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4N Genetics

Discussion in 'Orchid Species' started by Wren, Feb 23, 2017.

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  1. Wren

    Wren New Member

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    I've been thinking about getting a Phal. schilleriana var. purpurea (4N). Since it is advertised as having double the genes it should have more, longer lasting flowers and be a more vigorous grower. I want to know more about 4N orchids - how are they made, how do I know a seedling is a 4N, and if they are better growers. Thanks everyone!
     
  2. naoki

    naoki Well-Known Member

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    There are several ways to produce artificial polyploids in plants. In orchids, I think most of the time people use germinating seed treatment. You soak the seeds in a chemical (e.g. colchicine) which disturb some aspects of cell division. If you do it too much the seedlings will die, and if it isn't enough, they will remain diploid, so they may try it at several concentration and duration. A small portion of them will double their genome and become tetraploids (4x) through this treatment. To differentiate 4x survivor from 2x survivor, easiest way is to use something called flow cytometry (basically it measure the size of nucleus). But the instrument is expensive and many breeders won't have the access. Alternatively, chromosome count can be done. But it requires lots of patience. Or you can look at the size of stomata cells under a compound microscope (i.e. typical microscope). Generally, the size of cells becomes much bigger.

    Once you selected 4x plants, then you can cross 4x plants to produce bunch of 4x offspring.

    Genetically, early generation artificial polypolids are "screwed up". In some genes, copy numbers of a gene influence their action and interaction. During the first couple generations of 4x breeding, breeders (unintentionally) select the individuals which can handle the imbalance, and we believe that rapid genome restructuring occurs (there are some evidence). So they can become stabilized.

    Effect of artificial polyploid could vary depending on species. In many cases, each cell becomes larger, so each part (leaf, flower etc) could become larger. This is the effect many orchid breeders who are into large flowers are after. If it is early generation 4x, it could be a slower grower than 2x in theory since they may not have recovered from genome doubling shock.

    I generally avoid artificial 4x because they are kind of artificial (like hybrids). But if you enjoy larger flowers, it may be worth it. In hybrid phals, where people think bigger and rounder is better, quite a few of them are polyploids, I believe.
     
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  3. carl

    carl Active Member

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    I believe some of the big whites are hexaploids; possibly octaploids.
     
  4. naoki

    naoki Well-Known Member

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    I didn't know that. I wonder if they will keep increasing the ploidy and what would be the consequence. It probably is a diminishing return (in terms of flower size), and they may grow slower.