Horticulture Theory Unit 2 PDF

Principle of Horticulture Dr/ M. A. Taha Hort. Dept. Theory UNIT- II: Conditions required for successful vegetable cultivation Climate Climate involves the temperature, moisture, daylight, and wind...

Principle of Horticulture Dr/ M. A. Taha Hort. Dept. Theory UNIT- II: Conditions required for successful vegetable cultivation Climate Climate involves the temperature, moisture, daylight, and wind conditions of a specific region. Climatic factors strongly affect all stages and processes of plant growth. Temperature Temperature requirements are based on the minimum, optimum, and maximum temperatures during both day and night throughout the period of plant growth. Requirements vary according to the type and variety of the specific crop. Based on their optimum temperature ranges, vegetables may be classed as cool-season or warm-season types. Cool-season vegetables thrive in areas where the mean daily temperature does not rise above 70° F (21° C). This group includes the artichoke, beet, broccoli, brussels sprouts, cabbage, carrot, cauliflower, celery, garlic, leek, lettuce, onion, parsley, pea, potato, radish, spinach, and turnip. Warm-season vegetables, requiring mean daily temperature of 70° F or above, are intolerant of frost. These include the bean, cucumber, eggplant, lima bean, okra, muskmelon, pepper, squash, sweet corn (maize), sweet potato, tomato, and watermelon. Premature seeding, or bolting, is an undesirable condition that is sometimes seen in fields of cabbage, celery, lettuce, onion, and spinach. The condition occurs when the plant goes into the seeding stage before the edible portion reaches a marketable size. Bolting is attributed to either extremely low or high temperature conditions in combination with inherited traits. Specific vegetable strains or varieties may exhibit significant differences in their tendency to bolt. Young cabbage or onion plants of relatively large size may bolt upon exposure to low temperatures near 50° to 55° F (10° to 13° C). At 1 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. high temperatures of 70° to 80° F (21° to 27° C) lettuce plants do not form heads and will show premature seeding. The fruit sets of tomatoes are adversely affected by relatively low and relatively high temperatures. Tomato breeders, however, have developed several new varieties, some setting fruits at a temperature as low as 40° F (4° C) and others at a temperature as high as 90° F (32° C). Moisture The amount and annual distribution of rainfall in a region, especially during certain periods of development, affects local crops. Irrigation may be required to compensate for insufficient rainfall. For optimum growth and development, plants require soil that supplies water as well as nutrients dissolved in water. Root growth determines the extent of a plant’s ability to absorb water and nutrients, and in dry soil root growth is greatly retarded. Extremely wet soil also retards root growth by restricting aeration. Atmospheric humidity, the moisture content of the air, also contributes moisture. Certain seacoast areas characterized by high humidity are considered especially adapted to the production of such crops as the artichoke and lima bean. High humidity, however, also creates conditions favorable for the development of certain plant diseases. Daylight Light is the source of energy for plants. The response of plants to light is dependent upon light intensity, quality, and daily duration, or photoperiod. The seasonal variation in day length affects the growth and flowering of certain vegetable crops. Continuation of vegetative growth, rather than early flower formation, is desirable in such crops as spinach and lettuce. When planted very late in the spring, these crops tend to produce flowers and seeds during the long days of summer before they attain sufficient vegetative growth to produce maximum yields. The minimum photoperiod required for formation of bulbs in 2 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. garlic and onion plants differs among varieties, and local day length is a determining factor in the selection of varieties. Each of the climatic factors affects plant growth, and can be a limiting factor in plant development. Unless each factor is of optimum quantity or quality, plants do not achieve maximum growth. In addition to the importance of individual climatic factors, the interrelationship of all environmental factors affects growth. Certain combinations may exert specific effects. Lettuce usually forms a seed stalk during the long days of summer, but the appearance of flowers may be delayed, or even prevented, by relatively low temperatures. An unfavorable temperature combined with unfavorable moisture conditions may cause the dropping of the buds, flowers, and small fruits of the pepper, reducing the crop yield. Desirable areas for muskmelon production are characterized by low humidity combined with high temperature. In the production of seeds of many kinds of vegetables, absence of rain, or relatively light rainfall, and low humidity during ripening, harvesting, and curing of the seeds are very important. Soil The soil stores mineral nutrients and water used by plants, as well as housing their roots. There are two general kinds of soils—mineral and the organic type called muck or peat. Mineral soils include sandy, loamy, and clayey types. Sandy and loamy soils are usually preferred for vegetable production. Soil reaction and degree of fertility can be determined by chemical analysis. The reaction of the soil determines to a great extent the availability of most plant nutrients. The degree of acid, alkaline, or neutral reaction of a soil is expressed as the pH, with a pH of 7 being neutral, points below 7 being acid, and those above 7 being alkaline. The optimum pH range for plant growth varies from one crop to another. A soil can be made more acid, or less alkaline, by applying an acid-producing chemical fertilizer such as ammonium sulfate. 3 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. The inherent fertility of soils affects production quantity, and a sound fertility program is required to maintain productivity. The ability of a soil to support plant life and produce abundant harvests is dependent on the immediately available nutrients in the soil and on the rate of release of additional nutrients that are present but not available to plants. The rate of release of these additional nutrients is affected by such factors as microbial action, soil temperature, soil moisture, and aeration. Depletion of soil fertility may occur as a result of crop removal, erosion, leaching, and volatilization, or evaporation, of nutrients. Soil preparation and management Soil preparation for vegetable growing involves many of the usual operations required for other crops. Good drainage is especially important for early vegetables because wet soil retards development. Sands are valuable in growing early vegetables because they are more readily drained than the heavier soils. Soil drainage accomplished by means of ditches or tiles is more desirable than the drainage obtained by planting crops on ridges because the former not only removes the excess water but also allows air to enter the soil. Air is essential to the growth of crop plants and to certain beneficial soil organisms making nutrients available to the plants. When crops are grown in succession, soil rarely needs to be plowed more than once each year. Plowing incorporates sod, green- manure crops, and crop residues in the soil; destroys weeds and insects; and improves soil texture and aeration. The soil for vegetables should be fairly deep. A depth of six to eight inches (15 to 20 centimeters) is sufficient in most soils. Soil management involves the exercise of human judgment in the application of available knowledge of crop production, soil conservation, and economics. Management should be directed toward producing the desired crops with a minimum of labour. Control of 4 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. soil erosion, maintenance of soil organic matter, the adoption of crop rotation, and clean culture are considered important soil-management practices. Soil erosion, caused by water and wind, is a problem in many vegetable-growing regions because the topsoil is usually the richest in fertility and organic matter. Soil erosion by water can be controlled by various methods. Terracing divides the land into separate drainage areas, with each area having its own waterway above the terrace. The terrace holds the water on the land, allowing it to soak into the soil and reducing or preventing gullying. Maintenance of the organic-matter content of the soil is essential. Organic matter is a source of plant nutrients and is valuable for its effect on certain properties of the soil. Loss of organic matter is the result of the action of micro-organisms that gradually decompose it to carbon dioxide. The addition of manures and the growing of soil-improving crops are efficient means of supplying soil organic matter. Soil- improving crops are grown solely for the purpose of preparing the soil for the growth of succeeding crops. Green-manure crops, grown especially for soil improvement, are turned under while still green and usually are grown during the same season of the year as the vegetable crops. Cover crops, raised for both soil protection and improvement, are only grown during seasons when vegetable crops do not occupy the land. When a soil-improving crop is turned under, the various nutrients that have contributed to the growth of the crop are returned to the soil, adding a quantity of organic matter. Both legumes, those plants such as peas and beans having fruits and seeds formed in pods, and nonlegumes are effective soil-improving crops. The legumes, however, are more valuable, because they contribute nitrogen as well as humus. The rate of decomposition of plant material depends on the kind of crop, its stage of growth, and soil temperature and moisture. The more succulent the material is at the time it is turned under, the more quickly it decomposes. Because dry material decomposes more slowly than green material, it 5 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. is desirable to turn under soil-improving crops before they are mature, unless considerable time is to elapse between the plowing and the planting of the succeeding crop. Plant material decomposes most rapidly when the soil is warm and well supplied with moisture. If soil is dry when a soil-improving crop is turned under, little or no decomposition will occur until rain or irrigation supplies the necessary moisture. The chief benefits derived from crop rotation are the control of disease and insects and the better use of the resources of the soil. Rotation is a systematic arrangement for the growing of different crops in a more or less regular sequence on the same land. It differs from succession cropping in that rotation cropping covers a period of two, three, or more years, while in succession cropping two or more crops are grown on the same land in one year. In many regions vegetable crops are grown in rotation with other farm crops. Most vegetables grown as annual crops fit into a four-or five-year rotation plan. The system of intercropping, or companion cropping, involves the growing of two or more kinds of vegetables on the same land in the same growing season. One of the vegetables must be a small-growing and quick-maturing crop; the other must be larger and late maturing. In the practice of clean culture, commonly followed in vegetable growing, the soil is kept free of all competing plants through frequent cultivation and the use of protective coverings, or mulches, and weed killers. In a clean vegetable field, the possibility of attack by insects and disease-incitant organisms, for which plant weeds serve as hosts, is reduced. Planting Most vegetable crops are planted in the field where they are to grow to maturity. A few kinds are commonly started in a seedbed, established in the greenhouse or in the open, and transplanted as seedlings. Asparagus seeds are planted in a seedbed to 6 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. produce crowns used for field setting. Some vegetables can be either directly seeded in the field or grown from transplants. These include broccoli, cabbage, cauliflower, celery, eggplant, leek, lettuce, onion, pepper, and tomato. The time and method of planting seeds and plants of a particular vegetable influence the success or failure of the crop. Important factors include the depth of planting, the rate of planting, and the spacing both between rows and between plants within a row. Factors to be considered in determining the time of planting include soil and weather conditions, kind of crop, and desired harvest time. When more than one planting of a crop is made, the second and later plantings should be timed to provide a continuous harvest for the period desired. The soil temperature required for germination of the planted seed varies markedly with the various kinds of vegetables. Vegetables that will not germinate at a temperature below 60° F (16° C) include the bean, cucumber, eggplant, lima bean, muskmelon, okra, pepper, pumpkin, squash, and watermelon. Temperatures higher than 90° F (32° C) are not favorable for the germination of seeds of celery, lettuce, lima bean, parsley, pea, and spinach. Care of vegetable crops during growth Practices required for a vegetable crop growing in the field include cultivation; irrigation; application of fertilizers; control of weeds, diseases, and insects; protection against frost; and the application of growth regulators if necessary. Cultivation Cultivation refers to stirring the soil between rows of vegetable plants. Because weed control is the most important function of cultivation, this work should be performed at the most favourable time for weed killing, when the weeds are breaking through the soil surface. When the plants are grown on ridges, it is necessary to cover the basal plant portion with soil in the case of such vegetables as asparagus , carrot , garlic , leek , onion, potato, sweet corn, and sweet potato. 7 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. Irrigation Vegetable production requires irrigation in arid and semi-arid regions, and irrigation is frequently used as insurance against drought in more humid regions. The two types of land irrigation generally suited to vegetables are surface irrigation and sprinkler irrigation. A level site is required for surface irrigation, in which the water is conveyed directly over the field in open ditches at a slow, nonerosive velocity. Where water is scarce, pipelines may be used, eliminating losses caused by seepage and evaporation. The distribution of water is accomplished by various control structures, and the furrow method of surface irrigation is frequently employed because most vegetable crops are grown in rows. Sprinkler irrigation conveys water through pipes for distribution under pressure as simulated rain. Irrigation requirements are determined by both soil and plant factors. Soil factors include texture, structure, water-holding capacity, fertility, salinity, aeration, drainage, and temperature. Plant factors include type of vegetable, density and depth of the root system, stage of growth, drought tolerance, and plant population. Fertilizer application Soil fertility is the capacity of the soil to supply the nutrients necessary for good crop production, and fertilizing is the addition of nutrients to the soil. Chemical fertilizers may be used to supply the needed nitrogen, phosphorus, and potassium. Chemical tests of soil, plant, or both are used to determine fertilizer needs, and the rate of application is usually based on the fertility of the soil, the cropping system employed, the kind of vegetable to be grown, and the financial return that might be expected from the crop. Methods of fertilizer application include scattering and mixing with the soil before planting; application with a drill below the surface of the soil at the time of planting; row application before or at planting time; and row application during plant growth, also called side-dressing. Plowed down broadcast 8 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. fertilizers have recently been used in combination with high analysis liquid fertilizers applied at planting or as a side-dressed band. Mechanical planting devices may employ fertilizer attachments to plant the fertilizer in the form of bands near the seed. For most vegetables, the bands are placed from two to three inches (five to 7.5 centimeters) from the seed, either at the same depth or slightly below the seed. Weed control Weeds (plants growing where they are not wanted) reduce crop yield, increase production cost, and may harbour insects and diseases that attack crop plants. Methods employed to control weeds include hand weeding, mechanical cultivation, application of chemicals acting as herbicides, and a combination of mechanical and chemical means. Herbicides, selective chemical weed killers, are absorbed by the plant and induce a toxic reaction. The amount and type of herbicide that can be safely used to protect vegetable crops depends on the tolerance of the specific crops to the chemical. Most herbicides are applied as a spray, and the appropriate time for application is determined by the composition of the herbicide and the kind of vegetable crop to be treated. Preplanting treatments are applied before the crop is planted; preemergence treatments are applied after the crop is planted but before its seedlings emerge from the soil; and postemergence treatments are applied to the growing crop at a definite stage of growth. Frost protection Frost protection may be accomplished by increasing the amount of heat radiated from the soil when frost is likely to occur. Irrigation on the day before a predicted frost provides additional moisture in the soil to increase the amount of heat given off as infrared rays. This extra heat protects the plants from frost injury. A continuous supply of water provided by sprinkler irrigation may also protect plants from frost. As the water freezes on the plant leaves, it loses heat that is absorbed by the plant leaves, maintaining leaf temperature at 32° F (0° C). Because 9 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. of the sugars and other substances in plant cells, the freezing point of cell sap is somewhat lower than 32° F. Growth regulators It is sometimes desirable to retard or accelerate maturity in vegetable crops. A chemical compound may be applied to prevent sprouting in onion crops. It is applied in the field sufficiently early for absorption by the still-green foliage but late enough to avoid suppressing the bulb yield. Another substance may be used to end the dormancy, or rest period, of newly harvested potato tubers intended for planting. The treated seed potatoes have uniform sprout emergence. The same substance is applied to celery from two to three weeks before harvest to elongate the stalks and increase the yield and is also used to accelerate maturity in artichokes. A chemical compound, applied when adverse weather conditions prevail during the period of fruit setting, has been used to encourage fruit set. Harvesting The stage of development of vegetables when harvested affects the quality of the product reaching the consumer. In some vegetables, such as the bean and pea, optimum quality is reached well in advance of full maturity and then deteriorates, although yield continues to increase. Factors determining the harvest date include the genetic constitution of the vegetable variety, the planting date, and environmental conditions during the growing season. Successive harvest dates may be obtained either by planting varieties having different maturity dates or by changing the sequence of planting dates of one particular variety. The successive method is applicable to such crops as broccoli, cabbage , cauliflower, muskmelon, onion, pea, sweet corn (maize), tomato, and watermelon. Certain varieties of the carrot, celery , cucumber , lettuce, parsley, radish, spinach, or summer squash can be sown in succession throughout most of the year in some climates, thus prolonging the harvest period. 10 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. Hand harvesting is employed along with various mechanical aids for broccoli, cabbage, cauliflower, muskmelon, and pepper crops. Many vegetables grown for processing and some vegetables destined for the fresh market are mechanically harvested. Harvesting operations may be performed by a single machine in a single step for such vegetable crops as the bean, beet, carrot, lima bean, onion, pea, potato, radish, spinach, sweet corn, sweet potato, and tomato. Designers of harvesting machinery have been working to develop a multiple-picking harvester capable of adjustment for use with more than one crop. Vegetable breeders have been able to produce vegetables , with characteristics suitable for machine harvesting, including compact plant growth, uniform development, and concentrated maturity. 11 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. Session 2: Vegetable Propagation Techniques Plant Propagation Plant propagation is the process of multiplying the numbers of a species, perpetuating a species, or maintaining the youthfulness of a plant. There are two types of propagation, sexual and asexual. Sexual reproduction is the union of the pollen and egg, drawing from the genes of two parents to create a new, third individual. Sexual propagation involves the floral parts of a plant. Asexual propagation involves taking a part of one parent plant and causing it to regenerate itself into a new plant. Genetically it is identical to its one parent. Asexual propagation involves the vegetative parts of a plant: stems, roots, or leaves. The advantages of sexual propagation are that it may be cheaper and quicker than other methods; it may be the only way to obtain new varieties and hybrid vigor; in certain species, it is the only viable method for propagation; and it is a way to avoid transmission of certain diseases. Asexual propagation has advantages, too. It may be easier and faster in some species; it may be the only way to perpetuate some cultivars; and it bypasses the juvenile characteristics of certain species. Sexual Propagation Sexual propagation involves the union of the pollen (male) with the egg (female) to produce a seed. The seed is made up of three parts: the outer seed coat, which protects the seed; the endosperm, which is a food reserve; and the embryo, which is the young plant itself. When a seed is mature and put in a favorable environment, it will germinate, or begin active growth. In the following section, seed germination and transplanting of seeds will be discussed. Asexual Propagation Asexual propagation, as mentioned earlier, is the best way to maintain some species, particularly an individual that best represents that species. Clones are groups of plants that are identical to their one 12 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. parent and that can only be propagated asexually. The Bartlett pear (1770) and the Delicious apple (1870) are two examples of clones that have been asexually propagated for many years. The major methods of asexual propagation are cuttings, layering, division, budding and grafting. Cuttings involve rooting a severed piece of the parent plant; layering involves rooting a part of the parent and then severing it; and budding and grafting is joining two plant parts from different varieties. Asexual propagation, sometimes referred to as vegetative propagation, involves taking vegetative parts of a plant (stems, roots, and/or leaves) and causing them to regenerate into a new plant or, in some cases, several plants. With few exceptions, the resulting plant is genetically identical to the parent plant. The major types of asexual propagation are cuttings, layering, division, separation, grafting, budding, and micropropagation. Advantages of asexual propagation include: It may be easier and faster than sexual propagation for some species. It may be the only way to perpetuate particular cultivars. It maintains the juvenile or adult characteristics of certain cultivars. It allows propagation of special types of growth, such as weeping or pendulous forms. It may more quickly result in a large plant (compared to one propagated by seed). Vegetable propagation is a rewarding and cost-effective way to grow a wide variety of vegetables in your own garden or even in containers. By propagating vegetables, you can save money, control the quality of your produce, and enjoy the satisfaction of growing your own food. In this article, we will explore various techniques and methods for vegetable propagation, from seeds to cuttings and beyond. 13 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. 1. Seed Propagation 1.1 Choosing High-Quality Seeds When it comes to seed propagation, selecting high-quality seeds is essential. Look for reputable seed suppliers or save seeds from your own healthy and well-adapted plants. Choose open-pollinated or heirloom varieties for seed saving, as they will produce offspring true to the parent plant. 1.2 Germination Requirements Successful seed germination requires specific environmental conditions. Factors like temperature, moisture, and light influence the germination process. Research the germination requirements of each vegetable species to provide the optimal conditions. Some seeds may require stratification (exposure to cold temperatures) or scarification (breaking seed coat dormancy). 1.3 Seed Starting Mix and Containers Use a well-draining seed starting mix that provides adequate moisture retention. You can purchase commercial mixes or create your own by combining peat moss, vermiculite, and perlite. Choose containers with drainage holes, such as seed trays, peat pots, or recycled containers. Label each container with the plant name and sowing date to keep track of your seedlings. 1.4 Sowing and Transplanting Sow seeds at the recommended depth, usually two to three times the seed’s diameter. Maintain consistent moisture levels throughout the germination period. Once the seedlings develop true leaves and outgrow their containers, transplant them into larger pots or directly into the garden bed. 2. Vegetative Propagation 2.1 Stem Cuttings 14 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. Many vegetables can be propagated through stem cuttings. Select healthy, disease-free stems and cut them just below a node. Remove any lower leaves and dip the cut end in a rooting hormone to encourage root development. Plant the cutting in a well-draining propagation medium, mist regularly, and provide warmth and humidity until roots form. 2.2 Division Some vegetables, such as rhubarb and chives, can be propagated through division. Carefully dig up the mature plant and separate the clumps into smaller sections, making sure each division has roots and shoots. Replant the divisions in prepared soil and provide proper care until they establish themselves. 2.3 Layering Layering is another technique for vegetative propagation. It involves bending a low-growing stem to the ground, making a small wound, and burying it in soil while keeping the tip exposed. Over time, roots will develop along the buried section. Once rooted, sever the new plant from the parent and transplant it to its permanent location. Germination Germination is the resumption of active embryo growth after a dormant period. Three conditions must be satisfied for a seed to germinate: The seed must be viable; that is, the embryo must be alive and capable of germination. Internal conditions of the seed must be favorable for germination; that is, any physical, chemical, or physiological barriers to germination must have disappeared or must have been removed by the propagator. 15 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. The seed must be subjected to appropriate environmental conditions, including water (moisture), proper temperature, oxygen, and, for some species, light. The first step in germination is absorption of water. An adequate, continuous supply of moisture is important to ensure germination. Once germination has begun, a dry period can kill the embryo. Light can stimulate or inhibit seed germination of some species. Plants that require light for germination include ageratum, begonia, browallia, impatiens, lettuce, and petunia. Other plants germinate best in the dark. These include calendula, centaurea, phlox, and verbena. Some plants germinate in either light or dark. Seed catalogs and seed packets often list germination and cultural information for particular plants. When sowing light-requiring seeds, sow them on the soil surface. Supplemental light can be provided by fluorescent fixtures suspended 6 to 12 inches above the soil surface for 16 hours a day. Respiration in dormant seeds is low, but they do require some oxygen. Respiration rate increases during germination. The medium in which the seeds are sown should be loose and well aerated. If the oxygen supply during germination is limited or reduced, germination can be severely retarded or inhibited. Temperature affects the germination percentage and the rate (speed) of germination. Some seeds germinate over a wide range of temperatures; others have a narrow range. Many species have minimum, maximum, and optimum temperatures at which they germinate. For example, tomato seeds have a minimum germination of 50°F, a maximum of 95°F, and an optimum germination temperature of 80°F. When germination temperatures are listed, they are usually optimum temperatures. For most plants, 65 to 75°F is best. Seed Dormancy 16 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. Viable seeds that do not germinate are dormant. Dormancy can be regulated by the environment or by the seed itself. If a seed is not exposed to sufficient moisture, proper temperature, oxygen, or for some species, light, the seed will not germinate. In this case, the seed's dormancy is caused by unfavorable environmental conditions. Some seeds may not germinate because of some inhibitory factor of the seed itself. This kind of dormancy consists of two general types: (a) seed coat (or external) dormancy and (b) internal (endogenous) dormancy. A seed can also exhibit both kinds of dormancy. Techniques to Break Dormancy Seed Scarification External dormancy results when a seed's hard seed coat is impervious to water and gases. The seed will not germinate until the seed coat is altered physically. Any process of breaking, scratching, or mechanically altering the seed coat to make it permeable to water and gases is known as scarification. In nature this may occur during the winter, when freezing temperatures crack the seed coat or while microbial activities modify the seed coat as the seed lies in the soil. Scarification may also occur as the seed passes through the digestive tract of an animal. Scarification can be forced, rather than waiting for nature to alter the seed coats. Commercial growers scarify seeds by soaking them in concentrated sulfuric acid. Seeds are placed in a glass container, covered with sulfuric acid, gently stirred, and allowed to soak for 10 minutes to several hours, depending on the species. Reference books give appropriate concentrations and durations. When the seed coat has been modified (thinned), the seeds are removed, washed, and sown. Sulfuric acid can, however, be very dangerous for an inexperienced individual and should be used with extreme caution. 17 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. Vinegar is safer and can be used for some species; the technique is the same as with sulfuric acid. With mechanical scarification, seeds are filed with a metal file, rubbed with sandpaper, or cracked gently with a hammer to weaken (break) the seed coat. Another method is hot water scarification. Bring water to a boil (212°F), remove the pot from the stove, and place the seeds into the water. Soak the seeds until the water cools; then remove them and let them dry. Seed Stratification The second type of imposed dormancy, internal dormancy, is regulated by the inner seed tissues. This dormancy prevents seeds of many species from germinating when environmental conditions are not favorable for survival of the seedlings. There are several different types of internal dormancy. "Shallow" dormancy, displayed by many vegetable seeds, simply disappears with dry storage. No special treatment is necessary. However, other types require a particular duration of moist-chilling or moist-warming periods, or both. Cold stratification (moist-chilling) involves mixing seeds with an equal volume of a moist medium (sand or peat, for example) in a closed container and storing them in a refrigerator. Periodically, check to see that the medium is moist but not wet. The length of time required to break (remove) dormancy varies by species; check reference books for recommended times. This type of dormancy may be satisfied naturally if seeds are sown outdoors in the fall. Warm stratification is similar except temperatures are maintained at 68 to 86°F depending on the species. Seeds of some species exhibit double dormancy. This is a combination of two types of dormancy, such as external and internal dormancy. To achieve germination with seeds having both external and internal dormancy, the seeds must first be scarified and then stratified for the appropriate length of time. If the treatments are administered in 18 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. reverse order, the seeds will not germinate. After completing these treatments, plant the seeds under the proper environmental conditions for germination. Pollination in vegetable crops Vegetables are pollinated in two ways: self-pollination and cross- pollination. Self-pollinators are plants that produce flowers that are usually fertilized by their own pollen, commonly when the male and female flower parts are contained within the same flower. Cross pollinators are plants with flowers that require pollen from another flower (a male flower on the same plant–thus a form of self- pollination–or from another plant) to produce a fertilized seed. Cross- pollinators commonly require the help of insects or the wind to achieve pollination. 19 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. VEGETABLE CLASSIFICATION Quite a large number of vegetable crops are grown in the country either on a commercial scale or limited to backyards of homesteads. A few crops have similarity while others have dissimilarity in their climatic and soil requirements, parts, used, method of cultivation etc. While describing individual vegetables, there is a possibility of repetition in many aspects. In order to avoid repetition, it is essential to classify or group into different classes/groups. Different methods of classification followed in vegetables are described below: Botanical classification Botanical classification is based on taxonomical relationship among different vegetables. Plant kingdom is divided into four viz. Thallophyta, Bryophyta, Pteriodophyta and Spermatophyte. All vegetables belong to division Angiospermae of Spermatophyta. It is further divided into two classes viz., Monocotyledoneae and dicotyledoneae. The family wise distribution of vegetables under the classes is as follows: Monocotyledoneae: Family - Alliaceae Allium cepa Onion Allium cepa var. Aggregatum Multiplier onion Allium cepa var. Viviparum Top onion Allium porrum Leek Allium sativum Garlic Allium fistulosum Welsh onion Allium ascalonicum Shallot Allium schoenoprasum Chive Family - Liliaceae Asparagus officinalis Asparagus 20 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. Family - Araceae Dioscorea alata Larger yam Dioscorea esculenta Lesser yam Colocasia esculenta Taro Family - Poaceae (Graminae) Zea mays Sweet corn Dicotyledoneae: Family - Chenopodiaceae Beta vulgaris Beetroot and Palak Beta vulgaris var. cicla Swiss chard Spinacia oleracea Spinach Family - Asteraceae (Compositae) Cichorium intybus Chicory Cichorium endivia Endive Lactuca sativa Lettuce Cynara scolimus Artichoke Family - Convolvulaceae Ipomoea batatas Sweet potato Family - Brassicaceae (Cruciferae) Brassica oleracea var. acephala Kale Brassica oleracea var. gemmifera Brussels sprouts Brassica oleracea var. capitata Cabbage Brassica oleracea var. botrytis Cauliflower Brassica oleracea var. italica Sprouting broccoli Brassica caulorapa Kohlrabi or knol khol Brassica napus var. napobrassica Rutabaga Brassica campestris var. rapa Turnip Brassica juncea Leaf mustard Brassica chinensis, B. pekinensis Chinese cabbage Armoracia rusticana Horse-radish Raphanus sativus Radish Family - Cucurbitaceae Cucurbita peop Summer squash Cucurbita moschata Pumpkin Cucurbita maxima Winter squash Cucurbita lanatus Water melon 21 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. Cucumis melo Musk melon Cucumis melo var. momordica Snap melon Cucumis melo var. utilissimus Long melon Cucumis melo var. conomon Oriental picking melon Cucumis sativus Cucumber Luffa acutangula Ridge gourd Luffa cylindrica Sponge gourd Lagenaria siceraria Bottle gourd Trichosanthes dioica Pointed gourd / Parwal Trichosanthes anguina Snake gourd Momordica charantia Bitter gourd Benincasa hispida Ash gourd Family - Euphorbiaceae Manihot esculenta Tapioca Family - Fabaceae (Leguminosae) Pisum sativum Peas Phaseolus vulgaris French bean Phaseolus lunatus Lima bean Vicia faba Broad bean Vigna unguiculata Cowpea Cyamopsis tetragonoloba Cluster bean Vigna unguiculta var. sesquipedalis Asparagus bean Lablab purpureas Lablab bean Glycine max Soybean Psophocarpus tetragonolobus Winged bean Tigonella foenum graecum Methi / fenugreek Tigonella corniculata Kasuri methi Family - Malvaceae Abelmoschus esculentus Okra / Bhendi Family - Solanaceae Solanum tuberosum Potato Solanum melongena Eggplant Solanum lycopersicum Tomato Capsicum annuum Chilli / Pepper Family - Apiaceae (Umbelliferae) Daucus carota Carrot Petroselinum crispum Parsley 22 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. Apium graveolens Celery Cultural and climatic requirements of crops belonging to a family are not always similar. Cultural requirement of radish is entirely different from that of cabbage. Similarly climatic requirement of peas are different from that of cowpea. Classification based on hardiness: This classification is based on ability to withstand frost and low temperature, and it will be useful to know season of cultivation of a crop. Here the vegetable crops are classified into hardy, semi hardy and tender. Hardy vegetables tolerate frost and low temperatures and are basically winter or cool season or temperate vegetables. Warm season or subtropical or tropical vegetables are considered tender since they cannot withstand frost. Temperate vegetables, in general, can be stored for long periods under low temperatures. Tropical vegetables are bulky, and more perishable compared to temperate vegetables. Classification based on cultural requirement This is the most convenient and widely used system of classification of vegetables. Vegetables having similar cultural requirements are grouped together and placed in one group. For e.g., crops belonging to the group Cucurbits are seed propagated, direct sown, trailing and vigorous growing, cross pollinated and the cultural practice are almost same. 1. Solanaceous fruit vegetables 2. Cucurbits 3. Peas and beans 4. Cole crops 5. Bulb crops 6. Root crops 23 Principle of Horticulture Dr/ M. A. Taha Hort. Dept. 7. Potato 8. Tuber crops 9. Okra 10. Pot herbs / greens 11. Salad crops 12. Perennial vegetables 24