https://scitechdaily.com/researchers-su ... rootstock/

Interesting read. The epigenetically modified gene of the Rootstock was passed on to the Scion progeny. How could that be possible?

Cool.... there's always more to learn about genetics.
It makes perfect sense to me that, for example, a tomato plant that had activated its cold tolerance genetics in a given season, would pass on those epigenetic settings to its progeny as a default.
This would explain why we see adaptation of varieties to specific environments, so that your saved seed is pre-adapted and does better than the parent seeds.
Of course those observations are anecdotal... a real test would be to grow parent and offspring seeds side by side and at least 30 plants each. Giant plantation anyone?

Obviously these Rootstocks had a gene 'Turned On', but the result could potentially occur naturally too. Which I find very cool.

Theoretically, you could have a very dry season in which your produce was limited. However, if you've saved seeds from that crop, you potentially have a seed that grows into a hyper active plant and produce significantly better than its parents. In addition, this study shows that it's not just the following year, but 5 years after the initial drought season!

I guess I should look back and see if any of these old seeds I have came from a harsh year.

PS
My mad scientist thoughts are stirring.
Taking cuttings from a plant that has its 'Stress Memory' activated, its possible to use it was a Rootstock for your other plant varieties and induce the same affect. At least, that's what I'm gathering from this study.