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Thread: Triploid Fruit Trees

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    FB.'s Avatar
    FB.
    FB. is offline Early Fruiter
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    Default Triploid Fruit Trees

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    When triploid is mentioned, it brings visions of large, vigorous trees which require two other trees for good pollination. Well-known triploids include Bramley, Blenheim Orange and the pears Catillac and Vicar of Winkfield.

    For those who are unfamiliar with the term triploid and its implications, a simplification would be that the “mother” divides its genetic material by half and then gives one of those genetic halves to an offspring, with the other half of the offsprings genetic material being contributed by the “father”. With fruit trees, the “mother” would be the flower and the “father” would be the pollen grain from another tree, carried by a bee, to the flower. Apples and pears have 34 chromosomes, arranged into 17 pairs, with one of each pair being contributed by each parent.

    Triploids arise when the mother or father’s genetic material is not divided into two, such that the mother might provide all its genetic material to the offspring, plus the father adds its share. This results in 34 chromosomes from the mother and an additional 17 chromosomes from the father. The result being a triploid – with three copies of each of the 17 chromosomes.
    Having three of each chromosome (3x 17 sets = 51 in total), triploids can't divide the uneven number into two halves of 17 chromosomes when their pollen is produced, with the result that almost all their pollen grains have genetic abnormalities and therefore usually not very viable - the pollen is mostly sterile, so to speak.

    Occasionally, the offspring might have all 34 from its mother and all 34 from its father, which would result in a tetraploid – with four copies of each of the 17 chromsomes.
    Very occasionally, a chromosome gets “lost”, or copied, or unevenly divided during reproduction, resulting in an offspring with, say 17+1 chromosomes from one parent and the usual 17 from the other parent. This makes an aneuploid, which often is not a viable seed, but a few are capable of a relatively normal life. An example of this in humans is three copies of chromosome number 21 and two copies of all the others, which we all know as “Down’s Syndrome” (“trisomy 21”).

    When browsing nursery catalogues, it is assumed that the nursery has conveniently labelled all the triploids, so that we might be able to meet the triploids' requirements for additional room to grow and for additional pollinators.

    However, it is my belief that there are many more triploid fruit varieties than we are told. The reason being that there simply hasn’t been thorough enough research to identify all the triploids. The commercial orchards frankly don’t care about old, rare varieties, so why would anyone have bothered to do a detailed genetic analysis?
    It is also my belief that there are some polyploid varieties (several sets of chromosomes) and also some aneuploid varieties (which have additional chromosomes but not meeting a precise pairing number 2x=diploid, 3x=triploid, 4x=tetraploid, 2x+1 would be aneuploid).

    Having studied fruit trees intensively for a number of years, I have noticed – and heard from others – that triploids (or others with unusual chromosome numbers such as aneuploids) often show multiple unusual features, such as:

    Vigorous growth.
    Large fruits.
    Large blossoms (often very attractive).
    Large leaves.
    Thick, stiff, leathery leaves.
    Unusually dark-coloured leaves.
    Unusual-shaped leaves, such as relatively rounded shapes.
    Distorted leaf shape, such as off-centre leaf tips, crimped or partially folded leaves.
    Low seed count, or deformed-looking seeds.

    Not all of these features are evident in all cases.


    .
    Additionally, triploids tend to show the following features:

    More disease resistance (due to more genetic material which may contain resistance genes).*
    Better tolerance of difficult growing conditions (due to extra vigour and disease resistance).
    Erratic cropping (due to the need for good pollination from a diploid variety).
    Tendencies for fruit disorders such as bitter pit (due to poor seed content of the fruit; good seeds promote good fruit).

    *
    The usually-greater disease resistance of triploids can still be overcome by diseases if the variety is/was grown so widely that the diseases are/were forced to evolve to live on it or risk becoming extinct. Bramley was once highly resistant, but, having been grown for two centuries, the diseases are now getting well-adapted to attack it, with the result that Bramley's disease resistance is only about average nowadays.

    Tetraploids, being able to divide their genetic material equally, tend not to have the fruiting or fertility problems associated with triploids, but tetraploids may still show many of the features such as large leaves and blossoms.


    Over the years, I have grown or observed a number of varieties. Based on my observations, I would suggest their genetic constitution is as follows:

    “Normal” diploids and “fertile” others, such as tetraploids:
    Beauty of Bath: diploid (2x)
    Crawley Beauty: diploid (2x)
    Tydeman’s Late Orange: diploid (2x)
    Spartan: diploid (2x)
    Court Pendu Plat: diploid (2x)
    Discovery: diploid (2x)
    Bountiful: diploid (2x)
    Laxton’s Superb: diploid (2x)
    Red Devil: diploid (2x)
    Ellison’s Orange: diploid (2x)
    Scrumptious: diploid (2x)
    Fiesta/Red Pippin: diploid (2x)
    Egremont Russet: diploid (2x)
    Golden Delicious: diploid (2x)
    Cox's Orange Pippin: diploid (2x)
    Charles Ross: diploid (2x)
    Worcester Pearmain: diploid (2x)
    James Grieve: diploid (2x)
    Lord Lambourne: diploid (2x)
    Laxton’s Epicure: tetraploid (4x)
    Winter Majetin: tetraploid (4x)


    “Abnormal” triploids and aneuploids:
    Belle de Boskoop: triploid (3x)
    Jupiter: triploid (3x)
    Gasoyne’s Scarlet: triploid (3x)
    Hambledon Deux Ans: triploid (3x)
    Coeur de Boeuf: triploid (3x)
    Edward VII: triploid (3x) or aneuploid
    D’Arcy Spice: aneuploid
    Norfolk Beefing: triploid (3x)
    Blenheim Orange: triploid (3x)
    Bramley: triploid (3x)
    Alfriston: triploid (3x)
    Ashmead’s Kernel: triploid (3x)
    Annie Elizabeth: triploid (3x) or aneuploid
    Jumbo: triploid (3x)
    Suntan: triploid (3x)



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    Please bear in mind that the above is WHAT I THINK. I might be wrong – and what I have written is certain to have its disbelievers and critics.

    I hope that's of interest.
    Last edited by FB.; 09-12-2011 at 10:48 AM.

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    Speed Gardener is offline Sprouter
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    FB - we are not worthy!!!
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    yummersetter is offline Rooter
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    See how far I've got through the archives!

    This is really a fascinating posting. The whole field of genetic differences in apples is so interesting.
    I have dozens of unusual varieties of apples and suspect that several are unrecorded triploids. This year, being a bad year for fruit, seems to be a great year for foliage and I'm considering making a set of photos of each variety's leaves, I've never seen them look so healthy at this time of year. The puzzle is that on each branch there are differing sizes and shapes - when you photographed yours did you just go for the average / majority?

    I guess that any day now we'll be sending bits of apple to Brogdale for a genetic ID, rather than counting the notches round a leaf edge.

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    FB's informed guess (last year) that Ashmead's Kernel was a triploid was recently confirmed in a scientific paper published by Defra.
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    yummersetter is offline Rooter
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    Hello, OP! Yes, A'sK and Suntan were the eyebrow-raisers for me on that list. And to know that there were such weird things as aneuploids, I need to learn more about this.
    I think in our old orchard a lot of the ancient survivors are triploids, almost by definition, so I had to think what to put where and why when I replanted.

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    yummersetter is offline Rooter
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    I've just found the DEFRA DNA tested triploid list from a link on your website, Orange Pippin, extraordinary! A lot of my triploid spotting by leaf this morning confirmed, Morgan Sweet, Orleans Reinette and Tom Putt, the Golden Russett isn't at Brogdale and the others were known triploids when I planted them. It's a nuisance that quite a few of the diploids I've planted are biennial, as now I see that they're carrying more of the pollination load than I intended.

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    orangepippin is offline Tuber
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    Suntan is listed in the excellent Hessayon Fruit Expert book as a triploid.

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    Quote Originally Posted by orangepippin View Post
    Suntan is listed in the excellent Hessayon Fruit Expert book as a triploid.
    Yes, Suntan is triploid.
    Cox contributed two sets of chromosomes and Court Pendu Plat contributed one.

    Suntan has thick shoots like a Bramley.

    I found Suntan to be hopelessly prone to powdery mildew - then the MM106 rootstock began to die from crown rot, so I removed the tree.

    I can't say that I'm a fan of Hessayon. The book is OK as a starter, but I think that Hessayon has an obsession with "spray, spray and spray some more" and also lacks an appreciation of the way different varieties, soils and climates interact.
    The book also writes off vigorous rootstocks as "too big" (not true in many dry, chalky Eastern areas when unsprayed!) and only discusses common and popular varieties - failing to mention many of the excellent old varieties.
    Last edited by FB.; 12-07-2012 at 11:34 AM.
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