Building the Perfect Esrog

A couple of years back I wrote about how much an esrog is really worth. Are some features (like גידול) objectively worth more than others, or are prices driven by irrational consumer markets? At the same time, I also discussed how, for practical reasons, it's impossible to fully comply with the Chazon Ish's preference to avoid esrogim descended from the products of grafted branches (harchava).

Thinking about all that recently got me wondering about whether it might be possible to analyze the genome of modern esrogim to objectively determine whether there's any grafting or hybrid parentage in their history. As it turns out, the quick answer is that it is indeed possible - in fact it's already been done - and, as it further turns out, modern esrogim are pretty much universally pure.

This is true even though people have been grafting esrog branches on to foreign root stock (like lemon trees) for many centuries. Such grafting will indeed improve the subsequent fruit, but there's apparently no transfer of genetic material from the parent tree: the resulting fruits are still 100 percent esrog. That doesn't mean we're allowed to use such esrogim for the mitzva, but that whatever the reason for the prohibition, it's unrelated to the fruit's DNA.

But that's not quite the whole story.

The citron family is an important genetic ancestor of many modern citrus fruits. And there's heavy commercial demand for creating improved strains of those popular fruits that are, say, disease-resistant or capable of growing on less water. Partly to help with those projects, the citron (Citrus medica) genome has been extracted, published, and carefully studied.

I downloaded and dove into the 605 page book (“The Citron Compendium”) that came out the other end. Believe it or not, it's fascinating to read how geneticists can identify the individual genes responsible for specific attributes and simply switch those genes on or off to precisely control the fruit. This is a very big deal when it comes to protecting vulnerable food supplies or increasing the profitability of marginal products. And there's an enormous amount of money to be earned.

But as far as I can tell, there haven’t yet been any indications of geneticists playing around with our esrog stocks. However, being able to reliably produce visually and genetically perfect esrogim could prove immensely profitable. Would it be a problem if someone did edit the genome (or if someone already has)?

To be clear, genome editing is not the same as creating a hybrid fruit or grafting the branch on a foreign stock. Fruits from such exercises would be invalid - and the exercises themselves would, of course, be forbidden as כלאים. But simply modifying individual genes at the molecular level doesn’t involve adding or removing anything. Presumably, as long as the resulting fruit would look, smell, and taste like an esrog, there might not be a problem.

This obviously goes way beyond my limited expertise. But it’s still a question worth asking.