Focus on: domestication, details on selection of orange color
BABY CARROTS
From Ugly Root to Adorable Snack Food
Introduction
Baby cut carrots, those adorable little carrot nuggets, are a healthy convenient alternative to junk food. No cutting or peeling required; just open the package and start crunching! Where do they come from? The baby cut carrot is very different from the wild carrot, its closest relative. The change from wild to familiar is a story of choices, and an ingenious idea! Look deeper to learn more about each chapter of the baby cut carrot's story.
How well do you know carrots? Which of these unfamiliar items is actually a carrot?
About the Organism
As members of the kingdom Plantae, carrots are organisms that make their own food during photosynthesis. The carrot's stem grows above ground where it connects the root to the leaves, the site of photosynthesis, and the flowers, which house the plant's reproductive structures. Photosynthesis in the carrot's leaves produces sugars which are transported in the phloem and are stored down in the cortex of the carrot root. The plant stores energy underground to survive winter and be ready for fast regrowth in spring—a two year or biennial life cycle. We interrupt this cycle and capitalize on the plant's strategy by harvesting the roots packed full of energy in the fall.
The carrot's root has other functions too. Root hairs on the outer layers absorb water and nutrients, most of which are moved up to the stems and leaves. The core, the innermost section of the root, is the woodiest part because it contains the xylem, the water transporting tissue that carries water up the stem to the leaves.
What makes carrots orange? Pigments—chemical structures that reflect certain wavelengths of light—cause the colors we see in nature. A group of pigments called carotenes make carrot roots orange. The most common carotene is beta-carotene, a precursor to Vitamin A, but carrots also make several other carotenes. Of course, not all carrots are orange! Different carrot colors are due to different pigments in the plants.
What makes carrots orange? Pigments—chemical structures that reflect certain wavelengths of light—cause the colors we see in nature. A group of pigments called carotenes make carrot roots orange. The most common carotene is beta-carotene, a precursor to Vitamin A, but carrots also make several other carotenes. Of course, not all carrots are orange! Different carrot colors are due to different pigments in the plants.
- The white carrot has barely any pigments.
- The orange carrot's color is due to carotenoid pigments—mainly to beta-carotene, with some alpha-carotene.
- Red carrots contain the pigment lycopene, another type of carotene, which is also found in tomatoes and watermelon. Red carrots also contain alpha- and beta-carotenes.
- The yellow carrot's color is caused by xanthophylls, another type of carotene.
- The purple carrot, however, has color from a different family of pigments called anthocyanins. Other vegetables like beets and purple cabbages also have anthocyanins.
Different amounts of different pigments lead to a rainbow of carrot colors.
How Nutritious?
Orange carrots are an excellent source of fiber, as well as vitamins and minerals including Vitamin A, Vitamin K and manganese. They are also a good source of Vitamin C, several B vitamins, iron, potassium and copper. They are low in saturated fat and cholesterol.
Carrots can be eaten raw or cooked. They have a crunchy texture that softens when cooked.
Carrots can be eaten raw or cooked. They have a crunchy texture that softens when cooked.
The Challenge:
How can an ugly vegetable be transformed into a popular replacement for junk food?
How can an ugly vegetable be transformed into a popular replacement for junk food?
The transformation of wild carrots into the forms we know today occurs in three steps.
The Solution:
From Sallow and Scrawny To Lovely Orange: Using Artificial Selection to Develop Desired Traits
The baby carrots in your lunch neither look nor taste like wild carrots. Modern carrots have been carefully bred over hundreds of years to include traits like uniformity, crunchiness, sweetness and color that are desirable to humans. This is a solution that occurred in three parts: First, people domesticated wild carrots into cultivated ones. Second, people made choices that resulted in orange-colored carrots. Third, a brilliant idea led to tiny packaged carrots.
Humans domesticated many plants and animals over the last 12,000 years. Carrots are one of the most recent organisms to be domesticated.
> Part 1: Domestication from the Wild Plant
Adapting wild animals or plant for human use is called domestication. Domesticated organisms have different traits from their wild ancestors, differences that are highly desirable to humans. Humans began domesticating plants and animals about 12,000 years ago. Carrots have been domesticated less than a thousand years; compared to other crops, that's a recent domestication.
Adapting wild animals or plant for human use is called domestication. Domesticated organisms have different traits from their wild ancestors, differences that are highly desirable to humans. Humans began domesticating plants and animals about 12,000 years ago. Carrots have been domesticated less than a thousand years; compared to other crops, that's a recent domestication.
Carrots were domesticated from wild carrots, also known as Queen Anne's Lace. What were the major changes between the wild and domesticated carrots? The thinner wild carrot roots are more woody and bitter than roots of domesticated carrots. Domesticated carrots have a single big root packed with lots of stored sugars, rather than lots of side roots. Additionally, the root color of early domesticated carrots was yellow or purple rather white, like the wild carrot. The combination of these traits meant that domesticated carrots were much tastier to humans.
When an organism is domesticated, it loses genetic variation. In a wild population, organisms have lots of genetic diversity. Only a few wild relatives (and their genes) are the basis for domesticated, cultivated plants, so the genetic diversity decreases dramatically after domestication. This reduction in genetic diversity is called a bottleneck. Only the genetic diversity that survives the bottleneck will be represented in future generations—no matter how many individuals there may be.
A bottleneck is a reduction in genetic diversity.
A wild population has lots of genetic variation (left panel).
After domestication occurs (center panel) the amount of genetic variation decreases dramatically (right panel).
A wild population has lots of genetic variation (left panel).
After domestication occurs (center panel) the amount of genetic variation decreases dramatically (right panel).
However, compared with other domesticated plants, the carrot retains an unusual amount of genetic diversity. In other words, the genetic bottleneck is not much of a genetic bottleneck. Why would carrots have such a limited bottleneck? The answer probably lies in the carrot plant's biology. Carrots freely cross-pollinate with wild relatives, constantly moving wild genes into the domesticated population.
Think and Apply
Carrots retain an unusual amount of genetic diversity. Which way would you redraw the domestication figure for carrots?
Try Again
Carrot populations have much of the diversity that wild relatives do. Recall that carrot diversity comes from cross-pollinating with wild relatives, not from a weak bottleneck at domestication.
Correct!
Answer: B. Carrots have a normal domestication bottleneck (middle panel). However, cultivated carrots have a lot of genetic diversity (right panel) because of crosses with wild relatives that carry in wild genes. The domesticated and modern varieties have almost as much genetic diversity as the wild species, which is very unusual for crops.
Think and Apply
Where were carrots domesticated?
Based on where carrot diversity is found today, researchers proposed that carrots originated in Central Asia—what is now Afghanistan. Does the phylogeny generated in a recent genetic study support this hypothesis (Hint: which branches of the family tree are most closely connected to the orange cultivated carrots?)
Image from Iorizzo, M et al. 2013. Genetic structure and domestication of carrot (Daucus carota subsp. sativus) (Apiaceae). Botany. https://doi.org/10.3732/ajb.1300055.
Based on where carrot diversity is found today, researchers proposed that carrots originated in Central Asia—what is now Afghanistan. Does the phylogeny generated in a recent genetic study support this hypothesis (Hint: which branches of the family tree are most closely connected to the orange cultivated carrots?)
Image from Iorizzo, M et al. 2013. Genetic structure and domestication of carrot (Daucus carota subsp. sativus) (Apiaceae). Botany. https://doi.org/10.3732/ajb.1300055.
Yes - Correct! The phylogeny shows the samples of wild carrots from Central Asia (green) to be most closely related to the cultivated carrot samples (orange semi-circle).
No. Incorrect - Look more closely. Which of the geographic groups (blue circles) are most closely connected to the orange cultivated carrots (orange semi circle)?
Domesticated carrots are different than their wild relatives - tastier, prettier and more nutritious. In spite of the unusual diversity and movement of the wild genes into cultivated carrots, the genes present in cultivated carrots produce traits that appeal to humans.
>Part 2: Becoming Orange via Selection – Artificial Selection as the First Plant Breeding Technology
One trait stands out in carrots: the orange color. Orange carrots have only been around for the last six hundred years—early carrots were purple and yellow. Early carrots, like all carrots, produced low levels of beta- carotene in the leaves, where it aided in photosynthesis and protected plants from over-exposure to sunlight. The first orange carrots had a mutation that caused accumulation of beta-carotene pigment in the root.
Why did people prefer orange carrots? One carrot researcher, Phillip Simon, has suggested that orange color might have allowed carrot growers to easily see if their carrot patches had been "polluted" by pollination with nearby (non-orange) wild carrots. Another popular idea is that orange carrots developed as a tribute to William of Orange, who led the Dutch revolt for independence. Whatever the reason, people liked the orange color, and plant breeders continued to select for varieties that concentrated more and more orange in the roots.
How did plant breeders make these changes? With the power of their choices, through simple selection.
One trait stands out in carrots: the orange color. Orange carrots have only been around for the last six hundred years—early carrots were purple and yellow. Early carrots, like all carrots, produced low levels of beta- carotene in the leaves, where it aided in photosynthesis and protected plants from over-exposure to sunlight. The first orange carrots had a mutation that caused accumulation of beta-carotene pigment in the root.
Why did people prefer orange carrots? One carrot researcher, Phillip Simon, has suggested that orange color might have allowed carrot growers to easily see if their carrot patches had been "polluted" by pollination with nearby (non-orange) wild carrots. Another popular idea is that orange carrots developed as a tribute to William of Orange, who led the Dutch revolt for independence. Whatever the reason, people liked the orange color, and plant breeders continued to select for varieties that concentrated more and more orange in the roots.
How did plant breeders make these changes? With the power of their choices, through simple selection.
Simple selection, simplified. Selection—the power of choice—can change organisms dramatically. How does it work?
As early plant breeders changed the carrot's color, they changed its genes. Orange color in the carrot root is best explained with a two gene model.The first gene, called Y, is a dominant gene that blocks production of yellow and orange pigments. In other words, a non-pigmented, white carrot is the dominant trait. An orange carrot requires two recessive copies of the Y gene. A second gene, called Y2, determines whether orange pigments accumulate in the root. An orange carrot has two recessive copies at two genes: yy and y2y2. Recent sequencing of the carrot genome identified a likely candidate for the Y gene—linking the genetic model to the carrot genome.
Modern plant breeders continue to improve orange color, or more specifically the beta-carotene levels in carrot roots. Increasing the amount of beta-carotene in carrot increases its nutritional content. Since the 1970s, plant breeders have increased beta-carotene levels by 40%, simply by selecting for deeper, stronger orange color. Beta-carotene is especially important to humans because the human body converts it into retinal and then into Vitamin A or retinol. Vitamin A plays important roles in vision, the immune system, skin health and bone growth.
Modern plant breeders continue to improve orange color, or more specifically the beta-carotene levels in carrot roots. Increasing the amount of beta-carotene in carrot increases its nutritional content. Since the 1970s, plant breeders have increased beta-carotene levels by 40%, simply by selecting for deeper, stronger orange color. Beta-carotene is especially important to humans because the human body converts it into retinal and then into Vitamin A or retinol. Vitamin A plays important roles in vision, the immune system, skin health and bone growth.
Carrot breeders use controlled crosses and careful pollination between parents with desirable characteristics.
What traits do modern carrot breeders work to improve? Desirable traits depend upon the carrot's use, the market, the farmer and the growing conditions. Beyond color, there are a wide variety of traits that are desirable to carrot growers. Breeders look to the diverse wild and cultivated germplasm for varieties with these traits, and then try to breed those traits into cultivated lines.
Uniformity and strength of crop traits
- Smoothness of the root
- Quality of the root
- Resistance to splitting
- Resilience in processing
- Strength of attachment between roots and leaves for mechanical harvesting
- Seed yield
Resistance to pests and disease traits
- Resistance to Alternaria leaf blight
- Protection from aster yellows
- Resistance to carrot fly
- Resistance to nematodes
- Resistance to powdery mildew
Improving taste and texture traits
- Crunch
- Sweetness
- Reduced bitterness
- Texture
> Part 3: An Ingenious Idea: From Orange to Adorable
How do we get from lovely orange to absolutely adorable little baby cut carrots? Carrots don't actually grow that way. In fact, you can think of them as little carrot sculptures. Baby cut carrots are the brainchild of a Mike Yurosek, a farmer in California. In 1986, Yurosek was trying to figure out ways to increase sales of carrots and used an industrial green bean cutter to cut the carrots into little 2" nubs. He sent a bag off to the grocery store, and they immediately wanted more. Today baby cut carrots represent 70% of the carrot sales in the United States.
Baby cut carrots helped revive the carrot industry that was struggling. They have also helped reduce farm waste, since scraps are reused for carrot juice or animal feed. Most importantly, baby cut carrots are a fun, healthy snack!
How do we get from lovely orange to absolutely adorable little baby cut carrots? Carrots don't actually grow that way. In fact, you can think of them as little carrot sculptures. Baby cut carrots are the brainchild of a Mike Yurosek, a farmer in California. In 1986, Yurosek was trying to figure out ways to increase sales of carrots and used an industrial green bean cutter to cut the carrots into little 2" nubs. He sent a bag off to the grocery store, and they immediately wanted more. Today baby cut carrots represent 70% of the carrot sales in the United States.
Baby cut carrots helped revive the carrot industry that was struggling. They have also helped reduce farm waste, since scraps are reused for carrot juice or animal feed. Most importantly, baby cut carrots are a fun, healthy snack!
Where do baby carrots come from?
Think and Apply
Imagine you are a farmer who would like to produce baby cut carrots. What carrot traits would you ask plant breeders to develop in your carrots?
One Perspective
As you can imagine, big farms that are growing carrots to make baby cut carrots need a number of different traits in their carrots. Some highly desirable traits include:
- seeds that produce reliably uniform shaped carrots
- resistance to common carrot diseases
- high beta-carotene levels so that they have attractive orange color and are nutritious
- excellent taste, meaning they have good crunch, low bitterness, and high sweetness
- a strong attachment where the leaves connect to the roots, so the machines can pull them from the ground without harm
Conclusion
The baby cut carrots we eat as snacks are a modern invention, shaped by simple, traditional plant breeding. Baby cut carrots are the product of a recent innovative processing idea—cutting and tumbling the carrots to produce a nutritious snack. The orange color we associate with carrots is the result of the concentration of beta-carotene—an orange plant pigment—in the carrot's root. Over 600 years, plant breeders have intensified the orange color by simple selection—efforts that continue successfully today. The carrot was domesticated from its wild relative, Queen Anne's Lace, in the last 900 years—a relatively recent domestication compared to many other food plants.
