Onion and Leek Seed Production
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PNW 433 ONION AND LEEK SEED PRODUCTION M. K. THORNTON, s. K. MOHAN, D. 0. WILSON, R. G. BEAVER, & w. M. COLT Onion (Allium cepa) and to a lesser degree leek (Allium ONION PRODUCTION porrum) are important vegetable crops in the Pacific Northwest. METHODS Most of the seed for these crops is produced under contract in Onions are a biennial crop, and the irrigated areas of the Snake River Valley of Idaho and most seed is produced from bulbs that Oregon. Smaller acreages are also grown in the Willamette are grown from seed planted in the Valley and Madras regions of Oregon and in the Columbia spring and carried over through the Basin of Washington. winter as small plants in the field. Production practices vary among the growing areas of These plants flower the following the Pacific Northwest due to variations in amount of rainfall, spring. This is called the seed-to-seed seasonal temperatures, and disease incidence. Net returns vary method. Onion seed is also produced depending upon cost of production and gross returns as influ from bulbs grown, harvested, and enced by seed yield, quality, purity, and type of contract. replanted in the fall, or stored and replanted the following spring. This approach, known as the bulb-to-seed method, is more expensive, but offers certain advantages. SEED-TO-SEED METHOD Yield of onion seed produced by the seed-to-seed method is often higher than that from the bulb-to-seed method because most of these fields have a greater number of plants per acre. Production costs are lower be cause the plants are produced directly from seed and bulbs are not harvested and stored. The higher seed yields and lower costs are the reasons most com mercial onion and leek seed is now produced by the seed-to-seed method. A Pacific Northwest Extension Publication Idaho - Oregon - Washington The seed-to-seed method is most successful when careful Planting should be done as soon as the attention is given to pest control and when pure stock seed and soil can be prepared. winter hardy varieties are used. Limited roguing may be re Onion seed bulbs planted in the quired to remove off-type plants. fall should be planted early enough that Seed-to-seed onions must be planted early enough so that the bulbs can become well rooted most of the bulbs will reach Y4 inch in diameter before winter. before the ground freezes. Extra protec Bulbs must reach this size in the fall to ensure that the plants tion should be provided by hilling soil produce seed stalks the following spring. Planting between June over the bulbs before the ground 15 and July 15 will allow most varieties of onions to achieve the freezes. needed size. When onions are seeded during this period, fields The most desirable bulbs are 2 need to be irrigated before seeding. Irrigation is also required \h to 3 inches in diameter. Although during the summer months. larger bulb size gives a slight increase Seed is planted \h to 1 inch deep in rows 22 to 30 inches in seed yields and an increased number apart at a rate of 3 to 4 pounds per acre. Higher seeding rates of seed stalks per plant, the increases and closer row spacing ( 18 inches) have resulted in higher seed usually do not justify the extra expense yields provided irrigation is adequate and diseases, insects, and in handling the additional tonnages of weeds are controlled. bulbs. With medium-sized bulbs, 7,500 to 10,000 pounds of bulbs are required BuLB-TO-SEED METHOD to plant an acre. The bulb-to-seed method is preferable to the seed-to Bulbs are planted upright in seed method for the maintenance of onion stock seed. Bulb rows about 3 feet apart with individual production for seed differs from commercial onion production in bulbs placed shoulder to shoulder that planting rates are higher so that more bulbs are produced within the row so their tops are near the per acre. level of the soil surface. If bulbs are Often, seed companies contract with growers to produce planted shallower than this, support seed onion bulbs to be used for onion seed production. In other must later be provided to the seed instances, onion seed producers grow and store their own bulbs. stalks by hilling soil around them. Onion seed bulbs to be planted in the spring should be The bulb-to-seed method stored under cool, well-ventilated, and dry conditions. The bulbs provides an opportunity to discard off should be maintained at 35° to 40°F with a relative humidity types and diseased or otherwise unde near 65 percent. Potato and apple storage facilities are not sirable bulbs. Desirable bulbs can be suitable for onion bulb storage because of their high humidity. selected at harvest and again at trans planting. BULB PRODUCTION FOR BULB-TO-SEED CROPS Seeding is done in early spring. The usual method is to plant 4 to 6 pounds of seed per acre in single or double rows spaced 22 inches apart on each bed. Seed should be planted \h to 1 inch deep, depending on soil type. The harvest of seed bulbs is similar to that of commercial dry onions bulbs. Bulbs should be mature and carefully cured. This is particularly important for bulbs to be stored over winter. As soon as three-fourths of the tops fall over, the bulbs should be lifted and placed in windrows to cure. 2 Another method is to lift and top the For stock seed production, frequent roguing of the bulbs and then cure them in slatted female (A) line is important to remove any male-fertile or other crates protected from direct sun and rain. off-type plants. This is done early in the morning when newly shedding pollen can be seen. Rogued plants should be pulled out HYBRID ONION SEED completely, and any emerged flowers should be buried. Onion seed may be either open pollinated or hybrid. Hybrids generally LEEK PRODUCTION METHODS have replaced open-pollinated varieties Leeks do not produce bulbs and must therefore be propa because hybrids have greater unifor gated by seed or transplants. Because of the high cost associated mity, higher yields, and more disease with hand transplanting, most leek seed is produced by the seed resistance. Since the first onion hybrids to-seed method. were introduced on the market in the Leeks are generally planted about 1 month earlier than 1950s, seed production has shifted onion seed fields because leek seed germinates slowly, and the toward hybrid lines. plants must produce approximately seven leaves before flower Hybrid onion seed is produced stalk induction can occur during the winter. The following by both bulb-to-seed and seed-to-seed spring, tlowering is stimulated by the lengthening of the days. methods. The seed-producing inbred Leeks female line is designated as (A) and the usually flower pollen-producing male line as (C). A later than onions, third line, designated the maintainer (B) which may cause line, is virtually identical to (A) except problems with that it produces pollen. Pollen from the maturity in a short maintainer line is used to pollinate growmg season flowers of the male-sterile (A) line, location. As with which otherwise could not produce onions, hybrid seed. In this way the male-sterile leek seed produces female line (A) is propagated. To more uniform produce hybrid seed, the female line plants than open (A) is pollinated by the male line (C). pollinated seed. The (A), (B), and (C) lines are usually maintained by the bulb-to-seed method ISOLATION under stringent isolation. Onion Sometimes a three-way cross is varieties intercross used to produce hybrid seed. In this readily, so atten system a single-cross male-sterile tion must be given hybrid is used as the female seed parent to isolation dis instead of an inbred female line. The tances when seed vigorous male-sterile hybrid plants fields are located. produce higher seed yields. Leek varieties also The ratio of female (A) to male intercross and (C) rows varies with different hybrids; must be isolated usually an 8-to-2 or 10-to-2 arrange by a suitable ment of rows is used. For pollination to distance (table 1). be successful, the (A) and (C) lines must flower at nearly the same time. For some hybrids, the two parent lines must be planted at different times to have the flowering dates coincide. The time a given line flowers can be changed by the bulb storage temperature. 3 Table 1. Recommended isolation distances for onion and leek seed production. Production fields Isolation distance (miles) Hybrid onions (should be posted as male parent) From hybrids of different color 3 From open-pollinated (O.P.) of different color 3 From hybrid or O.P. of same color but different shape 2 (i.e., globe shape vs. flat) From O.P. of same color and shape 2 From hybrid of same color but different type 2 (i.e., globe vs. Spanish) From hybrid of same color, shape, and type 1 (i.e., yellow Spanish) From bunching onions (Alliumfistulosum), chives, or leyk None Open-pollinated onions From hybrid of different color or shape 3 From O.P. of different color 3 From O.P. of same color but different shape 2 (i.e., yellow globe vs. yellow high globe) From hybrid of same color and shape 2 From O.P. of same color but different type 1 Y2 (i.e., yellow Spanish vs. yellow globe) From O.P. of same color, type, and shape 1 (i.e., yellow Spanish) From bunching onions (Alliumfistulosum), chives, or leek None Leeks From onion, bunching onion, or chives None From another variety of leek 1 4 POLLINATION CuLTURE Onions and leeks are pollinated SITE SELECTION AND PREPARATION by insects, particularly honeybees and Fields to be used for onion or leek seed production leafcutter bees.