By Will Dunham

WASHINGTON, May 9 (Reuters) - Scientists have gotten to the root of the carrot, genetically speaking.

Researchers said on Monday they have sequenced the genome of the carrot, an increasingly important root crop worldwide, identifying genes responsible for traits including the vegetable's abundance of vitamin A, an important nutrient for vision.

The genome may point to ways to improve carrots through breeding, including increasing their nutrients and making them more productive and more resistant to disease, pest and drought, the researchers said.

The vitamin A in carrots arises from their orange pigments, known as carotenoids. The study identified genes responsible for carotenoids as well as pest and disease resistance and other characteristics. In addition to eyesight, vitamin A also is important for immune function, cellular communication, healthy skin and other purposes.

The researchers sequenced the genome of a bright orange variety of the vegetable called the Nantes carrot, named for the French city. The carrot genome contained about 32,000 genes, a typical total for plants, which average around 30,000 genes, which is more than the human genome.

"Carrots are an interesting crop to work on because of their wide range of diversity. They are familiar to everyone, and generally well-regarded by consumers, but like most familiar things, people don't necessarily know the background stories," said University of Wisconsin horticulture professor and geneticist Phil Simon, who led the study published in the journal Nature Genetics.

Worldwide carrot consumption quadrupled between 1976 and 2013 and they now rank in the top 10 vegetable crops globally, the researchers said. In the past four decades, carrots have been bred to be more orange and more nutritious, with 50 percent more nutrients.

The earliest record of carrots as a root crop dates from 1,100 years ago in Afghanistan, but those were yellow carrots and purple ones, not orange ones. Paintings from 16th century Spain and Germany provide the first unmistakable evidence for orange carrots.

Knowledge of the carrot genome could lead to improvement of similar crops, from parsnips to the cassava, the researchers said. Close relatives of carrots include celery, parsley, parsnips, coriander, cilantro, dill, fennel, cumin and caraway. The common weed called Queen Anne's Lace is a wild carrot.

The wild ancestors of carrots were white, the researchers said. While orange carrots are most commonly grown, some purple and yellow carrots are grown from the Middle East to South Asia, while some red carrots are grown in Asia.

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