Braeburn Apple Tree looks poorly - Help!

[FB.]

And it doesn't just stop at scion diseases.
When first released, the MM106 rootstock was resistant to phytophthora crown rot. But due to MM106 being so widely grown, specialised "rootstock-specific" crown rot strains evolved to attack it - and can now do so very efficiently.
The "wonder rootstock" M116 is resistant to MM106 crown rot, and so is MM111 (as proven by me planting M116 and MM111 directly into the hole where a dead MM106 was removed).

But if M116 or MM111 become popular in the future, it would be expected that they will also lose resistance to new races of disease.

However, I concede that some cultivars and some rootstocks will have more intrinsic resistance than others because of genetic variation and to some extent the inheritance of good or bad genes from their parents - perhaps three minor resistance genes in one variety, only two minor resistance genes in another variety; tipping the odds that the one with least resistance genes would be the easiest for the diseases to overcome, with some further modification depending on whether the resistance genes were already overrun in their parents.

[StephenH]

Thanks for all the fascinating info!
As FB says a few posts above, 'Brownlees' Russet' is indeed from Hertfordshire. In fact it's more local to me than that: it was raised in Hemel Hempstead, where I live, in the 1840s. In fact, it could be very local indeed, because I have heard that the housing estate I live in, which dates from the early 50s, used to be orchards. However, I don't know how widely grown it is nowadays: it's not a particularly well-known variety.

[FB.]

We could also make an approximate guess at the intrinsic scab resistance of each variety (i.e. how lucky it was in what it inherited from its parents), by adding-up the severity scores when inoculated by scab from other cultivars.


Boskoop:
Average susceptibility vs other five cultivars: 1.2 (resistant)

Glockenapfel:
Average susceptibility vs other five cultivars: 1.0 (very resistant)

Golden Delicious:
Average susceptibility vs other five cultivars: 3.6 (very susceptible)

Idared:
Average susceptibility vs other five cultivars: 3.2 (susceptible)

Maigold:
Average susceptibility vs other five cultivars: 3.4 (susceptible)

Spartan:
Average susceptibility vs other five cultivars: 2.8 (intermediate)

.......


So in order of disease resistance:

1. Glockenapfel (resistant to scab from all other cultivars)
2. Belle de Boskoop
3. Spartan
4. Idared
5. Maigold
6. Golden Delicious (susceptible to scab from all other cultivars)

Notable that the two most resistant varieties are either very old, or triploid.

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But none of the above varieties are immune to scab, since each has its own well-adapted strain which is highly virulent (grade 3 or 4 attack).
These well-adapted strains will have arisen due to varieties being widely planted for a long time, or from being grown in monoculture which forces the diseases to adapt or become extinct.

[orangepippin]

Various research stations have proven that with today's "monoculture" orchards (vast blocks of thousands of trees of the same variety, on the same rootstock), scab and other diseases have evolved to be cultivar-specific; a "one-trick-pony" which is highly specialised and very efficient at attacking just one variety.

In the UK this would only realistically be an issue in small areas of Kent, where climate and soil makes modern intensive orchards feasible. Elsewhere cultivar-specific scab strains would be unlikely to succeed, compared to those which were adapted to a wider range of cultivars.

In fact whilst there may be millions of Braeburn or Gala trees in Kent, in the rest of the UK they are probably fairly rare. You might find that in Hemel Hempstead there are actually more Brownlees Russet trees than Braeburn or Gala trees, and local scab strains that were oriented towards the (common-in-that area) Brownlees Russet might not be able to attack the (usually more scab-prone) Braeburn and Gala.

[FB.]

In fact whilst there may be millions of Braeburn or Gala trees in Kent, in the rest of the UK they are probably fairly rare.

Yes, but both were chosen for commercial growing and not for disease resistance. So any resistance they have may be weak and not last long.
I'd tried growing Gala pips and Braeburn pips and they make especially sickly seedlings - life expectancy of a few weeks. Seedlings from (say) Discovery (a variety with quite good natural disease resistance) at least manage to last a year or two.

You might find that in Hemel Hempstead there are actually more Brownlees Russet trees than Braeburn or Gala trees, and local scab strains that were oriented towards the (common-in-that area) Brownlees Russet might not be able to attack the (usually more scab-prone) Braeburn and Gala.

Quite possibly true.
But as my earlier comments above: I don't think Braeburn or Gala have as much natural resistance.
So while Brownlees' Russet may be able to be attacked by BR-specific strains, I suspect it is fairly resistant to strains from other cultivares. But Gala and Braeburn are like Golden Delicious in the example above; prone to easily catching diseases from other varieties as well as from themselves.

[FB.]

As a former scientist who specialised in infectious diseases (human diseases - in my two decades in a lab I've isolated thousands of MRSA, VRE, ESBL, C.difficile and other "superbugs"), I find resistance, susceptibility, evolution, mutation and the like to be quite an interesting subject.

It may be interesting to others that even the "susceptible" Golden Delicious actually has a scab resistance gene, known as Vg.
Even more interesting is that although Vg offers no resistance against the common strains of scab, which now all must carry anti-Vg mechanisms, but Vg has been found to offer resistance against Vf-scab strains which threaten the latest generation of "scab-immune" Vf-gene cultivars.

So I dare say that Golden Delicious, in its time (a century ago) was as resistant as the current generation of Vf cultivars such as Saturn, Liberty, Prima and so on.

A quick and easy-to-read link about Prima having both Vf and Vg resistance working together is here:

Vg gene and QTLs for resistance to scab

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Another study points out:

"...At least seven different major genes for scab resistance have been identified (Vf , Va, Vm, Vr , Vb, Vbj and Vg)..."

http://edepot.wur.nl/38166

Golden Delicious has major resistance gene Vg, but it's been around so long that almost every strain of scab on earth has anti-Vg mechanisms.


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[orangepippin]

I think the take-home message is that some varieties - including many russets - are simply better at resisting disease pressures than others. However I think it would be wrong to generalise that all varieties developed for commercial growers have poor disease resistance.

Firstly commercial growers value disease resistance as much as everyone else, perhaps even more so. You won't have a hope of introducing a major new commercial variety if it doesn't have good disease-resistance credentials.

Secondly the most commonly-found varieties in the UK are by no means the major commercial varieties, but are likely to be popular home varieties such as Egremont Russet or Bramley augmented by locally-specific traditional varieties. If you believe that planting rarer varieties is a good route to achieving a healthy tree then Golden Delicious or Red Delicious are valid choices. The latter has long-standing disease resistance, and these are both pretty good apples when home-grown.

[FB.]

I think it would be wrong to generalise that all varieties developed for commercial growers have poor disease resistance..... You won't have a hope of introducing a major new commercial variety if it doesn't have good disease-resistance credentials.

Agreed - but, unfortunately, as soon as large blocks of the tree are planted, the diseases will begin to adapt, and lots of trees give lots of opportunities to perfect the art of attack (lot of places for that random mutant spore to settle).
So, several years after commercial introduction, it's quite likely that specialised diseases will start to evolve.

Here's another interesting discussion about dependence on Vf resistance and its failure (and mention of how scab also gradually acquires resistance to chemical sprays):

"...Since 1970, nearly 90 percent of the scab-resistant varieties that have been released worldwide reportedly carry that Vf resistance gene......reliance on a few fungicides has resulted in fungicide resistance, reliance on disease-resistant apple varieties in the absence of other management has resulted in the breakdown of Vf-based scab-resistance ......"

Scab resistance breakdown - Good Fruit Grower - February 15th 2009 -

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[boundtothesoil]

FB, I notice that in the Good Fruit Grower article you've flagged up, the advice includes not growing scab resistant varieties adjacent to scab susceptible varieties. I have observed the probable downside associated with not following this advice with my own trees.

I have George Cave, James Grieve and Sunset trees, all planted at the same time and now fairly mature, in a row. The George Cave has always been very prone to scab. Until three or four years ago, the James Grieve was scab-free, but subsequently has become progressively scab-prone (although still not as severely as the GC). Until this year the Sunset was also scab-free, but, unfortunately, this is no longer so. Although this trend might have other explanations, it could be that the large pool of GC scab has produced strains adapted to the previously pretty resistant adjacent varieties. It's taken 15 years to reach this unpromising state, and I'm reminded of a discussion in another thread, where regular grubbing up and replanting with different varieties was suggested as a (not very practical) means of avoiding being over-run in the long term by scab, at least in a 'no-spray' situation.

[yummersetter]

If you believe that planting rarer varieties is a good route to achieving a healthy tree then Golden Delicious or Red Delicious are valid choices. The latter has long-standing disease resistance, and these are both pretty good apples when home-grown.

The trouble with the Red Delicious that I grow is that only the RED in the name is true.

[FB.]

.......it could be that the large pool of GC scab has produced strains adapted to the previously pretty resistant adjacent varieties. It's taken 15 years to reach this unpromising state......

Yes, I think that's most likely what happened. You've been watching evolution in progress! Congratulations: you've successfully raised some new apple diseases, so now you need to raise some new apple varieties to keep one step ahead!

The strains of scab which were attacking the GC all those years have thrown off occasional mutants and new genetic recombinations (possibly assisted by some spores which blew in from other trees nearby and which cross-bred with your local scab strain)s. Eventually one or two of those new or mutant strains just happened to have a lucky combination of genes which allowed the strain to begin to attack a new variety.

Just like a seedling apple creates a new variety, a fungal spore can also create a new variety (of which billions can be produced in a year - disease eveloution can happen quite quickly due to the sheer numbers involved).
Generally speaking, scab clones itself during the leafed-out season (asexual reproduction) but when the leaves fall it allows different scab strains to come together in the leaf litter to cross with other strains of scab (sexual reproduction).
So the recommendation to clear up leaf litter is most likely going to be the most effective because it significantly reduces sexual reproduction therefore limiting the creation of new strains of disease.

"In the wild", there would be no grafting and no cloning; each tree would be a genetic individual, so the diseases would need mechanisms for gradual adaptation to new apple varieties (seedlings).

[orangepippin]

The trouble with the Red Delicious that I grow is that only the RED in the name is true.

I would previously have agreed with you, but I was able to taste some at a processing plant in Virginia last autumn and I was pleasantly surprised at the flavour and texture. OK, it is not outstanding by any means, but there was a definite floral note that you sometimes get in Kidd's Orange Red. However there are lots of versions of Red Delicious and I don't know which these were.

Is it reasonably disease-resistant in your area?

[FB.]

Hi again btts

Back to my regular comments about triploids: they have an additional 50% DNA compared to diploids, and this means the average triploid would have 50% more resistance genes than the average diploid, suggesting that the disease resistance of triploids is more likely to be long-lasting. Belle de Boskoop in my earlier example makes a good case for this.

In fact, I suspect that triploids are effectively more than 50% more resistant. If you've ever played military strategy types of games you'll be aware of "the square rule of a superior force".
I'll detail a simple example to illustrate this (bear with me)...

Suppose we're on the Western Front in WW2 and there's about to be a major tank battle - say a hundred Sherman tanks against a hundred Panzer IV tanks, which are a fairly equal match.

Suppose the Shermans split into two groups of fifty, while the Panzer IVs stay as one group of a hundred.
Each tank has a 50% chance of destroying an enemy tank in each volley of shots.
One group of 50 Shermans attacks the Panzers.
The 50 Shermans destroy 25 Panzers with their first volley. The 100 Panzers destroy all 50 Shermans with their first volley.
After the first stage of the battle, 25 Panzers are destroyed and 50 Shermans are destroyed, leaving 75 Panzers to take on the remaining 50 Shermans.
In the first volley of the next battle, the 50 Shermans destroy 25 Panzers and the 75 Panzers destroy 38 Shermans.
50 Panzers remain against 12 Shermans. The Shermans destroy a further 6 Panzers with the second volley while the Panzers destroy all of the remaining Shermans.

At the end of the battle:
44 Panzers operational.
56 Panzers destroyed/non-operational.
0 Shermans operational.
100 Shermans destroyed/non-operational.

So as you can see - and getting back to the point - a single concentrated force (or triploid v diploid) is much more powerful than a split force. Despite the original tank forces being equal (100 Panzers facing 100 Shermans), the concentration of force against two smaller forces gave an overwhelming victory.

So it might be expected that a triploid apple, when attacked by fungi, is a much more formidable opponent due to its greater amount of genetic material.
With 50% more genetic material, I'd expect the "square rule of a superior force" to apply, and that an average triploid would be much more able to resist disease attack, or delay the evolution of adapted disease strains, than an average diploid.

I suspect that's why only one-in-a-thousand apple seeds is triploid, yet around one-in-ten known cultivars is triploid - a far higher proportion of triploids than ought to be the case in a natural population which suggests triploids have better suriviability.
It's especially notable that many old hand-me-down varieties from our ancestors of centuries past are turning out to be triploid.

[yummersetter]

Answering OP's Red Delicious question - I have about 6 trees, half-standard and bush and they're really healthy, growing well, masses of blossom every year that sets loads of fruit. The apples always look very attractive, virtually no disease or damage and utterly RED. It's just got very little flavour, I think I'd say its not aromatic. I have plans to take them at the Farmer's Market thought, they will sell, for sure - and I'll also sell other varieties that taste great and don't look so perfect.

Here's one of the bush trees a month ago

[Flymo]

Thanks to all who replied with helpful information.
Thanks also to StephenH for hijacking the thread.

Flymo