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HORT410 - Vegetable Crops

Onion and its Relatives - Notes

  • Common name: onion.
  • Latin name: Allium cepa L.
  • Family name: Amaryllidaceae (Liliaceae, Alliaceae) [Liliaceae Images].
  • Diploid (2n = 16).
  • Monocotyledon.
  • Harvested organ: swollen base of the stem (bulb) with numerous fleshy leaves.
  • Economically most important bulb vegetable.
  • Origin: Persia.
  • Cultivated by the Egyptians, Greeks and Romans.
  • Brought to N. America by the Spaniards.
  • Long considered of medicinal value.
  • Onion history (TAMU).
  • Distinctive flavor and odor of Allium species occurs when plant tissue is bruised, cut or macerated
  • Enzyme alliinase (cysteine sulfoxide lyase) catalyzes the conversion of alliins to allicins.
  • These flavor compounds have antimicrobial activity.
  • Onion divided into 3 main groups:
      1. The common onion
      • bulbs are formed as single plants
      • inflorescence does not form bulbets
      • biennial, often grown as an annual
      • most important commercially
      • propagated in the main from true seeds
      • sometimes planted as transplants
      • small bulbs (sets) are produced from thickly planted seed
      • when sets are replanted, these bulbs reach maturity rapidly
      • cultivars vary for bulb shapes, dry scale color (white, yellow, and red), pungency (ranging from mild and sweet to pungent), soluble solids, adaptation to different day lengths
      • when harvested early they produce spring or bunching onions
      • mature bulb onions are usually dried before marketing

      2. The aggregatum group
      • with many lateral bulbs or shoots
      • inflorescences lacking bulbets
      • sterile seed production
      • propagation by vegetative means
      • includes the potato onion or multiplier onion, ever-ready onions, and shallots
      • shallots are sometimes called scallions, a source of confusion because A. fistulosum is also called scallions

      3. The proliferous (proliferum) group
      • ground bulbs are sometimes poorly developed
      • infloresence bears bulbets
      • true seed is usually lacking
      • reproduction is by vegetative infloresence and bulbets
      • not commercially cultivated
      • almost exclusively for home gardening
      • includes tree onions, top-set onions, and Egyptian onions
  • Major diseases of onions in the Midwest:
  • Insect pests of onions in the Midwest:
  • Onion seed production industry has moved away from open-pollinated types to hybrid production systems
  • Cytoplasmically inherited male sterility factor (S) and a nuclear encoded gene (Ms) which can normally override the male sterility or "restore" the plant to a normal fertile phenotype
  • When this "restorer" gene is in the homozygous recessive condition only in the S cytoplasm does male sterility result
      S msms ( = sterile)
      S Msms ( = fertile)
      S MsMs ( = fertile)
      N msms ( = fertile) (N msms plants are known as maintainers)
      N Msms ( = fertile)
      N MsMs ( = fertile)
  • Onion is insect (bee) pollinated
  • In hybrid production important to have both parental lines flowering at the same time
  • Ratio of 8 female : 2 male rows commonly used.
  • Three-way hybrids prepared by crossing an S msms F1 hybrid (male sterile) to a third inbred parent
  • Similar male sterility system in chives (A. schoenoprasum)
  • In chives, male sterility caused by the S cytoplasm is reversed by the dominant restorer gene X
  • Plants only with the genetic constitution Sxx are male sterile
  • Five major genes determine onion bulb color:
      I- inhibits the production of color and the bulbs are white (the expression of red, yellow or chartreuse pigments requires that the plant be ii)
      C locus conditions the production of colored bulbs
      all iicc bulbs are white
      plants with a dominant allele at the C locus and homozygous recessive rr at the R locus are yellow to brown in color
      red bulbs are conditioned by dominant alleles at both the C and R loci (iiC-R-)
      a dominant allele at the G locus conditions a golden color without pink
      chartreuse bulbs are homozygous recessive at the G locus
      L conditions a red pigment when the plant has the genotype iiC-rrG-L-
  • Over 600 Allium species known.
  • Related alliums used as vegetables and/or herbs include:
      A. schoenoprasum L., chive; slender hollow leaves; used as a flavoring for salads; bulbs narrow.

      A. fistulosum L., Japanese bunching onion, scallions or Welsh onion; like large and very coarse chives; hollow evergreen leaves; almost no bulb at the base; not clear how this onion came to be associated with Wales (origin = China); may be derived from the German welsche = foreign.

      A. sativum L., garlic, grown for its bulb with a distinctive and strong flavor; propagates only vegetatively; a bulb consists of up to 10 cloves.

      Image of Leek, by Patrick J. Rich A. ampeloprasum L. var. porrum (syn. A. porrum), leek; commonly grown for its thickened and overlapping leaf bases; generally white; self-compatible outbreeding tetraploid.

    (see: ID-56: Midwest Vegetable Production Guide for Commercial Growers 2003 - Onions (Bulb and Green) (PURDUE) [pdf] for onion crop recommendations (varieties, spacing and seeding, fertilizing, disease, weed and insect control) recommendations for the Midwest)

    Sources of information:

  • Davis, M.K., Grafius, E., Cranshaw, W., Royer, T. Onions. In "Vegetable Insect Management With Emphasis on the Midwest" (ed. R. Foster, B. Flood), Meister Publishing Co., Willoughby, Ohio, pp. 139-146 (1995).
  • Nonnecke, I.L. "Vegetable Production", Van Nostrand Reinhold, NY (1989).
  • Phillips, R., Rix, M. "The Random House Book of Vegetables", Random House, NY (1993).
  • Lorenz, O.A. Onion. In "The Software Toolworks Multimedia Encyclopedia", Version 1.5, Grolier, Inc. (1992).
  • Tatlioglu, T. Chive, Allium schoenoprasum L. In "Genetic Improvement of Vegetable Crops", (ed. G. Kalloo, B.O. Bergh), Pergamon Press, Oxford, U.K., pp. 3-13 (1993).
  • Batchvarov, S. Garlic, Allium sativum L. In "Genetic Improvement of Vegetable Crops", (ed. G. Kalloo, B.O. Bergh), Pergamon Press, Oxford, U.K., pp. 15-27 (1993).
  • Pink, D.A.C. Leek, Allium ampeloprasum L. In "Genetic Improvement of Vegetable Crops", (ed. G. Kalloo, B.O. Bergh), Pergamon Press, Oxford, U.K., pp. 29-34 (1993).
  • Havey, M.J. Onion, Allium cepa L. In "Genetic Improvement of Vegetable Crops", (ed. G. Kalloo, B.O. Bergh), Pergamon Press, Oxford, U.K., pp. 35-49 (1993).
  • Ford-Lloyd, B.V., Armstrong, S.J. Welsh Onion, Allium fistulosum L. In "Genetic Improvement of Vegetable Crops", (ed. G. Kalloo, B.O. Bergh), Pergamon Press, Oxford, U.K., pp. 51-58 (1993).
  • Midwest Vegetable Production Guide for Commercial Growers, ID-56, eds. R. Foster, D. Egel, E. Maynard, R. Weinzierl, H. Taber, L.W. Jett, B. Hutchinson, Purdue University Cooperative Extension Service, 2003.
  • Warade, S.D., Kadam, S.S. Onion. In "Handbook of Vegetable Science and Technology: Production, Composition, Storage, and Processing", (ed. D.K. Salunkhe, S.S. Kadam), Marcel Dekker, Inc., NY, pp. 373-396 (1998).
  • Warade, S.D., Shinde, K.G. Garlic. In "Handbook of Vegetable Science and Technology: Production, Composition, Storage, and Processing", (ed. D.K. Salunkhe, S.S. Kadam), Marcel Dekker, Inc., NY, pp. 397-413 (1998).
  • Warade, S.D., Shinde, K.G. Other Alliums. In "Handbook of Vegetable Science and Technology: Production, Composition, Storage, and Processing", (ed. D.K. Salunkhe, S.S. Kadam), Marcel Dekker, Inc., NY, pp. 415-431 (1998).

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  • David Rhodes
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    Last Update: 03/11/09