Apple Pollination Groups Affected By Rootstock - Revisited.

[FB.]

Last year, I put up a thread on how apple rootstocks, when grafted with the same variety, seem to flower at slightly different times. I have taken detailed notes this year and combined them with my rough notes, "gut feeling" and "memory" from previous years, to make some interesting conclusions.

The National fruit collection, from which the data on pollination groups has been complied, is grown on M9 rootstock.
Therefore, relative to the Brogdale and "official" pollination groups and dates, it seems that - in my area - the following rootstock adjustments to flowering time should be applied:

M27 (very dwarf): no adjustment.

M9 (dwarf): no adjustment.

M26 (semi-dwarf): brings forward flowering by one pollination group (4 days).

MM106 (semi vigorous): a simplification for MM106 would be to assume two pollination groups earlier (8 days) for all varieties.
In more detail; MM106 brings forward flowering by three pollination groups (12 days) for early/mid-flowering varieties (groups A-D), two pollination groups (8 days) for mid-flowering varieties (groups C-E), and by one pollination group (4 days) for mid/late-flowering varieties (groups D-F).

MM111 (vigorous): brings forward flowering by one pollination group (4 days).

M25 (very vigorous): brings forward flowering by one pollination group (4 days).

Therefore, simply choosing suitable pollinators may not be enough if choosing apples on unknown or different rootstocks, if the rootstock influence is not taken into consideration. Ideally, any pollinator for an apple tree should also be on the same rootstock, otherwise, due to rootstock influences, they may not flower at the same time, despite being in the same “official” flowering group. The above "conversion table" might help choose pollinators if two "pollination partners" need to be grown on different rootstocks.

I hope that is of interest, but don't hold me responsible for your decisions on rootstock choice.

FB

[FB.]

....and while I'm muttering about pollination groups.....

Cross-pollination is more likely if the apple trees are side-by-side (subject to adequate spacing for rootstock size). It encourages the bees to move freely from one tree to the other.

If several apples are being grown, planting them in a line, with pollination partners close to each other, is ideal - the bees seem to prefer to move down a line of trees and will often move between two adjacent trees, but are not so keen to move between rows of trees.
I would make an educated guess that a line of trees facing North-to-South or, more precisely; NNE-to-SSW, would be optimum.

If the apples are planted at opposite ends -or corners- of an allotment or garden, the bees don't generally tend to bother flying between the trees, since it's far easier just to harvest from one tree and then go home. Pollination may still be adequate, if the bees visit one tree on one trip and teh other tree on teh other trip. I have heard many reports that bees will have a "favourite" tree and will continue heading for the same tree on almost every trip.

[FB.]

....and finally.....

Most apples have self-incompatibility genes that cause their flowers to recognise and destroy their own (or related) pollen, to prevent in-breeding.

This is becoming an increasing problem for choosing pollination partners, since most modern apples are descended from either Cox's Orange Pippin or Golden Delicious.
The self-incompatibility genes mean that the offspring are poor pollinators of each other and their parents.
Some examples of the incompatibility genes:
Cox: 5 and 9
Golden Delicious 2 & 3

Cox's or G.D offspring that share either number 2,3 5 or 9 incompatibility:
Kidd's Orange Red: 5 & 9 (likely to be unable to pollinate Cox)
Meridian: 5 & 9 (likely to be unable to pollinate Cox)
Fiesta: 5 & 3 (likely to be poor pollinator for Cox and Golden Delicious)
James Grieve: 5 & 8 (likely to be poor pollinator for Cox)
Gala: 5 & 2 (likely to be poor pollinator for Cox and Golden Delicious)
Greensleeves: 5 & 2 (likely to be poor pollinator for Cox and Golden Delicious)
Red Windsor: 5 & 22 (likely to be poor pollinator for Cox)

The list goes on, but the point is made.

[Two_Sheds]

They were talking about this on GQT today, but I didn't really pay attention (too much going on).

Listen again?

[FB.]

They were talking about this on GQT today, but I didn't really pay attention (too much going on).

Listen again?

Which bit were they talking about?
Was it rootstock effect on flowering, positioning of trees, or incompatibility between some apples?

[FB.]

Thinking a little deeper into how rootstocks affect flowering and leafing-out times, I can see theoretical ways to try to improve cropping, or to reduce disease.

For example....

Later-flowering apple trees (perhaps influenced by rootstock) will have more attention from bees, as the bee numbers start to increase.
Possible effect = better pollination, better fruit quality and more fruit?

Late-flowering apples (perhaps influenced by rootstock) will have less chance of frost damage.
Possible effect = more fruit and more predictable?

Late-flowering apples (perhaps influenced by rootstock) may find themselves at increased risk of disease attack, since young (immature, soft, thin-skinned, tender) leaves, shoots and fruits are more vulnerable to attack and damage than older leaves, shoots or fruits. As spring progresses and temperatures rise, so does disease activity, so perhaps the earliest-flowering will be more disease-resistant; just a week earlier in leafing-out and flowering might well allow the leaves or fruit to be more disease-resistant.
Possible effect = more risk of scab damage to fruit?

But bear in mind that not all rootstocks are suitable for all soil conditions.

[FB.]

Well, the blossoms are falling and the fruitlets are developing.

I commented a few weeks ago about a severe shortage of bees in the area and it is now coming apparent that the earliest flowering varieties on MM106 that are not self-fertile seem as if they'll have no fruit, except for the central flower of each cluster, which I hand-pollinated.

It would seem wise not to grow self-sterile, early flowering varieties on MM106, since nowadays, there are so few bees flying earlier in the season to pollinate them (especially with MM106 bringing the season even earlier).