Daucus carota

Abstract

Carrots (Dauetts carota L.) belong to the family Umbelliferae (Apiaceae) which includes other species such as anise , caraway , celery , celeriac , coriander, dill, parsnip, parsley, wild carrot (Queen Anne's Lace) , and water hemlock. The genus Daucus contains nearly 60 species , but about half of them are subspecies or forms of the polymorphic species D. carat a. Although information on the origin of the carrot is scarce, a purple-rooted carrot was native to the central Asiatic area (Afghanistan) and spread to the Mediterranean area during the lOth to 12th centuries and to Western Europe in the 14th and 15th centuries. 1 The common Western or "Mediterranean" orange-rooted carrot developed from this or a yellow variant form. The The cultivated carrot is considered a biennial since it remains vegetative the first year producing a large , fleshy root surmounted by a rosette of leaves. The carrot becomes reproductive the following growing season after overwintering, forming a branched flower stalk and seeds. Flowering of carrots occasionally occurs in the first year of growth. These premature bolters, or "annual seeders", are no doubt simply individual plants of the pop- ulation which have a higher threshold level for floral induction (see below). The vegetative carrot plant presents the following parts when viewed externally: petiole, or leaf stalk; neck, which is composed of the collective petiole bases; collar, or stem plate from which the petioles arise: shoulder, or crown which functions as a stem; root or fleshy storage organ; base or tip of the fleshy root; and taproot. 2 In this classification of parts, it is more appropriate to consider the collar as the compound stem plate rather than the crown, which is actually the uppermost portion of the fleshy root. The enlarged fleshy storage organ is composed of both hypocotyl and root tissue. Approximately 2.5 cm of the upper portion of the fleshy organ is hypocotyl at maturity; however, this length varies somewhat with seed depth at planting. Carrots Carrots as a biennial require an exposure to temperatures below a critical level (vernali- zation) for flower induction (see below). Seed production under field conditions involves 2 years for one generation: growing mature roots from seed the first year, harvesting and storing the roots at a low temperature during the winter, and replanting the roots (stecklings) in the spring to complete the reproductive cycle. The use of cold storage and greenhouses in the winter shortens the period to I year for research purposes. Another method, called the "seed-to-seed" method, allows the carrots to overwinter in the field where temperatures are, not too severe. APICAL