Out of One, Many: Brassica domestication
Wild cabbage. It sounds gross. It is a plant whose relative is already a tough sell to most people and to see it labeled as “wild” only makes it even more ambiguously unappealing. You’ve probably come across it or a close relative and thought nothing of it, but if you peered a little closer, you’d notice that it looks very familiar.
The ruffled leaves might look edible enough for a salad. The unopened flower buds might be tasty after they are roasted, with a little salt, pepper, garlic powder, and olive oil. Wild cabbage is the wild relative of the Brassicas that we eat today and is a prime example of how the characteristics of one plant have been drastically changed by selection.
Brassica oleracea or wild cabbage has had several traits selected for the create the many accessions (a group of related plants from a single species) you are probably familiar with. These include plants such as cabbage, Brussel sprouts, kale, kohlrabi, broccoli, and cauliflower.
The traits that were selected for impact both vegetative (where the plants produce leaves, stems, and roots) and reproductive stages (when flowers are formed) of the plant’s life cycle. Humans have exploited these traits to modify the various parts of wild cabbage and created the crops we eat today.
For example, modern cabbage is much shorter than wild cabbage due to the compressed stem (that tough white part that you cut out before you eat it) causing the leaves to fold over one another and give us the compact cabbage look that’s so familiar to us today.
Brussel sprouts on the other hand have a long, central stem. But their branches are compact, which is why they look like miniature cabbages. A subtle difference like this has a major impact on the crop that’s produced. We saw this before with corn domestication.
Brussel sprouts on the stalk
Broccoli and cauliflower have a similar relationship. During plant development, a single flower is formed after a structure, called the floral meristem, switches its genetic makeup to begin producing a flower. Broccoli has an over-proliferation of floral meristems meaning that one plant makes a TON of floral meristems. Each floral meristem will produce a single flower bud which are those little green things that make up a head of broccoli and give broccoli its classic look.
Cauliflower is one developmental stage younger than broccoli. The white, edible part is made up of thousands of floral meristems. However, cauliflower has been bred to carry a mutation that prevents the floral meristems from making flowers showing how a small change in the genome of a plant can have a big impact on what it looks like.
Much more is known about Brassica domestication than is described here. We are beginning to unravel the mysteries behind domestication of the Brassicas including the genes specifically involved in the domestication process. Just like the domestication of corn, none of these plants would exist without human intervention, providing a good example of how genetic modification can have a positive and large impact on our crops.