ONION
Allium cepa L., family AmaryllidaceaeOnions are grown in just about every country in the world. They are used in salads, as a raw or cooked vegetable, and as a condiment. Five related species of Allium, sometimes grouped with or referred to as onions, are also used in lesser amounts for food seasoning or embellishment. These include A. ascalonicum L., shallot; A. fistulosum L. (see "Welsh, Japan, or Spring Onion"); A. porrum L. (see "Leek"); A. sativum L., garlic; and A. schoenoprasum L. (see "Chives"). Garlic and shallot present no pollination problem, as they seldom flower, and when flowers do appear on garlic they are sterile so seeds are unknown. Both are propagated by bulblets or cloves (Bailey 1949*, Mann 1952, Mann and Little 1957).
As shown in table 14, the six Allium species can generally be distinguished from each other by gross characteristics.
[gfx] FIX TALBE 14. below:
TABLE 14.ÑGross characteristics of Allium species __________________________________________________________ Species Length of Shape of of Character Allium leaves stalk of bulb __________________________________________________________ Inches Onion ............... Round, hollow 24-48 Large. Welsh onion ............. do .............. 12-20 Indistinct. Chive .............. Round and hollow, 6-24 Do. forming tufts and sods Shallot ........... Round, hollow (1) Numerous, small. Garlic ............. Flat, narrow; (1) Bulbs with several 24 to 36 inches parts (cloves). long, 1 inch wide Leek ................ Flat and leafy 24-36 Slightly broader toward base; than the stem. 24 to 36 inches long, 2 inches wide __________________________________________________________ 1 Flower stalk rare.
About 4,000 acres of onions were grown for seed in 1969, the value of the seed being about $4 million. This seed was used to produce 100,750 acres of green (shallot, scallion) or bulb onions of commerce, valued at $107.8 million.
Seeds of the southern types of onions are produced in southern California and southwestern Arizona. Northern type seeds are produced primarily in Colorado, Idaho, New York, Oregon, and Utah (Hawthorn and Pollard 1954*). Better seed growers obtain 800 to 1,000 pounds of seed per acre (Comin 1946), although there are great variations in yields with years, growers, fields, and cultivars. Best seed yields are obtained when the seeds are produced on non-transplanted or seed-to-seed plants (500 to 700 lb/acre with more than 1,500 lb/acre reported) as compared to 300 to 500 lb/acre with up to 1,000 lb/acre reported from seed-to-bulb-to-seed production (Duncan 1965). Sakharov (1958) reported the equivalent of 533 lb/acre in Russia.
Plant:
When the plant is grown for production of green or bulb onions, it is treated as an annual, which rarely gets more than about 1 foot tall. The seeds are planted in the field or started in protected areas then transplanted, when a few inches tall, into the field. A few weeks later, when the top growth or the bulb has reached the proper size or condition, the entire plant is harvested and the desirable parts marketed. No seeds are produced and no pollination is involved.
When seeds are produced in western Idaho and eastern Oregon the mother bulb is replanted either late in the fall to overwinter in the soil or held in storage for spring planting. Seed-to-seed production is accomplished in the same area and in the Southwest by sowing seed in July and leaving plants to develop a seedstalk the following spring. According to Vincent (1960), larger bulbs of 3 inches or more produce more seeds per acre (690 pounds) than smaller ones; 2 1/2 to 3 inches (685 pounds), 2 to 2 1/2 inches (680 pounds), or 1 1/2 to 2 inches (495 pounds).
In the springtime, the bulbs initiate normal growth, then produce from 1 to 20 flower stalks, 3 to 4 feet tall. This is referred to as "bolting," an undesirable trait in green or bulb onion production but essential in seed production. Bolting is strongly influenced by day length and temperature (Jones and Emsweller 1936), and cultivars are bred to bolt at certain times in different areas. For this reason, northern and southern types are not interchangeable. Many cultivars have been developed for different regions and purposesÑnorthern and southern, purple and white bulbs, strong and mild-flavored (Magruder et al. 1941).
Inflorescence:
The ashy-gray, 50 to 2,000 florets are borne in a simple oval umber 6 to 8 inches across at the top of the elongated seedstalk. The individual floret, only 3 to 4 mm in length, has six stamens in two whorls of three each, a simple wandlike style leading to a three-celled ovary with two ovules in each cell (fig. 135). The anthers of the three inner stamens open first, and one after another, shed their pollen. Then the anthers of the outer whorl open, also at irregular intervals. Most of the pollen is shed between 9 a.m. and 5 p.m. of the first day the flower is open. All of it is shed within 24 to 36 hours after the flower opens and before the stigma becomes receptive (Jones and Rosa 1928*, Rodrigo et al. 1936). Nectaries occur at the base of the stamens, and the nectar accumulates between the ovary and the inner stamens (Knuth 1909*, pp. 453-458; Roberts and Struckmeyer 1951).
When flowering begins, only a few flowers open each day on an umber, but the number increases until at full bloom 50 or more florets may be open on a single day. They continue to open over a 2-week period, and 30 days or more may be involved in the flowering on all of the flower stalks. Moll (1954) showed that a flower may be pollinated as much as 6 days after it opens and found no significant difference in the percentage of set flowers pollinated 1 or 3 days after opening. Mann and Woodbury (1969) stated however, that pollen germination declined rapidly after the first day to zero percent by the sixth day. They concluded that the decline would be much more rapid under field conditions, making the age of the pollen an important factor in pollination. Nye et al. (1971) were in agreement in that they found that pollen taken from flowers opening in the morning was two or three times as viable as that taken from the flowers in the afternoon.
The flowers are attractive to many species of bees and other hymenoptera, flies and other diptera, and numerous other orders of insects that feed upon the nectar, pollen, or both (Lederhouse et al. 1968, Bohart et al. 1970, Jones and Emsweller 1934, Shaw and Bourne 1936). The nectaries are shallow, and, unless the nectar is rapidly removed by insects, it can be easily seen glistening in the sunlight like a tiny jewel.
Beekeepers occasionally obtain crops of onion honey with a characteristic onion flavor that disappears after a few weeks. Ewert (1942) reported that superphosphate and potassium fertilizers caused the nectar of onions to be richer in sugar, but the volume was not increased. The effect on the insect visitors was not reported. Waller (1970) and Waller et al. (1972) believed that a high level of potassium in the nectar might be an important clue to the reluctance of bees to visit onion flowers. Jula et al. (1965) calculated that onions produced 71 percent as much nectar per day as the highly attractive sainfoin.
[gfx] FIGURE 135. - Onion floret, x10. A, Male or staminate stage, with anthers releasing pollen, but style short and stigma not receptive; B, female or pistillate stage, with anthers no longer releasing pollen, but style elongated and stigma receptive.
Pollination Requirements:
Pollination in the onion flower occurs when pollen is transferred from the dehiscing anthers of one floret to a receptive stigma of another floret. Effective transfer of pollen between florets on an umber or on an individual plant can transpire through the action of an outside agent, but self-pollination within the floret is impossible. Cross-pollination between plants is common and even obligatory in the fertilization of male-sterile onions used in hybrid seed production. Van der Meer and van Bennekom (1968) reported only 9 percent self-fertilization, and later (1969) they concluded that seed set was less at lower temperatures than at higher ones.
The discovery of male sterility in onions (Jones and Emsweller 1936) made the production of hybrid onions possible under commercial conditions, and most of the onion seed produced now is hybrid seed. The procedure for utilization of male-sterility in the onion, which should be applicable to any crop plant in which male sterility is inherited in a similar way, was shown in detail by Jones and Clarke (1943).
In the production of hybrid seed, the grower plants a male-fertile row of a desired line to supply pollen to three to 10 rows of the male- sterile line (Franklin 1958), from which the hybrid seed will be obtained. Naturally, the greatest volume of hybrid seed possible is desired; therefore, the male-fertile or "bull" rows are kept at a minimum provided pollen is distributed sufficiently to set seed. Erickson and Gabelman (1956) showed that pollen dispersal from a point was logarithmic, with pollination at 7 feet from a source being only one-half that occurring at 1 foot. To secure maximum seed set, the grower encourages pollen dispersal to the maximum degree possible (Jones and Mann 1964).
MacGillivray (1948) showed that highest seed production occurred at Davis, Calif., when plants received more than sufficient irrigation. Likewise, Hawthorn (1951) obtained consistently higher seed yields with higher soil moisture. Nye (1970) reported that pollinator response to "wet" treatments was scarcely apparent, but use of nitrogen and phosphorus fertilizerscaused decreased flower attractiveness.
Pollinators:
Wind is not a factor of significance in onion pollination (Erickson and Gabelman 1956). Insects are the primary vectors. When onion breeders want to get seed from a specific plant, they enclose the flowering umber within a bag or cage and introduce flies to transfer the pollen, or, if cross-pollination is desired, the umbels of the two lines are enclosed (Jones and Emsweller 1933). In large cage breeding work or pollination studies, honey bees are the primary agents used (Bohart et al. 1970, Moffett 1965, Shirck et al. 1945, Walsh 1965).
In commercial production of seed, the provision of an adequate number of flies is impractical so the industry depends upon the honey bee as the primary pollinating agent. Bohart et al. (1970) reported 267 species of insect visitors on onion flowers, the most important of which were honey bees, small syrphid flies, halictid bees, and drone flies (fig. 136). Of these, only the honey bee can be manipulated and used in large-scale onion seed production. Kordakova (1956) and Sakharov (1956) gave major credit to the honey bee as a pollinator of onions in Russia.
Honey bees are effective pollinators of open-pollinated onions because both pollen and nectar are available on all umbels (fig. 137). In hybrid seed production where male-sterile plants are used, only the nectar collectors move freely from pollen-sterile to pollen-fertile plants, making the necessary transfer of pollen from male parent to female parent. Honey bees then become less than ideal pollinators of male-sterile onions. Pollen-collecting bees confine much of their activity to the pollen-producing rows without adequately visiting and cross-pollinating the male-sterile rows (Lederhouse et al. 1972). A strictly nectar- collecting type of honey bee would be ideal because it would cross-visit and effectively pollinate the male-sterile flowers. In the absence of this perfect type of bee, the grower can only try to compensate by having more honey bees present in the field. Shasha'a's30 conclusion, that too many bees may be detrimental, needs further study.
The lack of intense attractiveness of onions to bees, may cause the bees to neglect the crop, particularly if another highly attractive crop is in flower. The grower's only alternative is to make his crop as attractive as possible with best cultural practices and to use a heavy population of bees. Even then, the seed yielding potential of the crop may never be attained (Franklin 1970).
More research is needed on the factors that affect attractiveness of onions to honey bees (Sanduleac 1969, Singh and Dharamwal 1970). Franklin (1970) noted that mere placement of colonies of honey bees in the onion field does not guarantee that the bees will work the onion. Although Nye et al. (1971) reported an average of 100 bees per 100 feet of male fertile rows and a maximum of 40 per 100 feet on the male sterile rows, the number of honey bee visitors needed per onion plant, umber, or linear feet of row has not been determined.
Stuart and Griffin (1946) used different rates and times of application of nitrogen on onions in the greenhouse, and used honey bees to provide the pollination. Their best production was 3.2 seed stalks per plant and 7.5 grams of seed per plant with a high nitrogen application from August 15 to January 1, low nitrogen during January-February (blooming), then high nitrogen until maturity.
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30 SHASHA'A , N. S. LIMITATION STUDIES OF SEED SET IN THE ONION (ALLIUM CEPA L. ) (LILIACEAE). Ph. D. dissertation, Utah State Univ., Logan. 1972. [Unpublished.]FIGURE 136. - Onion breeders place flies in a cage with onion flower heads to cross-pollinate specific plants.
FIGURE 137. - Honey bee collecting pollen from onion blossoms.Pollination Recommendations and Practices:
As early as 1936, Shaw and Bourne (1936) indicated that growers of onion seed might find it useful to provide themselves with a supply of bees. They did not go into detail as to number of colonies, strength, or location. In a brief note without details, Hamilton (1946) stated that a grower produced much more onion seed than he had in the past after he rented eight colonies of bees. Sanduleac (1961 ) stated that bees increase production of onion and leek seed in Romania eight to 10 times, and he recommended about two colonies per acre. Without supporting data, Le Baron (1962} stated that the use of bees for pollination of onions in the Imperial Valley of California was a "must," and that two colonies per acre had given good results (fig. 138).
There have been no clear-cut guidelines on the use of bees for maximum onion seed production, and many beliefs based on limited observation have arisen. These include the size of the colony cluster, its relative stage of development, and previous usage. The growers have learned through experience that the use of honey bees is essential and are frequently frustrated by the erratic activity of the bees. They have generally adopted the practice of renting five to 15 colonies of bees per acre and having them placed in or adjacent to their seed fields at flowering time. One suggestion has been to have about two colonies per acre delivered when flowering is well started, then an additional two per acre at 3- to 4-day intervals to take advantage of "naive" bee behavior and maintain some level of nectar foraging activity throughout the blooming period.
Much information is needed on the factors that influence the activity of bees on onion flowers because, as Franklin (1970) pointed out, the mere placement of colonies in the field does not guarantee that the bees will work the onions. Continuous nectar foraging activity is the essential factor in hybrid onion fields especially during the peak period of flowering.
[gfx] FIGURE 139. - Honey bee colonies placed by onion field to pollinate the flowers in commercial seed production.
LITERATURE CITED:
BOHART, G. E., NYE, W. P., and HAWTHORN, L. R.
1970. ONION P0LLINATION AS AFFECTED BY DIFFERENT LEVELS OF POLLINATOR ACTIVITY. Utah Agr. Expt. Sta. Bul. 482, 60 pp.COMIN, D.
1946. ONION PRODUCTION. 186 pp. Orange-Judd Publishing Co., Inc., New YorkDUNCAN, A. A.
1965. VEGETABLE SEED PRODUCTIONÑONION. Oreg. Agr. Ext. Serv. FS 88, Leaflet.ERICKSON, H. T., and GABELMAN, W. H.
1956. THE EFFECT OF DISTANCE AND DIRECTION ON CROSS- POLLINATION IN ONIONS. Amer. Soc. Hort. Sci. Proc. 68: 351-357.EWERT, E.
1942. [NECTAR PRODUCTION OF COOKING ONIONS.] Deut Bienenzucht 49: 234-235. [In German.]FRANKLIN, D. F.
1958. EFFECT ON HYBRID ONION SEED PRODUCTION OF USING DIFFERENT RATIOS OF MALE-STERILE AND POLLEN ROWS. Amer. Soc. Hort. Sci. Proc. 71: 435-439.______ 1970. PROBLEMS IN THE PRODUCTION OF VEGETABLE SEED. In The Indispensable Pollinators, Ark. Agr. Ext. Serv. Misc. Pub. 127, pp. 112-140.
HAMILTON R. P.
1946. ONIONS NEED BEES. Gleanings Bee Cult. 74: 23.HAWTHORN, L. R.
1951. STUDIES OF SOIL MOISTURE AND SPACING FOR SEED CROPS OF CARROTS AND ONIONS. U.S. Dept. Agr. Cir. 892, 26 pp.JONES, D. F., and CLARKE, A. E.
1943. INHERITANCE OF MALE-STERILITY IN ONION AND THE PRODUCTION OF HYBRID SEED Amer. Soc. Hort. Sci. Proc. 43: 189-193.JONES, H. A., and EMSWELLER, S. L.
1933. METHODS OF BREEDING ONIONS. Hilgardia 7: 625-642.______and EMSWELLER, S. L.
1934. THE USE OF FLIES AS ONION POLLINATORS. Amer. Soc. Hort. Sci. Proc. 31(sup.): 160-164.______and EMSWELLER, S. L.
1936. A MALE-STERILE ONION. Amer. Soc. Hort. Sci. Proc. 34: 582-585.______and MANN, L. K.
1964. ONIONS AND THEIR ALLIES. 286 pp. Leonard Hill Book CO., London.______POOLE, C. F., and EMSWELLER, S. L.
1936. B0LTING HABIT IN THE ONION. Abstract in Amer. Soc. Hort. Sci. Proc. 33: 490.JULA, F., PIRVU, E., and ILLYES, C.
1965. [THE MELLIFEROUS VALUE OF SAINFOIN (ONOBRYCHIS VICIIFOLIA) AND ONION (ALLIUM CEPA L.), UNDER THE SOIL AND CLIMATIC CONDITIONS AROUND CLUJ.] Lucr. Stiint. lnst. Agron. Cluj 21: 99-106. [In Romanian, English and Russian summaries.]KORDAKOVA, Z. M.
1956. [HONEY BEES AND POLLINATION OF SEED PLANTS OF THE COMMON ONION.] In Krishchunas, I. V., and Gubin, A. F., eds., Pollination of Agricultural Plants, Moskva, Gos. Izd-vo Selkhoz Lit-ry, pp. 163-171. [In Russian.]LE BARON, F. C.
1962. ONION SEED, SAMPLE COSTS AND PRODUCTION. Calif. Agr. Ext. Sen., Cost Data Sheet 22, Leaflet.LEDERHOUSE, R. C., CARON, D. M., and MORSE, R. A.
1968. ONION POLLINATION IN NEW YORK. New York's Food and Life Sci. 1(3): 8-9.CARON, D. M., and MORSE, R. A.
1972. DISTRIBUTION AND BEHAVIOR OF HONEY BEES ON ONIONS. Environmental Ent. 1: 127-129.MACGILLIVRAY, J. H.
1948. EFFECT OF IRRIGATION ON THE YIELD OF ONION SEED. Amer. Soc. Hort. Sci. Proc. 51: 423-427.MAGRUDER, R., WESTER, R. E., and others.
1941. DESCRIPTIONS OF TYPES OF PRINCIPAL AMERICAN VARIETIES OF ONIONS. U.S. Dept. Agr. Misc. Pub. 435, 87 pp.MANN, L. K
1952. ANATOMY OF THE GARLIC BULB AND FACTORS AFFECTING BULB DEVELOPMENT. Hilgardia 21(8): 195-235.______and LITTLE, T. M.
1957. GROWING GARLIC IN CALIFORNIA. Calif. Univ., Dept. Veg. Crops, Veg. Crops Ser. 89, 10 pp.______and WOODBURY, G. W.
1969. THE EFFECT OF FLOWER AGE, TIME OF DAY AND VARIETY ON POLLEN GERMINATION OF ONION, ALLIUM CEPA L. Amer. Soc. Hort. Sci. Proc. 94: 102-104.MEER, Q. P., VAN DER, and BENNEKOM, J. L. VAN.
1968. RESEARCH IN POLLEN DISTRIBUTION IN ONION SEED FIELDS. Euphytica 17: 216- 219.______and BENNEKOM, J. L. VAN.
1969. EFFECT OF TEMPERATURE ON THE OCCURRENCE OF MALE STERILITY IN ONION (ALLIUM CEPA L.). Euphytica 18: 389394.MOFFETT, J. O.
1965. POLLINATING EXPERIMENTAL ONION VARIETIES. Amer. Bee Jour. 105: 378.MOLL, R. H.
1954. RECEPTIVITY OF THE INDIVIDUAL ONION FLOWER AND SOME FACTORS AFFECTING ITS DURATION. Amer. Soc. Hort. Sci. Proc. 64: 399-404.NYE, W. P.
1970. POLLINATION OF ONION SEED AFFECTED BY ENVIRONMENTAL STRESSES. In The indispensable Pollinators, Ark. Agr. Ext. Serv. Misc. Pub. 127, pp. 141-144.NYE, W. P., WAILER, G. D., and WATERS, N. D.
1971. FACTORS AFFECTING POLLINATION OF ONIONS IN IDAHO DURING 1969. Amer. Soc. Hort. Sci. Proc. 96: 330-332.ROBERTS, R. H., and STRUCKMEYER, B. E.
1951. OBSERVATIONS ON THE FLOWERING OF ONIONS. Amer. Soc. Hort. Sci. Proc. 58: 214-216.RODRIGO, P. A., URBANES, P. S., and OLAN, V. R.
1936. PRELIMINARY STUDIES ON THE FLOWERING AND SEEDING OF ONIONS IN THE PHILIPPINES: I. Philippine Jour. Agr. 7: 1-20.SAKHAROV, M. K.
1956. [BEES AND ONION SEED PRODUCTION.] In Krishchunas, I. V., and Gubin, A. F., eds. Pollination of Agricultural Plants, Moskva, Gos. Izd-vo Selkhoz Lit-ry, pp. 172-173. [In Russian.]______ 1958. [POLLINATING ACTIVITY OF HONEY BEES ON SEEDBEARING PLANTS IN VEGETABLE CULTIVATION.] Sad i Ogorod 96(7): 21-23. [In Russian. ] AA-147/61.
SANDULEAC, E.
1961. [THE POLLINATION OF VEGETABLE SEED PLANTS.] Apicultura 14: 25-26. [In Romanian, English abstract. ]______ 1969. [THE ENTOMOPHYLOUS POLLINATION AND HYBRIDIZATION OF THE ONION.] Romania Inst. Cent. Cercetari Agricole. Stat. Cent. Apicultura si Sericult., Anale 9: 49-56. [ln Romanian, English summary.]
SHAW, F. R. and BOURNE, A. I.
1936. INSECTS POLLINATING ONIONS. Amer. Bee Jour. 76: 401-402.SHIRCK, F. H., DOUGLASS, J. R., and SHULL, W. E.
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1970. THE ROLE OF HONEY BEES IN SEED SETTING OF ONION AT PANT NAGAR, DIST. NAINITAL, UTTAR PRADESH, INDIA. Indian Bee Jour. 32(1/2): 23 - 26.STUART, N. W., and GRIFFIN, D. M. 1946. THE INFLUENCE OF NITROGEN NUTRITION ON ONION SEED PRODUCTION. Amer. Soc. Hort. Sci. Proc. 48: 398-402.
VINCENT, C. L.
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1970. PROBLEMS WITH ONION POLLINATION IN ARIZONA. In The Indispensable Pollinators, Ark. Agr. Ext. Serv. Misc. Pub. 127, pp. 145-149.______CARPENTER, E. W., and ZIEHL, O. A.
1972. POTASSIUM IN ONION NECTAR AND ITS PROBABLE EFFECT ON ATTRACTIVENESS OF ONION FLOWERS TO HONEY BEES. Amer. Soc. Hort. Sci. Proc. 97: 535-539.WALSH, R. S.
1965. POLLINATION OF ONION PLANTS BY HONEY BEES. New Zeal. Beekeeper 27(2): 18, 20.
