[NAFEX] Apple Rootstocks
list at ginda.us
Mon Nov 9 23:38:07 EST 2009
Here's something I wrote up for Pomona following the one NAFEX meeting
I attended. Professor Cummins spoke about the apple rootstocks Cornel
has been working on, and it mostly deals with those. But it has some
interesting general information. Oh, and when I was planting some
stuff, I spoke to Professor Cummins about rootstocks for my backyard,
in eastern MA, zone 6. Of the traditional semi-dwarf rootstocks (not
needing support) he recommended M7. It's an old reliable workhorse.
It's not the most fireblight resistant, nor the most hardy, nor the
most. . . . but it's pretty good in most ways.
Begin forwarded message:
> Jim Cummins on Newer Apple Rootstocks
> Professor Cummins spoke in the first session. Unfortunately, we
> started a bit late, and he wasn't able to get to pear rootstocks,
> but he did talk at length about apple rootstocks - where they were
> in his childhood, and where they have come today.
> Professor Cummins grew up on an old apple orchard with seedling
> rootstock. The trees were spaced on 40'x40' centers, for 27 trees
> per acre, and the canopy was full, with the trees just meeting
> overhead. This was the standard orchard until fairly recently. In
> contrast, modern orchards on dwarfing rootstock can have hundreds of
> trees per acre, up to 1900 (?? this sounds too high, but it's what
> I wrote down) with the smallest trellised trees. Today, most new
> apples trees are planted on M9, or occasionally M7 for intermediate
> sized trees. Very little M26 is planted due to its susceptibility
> to fireblight.
> These are relatively old rootstocks. The Malling and MM series of
> rootstocks became commercially available in the early 1900's, with
> newer rootstocks such as MM106 coming on line in the late 1960's and
> dwarfing rootstocks in general becoming widely used by the 1970s.
> This was the result of a process started back in 1922 when Lord Dowd
> started a breeding program in England. Shortly thereafter Dr.
> Budagovsky started a similar program south of Russia. Several other
> programs have since been started (in Canada, the US and Europe) and
> the program started by Dr. Budagovsky has moved to Poland.
> Most of these programs have looked primarily at horticultural
> aspects, especially including how easy they are to root. This has
> often been the first criteria used to cull seedlings. In 1968, the
> Geneva program decided to try something new - they decided to breed
> first for resistance to the major diseases of rootstocks, and
> secondarily for horticultural criteria. One side advantage of this
> is that their trees, being somewhat harder to root, are far less
> susceptible to burr knots. This can be a problem with several of
> the M and MM series (esp. MM111) and the Russia series.
> The major pests of apple rootstocks are collar rot and fireblight.
> In order to find resistant plants, the Geneva program would plant
> out thousands of seedlings from selected crosses. When the baby
> trees were 3" tall, they infected them with crown rot. This would
> kill between 75% and 100% of the plants. when the remaining plants
> reached 1 foot in hight, they injected them with fireblight
> bacteria. This would again kill off between 75% and 100% of the
> plants. From 100,000 seedlings evaluated, only about 500 survived
> this treatment. These ones were reinnoculated and tested for
> nursery performance, and the most promising of these will be
> released as the Geneva series of rootstocks.
> It takes a long time to fully evaluate a rootstock, and Dr. Cummins
> wishes for another 20 years, however, they are beginning to release
> their roots. Some of them will eventually come up lacking, but he
> is certain that some will be winners.
> Three rootstocks have currently been released, G30, G16, and G11.
> G30 might replace M7 but it has limitations. It yields early and
> heavy bearing (20-50% better than M7 in first ten years) and it is
> very cold-hardy (at least to -30F, probably to -35 or more) but it
> produces a very brittle graft union, especially with trees that tend
> towards brittleness, such as Gala and possibly Honeycrisp. Trees on
> G30 should have permanent support (an "artificial trunk") to 8'.
> Another problem with the rootstock is that it is a very poor nursery
> subject. In particular, the baby trees have short internodes and
> are very thorny. These thorns need to be removed if the plant is to
> be grafted. They can be removed early on by hand ("thumbing them
> off") somewhat later with sheers, or after the plants have been
> dug. The third is easiest, but it results in lots of open wounds on
> the nursery plants, and they tend to dry out and die.
> G16 might compete with M26. It has no thorns or burrknots, and
> doesn't sucker at all - it yields a perfectly smooth trunk. It is
> more productive than M9, winter hardy, with heat and drought
> tolerance similar to M7. Curiously, it gets this tolerance through
> a totally different mechanism than M7. M7 has a vertical root
> system, and the roots often find water by heading down. G16 has
> very heavy, aggressive roots that go everywhere. It appears to be
> adequately winter hardy but has not yet been subjected to a test
> winter. The problem with this otherwise very exciting rootstock is
> that it is very susceptible to common latent viruses, including
> applestem grooving virus. It is critical that it only be grafted to
> clean scion wood, or the tree will die. Because apple viruses are
> not transmitted sexually (e.g. by pollinators) or by leaf-eating
> insects, the tree is unlikely to be naturally infected in the
> field. (Nematodes do transmit some apple viruses, such as tomato
> ringspot, but this tree is not susceptible to those.) On the other
> hand, it could be infected by pruning equipment - this is a tree to
> treat carefully.
> There was an interesting side discussion about why G16 is dwarfing
> given the high vigour of its roots. Dwarfing is not well
> understood, and the "weaker roots" theory is not backed by any solid
> evidence. Dr. Cummins and others suggested two possible mechanisms
> for why this tree might be dwarfing. The first is that "wider
> pipes" in the tree's plumbing might limit the hight to which
> nutrients flow. Research done in Israel has shown that M9 has very
> large pipes and they appear to reduce the capillary action that
> helps bring sap up the tree. The second theory is that precocity is
> itself dwarfing - once a tree has started to fruit (even if you
> remove the young fruits) it simply puts less energy into growing
> trunk and branches.
> G11 has just been released this year. It is in the same size class
> as G16 and M26. It is not as fireblight resistant as the other two,
> but it is probably good enough for most uses (comparable to M7) and
> has adequate resistance to phytopthera. There are (so far) no known
> virus problems with this rootstock. It is also an early and heavy
> bearing variety, and is also a good nursery subject.
> At this point Dr. Cummins ran out of time, and quickly ran through a
> couple of "things to come" from the Cornell-Geneva program, and
> answered some questions about the other new rootstock series.
> CG3041 is more dwarfing than M9, and much less brittle. CG5935 is a
> bit more vigorous than M26. Both are still undergoing testing
> (along with G5202, described in his handout.) According to the
> handout, CG5202 is also highly resistant to wooly apple aphid, and
> has been introduced in New Zealand, where WAA is a major pest.
> Bud9 (or red leafed paradise) is similar to M9 but more cold hardy,
> with a smooth shank. It has better fireblight tolerance than M9.
> It was introduced in Russia in 1948 and is now widely available in
> the US. Bud118 produces a tree about 90% as large as standard.
> Like M111, it seems to delay the onset of fruiting, but once it
> starts it is very efficient and very well rooted. He believes it
> would be good under Honeycrisp.
> He has had trouble propagating the Polish series (coincidentally the
> "P" rootstocks, although the "P" stands for the Polish word for
> rootstock, not for Poland.) and had little to say about it. He is
> skeptical of the German supporter series, which he doesn't think has
> been adequately tested outside of Germany. He feels that program is
> under pressure to release stuff. He has found this series to be
> susceptible to fireblight. The least susceptible to fireblight of
> the lot (Supporter 4) is still somewhat susceptible, and is also
> susceptible to collar rot like M9 and seemed to yield poor cropping
> in his tests. Some trees died from apple aphid.
> At this point we really ran out of time for the first session.
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