3 year Chestnut blight survivor

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#1)  3 year Chestnut blight survivor

Postby Rand » Sat Oct 29, 2016 8:07 pm

I have been watching over some chestnut sprouts in various clearcuts in Tar Hollow State Forest for the last 10 years or so.  It was fun to watch them grow, and no so fun to watch them fail as the blight settled in on them.  In general, it seems to take ~ 3 years for the blight to kill a small tree, say 3"-5" dbh, once it gets established.  Curiously, it does seem like a small tree can handle a single canker, walling it off with fresh callous once it gets the size of your fist or so.  However, once a single canker gets established, it soon spawns numerous secondary cankers all over the trunk and nearby branches.  It does seem like the shear number of cankers is what dooms the tree, as if it has only so much fungi fighting ability that is exhausted when attacked in numerous locations.  It's pretty common to see a smallish canker start to burl up with callous and stabilize for a season or two.  Inevitably though, the fungus reasserts itself and breaks out of the callous to girdle and kill the tree.

Anyway in one clearcut I've watch a half dozen or so sprouts die off back to the roots.  However, there is one survivor of the group that has survived 3 years under heavy attack, more or less intact.

Pictures from Sept 2013:
               
                       
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Compared to Oct 2016:
               
                       
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It's lost a few branches in the crown, but somehow it is still hanging tough:

               
                       
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I picked 16 nuts off of it this year.

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#2)  Re: 3 year Chestnut blight survivor

Postby jclarke » Fri Jun 02, 2017 10:37 am

I think I would be planting as many nuts off that tree as I could.  There seems to be a slow gathering up of small, horizontal, additive resistance genes.  Trees that can produce some nuts in the presence of blight attack may have some some favourable genes.  if the nuts from several of those could be pooled and shared, it might be possible to accumulate useful numbers of genes in the population.  Food for thought?

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#3)  Re: 3 year Chestnut blight survivor

Postby Rand » Wed Aug 02, 2017 12:13 pm

I found a lecture that talks about the latest understanding of the genetics behind blight resistance.  It appears that 3 genes control ~40% of the resistance, but the rest is poorly understood:

https://youtu.be/3MtbX0V62cs?t=3543

When ACF originally started in the 1980's it was thought that only two genes controlled the lion's share of the resistance.  This disappointment is clearly reflected in the 'potentially blight resistant, Restoration Chestnut 1.0' trees you can get from them today.  In their tests only 20-30% of these trees have a level of resistance comparable to their Asian parents.
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#4)  Re: 3 year Chestnut blight survivor

Postby jclarke » Sat Aug 05, 2017 1:55 pm

The Canadian Chestnut Council has been backcross breeding for blight resistance, and also gathering up small resistances from local pure species trees.  The average resistance of both groups is about the same, with some really resistant trees in both groups.  It appears both approaches work.  I remember reading that the soy beans who had resistance bred up from
smaller additive resistance genes did as well as the GMO OxOx ones, so Canada discontinued the GMO soy beans.............mostly to protect exports to Europe.

I think something similar happened in corn, rust being the issue at the time.

Blight resistance has been bred into tomatoes, from the little currant types which already have it...think Candi Too and other grocery store types.

Think potatoes too, which can be had in blight resistant strains, both GMO and traditionally bred up.

This might work in chestnuts  :)

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#5)  Re: 3 year Chestnut blight survivor

Postby Rand » Thu Oct 12, 2017 3:54 pm

I went back to the survivor chestnut last weekended (10/6).  It had lots of nuts, but they were too far in the air to reach (+25' feet in the air).
               
                       
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There is probably something to the claim that chestnuts are adapted to be dispersed primarily by blue jays (and other corvids).  So the best thing I could do is clear more of the competing trees from around it, and see if that will encourage fruiting on the lower limbs.  In the process I got some better pictures.

View from the uphill side.  Note all the sprouts stimulated by last year's clearance, and the dieback of the major limbs caused by extensive cankering at their bases.  The cankering was so bad, the limbs looked too unsound to climb.
               
                       
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The tree looks a lot better from the downhill side:
               
                       
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A better view of the cankering:
               
                       
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Here's another tree that survived 5+ years with the blight, dieing back little by little until this year nothing was left alive on the original trunk.  It did bear some nuts, but the seedlings didn't survive.  
               
                       
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I cut everything off in the hope this would decreased the innoculum load enough for the sprout to grow properly long enough to serve as a pollen source for the other remaining tree.
               
                       
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There are a half dozen other sprouts with a hundred or so feet of these two trees, but they all died back much more quickly from the blight.  Unfortunately once the blight is established on the tree, any sprouts tend to be infected before they get any thicker than your finger.  Then the blight jumps from last year's dead sprout to this year's new sprout, killing that in a season or too, until the tree is exhausted and dies.  I cut everything off showing signs of the blight on the remaining living trees this year and we'll see if that improves the sprout survival.
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