Vegetable Seed Production - "Wet" Seeds
Tomato
Introduction
Tomatoes originated in Peru and Bolivia as small, wild fruits. Migration of local natives brought the tomato to Central America and Mexico where large, domesticated fruits were developed. Archaeological evidence reveals that tomatoes were a popular fruit of the Aztec and Toltec Indians who planted them with their corn. Spanish settlers to the New World carried tomatoes back to Europe where they quickly became established throughout the continent. Initially, tomatoes were grown as ornamentals because of their colorful, bright red fruits and the assumption that the fruits were poisonous. By 1750, however, tomatoes were cultivated in England and were a popular component of soups. Tomatoes came to the United States in the late 1700's by European colonists. Seed catalogues offered tomato seeds for sale as early as 1812 but tomatoes were not considered a major food crop until the 1860's. During that period, ambitious breeding programs were established to expand the number of tomato varieties. Today, continuing efforts at improvement of extra early varieties, development of disease resistant varieties, and improvements in plant type and fruit quality have led to tomatoes being accepted as one of the world's most versatile food crops.
Tomatoes are the second most consumed vegetable in the world behind only the potato. They are eaten fresh or processed and can be stewed, fried, baked, or used as juice. In addition to this versatility, tomatoes are also nutritional. They are low in calories (20 calories per average size fruit) and an excellent source of iron and vitamins A and C. They also contain small amounts of the B complex vitamins thiamin, niacin, and riboflavin.
Plant Development
The tomato is a warm-season herbaceous perennial that requires three to four months from seeding to production of fruit. It grows best at temperatures between 18 and 29oC (65 and 85F), is often killed at temperatures below freezing, and does not grow at temperatures above 35oC (95F).
Seed. Tomato seeds are 3 to 5 mm (0.12 to 0.20 inches) in size, flat, reniform, and have a grey, slightly hairy seed coat. The embryo is large and coiled in a limited, fleshy endosperm (Figure 00.2).
Vegetative. Tomato plants are typically viny, prostrate, and are either determinate or indeterminate based on whether the apical stem terminates in an inflorescence. Most shoots form in the axils of leaves. The tomato plant produces a deep tap root with extensive secondary roots.
Reproductive. Tomato flowers are yellow and formed on racemes. The stamens are fused with the lower part of the corolla forming a staminal cone. Generally, pollen release occurs prior to elongation of the style through the staminal cone resulting in self-pollination. However, temperature has a major effect on this process. If temperatures are below 15oC (60F) or above 29oC (85F), pollen release is restricted resulting in incomplete fertilization of ovules. This causes collapsed fruit walls and formation of deep indentations in the fruit, a phenomenon called "catface." Hot, drying winds also cause tomato flowers to abscise from the plant. The best shaped and fullest tomato fruits result from optimum fertilization of ovules. The mature tomato fruit is botanically a berry. Fruit color varies from the common red to yellow, pink, and orange.
Self-pollinated and hybrid tomato seeds are produced and marketed. Production of hybrid tomato seeds requires the planting of male (pollen) and female (hybrid fruit) parents. A ratio of 1:5 male to female plants is adequate for hybrid seed production. The male parent is typically planted earlier than the female in order that sufficient flowers are available for pollen collection prior to flowering of the female. Pollen is collected from the male plants by a mechanical hand-held vibrator that is placed on opened flowers. The vibration causes the anthers to release their pollen which is collected on a receptive plate, disk, or tube attached to the vibrator. Female plants are often supported in the field so that the flowers and developing fruit are off the ground. Hybridization is accomplished by selecting flowers from the female plant in the morning for emasculation. Flowers must be in the late bud stage of development. The bud is opened with a pair of forceps and the staminal cone removed. Care must be taken to ensure that the receptive sigma is not damaged during this process. Usually, transfer of the male parent pollen is accomplished by dabbing the pollen onto a fine brush that is then placed on the stigma of the emasculated flower within a day or two after pollen isolation. After pollination, the flower is tagged and half of the calyx removed to document that the developing fruit is a hybrid.
Seed Production
Tomatoes are grown for three principal purposes: processing, field shipping, and greenhouse production. The processing areas are located in the eastern (Ohio, Indiana, and Ontario) and western (California) parts of North America. The major production of tomatoes for local shipping are produced in Florida, California, and South Carolina. Greenhouse tomatoes represent 65 to 75% of the vegetable production that occurs in greenhouses. The leading areas are Michigan, Pennsylvania, Virginia, Illinois, and Ontario.
Seed production in greenhouses has occurred on a limited scale. As a result, most of the following discussion will consider tomato seed production as practiced under field conditions.
Tillage. Crop rotations are useful in tomato seed production because of the crop's susceptibility to a variety of diseases. Rotations with soybeans, sugar beets, wheat, and beans have been successful. One of the most common rotations in the California San Joaquin Valley is with cotton. Fields used in tomato seed production should be Fall plowed to a depth of 20 cm (8 inches). This practice not only improves the physical structure of the soil but also encourages the decay of roots and other plant parts thereby enhancing the level of soil organic matter. If organic matter remains low, manure can be applied at a rate of 13,440 to 17,920 kg per hectare (6 to 8 tons per acre) and incorporated into the soil at the time of Fall plowing. Manure applications should not be applied in the Spring because microorganism activity is increased and competes with the tomatoes for available nitrogen. After plowing, beds are prepared 137 to 167 cm (54 to 66 inches) apart with furrows 20 to 15 cm (8 to 10 inches) deep depending on the soil type. The beds allow more uniform fruit ripening and better drainage following heavy rains.
Planting. Tomatoes can be planted either by direct seeding or transplants. When 152 cm (5 foot) rows are used, seed is planted to give a spacing of 20 to 30 cm (8 to 12 inches) or 30 to 40 cm (12 to 16 inches) if double rows are used. Planting should not begin until the soil temperature has reached 10C (50oF) since germination will not occur below this temperature. The optimum range of soil temperatures for seed germination is between 15C and 29C (60oF to 85oF).
Direct seeding is accomplished by precision planters that equally space the desired number of seeds in the row. Seeds should be planted at a depth of 1.3 to 2.0 cm (1/2 to 3/4 inch) to obtain a population of 24,700 to 49,500 plants per hectare (10,000 to 20,000 plants per acre) in single rows. Planters should be modified to allow the application of anticrustants (keep the soil from crusting and thereby facilitating uniform seedling emergence) and starter fertilizers applied either in a solid or liquid form (Figure 00.3). Tomato seeds can also be pelleted with clay/fertilizer coatings that allow the use of traditional plate planters. Because rapid emergence and seedling establishment are desirable in tomatoes, another approach has been to pregerminate tomato seeds in a solution of anticrustants and fertilizers. The germinated seeds are planted by a planter which makes a furrow, the germination medium including the seeds flows into the furrow, and the furrow is closed. Many seed companies are using a variation of this approach for marketing tomato seeds. They osmocondition the seed (a prehydration process) in an osmoticum such as a salt or in a solid matrix such as vermiculite. The seeds are hydrated to a moisture content below that required for germination and then redried. Following osmoconditioning, the dried seeds are handled and packaged in traditional ways. Studies have shown that osmoconditioning enhances the rate and uniformity of tomato seed germination.
Transplanting is another important planting approach used in tomato seed production. Transplants can be obtained either from local greenhouses or can be from transplants produced using grower seed. They are at the correct stage for planting when the first pair of seedling leaves appear. When possible, transplanting should be done either during the afternoon or on a still, cloudy day to avoid transplant shock. The transplants should be thoroughly watered before planting and a starter fertilizer high in phosphorus added. Transplants every 40 to 45 cm (16 to 18 inches) in rows 168 cm (66 inches) apart provide a population of 14,800 to 19,700 plants per hectare (6,000 to 8,000 plants per acre).
The choice of direct seeding or transplants is made by the seed grower. Advantages of direct seedling over transplants are: 1) reduced cost per hectare (acre), 2) less introduction of plant diseases, and 3) greater flexibility of planting time, variety selection, and plant population. Transplanting, when properly done, offers the advantage of more rapid plant establishment and higher seed yields.
Fertilization. While tomatoes grow on almost any soil, soils that are sandy, light, well-drained, and high in organic matter and mineral nutrients produce the best quality and highest fruit yields. Optimum soil pH should range from 6.0 to 6.5. Tomatoes require an abundance of the three major elements: nitrogen, phosphorus, and potassium. Adequate nitrogen is important to enhance foliage growth which has a major bearing on crop maturity and protects fruits from sunscald. Phosphorus influences fruit quality by stimulating vigorous root growth that enables more nutrients to enter the plant thereby promoting sturdy stem growth and healthy leaf formation. Tomatoes use large amounts of potassium. This element is important in stimulating early plant growth and regulating normal carbohydrate and protein metabolism.
Fertilizers are generally applied broadcast before Fall plowing. All the phosphorus and potassium and one-half the nitrogen are added at this time. Between the time the plants have two to three leaves and when the flowers are first observed, a side-dress nitrogen application is useful. Nitrogen should not be applied after fruit formation because it stimulates vegetative growth.
Because fields vary in the absolute quantities of fertilizers to apply for optimum tomato growth, it is difficult to make specific recommendations without a soil analysis. However, the following general guides of fertilizer ratios (N-P-K) may be useful for certain situations: 1) tomatoes grown on light soils in rotation with other crops (1-2-1 or 1-2-2), 2) tomatoes grown on sandy soils (1-2-2), and 3) tomatoes grown on loam, silt loam, and clay loam soils (1-3-1 or 1-4-1).
Tomatoes are sensitive to deficiencies in the minor elements manganese, boron, copper, zinc, and molybdenum. Lack of rapid calcium movement from vegetative to fruit tissues under conditions of high moisture often results in a condition known as blossom-end rot of the fruit.
Weed and Pest Control. Mechanical and chemical control of weeds is practiced in tomatoes. Cultivation to eradicate weeds begins soon after seedling emergence. Early cultivations are close to the seedling and 2.5 to 5.0 cm (1 to 2 inches) deep. Later cultivations are further from the plants and shallower to minimize injury to rapidly spreading surface roots. Chemical control also involves application of an array of pesticides specific to the weed problem. Weeds that are difficult to control in tomato fields include nightshade, pigweed, lambsquarters, green foxtail, wild oats, nutsedge, smartweed, and morningglory.
Tomatoes are subject to a variety of disease and insect pests. Crop rotations on a two to three year cycle with nonsolanaceous species reduce pest problems and are a sound seed production practice. Very few of these diseases infect the seed directly but they can reduce seed yields and cause decreases in seed quality as a result of reduction in vegetative growth.
Common tomato diseases include early blight, septoria leaf spot, bacterial canker, bacterial wilt, fusarium wilt, damping-off, and tobacco mosaic virus. Early blight (Alternaria solani) affects the plant at any stage of development but the greatest plant injury is observed when the fruit begins to mature. Injury is first observed with the formation of small, irregular dead spots that enlarge and commonly show a ridged, concentric ring pattern. The pathogen is believed to be soil-borne and can be carried by infected seeds to new locations. Septoria leaf spot (Septoria lycopersici) is one of the most destructive tomato leaf diseases. It appears first as small water-soaked spots on the underside of leaves, usually after fruit formation. Fruits are rarely affected but severely infected leaves completely dry out. Bacterial canker (Corynebacterium michiganese) causes a downward curling of the lower leaves which eventually wilt and die. A diagnostic feature of this disease is the presence of a shiny reddish-brown streak in the vascular tissue of a stem cut lengthwise. The fruit is also invaded and snowy white raised spots appear on its surface. Developing seeds are infected and can carry the disease to new fields. Bacterial wilt (Pseudomonas solanacearum) causes a rapid wilting and death of the entire plant unaccompanied by any yellowing of leaves or spotting of fruit. Freshly cut stems reveal a grayish, slimy exudate in the water soaked pith. Two important bacterial diseases which invade the seed are bacterial spot (Xanthomonas vesicatoria) and bacterial speck (Pseudomonas syringee). Fusarium wilt (Fusarium oxysporum f. sp. lycopersicum) is a common tomato disease that is manifested by a yellowing, wilting, and death of tomato leaves that begins at the base of the plant and moves upward. Damping-off (Pythium spp., Phytopthera spp.) attacks small seedlings at the soil surface. Initially the stems shrivel, then the plant topples over and dies. Other important fungal diseases of tomato are corky root (Phyrochaeta lycopersici), verticillium wilt (Verticillium dahliae), and powdery mildew (Leveillula taurica). Tobacco mosaic virus causes mottled, distorted foliage that reduces fruit yields. Insects spread the diseases after feeding on infected plants.
The principal insects that damage tomatoes are cutworms, flea beetles, aphids, hornworms, grasshoppers, and wireworms. Of these, only the cutworms and hornworms are consistent problems in tomato producing areas. Cutworms are smooth, plump caterpillars that feed at night on young tomato plants. They ultimately cut the plant off at the soil surface. Hornworms are green caterpillars characterized by distinctive V-markings on the side and a large horn on the end. They are voracious feeders and one or two hornworms can completely defoliate a mature plant.
Harvesting. Tomato fruits can be hand or machine harvested. In the case of hybrid seed production, the marked or tagged fruits are always hand harvested. All mechanical tomato harvesters are based on a "once-over" principle in which the entire tomato plant is harvested. They have four components: pick-up mechanism, fruit and vine separating area, fruit sorting area, and container loading mechanism. The pick-up mechanisms cut the vine at or slightly below the ground surface and the plant and fruit are moved by a conveyor to the fruit and vine separating area. There the plants are transferred to a reciprocating mechanism that begins a shaking action which allows the fruit to be separated from the plant and to be conveyed to sorting belts. The remaining plant is discharged into the field. Unacceptable fruits are removed by hand sorters or electronic color sorters. Acceptable fruits continue to the discharge area where they are loaded into containers. After harvesting, the tomato fruits are transported to an area dedicated to seed extraction, washing, drying, cleaning, and storage.
Extraction. The tomato fruit is placed into a crusher that pulverizes the fruit and separates the gelatinous seed from the remaining fruit tissues by pressing them through screens. The extract containing the gelatinous seed material must still be separated from the remaining pulp. This is accomplished naturally by fermentation or with chemicals. When fermentation is used, the seeds remain in the extract until the gelatinous coating has been degraded by microorganisms; a process that can take up to three days under normal field conditions. The fermentation mixture is frequently stirred and inspected until this occurs. Excessive fermentation reduces seed quality. Chemical methods include the use of hydrochloric acid or sodium carbonate. Enough concentrated hydrochloric acid is added to the fermenting extract to make a 5% concentration. The acid rapidly degrades the gelatinous seed coating resulting in the production of a clean seed sample. Similar cautions concerning excessive digestion time on seed quality and concern about worker safety when using concentrated acids need to be emphasized with this technique. Sodium carbonate accomplishes the same task as hydrochloric acid without the potential danger to workers. However, it darkens the seed coats and makes the seeds less attractive as a commercial product. After seed extraction, the seeds are immediately washed to remove digested materials and any remaining chemicals. This is accomplished by placing the seeds and extraction in long, slightly angled water troughs that contain a series of riffles at specific intervals.
Conditioning. Tomato seeds are generally clean and free of unwanted material and other crop seeds following washing. They are further cleaned and sized on an air-screen cleaner.
Storage. When stored under cool, dry conditions and at a seed moisture content of 6%, tomato seeds are relatively long lived. They can be successfully stored under these conditions for 4 to 6 years.
Atherton, J. G., and J. Rudich (eds.). 1986. The Tomato Crop. A Scientific Basis for Improvement. Chapman and Hall, New York.
Bassett, M. J. 1986. Breeding Vegetable Crops. Avi Publishing, Westport.
George, R. A. T. 1985. Vegetable Seed Production. Longman Press, Essex.
Gould, W. A. 1992. Tomato Production, Procesing, and Technology. CTI Publications, Baltimore.
Cucumber
Introduction
Cucumber likely originated in India because a close weedy relative, Cucumis hardwickii, has been located there. Evidence exists that the cucumber was cultivated in western Asia over 3,000 years ago. From there, it spread westward into Egypt and was introduced throughout Europe by the Greek and Roman empires. Columbus and Spanish settlers brought cucumbers to North America where they quickly became established as a popular crop.
Cucumbers are used in two principal ways: 1) fresh when they are sliced, diced, and cubed in salads and 2) pickled in sweet, sour, and dill brines. Nutritionally, the cucumber is low in calories and low in mineral and vitamin food value. Its excellent flavor and texture, however, continue to make cucumbers among the most prized of vegetables.
Plant Development
Cucumbers are considered a warm-season crop which grows best at average daily temperatures from 18 to 24oC (65 to 75F). Young plant development can be severely retarded if exposed to frost. Cucumbers are noted for requiring the shortest interval from planting to fruit production of any major vegetable crop.
Seed. The seed is flat, oval-ovate in shape, 10 to 15 mm (0.4 to 0.6 inches) long, pointed at the hilum end and rounded at the opposite end (Figure 00.8). The seed coat is smooth, white to black, with a marginal groove on each side near the base. Internally, the embryo is surrounded by a thin perisperm. The embryo is large, having completely digested the endosperm, and is composed of two leafy cotyledons, each with a prominent midrib, attached to a small, straight embryonic axis. The 1,000 seed weight is 25 g (18,000 seeds per pound).
Vegetative. The cucumber is an herbaceous, prostrate, annual vine that produces from three to eight angled stems covered with short, stiff hairs. The leaves are simple, large, triangular and palmately five-lobed with the middle lobe being sharply pointed. The root system produces a taproot that penetrates more than a meter (39 inches) into the soil with numerous shallow, lateral secondary roots. The lateral root extension is often equal to that of the above ground shoot growth.
Reproductive. Cucumbers are typically monoecious plants that produce imperfect yellow male and female flowers. The flowers are yellow and 2 to 3 cm (0.8 to 1.2 inches) in diameter. Male flowers generally appear first and in clusters in the leaf axils. Female flowers occur after the male flowers appear with usually one flower found in each leaf axil. The appearance of either male or female flowers can be altered by the environment. Male flowers are generally formed under long days while female flowers occur under short days. The flowers are cross-pollinated by insects. Bee hives are often placed around the periphery of cucumber seed fields to enhance pollination. One hive may pollinate up to 1.2 hectares (3 acres) of cucumbers.
Hybrid cucumbers have been developed with the recent discovery of plants that possess a gynoecious flowering habit. Such plants produce primarily female flowers. This unique genetic trait is retained by treating the gynoecious plant with gibberellic acid (1,000 ppm) or silver nitrate (600 mg/L) to induce the formation of male flowers for self-fertilization for production of stock seed of the female parent. Hybrid seed production is achieved by planting gynoecious varieties treated with ethylene to suppress male flower formation. If ethylene is not used, male flowers must be removed by hand from the seed plants every morning. The female:male row ratio is typically 4:1 arranged in a pattern of 8 female rows between two male rows. After flowering and pollination, the male parent row is plowed under so that only hybrid fruit are harvested. Hybrid cucumbers are noted for being earlier, producing a concentrated set of fruit, and being higher yielding than open-pollinated varieties.
The cucumber fruit is oblong and contains three seed-bearing placentae. Developing seeds enhance fruit growth. Unevenly shaped fruit can be attributed to incomplete pollination or environmental stresses that hinder uniform seed development.
Seed Production
Cucumbers can be grown almost anywhere. They require warm, dry weather for maximum production and are particularly sensitive to frost. Major cucumber producing states are Florida, Texas, Michigan, and California. Most cucumber seed is produced in the Sacramento Valley of California, and in Colorado and Michigan.
Tillage. Cucumber seed fields should be rotated from other cucubits such as melons. Cucumbers can be grown on almost any soil. Cucumber fields should be plowed deeply and early so that the field is settled prior to planting. Additional disking and harrowing operations may be necessary to smooth the seedbed. If irrigation is used or if the soil is poorly drained and heavy, raised beds are necessary. This is accomplished using a lister (a double moldboard plow) that makes the furrows 20 to 25 cm (8 to 10 inches) deep and the beds are formed by back-furrowing with a turn plow. A raised seed bed offers two important benefits: 1) the vines and fruits remain above the water level and 2) the raised beds are warmer; providing additional protection against frost injury.
Planting. The time of planting is delayed until the danger of frost is over. Because of the irregular, flat seed shape, most cucumber seed is coated so that precision planting can be accomplished. Direct seeding using drills into rows that are 91 to 122 cm (3 to 4 feet) apart at a rate of nine seeds per meter (three seeds per foot) is practiced. After emergence, the seedlings are thinned by cutting (pulling creates injury to the developing roots of the plant to be retained) to one plant per foot. When the initial vegetative leader stem has produced three to five leaves, it is removed by pinching to encourage growth of the remaining two lateral stems and their fruits. This results in the development of four or five fruits per parent plant.
Fertilization. Optimum growth of cucumbers requires soils with high organic matter and a pH of 6.5 or above. The organic matter is often supplied by green manure crops that are turned under before they reach maturity and become woody. It is difficult to provide a specific fertilization recommendation because of the diversity of soils on which cucumbers successfully grow. However, a fertilization regime of 1-2-2 is suitable before planting under non-irrigated conditions. Under irrigated conditions, the ratio should be 2-1-1 with half of the nitrogen applied a month after emergence to to replace that lost from leaching.
Weed and Pest Control. Chemical weed control in cucumber is expensive and uncertain so the most effective practices have concentrated on land management and mechanical cultivation. One approach has been to use a stale seedbed in which the field is left untouched until two weeks prior to planting. At that time, the site is sprayed with a contact herbicide to kill all plants followed by direct seeding of cucumber. Another approach has been to plow the killed plants under the soil following herbicide application to increase organic matter. Cultivation 5 to 10 cm (2 to 4 inches) deep begins as soon as seedlings have emerged. Later cultivations, however, must be shallow to avoid damage to subsurface roots and not close to the plant in order to minimize damage to the vine. After vines have covered the ground, further cultivation is not possible.
Cucumber is exposed to a variety of diseases and these are more prevalent in the humid eastern areas than the dry western areas of North America. Downy mildew, bacterial wilt, anthracnose, and root knot are common diseases that are destructive to cucumber as well as a number of other vegetable crops. Three specific diseases that affect cucumber are discussed because of their relationship with seed production: angular leaf spot, cucumber mosaic virus, and scab. Angular leaf spot (Pseudomonas lachrymans) causes small, angular, water-soaked spots on the leaves and fruits. The causative bacterial organism over winters in the soil and on the seed. Seeds should be tested to determine the presence of this organism. Cucumber mosaic virus causes a dwarfing, mottling, yellowing, and wrinkling of leaves, a warting of fruits leading to loss in yield. The virus over winters on the roots and seeds of common weeds including pokeweed, milkweed, and groundcherry. It is transmitted to the cucumber crop by aphids and the striped cucumber beetle. Control includes eradication of the host weeds and use of resistant cucumber varieties. Scab (Cladosporium cucumerinum) produces sunken, dark-brown spots on the fruits and is most damaging in cool, moist weather. The causative fungus over winters in the soil and on the seed. Control includes the use of seed treatments such as ziram and maneb.
Insects also reduce cucumber yields. The most destructive insects are cucumber beetles, aphids, and spider mites.
Irrigation. Cucumbers require high levels of water during vigorous vegetative and reproductive growth. Even in areas where rainfall is plentiful, periodic droughts substantially reduce yields and irrigation is necessary in these instances. While furrow irrigation is preferred, when overhead irrigation is used, it should be applied early in the day to permit the vegetation to dry out prior to nightfall and thereby minimize fruit rooting and foliar diseases.
Harvesting and Extraction. Fruit maturity affects seed quality in cucumber. For maximum seed quality, cucumber fruits must reach full maturity. This is signaled by a change in color from green to yellow and by a withering of the fruit stalk. Fruits can also be examined to determine seed maturity. Seeds that separate easily from the flesh of a sliced cucumber fruit are ready for harvest. At this stage, the fruits are typically harvested by hand and carried to a central seed extraction, drying, and storage facility for stock seed or small seed lots. For commercial seed, the plants are windrowed and then machine harvested. The slurry is augered into steel bins and then taken to the plant for seed extraction.
Seed extraction is accomplished by natural fermentation or acid treatment. In the former process, fruits are first sliced and macerated and the surrounding pulp, juice, and seeds allowed to ferment for about 4 to 6 days under normal field conditions. In the latter process, commercial hydrochloric acid (3 fluid ounces) or sulfuric acid (1 fluid ounce) added to and stirred with 11.3 kg (25 pounds) of the sliced, macerated fruit tissue. After 15 to 30 minutes, water is added to the mixture and the mature seeds sink to the bottom while the digested pulp floats to the top.
Whether fermentation or acid extraction is used, the seeds must be immediately washed to preserve seed quality. This is done by collecting the seeds on screens and adding the seeds to water troughs with riffles as described for tomato seeds. The remaining pulp material and acid float off while the cleaned seeds are retained on the riffles.
Drying. After extraction, the seeds are immediately dried. This is done either in the sun with frequent stirring and turning of the seed or with artificial batch driers that have a rotary paddle to expose the seed to heated air. The initial drying temperature should not exceed 40C (104oF) and the seed should be dried until it reaches a moisture content of 6% prior to cleaning and storage.
Cleaning. Cucumber seeds may still contain slight amounts of fruit debris following drying. This can be removed by an air-screen machine. Light and immature seeds can be separated from mature seeds on a gravity table.
Storage. Cucumber seeds stored at 6.5% moisture content under proper temperature and relative humidity conditions can remain viable for 5 to 7 years.
Bassett, M. J. 1986. Breeding Vegetable Crops. Avi Publishing, Westport.
George, R. A. T. 1985. Vegetable Seed Production. Longman Press, Essex.
Whitaker, T. W., and G. N. Davis. 1962. Cucurbits. Botany, Cultivation, and Utilization. Leonard Hill, London.