Thursday, August 22, 2019

Let's talk Grape Genetics and Selfing, and look at what sprouted in our potatoes!

Many thanks to Jon, one of the grapebreeders, and to Jean in Quebec and Troy in New Mexico for helping me understand this topic:

Most of you who are gardeners or farmers know that some seeds grow true and some do not. I've been told that a wild plum whose fruit I love wouldn't grow true from seed, so I was lucky to be able to root a cutting of it, and now the new tree is in a better spot (more sun, in our Middle Orchard). 

Grapes also don't grow true from seed. A grape's offspring will be different from their parent--maybe better, maybe worse. If an offspring is successful, it will tend to produce better offspring than its less-successful siblings. That is how evolution works.  

So, I found a grape seedling growing in one of our raised vegetable beds, amidst some potatoes. This was a very healthy young vine. I traced its unique leaf shape, color, and veining pattern to one of the grapes in the Epona Vineyard: the Delicatessen grape, one of my favorites. I've potted it up, and plan to raise it and see if and how its fruit is different. Growing a plant from its parent's seed is calling "selfing."

Here's Jon's response to my genetics question: 

"Yes, when you "self" a grapevine you will end up with new combinations of alleles, and the seedling is likely to be different in some respects to the parent.  There are some old American cultivars that are selfed seedlings of older cultivars. 

Here is a very basic summary of what is going on. Most cells in a grape vine have two copies of each chromosome, and thus can have two different copies of each gene. Consider a simple Mendelian scenario, where you have a dominant allele for big berries ("B"), and a recessive allele for small berries ("b"). You can have three genotypes: BB, Bb, and bb.  Since B is dominant, BB and Bb will both have big berries, and bb will have small berries. Now, when a  plant makes pollen and eggs, they only get one copy of each gene. So, with eggs and pollen from a parent with a heterozygous genotype (Bb), some will get B, and others will get b. When the plant fertilizes itself, depending on the combination of alleles inherited from the eggs and sperm, you could get embryos with any of the three genotypes, BB, Bb, or bb.  So, you can see how a parent that is heterozygous for big berries could produce big or small berried offspring.

Grapes are heterozygous for most genes, so in a selfing scenario, you have the above mechanism playing out countless times at the various loci (locations in the genome). This is what people mean when they mention that selfed seedlings get a "reshuffling" of their genes; No new genes can come into play, but new combinations of existing alleles surely will. 

So, your Deli seedling will surely have some differences, but will likely be very similar to the parent. One thing that is reputed to happen a lot with selfing is the production of runty, weak seedlings, resulting from the expression of normally masked recessive alleles, but it doesn't sound like you have one of these."

My hope is that this vine might bring some advantage compared to its parent Possible improvements (which I'll either see, or not see, in this offspring) are: greater vine vigor; more fruit yield; more complexity in flavor; earlier ripening.  We'll see. This is a "long game"--it will take 3-5 years to learn what we have here. It's the chase that fascinates growers. There's a tiny chance that this vine is something big, but it's far more likely that it will be so close to its parent that it doesn't deserve to be considered different. 


1 comment:

  1. Nice way to increase my knowledge poco a poco as they say.

    ReplyDelete

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