what is vinegar-pickled duakuan?

Question

it is ued in koean sushi

Answer 1

pickled daikon is called takuan, is that what you are talking about? It's colored yellow when pickled and sweet tasting.

Answer 2

I believe it is spelled daikon.
Daikon, literally "large root", (traditional Chinese) is a mild-flavored East Asian giant white radish. Though most widely known as daikon, the radish is also known under other names, including daikon radish, Japanese or Chinese radish, and winter radish. Although there are many varieties of daikon, the most common in Japan, the Aokubi Daikon, has the shape of a giant carrot, approximately 8 to 14 inches long and 2 to 4 inches in diameter. One of the most unlikely shaped daikon is Sakurajima daikon from Kagoshima Prefecture that is shaped like an oversized turnip with white outside and bright pink inside.
In Korea, it is often pickled, and used in kimchi.

http://en.wikipedia.org/wiki/Daikon