2 rows on M7. This story happened about 25 years ago.
Fireblight struck hard about 4 years after he planted this variety. The 2 rows on M26 were virtually wiped out. The 2 rows next to them on M7 had a few strikes but with pruning he managed to save them.
I was awestruck what a difference he had using a more fireblight resistant rootstock.
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The short answer is yes. If the rootstock dies the whole tree dies so having a resistant rootstock increases the likely hood of the tree surviving. Is still possible that scion may die leaving the rootstock alive but in general resistant rootstocks work. That’s the reason the Geneva series of dwarf rootstocks is commercially widely planted.
An exception of this is Bud 9. It appears to work differently and provides resistance by inducing changes in the scion and making the scion more resistant to fireblight directly.
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My experience is that it does not. lost trees to FB on G41 and G11 rootstocks where the chart from Cornell showed that the rootstocks were “resistant” or “very resistant” to FB. Lost about 20 % of Golden Delicious on G41 and closer to 25% of Pink Lady on G11. I started with 25 GD and 50 P Lady so I’m working from a small sample size. I live is an area very prone to FB where the Cornel computer model shows many days where conditions are perfect for FB infection.
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That’s correct. The way to understand it is: the tree growing above ground must meet the environmental conditions thrown at it and the roots grown below the tree has to meet the environmental conditions thrown at it. Each is their own system and there never is any transference of pest(s) resistance or hardiness, or none of the like.
Dax
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I am sorry you lost trees. But resistance does not mean that the trees have immunity unfortunately. NC-140 trials show basically where you have 100% tree deaths to fireblight on Gala/M9 in the same plot trees on G11 and Bud 9 have strikes but few or no tree deaths. I would expect if your trees were on M9 you would have lost all of them.
And of course we have few tools to fight fireblight unlike scab where many fungicides are available. It’s one of the reasons I have passed on some good cultivars that are susceptible to fireblight. I was afraid I would get the trees to maturity and then fireblight would kill all of them. I was mainly interested in old heirlooms like Hunt Russet and King David but looking at Purdue’s apple disease resistance chart many commercial cultivars are susceptible or very susceptible as well. You may be forced to plant resistant cultivars on resistance rootstocks if fireblight pressure is intense.
Turns out that I’m in a lousy apple growing area. FB is just one of the problems.
I agree that resistance and immunity are not the same, but the Geneva trees demonstrated less resistance to FB than the 800 B9 trees. Its hard to compare the rootstock resistance of 7 year old trees against 2 year old trees even with the same variety.
We have identified one variety that resist FB well as most diseases too on B9. Plan to graft 100 on G41 this year to get larger trees.
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This kind of goes right along with what you guys are talking about, this chunk of information I’ve put together:
Cornell University plant pathologist Herb Aldwinckle
‘Good Fruit Grower’ Feb 15, 2011
"In addition, the new high-density plantings have made these diseases much more expensive in their impact. The new shape of these trees—the short scaffold limbs—have made it more likely that fireblight strikes on the blossoms and shoots will make it to the trunks, where they can kill the tree or travel down the trunk and kill the rootstock.
“Resistant rootstocks will not protect susceptible scion varieties, he said, but a dead rootstock won’t support any scion variety at all.”
Aldwinckle of Cornell’s New York State Agricultural Experiment Station in Geneva, New York.
Geneva 41 is not the only rootstock that is resistant to fireblight. In evaluations Aldwinckle has done at Cornell, the rootstock Budagovsky 9 has proven resistant in orchards, although for some unexplained reason it did not show resistance in screening tests(…) "Absence of rootstock blight in the field is so consistent that we now recommend B.9 to growers as a fireblight-resistant rootstock to replace M.9,” he said.
Lush, vigorous new growth is more susceptible to fire blight. So one control measure is to manage tree growth. That might be fertility management, applications of growth regulators, pruning and training that reduces growth… Seems to me that could be one way rootstock might play a role?
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@MacApples That’s about as far as I understand it or anything further. I don’t know one thing about one rootstock vs. another. I kept reading often that rootstocks (might) play a role in where and how branch development occurs - that’s why I say that I agree that rootstock according to these guys (might tell) cultivars to grow differently, or so they think… are guessing at this moment. Or, the literature about this topic I’ve read has been outdated.
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Tough question. In my experience, the Geneva rootstocks work reasonably well. But, you have to help them out - use Cupromax early and spray Harbour or something like that. Also segregate from scions and stock that are not resistant. The feedback I get from the Alison Smith Center in Winchester is that a little streptomycin damage on the leaves is not a bad thing. 