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Triploid apple tree pollination

clarke.bruntclarke.brunt Posts: 215
in Fruit & veg
Some cultivated varieties of apple are what's called 'triploid' (Bramley's Seedling is one) - they have 3 sets of chromosomes instead of the usual 2. As a result, their pollen is incapable of pollinating other apples (and can't self-pollinate either). There is a common misconception that you need to grow 2 other varieties of apple nearby to pollinate the triploid tree - you don't - one is all it takes, but you might need another to pollinate the first one (and vice-versa).

Most web pages on the subject are confusing. I'll start with one that actually gets it right:

"So if you have a triploid apple tree, you will need a suitable apple tree nearby to pollinate it.

You will also need to remember that if the pollination partner is itself self-sterile, as many apple trees are, that apple tree will also need a pollination partner because it cannot be pollinated by the triploid apple tree. If however the pollination partner is self-fertile then it will not need another apple tree to pollinate it because it will not only pollinate the triploid apple tree (if in the correct pollination group) but also itself.

It is a common misconception that triploid apple trees need two suitable pollination partners but this is not true, they only need one"

And for examples of the confusing information:

"Some [apple] cultivars are triploid – they have sterile pollen and need two other cultivars for good pollination; therefore, always grow at least two other non-triploid cultivars with each one."
I fear they are just duplicating the usual confusing information.

"Certain cultivars known as 'triploids' (such as 'Bramley's Seedling') need a third cultivar nearby, as their pollen is ineffective at pollinating other trees."
At least they mention the actual (and only) problem: pollen from triploids won't pollinate anything else. But they fail to say why a 3rd tree is needed i.e. it's just if you want the 2nd tree pollinated (and vice-versa).



Posts

  • steephillsteephill Posts: 2,841
    When I first heard of triploid I struggled to work out how the pollen from two other trees would combine to form some sort of super pollen to fertilise the triploid tree. Or maybe it was a two stage process where the first pollen only made the triploid "half-pregnant". :/
    I guess all the advice about needing two other pollinators is based around commercial considerations of getting a crop from all the trees. It wouldn't be very efficient to keep a tree purely for pollination although even if that was the case you wouldn't need many for an orchard.
  • clarke.bruntclarke.brunt Posts: 215
    Indeed. I was a scientist - not in the correct field to fully understand genetics, but scientists have to question everything, to know the reason, rather than just taking what someone else says.

    I too only thought about this because I couldn't imagine a mechanism by which two pollen grains from different trees would be needed to pollinate a single flower.

    It's simpler to say you need 3 trees (if one is a triploid) with the assumptions that (a) most apples aren't self-fertile, and (b) the gardener probably wants fruit on all their trees, because otherwise you have to explain properly...


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