Principles of vegetable production:-

Principles deal with the factor affecting vegetable production. The factor may be divided into two groups i.e. abiotic & biotic factors referring to non-living & living factors or component of the environments. The abiotic factor includes climate & soil. The biotic factor includes beneficial & harmful insect & microorganisms, higher plants & animals.  In this chapter, we discus in abiotic factors.

The basic objective of the gardener in growing vegetables is as:-

·         To achieve an optimum growth of plants in the minimum time with the least labor cost.

·         To gain profit from selling the produced in the market.

·         To supply fresh vegetables to consumers & thus provide nutrition.

To achieve these objectives, a gardener must understand the principle of vegetable production, & he most has good control over the environment & variety. These are main factors (abiotic) which affect the growth & development of the vegetable crops.

Climate & weather:-

Climate determines what crop can be grown best in a particular location. The performance of the crop mainly depends on the weather condition.

The daily condition of environment can be described in terms of temperature, rainfall, light intensity & duration, wind direction & velocity & RH. Collective, this factor comprises the weather. The weather changes day by day, the changes in weather flow a certain patterns which repeats it year after year.

A.  Temperature:-

Of all the climatic factors, affecting vegetable production, temperature may be considered as the most important. Temperature affects growth & development of vegetable crops during different phases of growth such as seed germination, general survival, development of economic parts, flowering, pollination and fruit set, quality of produced, seed production, seed storage, seed dormancy, occurrence of diseases and pests. In this topic, low temperature is attained in high hills. Generally, there is a 0.6⁰C decreases in temperature for every 91.5 m rise in elevation above sea level. In the low land it is cooler during certain parts of the year. Temperature is the most important factor which determines what crop to be grown in a certain place.

Optimum temperature:-

Each vegetable crop grows well in a favorable range of temperature. This is called optimum temperature range in which the rate of photosynthesis is normal. So, net photosynthesis product is maximum. The growth & development of some of the vegetable crops are affected at temperature less than 5⁰C, warm season crops cease growing at that temperature. Growth normally increases with increasing temperature up to 40⁰C but not beyond that. Thus vegetables crops are classified as cool season & warm season crops. Cool season vegetables generally survive even at temperature ranging from 0 – 5⁰C. Some crops like asparagus, onion, rhubarb & spinach can withstand frost better than the others. Crops like garden beet, broad bean and Cole crops can tolerate a minimum temperature of 5⁰C but lower temperature at maturity may cause injury. Many of them when exposed to chilling temperature bolt. Carrot, cauliflower, peas, potato, lettuce, celery, chicory, parsley & mustard can tolerate a minimum temperature of 7⁰C. Thus according to their requirement of temperature for their growth and development, temperature below 18⁰C are cool season crops and temperature above 18⁰C are warm season crops.

Temperature range	Crops
7 – 130C	Cabbage, potato, garlic, onion, spinach, peas etc.
13 – 180C	Sweet pepper, carrot, radish, tomato etc.
18 – 300C	Cucurbits, okra, cow pea, brinjal etc.

Extreme temperatures:-

Vegetables crops grow well within a narrow temperature range. At 0⁰C temperature, plants are killed by frost & at 40⁰C, they are killed by heat. Many plants are permanently damaged at 10⁰C or even ahead 15⁰C and most of the crops lose their photosynthetic efficiency above 30⁰C.

Chilling temperature or injury:-

Crops requiring high temperatures are very susceptible to chilling temperature i.e. 0 – 12⁰C. Symptoms of chilling injury are the appearance of discolored area. Poor color development of depressed area on the surface of the leaf or fruits. Chilling injury is the result of interaction between the temperature and time of exposure. E.g. a short period of exposure to 8⁰C may cause as much damage as a long exposure to 12⁰C. Thus tropical vegetables cannot tolerate temperature below 12⁰C while the temperate crops can be stored at 0⁰C or near 0⁰C.

Heat stress:-

Heat injury caused by high temperature is expressed in the reduction of growth rate. Temperature above 30⁰C inhibit the germination of lettuce, celery and tuber formation in potato. The fruit set of solanaceous crops and legumes vegetables declines as the temperature exceeds 32⁰C. In tomato, under heat stress condition, cracks at the stems ends may occur and the fruits become puffy. Onion and radish become more pungent at high temperature condition. Heat injury is held due to starvation, toxicity or destruction of fruiting structure. At the temperature above 30⁰C, the stomata remains closed. Starvation results when net photosynthesis is zero. Toxicity may occur when the anaerobic respiration is initiated. The structural protein may be destroyed by a high temperature. The symptoms of heat injury are the appearance of dead areas in young stems in legumes and the leaves of onion, cabbage and lettuce.

Vernalization:-

The biennial crops and some cool season vegetables such as onion, carrot, cabbage, cauliflower and spinach initiates flower formation after the exposure to the low temperature. The duration of vernalization to initiate flowering declines as the temperature decreases. E. g. at the same exposure duration, the radish flowers sooner at 5⁰C than at 10⁰C.

Effect of temperature on:-

a.    Seed germination: - Optimum temperature ranges for seed germination of warm season vegetables are 24 – 30⁰C and optimum ranges of temperature for seed germination of cool season vegetables are 5 – 15⁰C. Most of the warm season vegetables crops so impaired germination at higher temperature beyond 30⁰C.

b.    General survival: - On the basis of temperature requirement, vegetables crops are classified as cool season and warm season crops. Cool season crops differ from warm season crops in the following respects.

·         Seeds of cool season vegetables germinate at cooler soil temperature.

·         They are hardy (frost tolerant).

·         They have smaller plant size.

·         Their root systems are shallower.

·         Harvested product is not subject to chilling injury at temperature between 0 – 10⁰C.

·         Some of the biennial crops need exposure to prolong cool weather for seed stalk development.

·         Most of the cool season vegetables after harvest are stored at or near 0⁰c. Cool season vegetables are grouped in hardy and half hardy crops. Hardy crops are tolerated to frost. Similarly, warm season vegetable crops are grouped as tender and very tender.

Cool season crops:-

Hardy	Half hardy
Amaranthus, broad bean, broccoli, cabbage, Brussels sprouts, garlic, fenugreek, onion, parsley,  peas, radish, rhubarb, spinach, turnip etc.	Beet, carrot, cauliflower, celery, chicory, endive, lettuce, parsnip, potato,  etc.

Warm season crops:-

Tender	Very tender
Cowpea, new Zealand spinach, soybean, Sweet corn, tomato, etc.	Cucumber, eggplant, musk melon, okra,  hot pepper, pumpkin, squash,  sweet potato, water melon, etc.

c.    Development of economic parts: -It is more important to know the optimum temperature ranges required for developments of economic parts of vegetables. Since yield is directly affected by temperature levels. Thus, it is quite essential to know the minimum, optimum and maximum temperature level required for vegetable crops during the development of their economic parts.

d.    Flowering: -On the basis of temperature requirement of flowering, vegetable crops can be grouped as chilling requirement and non-chilling requirement crops. On the basis of flowering and seed production, treatment (chilling) for flowering whereas most of the biennials requires chilling to some extent before they bolt and flower. The degree of chilling requirement differs from crop to crop. However, the average chilling should continue for 1 – 2 months.

Chilling requiring crops	Non-chilling requiring crops
Beet, Brussels sprout, cabbage,  carrot, celery, Swiss chart, onion, leek, parsley, parsnip, etc.	All cucurbits, eggplant, sweet pepper, tomato, tropical radish,  tropical cauliflower, tropical cabbage, tropical turnip, okra,  peas, beans, Chinese cabbage, etc.

e.    Pollination and fruit set: -For most of crops temperature determines pollination, pollen tube germination and percentage of fruit set. Generally, the optimum average monthly night temperature of tomatoes is 21 – 23⁰C for pollination and fruit set. In higher or lower temperature blossom drop occurs post pollen germination and pollen tube growth.

f.     Quality of produced:- The quality of produced is important for vegetable grower because vegetable produce under normal environmental condition are better in quality and better quality vegetables always fetch higher market prices. Some examples of effect of temperature are:-

i.        Colored development:-

·         Yellow and red pigment development in tomato is temperature dependent. Optimum temperature for color development is 10 – 30⁰C.

·         Yellow pigment developed at 10⁰C.

·         Red pigment development is suppressed above 30⁰C.

·         At 40⁰C and above mechanism of red pigment development is permanently damaged.

·         In carrot, the orange color is carotene and the optimum temperature for development is 15 – 22⁰C.

ii.        Physiological disorder:-

·         In cauliflower, exposure of early cultivars to cool temperatures causes buttoning. Buttoning means formation of miniature curds. Very low temperatures of 1 – 20⁰C can cause bolting.

·         Higher temperatures cause loose and leafy curds in cauliflower.

·         In radish, turnip and broad leaved mustard higher temperature causes bolting.

g.    Seed production: -The temperature requirement of vegetable crops for seed production is differ from different crops. Most of the cool season crops require lower temperature during their early growth period and higher temperature during flowering, fruit setting and seed maturity.

h.    Seed storage: -Viability of seed is the function of temperature and moisture content of the seed. If the moisture content of the seed is higher, the storage temperature will be low and vice-versa.

i.      Seed dormancy: -Freshly harvested seeds of some vegetable crops are dormant and sometime higher temperature breaks the dormancy (they start germination). Seed dormancy is controlled by physiological and genetic factor and temperature influences it.

j.      Occurrence of diseases and pests:-

·         Diseases and pests occur at certain temperature levels.

·         For examples late of blight of potato and tomato becomes epidemic at fairly lower temperature condition. Bacterial wilt of tomato wilt occurs at higher temperatures condition.

·         Insect population increases and becomes active in higher temperature conditions.

B.  Light:-

Light from the sun to the earth travel in the waves. The length of the waves is measured in nm (10^-9m).  Light is an electromagnetic radiation which is a form of kinetic energy. It is an integral part of photosynthetic reaction in which it provides the energy for the combinations of CO₂ and water in the formation of first manufacture compound. Manipulation of light can be made by alternating the planting season, the performance of crop is influenced by three aspects of light.

a)    Light quality: -

It refers to the predominating wavelength. Photosynthesis uses light which is visible to human eye. This light ranges from violet with a wavelength 380nm - red with wavelength of 670nm. Light quality becomes important when plants are grown under critical light condition. In the predominance of ultraviolet wavelength, the plant will be dwarf. Predominance of red wavelength causes the plant to be long and thin. Red light (660nm) promotes germination while infrared light (730nm) inhibit the process.

b)   Light intensity: -

The amount of brightness of light is referred as intensity. Light intensity changes with time of day, season, elevation and latitude. It is measured in terms of gm. cal/area/unit time. If the plant is exposed to bright sunshine, light intensity for that plant is high. It varies from location to location, day to day and season to season. On clear day, the light intensity at the top of the mountain may be 1.75gm cal/cm²/min, while at the sea level is 1.5gm cal/cm²/min. clouds, dust, fogs reduces the light intensity. The vegetable crops are divided into sun and shade loving plants. The sun loving plant requires high light intensity to maintain a high rate of photosynthesis. The shade plant requires low light intensity. The sun plants have a higher compensation point. It is the amount of light at which photosynthesis is equal to respiration. In most of the crop plants, the light intensity at compensation point is .0.215gm cal/cm²/min. the light saturation point determine the light requirement of crops plant. The sun plants have higher light saturation point than the shade plants. The vegetable crops are classified according to their light requirement.

Light level	vegetable
high	Cucurbits, brinjal, potato, tomato, sweet potato etc.
medium	Onion, carrot, lettuce and taro.
Low to all darkness	Ginger, mushroom and bamboo shoots.

c)    Light duration: -

The duration of light is measured by the number of hours from sunrise to sunset. It is called photoperiod or day length. It varies from a nearly a uniform 12 hours day at the equator to the continuous light or darkness throughout the 24 hours for a particular part of the air at the polar region. In the tropics the differences between the shortest and the longest less than 3 hours.

During the long light period, relatively large quantities of carbohydrates are produced in photosynthesis and vice versa. During the short duration of light (winter) small quantities of carbohydrate are available for growth and production and vice versa.

The plant developed some timing mechanism which counts the duration of day and night. The phenomenon is called periodism. On the basis of response to light, the plants are classified into four groups:-

Short day plants flowers rapidly when day become even shorter. They require short day of about 12 to 14 hours of continuous light for flowering. If short day plants are grown under long day condition, have abundant carbohydrates and protein resulting in vigorous growth and non-flowering. E.g. Some cultivars of cowpea, beans, sweet potato and some cultivar of potato and onion etc.

Long day plants flower fast when the days are longer. They require long day of 14 to 16 hours of continuous light for flowering. E.g. beans, Chinese cabbage, lettuce, radish, spinach and some cultivars of potato, onion and cowpea.

Intermediate plants require almost 12 hours of continuous light.

Day neutral plant influence no light period for flowering.E.g. some varieties of bean and cowpea.

The length of light and dark period influences the formation of storage organs such as long day stimulating bulbing in onion and short day stimulates the formation of tuber in potato, tuberous root in sweet potato and corm in taro. The long day stimulates the formation of staminate flowers in cucurbitaceous crops and reduces the yield. The low temperature and short days speed up the development of pistillate flower in cucumber.

For high yield of vegetables as well as speed in cucurbits, more female flower is important than male flowers.

Moisture (rainfall and humidity):-

Vegetables are composed of 80 – 90% of water and they have produced remaining 5 – 20% through photosynthesis. So water is one of the basic requirements for vegetable production. Both too much and too little moisture is harmful to vegetable crops and reduce yield. Moisture influences the seed germination, vegetative growth, flowering, fruit set, maturity, quality of vegetable, seed production, diseases and pest occurrence and seed viability in storage. Abundant water favors the vegetative phase of growth by rapid increase in cell division. Under the moderate water supply plant growth decreases. According to the water requirement, vegetable crops are classified into following five groups:-

1.       Great water users with poor roots penetration: -

 Vegetable crops such as cauliflower, cabbage, radish, leafy vegetables and cucumber require high amount of water for their poorly developed root system. They are very sensitive to drought condition.

2.       Economical water users with vigorous root penetration: -

Crops like melon, bitter guard and cucurbits have developed deep root system and large leaf area but the leaves are hairy and lobed.

3.       Economical water users with poor root penetration:-

Crops like onion, garlic and asparagus have poor root system but they have small and wavy leaves which reduces transpiration rate.

4.       Economical water users with moderate penetration:-

Solanaceous crops roots vegetables and legumes have less leaf area and leaves are hairy which reduces rate of transpiration.

5.       Extravagant water users with poor root penetration:-

Most aquatic vegetable such as water cress, some cultivar of taro which have poor root system without root hairs.

Water logging: -Under water logged condition, roots cannot uptake oxygen to maintain for nutrient and water uptake. Water logging causes death of root hairs, reduces absorption of nutrients and water, increases the formation of toxic compounds, retards growth of the plants and finally reduces the crop productivity. Flooding is more serious at high temperature conditions than at low temperature conditions. According to the sensitivity to flood, vegetables are divided into 3 groups: -

Sensitivity level	Vegetable crops
sensitive	Cole crops, beans, pumpkins, radish, tomato, water melon.
Moderately sensitive	Cucumber, brinjal, garlic, onion and peas.
Moderately tolerant	Sponge gourd, cowpea, sweet potato, Colacasia and water cress

Water balance:-

When  the rate of water absorption equal to the rate of transpiration, the guard cell become turgid, carbon dioxide enters rapidly into the leaves, the rate of photosynthesis is high, rate of respiration is normal, assimilation is enough and crop growth rate is maximum.

Droughts:-

When the water balance becomes negative, the stomatal opening decreases. The rate of photosynthesis and crop growth is also decreased. The effects of drought on determinate crops are greater than on the indeterminate crops.

The vegetables crops may be classified into 2 groups:-

1.    Drought avoiders: -

Drought avoiders avoid the drying of the tissue by maintain their water uptake and by reducing water loss. The plants may produces more root then shoots. They have ability to move their leaves, develop hairs to insulate the leaf surface and may become waxy. Generally, the legume crops are good drought avoiders.

2.    Drought tolerators: -

The tolerates survive drought by functioning normally even with a low amount of water in their tissues. Vegetable crops cannot sustain prolong drought stress without loss in yield and quality.

Humidity:-

Humidity plays the most important role in the occurrence of pests and diseases. Certain diseases like powdery mildew are associated with dry weather but humid condition is known to favor diseases like downy mildew and fungal blights affecting foliage. A cool humid place is ideal for growing cabbage, cauliflower, turnip, knolkhol, spinach, beet root, etc.especially for seed production. On the contrary, dry and higher temperature conditions are ideal for seed production for onion, broad leaved mustard, radish, cucumber, squash and pumpkin. In cucurbits, moist condition influences the onset of flowering significantly. Low humidity accelerates the appearance of staminate flowers, while high humidity favours the production of pistillate flowers. Crops like beans and caulis are known to tolerate and condition better than most other vegetables. Dry weather like low humidity is favourable for seed maturity and harvesting in most of crops. Seeds store under low humidity in storage. Humidity is inversely co related to temperature during storage.

Wind:-

During rapid growth of plants, carbon dioxide is rapidly depleted on the root surface. A slight wind is essential for the supply of carbon dioxide near the plant surface. In strong wind, the average velocity greater than 7.2 km/hours are limiting factor of vegetable production. Typhoons are very destructive to vegetable crops. A wind break is the structure that reduces the speed of wind. When the trees are used as wind break, they are called shelter belts. All the vegetables crops are very susceptible to the strong winds. E.g.the seed production of onion is problematic in terai due to windy weather at the bolting stage of the crops in March – April.

Soil:-

Vegetable crops generally grow well in fertile soils with continuous supply of nutrients and moisture. Due to the topographic variation in Nepal, many types of soil are available in many part of the kingdom. Generally sandy soil are best suitable for roots, bulb and tuber crops. Sandy soil is also preferred for early crops. Sandy soils allow fast development and easy harvesting of roots and tuber crops. Sandy soils cannot hold much water and nutrient. Loamy soils are ideal for vegetable production. They have good mixture of sand and clay. They have good nutrient and water holding capacity. They provide good aeration to the root zone. Clay soils are difficult to work when they are dry but they have good water and nutrient holding capacity.

Crops like onion, garlic, carrot, beet, radish, turnip, garden beet, potato, yams, sweet potato and tapioca do well in lighter soils. A heavier soil causes splitting of onion and malformed root. Growth in many root crops. Nutrient requirement of soils for vegetable grown are mainly influenced by the soil aeration. When the soil ph. is below 6.5, P₂O_5, Mg and Ca are not available for most of the crops. When pH is about 7, Fe, Mn, B and Zn become unavailable. Thus, vegetable crops may be grouped into the following categories based on their tolerance to soil pH.

Slightly tolerant (pH 5.5 – 6.8):- Beans, brinjal, carrot, garden beet, lettuce, musk melon, okra, onion, leek, celery and peas.

Moderately tolerant (pH 5.5-6.8):-beans,-brinjal carrot, cucumber, garlic, peas, pepper, radish turnip, knolkhol, etc.

Very tolerant (pH 5.0-6.8):-potato, sweet potato and watermelon.

Vegetable crops which are in the slightly tolerant group can be grown in the soils that are in the alkaline side up to pH 7.5.

Differences between determinate and indeterminate crops:-

S.N.	Determinate crops	S.N.	Indeterminate crops
1.      2.         3.	These crops flowers in each node and terminal parts end into a flowering shoots. They have discontinuous growth. They are very sensitive to drought condition.	1.      2.         3.	They flowers after five leaves and  the terminal part remains always vegetative. They have continuous growth. They are drought tolerant crop.

Variety development and testing:-

Variety: -A variety is a group of plants that has common qualities and it should be distinct from other groups of plants of the same species. To be a variety it should have three criteria. They are:-

1)    Distinctness: - The variety should be different from other varieties.

2)    Uniformity: - The variety should be uniform.

3)    Stability: - The characteristics of the varieties should be stable from one generation to other generation.

Types of varieties:-

1)    Traditional varieties: -Traditional varieties have been usually started by the farmer themselves. Such varieties are being used by many generations of farmers. E.g. Kathmandu local is a traditional variety.

2)    Landraces: - Landraces are the groups of traditionally used plants that do not satisfy the rigid criteria of a variety.

3)    Improved varieties: - These varieties have been developed from systematic plant breeding work and trueness of the variety is maintained by the trained personnel.

4)    Open pollinated varieties: - Seeds of these varieties are produced by natural pollination through successive generations.

5)    Hybrids: - Hybrids are varieties that result from controlled pollination involving 2, 3 or 4 parental lines.

6)    Pure line: -Pure line is the progeny of a single homozygous self – fertilized individual plant. Its progenies remain true to the type and uniform. Selection within pure line is ineffective.

7)    Clone: - Clone is a progeny of one vegetatively propagated plant.

8)    Strain: - A variety may have several strains with minor differences but having all the basic characteristics of the original varieties.

Characteristics of Improved Varieties:-

1)    Productivity: - One of the most remarkable achievements of the modern plant breeding is the improvement of crop productivity. It is measured in terms of yield/ area per time per fertilizer. It has been increased with the development of varieties having high yield potential, earliness, improved plant architecture and high harvest index.

2)    Adaptability: - Varieties have wide adaptability have been developed by the plant breeders.

3)    Reliability: - The crop performance should be reliable year after year.

4)    Quality: - It is the most important factor that determines the acceptance of a variety. The new varieties should meet the market standard. E.g. Color and firmness in tomato, dry matter content in onion 46% dry matter content is preferable in industries), non – bitter cucumber production.

Variety development:-

Varieties are developed through a process called plant breeding. It is the genetic adjustment of plants to the service of man. Selection is the major part of plant breeding. Selection is processing of selecting for the desired type in a variable population of plants. The method of selection varies according to the nature of pollination of the crops.

Breeding methods for self – pollinated crops:-

1)    Mass selection: - Mass selection is a form of selection in which individual plant is selected and the next generation continued from the aggregate of seeds of the selected plants. This is done by rouging out the undesired plants from the field and harvesting the seed crop of the remaining plants in bulk or mass. Another approach is to tag or mark the desirable plants and harvest them in bulk or mass.

2)    Pure line selection: -Pure line breeding generally includes 3 steps, sufficient number of selection are made from the originally available variable source population or material. The second step includes growing of progeny rows from the individual plants selection obtained in the first step. The final and the third step include the evaluation of remaining lines in the replicated trials to compare the selections among themselves and with established commercial variety. The outstanding line is finally selected and the seeds of that line are collected for further multiplication.

3)    Pedigree method: - This method of breeding consists of selection among individual plants and their progeny during inbreeding following crosses between selected donor parents. The selected plants are crossed in a single cross system. The F₂populations are subjected to desired character. The F₃ progenies are the selected F₂ plants are grown in rows. The most desirable F₃ progeny rows are selected and harvested seed from superior individual plants from each of the selected rows. This practice of selection continuous till F₅. F₆generation in which desirable rows are bulked within themselves and the bulks are evaluated in animplicated trial. A proper time of record is maintained of each generation of the plants.

4)    Single seed decent method: - In this method all the plants of the F₂ generation are advanced to the next generation the harvesting and growing one seed from each plant. This process is continued till F₅. In F₆ generation superior individual plants are selected finally. Adequate level of variability is maintained in all the generation. No potentially superior plant is estimated in early generation. It is cost effective as resources are required to follow the scheme of selection.

5)    Bulk method: - The growing of genetically diverse population of self-pollinated crops in a bulk plot or without mass selection followed by single plant selection in F₅ or F₆ generation is known as bulk breeding. In this method plants of segregating population are harvested together and the sample seed is used to the next generation. In F5 or F6 generation, selected individual plants are harvested and evaluated in individual plant progeny from which superior rows are selected and seeds are used to evaluate in the replicated trial. The major advantage of this method is that there is no problem in selecting the seeds in every generation.

6)    Back-cross method:-In this method, recurrent back crosses are made to one of the parents of hybrid for a specific characteristic known as back cross breeding. It is an efficient procedure to reconstitute most of the genotype of the recurrent parents. This method allows the introduction of new character from non-recurrent parents.

Advantages:-

·         It requires a small number of plants to be handled.

·         There is no role of environment on this breeding.

·         It is a stepwise breeding program.

·         The performance of the derived line is predictable but this method of breeding excludes the combination of genes from the parental cultivar which is a common feature.

7)    Multiline breeding: - Extension of back cross breeding.

8)    Mutation breeding.

Breeding method for cross-pollinates crops:-

1)    Mass selection:-

It is also known a positive mass selection. In this method, the best individual plants are uprooted and transplanted in the next field for seed production. Then the seeds are composite or bulked for raising next generation. The selection is based on the phenotype performance of the mother plant, without any progeny test. This process is repeated for several cycles till substantial achievement are obtained.

2)    Mass pedigree method:-

In this method the best individual plant with desired characters are selected on the basis of phenotypic performance from variable sources. Open pollinated seed of selected individual plants are divided into 2 halves. In the second year replicated progeny row trial is conducted using one set of half seeds from each plant. Based on the progeny performance, the best parental individuals are identified. The remaining or remnant half seeds from the superior parental lines are mixed and grown in isolation in the third year.

3)    Inbreeding:-

Self-fertilization is the most intense form of inbreeding. In plant breeding, nearly homozygous lines are produced by continued self-fertilization for 5 – 6 generations. This method can be used in those crops which do not show inbreeding depression. E.g. cucurbits.

4)    Recurrent selection:-

A number of plants are self-pollinated in a source of population in the first year. Superior plants base in phenotypic performance are selected. In the second year, seeds produce by self-fertilization of the selected plants are sown & crossed in all possible combination. The seeds are collected & bulked. Such cycle of selection & crossing is repeated.

5)    Synthetic variety:-

Synthetic variety is maintained from open pollinated seed following its synthesis by hybridization in all combination among a number of selected genotypes which have been tested for combining ability. The component of synthetic variety could be inbreed, clones, mass selected population or various other materials. The component units are maintained so that the synthetic may be reconstituted at regular intervals.

6)    Development of composite varieties:-

Composite varieties are derived from the varietal crosses in advanced generations. These are developed from open pollinated varieties or other heterozygous populations or germplasm which have originally not been subjected to inbreeding or have not been elaborately tested for their combining ability. Usually, they involved open pollinated varieties, synthetic, double crosses, etc. selected for yield performance, maturity, resistant to disease & pests. These composites often show a high order heterosis in F1 when widely diverse populations are crossed.

7)    Development of hybrid varieties:-

There are 2 steps for the development of hybrid varieties.

Step 1:-

Development of inbreed lines: - All the selected plants are self-pollinated& evaluated as a pure line selection until they reach a highly developed homozygosity. The final product of this process is a pure line.

Step 2:-

Combining ability test: - The inbreed lines are tested or for their combining ability to give an acceptable progeny in a hybrid combination with other inbreed lines.

8)    Plant introduction:-

Vegetable breeding programs are global on nature & every country has her own program. The best variety developed anywhere are introduce, acclimatized and cultivated in commercial scale. Plant introduction plays an active role as a method of breeding.

Seed viability test:-

Viability test is popularly recognized as an accurate means of estimating alive seed.

·         Tetrazolium test: - Tetrazolium test distinguishes between viable & dead tissues of the embryo on the basis of their relative respiration rate. About 50 – 100 seeds are taken from submitted samples. The seeds are soaked for 3 – 4 hrs. in water. Cut the seeds with the sharp blade exposing the main structures of the embryo. The one halves of the seeds are placed in petri-dish & covered with 1% tetrazolium solution. Keep the petri-dish in dark at the temperature of 35 – 40⁰C for 2 hrs. Then the tetrazolium solution is removed & filled with water. The live cells of the embryo become dark red stained & are evaluated under the magnifying glass.

Vigour test:-

Vigour is defined as the potential for rapid uniform germination & fast seedlings growth. The indirect method of measuring vigor is:-

a.    Seedling growth rate: - In this parameter, we can measure the plant height & dry matter content.

b.    Speed of germination:- Mathematical expression using germination speed as a measure of seedling Vigour is:

Vigour= No. of normal seedlings (first count) / days of first count + No. of seedlings at last count / days of last count.

The direct method of vigor test includes:-

a.    Brick gravel test: - In this method, the germinating seeds are covered with 13 mm layer of brick and gravel of 3 mm size. Only the vigorous seedlings emerge out from the gravel

b.    Paper piercing test: - A paper sheet of 0.4 mm thick & 90 gm./m² weight is placed above the germinating seeds. Only the vigorous seedlings come out piercing the paper sheet.

Moisture test:-

The moisture content of the seed sample is the loss in weight when it is dried. It is expressed as the percentage of the weight of the original sample. The hot air oven method is the routine method. Moisture content is determined by removing the moisture from the seeds in a hot air oven. There are 2 methods:-

a.    Low constant temperature oven method: - In this method the oven is maintained at 103⁰C and the sample is dried for 17 hrs. This method is used for the seeds having higher percentage of oil content. After drying, the sample is taken out & put in the desiccators for 35 minutes. After cooling the sample is weighed.

b.    High constant temperature oven method: - The oven is maintained at the temperature of 130 – 133⁰C for 1 – 2 hrs. This method is used for such crop seed like cucurbits, carrot, lettuce, peas & beans. Seed moisture should be below 12% in starch & below 10% in oily seeds for ordinary stages. For sealed container, the moisture content should be lower. The storage life of the seed becomes double,for every 1% decrease moisture content. This rate is useful between 0 – 16% moisture content. Below 6% there is no viability of embryo of seed.

Planting value of seed = purity% X viability% X 100.