Orchid Parentage/Reproduction/Genetics

[slipperfreak]

Originally Posted by camille1585

To get back to the original post, Z1, Z2 and Z3 can be perfectly identical to each other if the parent plants are both completely homozygous. Homozygous is when both alleles of a gene are the same, either both dominant or recessive. Homozygote = AABBCC and heterozygote would be AaBbCc for example.

I really don't know if this is the case in orchids, but in many crop plants, pure lines (homozygotes) are made by taking haploid gamete cells and treating them with colchicine to double it and obtain a diploid. Since you are doubling the single allele, you'll get homozygote diploids.

When you breed two different homozygotes, such as AABB x AABB, all offspring will be AABB. If you breed AABB x aabb, offspring are all AaBb.

But I don't know if many pure lines have been created in orchid breeding by the breeders, and if they have, they are more likely to be used as breeding stock rather than propagated and sold. Also, the fact that all orchids are cloned for mass production eliminates the need for the sexual production of identical offspring.

I haven't heard of this being done in orchids before, but I don't know of any reason why it couldn't be done.

Not all orchids can be cloned - tissue culture of slipper orchids is usually not successful. Although, OL has successfully cloned Paph. delenatii, and I've heard rumors of Cyp. reginae being successfully cloned...

[Royal]

Originally Posted by Connie Star

Fascinating thread. But how do you know if a plant is diploid, triploid or tetraploid? Does someone do karyotyping of the orchids, or is it just assumed somehow? Are there any haploid specimens, or any who are higher than 4N? Also, are there any mosaics with some cells 3n and some cells 4N on the same plant? I would love to be in a lab where they study this!

The only way to know for sure is to count the chromosomes. Tissue from an active root tip is treated to halt mitosis, stained, then spread and viewed under a microscope. I do not know of any labs that do counts as a service. There are only a few growers that are doing counts, even though there are many that are doing colchicine conversions to make more 4n plants. If you have the recources to induce polyploidy, then you have the resources to confirm whether the process worked.

The old "eyball" method of identifying tetraploids has proven to be inadequate, as has gaurd cell analysis. These should really just be a screening process for selecting plants to count. Sometimes the ones you would swear were converted succesfully turn out to be still diploid. Sometimes the successfully converted tetraploids show no visible differences from the diploids.

[Cym Ladye]

Royal,

A post script on the ploidy of species: You are absolutely correct in the designation of 2n on species. However, many Cymbidium species have been converted to 4n for breeding purposes. In some cases, it comes to the fact that doing this can bring the species the improved form of an early hybrid. Continual breeding of "best to best" can cause truly interesting results in species hybridizing. But this man-made selection process in sib x sib species hybridizing is a topic for another thread.

CL

[JenHowlett]

In relation to zygosity, I would say that its a safe assumption (though I'm certainly no geneticist) that many marketed orchids today are heterozygous rather than homozygous. I would argue this based solely on the fact that it is well known in food crops (corn, wheat, rye, barley, etc) that heterozygous hybrids (hybrids of different varieties within the same species) are not only healthier and more virulent than their homozygous relatives but also tend to have higher yields. If orchid virility (e.g. flower size) is any indicator, then its reasonable to expect that the heterozygous plants will be more popular than the homozygous varieties.

If anyone has actual lab data or experience, it would be interesting to know if this is a valid hypothesis.