Author Topic: How is it possible for apomixis to be lost in a cross?  (Read 534 times)

Melenduwir

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How is it possible for apomixis to be lost in a cross?
« on: March 29, 2022, 04:23:54 PM »
I've done a little research on nucellar reproduction in citrus, and I understand that it's associated with several different groups of genes.  It seems that there's no single collection of genes responsible.

I've also encountered some lists of types of citrus that have monoembryonic seeds, including specific cultivars or varieties of some species that vary on this trait.  And some of them (I'd have to go back and doublecheck, but I distinctly recall noticing several) are the result of crossing two or more citrus types that are characteristically polyembryonic and nucellar.

I can easily understand that crossing a true-breeding nucellar plant with a sexually-breeding one might or might not result in a plant that clones itself.  Given the right combinations of genes, I can even understand how two sexually-breeding plants could result in an apomictic one.

*edited to change treat to trait
But how in the world can a forced cross between two highly nucellar types of citrus result in a plant that breeds normally?

I'm particularly interested because I want to try making new citrus varieties from dwarfed, potted plants at home, and the most cold-hardy citruses I can locate are all true-breeding nucellar types.
« Last Edit: March 30, 2022, 02:45:57 PM by Melenduwir »

kumin

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Re: How is it possible for apomixis to be lost in a cross?
« Reply #1 on: March 29, 2022, 06:37:58 PM »
There are cultivars that are purely zygotic, as well as cultivars that are nearly all nucellar. Between these 2 types are many cultivars that have a mixture of types. Depending on whether zygotic, or nucellar seedlings are desired, one can select the preferred seedling type by rouging the undesired seedlings. Predominately nucellar types will often have a few zygotic seedlings.

C-35 citrange seedlings showing a mixture of zygotic and nucellar types. This particular rootstock cultivar is 85% nucellar and 15% zygotic.

« Last Edit: March 29, 2022, 06:43:52 PM by kumin »

Walt

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Re: How is it possible for apomixis to be lost in a cross?
« Reply #2 on: March 29, 2022, 11:23:54 PM »
What Kumin said was right.
Also, sometimes in a seed with more than one seedling, one of them is zygotic.  You could only tell by seeing a unique seedling among them.  Depending on the recessive genes in the 2 parents, such a zygotic seedling could give zygotic seeds.  But that would not be the way to bet.  Whenever possible, use a mostly zygotic variety as seed parent,

pagnr

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Re: How is it possible for apomixis to be lost in a cross?
« Reply #3 on: March 30, 2022, 06:59:22 AM »
I'm particularly interested because I want to try making new citrus varieties from dwarfed, potted plants at home, and the most cold-hardy citruses I can locate are all true-breeding nucellar types.

You could also research the presence of zygotic seeds in these types, often related to seed size. They can often be selected for based on seed size.
Also the presence of zygotic types is not a fixed %, and can vary in some cultivars, seasonally or possibly by pollination.
If cultivars are difficult to cross into, using their pollen is an option if they are not sterile.

Melenduwir

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Re: How is it possible for apomixis to be lost in a cross?
« Reply #4 on: March 30, 2022, 02:49:27 PM »
C-35 citrange seedlings showing a mixture of zygotic and nucellar types. This particular rootstock cultivar is 85% nucellar and 15% zygotic.

I'm guessing you tell which are which by comparing the seedling leaves to the mother plant, and hope that the crossed seedlings are visibly different?  Waiting years for trees to mature and bear fruit in order to identify a subtle cross would be a nightmare for anyone with less resources than a professional breeder.

Melenduwir

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Re: How is it possible for apomixis to be lost in a cross?
« Reply #5 on: March 30, 2022, 02:54:06 PM »
What Kumin said was right.
Also, sometimes in a seed with more than one seedling, one of them is zygotic.  You could only tell by seeing a unique seedling among them.
  Since the nucellar embryos in citrus begin developing earlier than the zygotic, could I identify which of multiple seedlings is likely to be zygotic by comparing their size?

pagnr

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Re: How is it possible for apomixis to be lost in a cross?
« Reply #6 on: March 30, 2022, 03:45:36 PM »
This particular rootstock cultivar is 85% nucellar and 15% zygotic
With rootstocks, you generally compare the seedlings in the batch to each other. The foliage of the mature seed tree is different to the clonal seedlings. Same for key limes, immature seedlings slightly different to seed tree, i.e. smaller and softer overall.
In my experience off types from nucellar seed lots are most often less vigorous, and you may need to graft them to rootstock for them to thrive.

 

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