Assignment Code: BAPI-007/ASST/TMA/2021-22

Course Code: BAPI-007

Assignment Name: Plant Propagation and Nursery Management

Year: 2021-2022

Verification Status: Verified by Professor

Marks: 50

Instruction: All question carry equal marks and are compulsory.

Q1) What do you mean by Sexual propagation? Explain the factors responsible for the Seed viability.

Ans) Sexual propagation is the process of propagating a plant primarily through seeds and the production of zygotic embryos. Asexual propagation is defined as propagation that occurs through segmentation of vegetative parts or through vegetative embryos. Plant propagation can be done sexually or asexually, depending on the importance and utility of the horticultural plant. To breed new varieties, the sexual method of propagation is commonly used.

The following are some of the factors that influence seed viability:

1. Environmental Conditions: Seed viability is affected by the weather conditions present at the time of maturation, ripening, and harvesting. Warm, dry weather at seed maturity favours the production of high-quality seeds, whereas adverse weather conditions at seed harvest, such as frost, excessive rainfall, or even drought, can have a negative impact on seed viability.

2. Mechanical Injuries: Mechanical injury to the seed during harvest or transportation has a negative impact on seed viability. Injury to developing embryos, in particular, has an impact on seed viability and seed germination.

3. Genetic Factors: Seeds from different species or varieties within the same species may have different viability patterns.

4. Storage Conditions: The temperature, light, and humidity at the time of seed storage all have an impact on seed viability. High relative humidity shortens the life of seeds in general. If seeds are stored at an ultra-low temperature, they can be kept viable for longer periods of time. However, not all seeds can be kept at such a low temperature. Another important factor that affects seed viability is aeration.

Q2) Explain the common methods employed to detect the seed viability. Also discuss the factors affecting the seed germination.

Ans) Seed viability can be determined using a variety of methods. The most common methods for detecting the seed viability are as follows:

1. Germination Test: This includes seed germination on artificial media and comparing the number of germinated seeds to the number of seeds cultured. This is a common method for ensuring seed viability in a variety of plant species, including horticultural crops. Seeds are germinated in sand, soil, perlite, and vermiculite contained in plastic trays or boxes, or in filter paper layers, petri dishes, or sand, soil, perlite, and vermiculite contained in plastic trays or boxes.

2. Excise Embryo Test: Extracted embryos are cultured on synthetic media or in petri dishes lined with moist filter papers. The excised embryo test is commonly used to determine the viability of seeds in tree species that require long periods of “after ripening” before true germination.

3. Tetrazolium Test: The traditional methods for determining seed germination capacity in petri dishes or sand are time-consuming and labour-intensive.

The majority of non-dormant fruit seeds take 7-21 days to germinate, while dormant seeds take several months. Citrus seeds have a short shelf life and must be stored under special storage conditions. As a result, a quick test that provides a rough estimate of seed germinability is preferred. Within 4-24 hours, the seed viability can be determined using the tetrazolium test. It has a distinct advantage over other biochemical tests in that it can be carried out on individual seed organs and tissues, which are essential for growth. The embryos of seeds capable of normal germination and growth contain reducing enzymes that convert the nearly colourless triphenyl tetrazolium chloride solution into a bright red stain on the cut surfaces of the embryo tissue.

Seeds are soaked in 2, 3, 5-triphenyltetrazolium chloride solution for a few hours during this test. TTC is converted to an insoluble red compound in living tissue. Thus, depending on the time of incubation, viable seeds turn red partially or completely, whereas non-viable tissues/seeds do not change colour.

Water, light, aeration, temperature, and the incidence of infections are the most important factors that are affecting seed germination.

1) Water: Moisture availability is a critical factor affecting seed germination. Furthermore, seeds should have access to the maximum amount of water possible. Seeds die for lack of water if the water content is low, and seeds in the developing stage die due to anaerobic conditions if the water content is high. Many factors influence the rate of water uptake, including the nature of the seed coat, the current temperature, and the available moisture content.

2) Light: It is yet another important factor that influences seed germination. It should be at its best. The amount of light required by different seeds varies. Furthermore, for some seeds, light is not a limiting factor in their germination. Certain plant seeds have a strict requirement for light and will not germinate if they are not exposed to it. Light intensity has a minor impact on seed germination, but photoperiod and wavelength have a greater impact. Red light, in general, stimulates seed germination, whereas far red light inhibits seed germination. The quality of light, in addition to the presence or absence of light, influences seed germination.

3) Aeration: For rapid and uniform germination, gas exchange between the germination medium and the embryo is required. The respiratory processes in the germinating seed require oxygen. Overabundance of water around seeds reduces oxygen supply, affecting seed germination. In other words, because germinating seeds have a high rate of respiration, adequate gas supply and exchange between the germinating medium and the embryo are required for rapid and uniform germination and subsequent seedling growth. Water availability and aeration are inextricably linked. The more water there is, the less leaching and thus aeration in the germination medium.

4) Temperature: It should be at its best. The lowest temperature for effective germination is the minimum, while the highest temperature for germination is the maximum. The temperature that the seed requires varies depending on the type of seed. Seeds that require a low temperature for germination, for example, will not germinate at a high temperature, and vice versa. The percentage of seeds that germinate and the rate at which they germinate are both affected by temperature. Every plant species has an optimum temperature requirement for germination, below which germination is inhibited, and above which germination is inhibited.

5) Incidence of Infections: Seed germination is hampered by fungal or bacterial infections, especially when the humidity around the seed is insufficient. Seedling mortality is caused by fungi that attack young seedlings. In papaya seedlings, damping off is a common problem.

6) Salinity: Seed germination is affected by the presence of salts in water or soil, especially when the concentration is higher than the optimum level. When the growing medium is light and irrigated with low-quality water, salinity becomes a problem. Salt deposits on the upper layer of soil, where seeds are usually sown, result from frequent light irrigation, inhibiting the germination process.

Q3) What do you mean by Seed dormancy? How is it broken in the common seeds? Discuss.

Ans) Seed dormancy is the inability of a viable seed to grow due to internal or external factors. Tropical and sub-tropical fruit seeds germinate quickly after being extracted from the fruit under ideal moisture, temperature, and aeration conditions. However, even under ideal environmental conditions, seeds extracted from temperate fruit plants such as pear, peach, and plum do not germinate, even if they are viable; this is known as dormancy. Such fruit plants have been given protection by nature, as they would otherwise perish in harsh winters. As a result, it is critical that you comprehend seed dormancy and the factors that contribute to enhancing or overcoming seed dormancy in such seeds.

To improve seed germination of the common seed that are broken due to seed dormancy, various methods such as stratification, scarification, and chemical treatment are used.

Stratification

Temperate fruits' seeds, such as apple, pear, peach, plum, and cherry, require moist chilling to break their dormancy. This is accomplished through the stratification of their seeds. Seeds are stratified by being placed in alternate layers of moist sand, peat, or loam soil and kept at a temperature of 7.2°C. Stratification takes anywhere from 30 to 180 days, depending on the species. Seed stratification can take place in either natural or cold storage conditions.

Scarification

It is a mechanical technique that entails breaking, rubbing, or injuring the seed coat in order for it to become permeable to water and gases, allowing for better germination. This treatment improves the germination of peach, plum, and Ber seeds, among others. Seeds can be scarified in a variety of ways, including rubbing them between sheets of sand paper or blowing small seeds against abrasive boards under pressure. The degree of scarification is determined by the seed coat's composition. Scarification that is insufficient may not improve germination, while scarification that is excessive may harm the embryo.

Hormonal Control of Seed Dormancy

Hormones play an important role in seed dormancy regulation. Growth hormones, whether endogenous or exogenous, play a role in seed dormancy control. Hormones are made up of both growth promoters and growth inhibitors. Gibberellins, cytokinin, and ethylene are the most common growth hormones, while abscisic acid is a potent growth inhibitor.

Q4) What is Asexual Propagation? Describe the use of Plant Growth Regulators used in the Asexual Propagation.

Ans) Plant vegetative parts such as stem segments or cuttings, as well as budding, layering, and grafting, are used in asexual propagation. Plants propagated by asexual methods are true to type, whereas plants propagated by seeds are not always true to their parent plant. Some plants can be propagated using both sexual and asexual methods at will, while others can only be propagated using sexual and asexual methods. Fruit plants such as papaya are commercially propagated through seeds, whereas bananas are only propagated vegetatively. Mango, guava, citrus, grapes, apple, and other fruits and vegetables are propagated using both methods. Ornamental and vegetable crops are in the same boat.

Asexual propagation relies heavily on plant growth regulators. The following are a few of them:

Auxins

1. IAA was discovered to be the first naturally occurring compound with auxin activity in 1934, and it helps to induce rooting in cuttings.

2. Later, it was discovered that two synthetic substances, IBA and NAA, were more effective in inducing rooting in cuttings.

3. A continuous supply of auxins is required for the first 3-4 days of rooting in cuttings.

4. The rooting process is unaffected by the absence of auxin during the root elongation process.

5. Once the rooting process has begun, cuttings do not respond to exogenous auxin application.

Cytokinin

1. These are in charge of the cells' growth and differentiation.

2. Cytokinin activity can be found in Zeatin, Kinetin, and 6-benzyl adenine.

3. Cuttings with high cytokinin activity are more difficult to root than those with low activity.

4. When cytokinin is applied artificially, root initiation is inhibited.

Gibberellins

1. These were discovered in Japan in 1939 and were discovered to promote stem elongation.

2. They inhibit root initiation in cuttings at higher concentrations but promote it at lower concentrations.

3. For commercial purposes, GA3 is the most commonly used gibberellin.

Abscisic Acid

1. Its function in the rooting of cuttings is unclear.

2. Its impact is determined by the concentration and nutritional status of the stock plant from which the cuttings were taken.

Ethylene

1. It has a promoting effect on cutting rooting at low concentrations, but this effect is inhibited at higher concentrations.

2. The synergistic effects of ethylene on auxin synthesis, which leads to root initiation, are responsible for its rooting promotion activity.

Q5) What is nursery management? How the Nursery is helpful for the improvement in the family income? Discuss in detail.

Ans) Nursery management is an important horticultural activity. The nursery serves as a storage facility for the plantation's back-end supply of seedlings. All of the practises required for the production of new plant seedlings are included in nursery management. Seed sowing, vegetative propagation, and regular agronomic practises for plant maintenance are examples of these practises. Nowadays, horticulture nurseries are a profitable business. Several nurseries occasionally procure exotic plant breeds and sell them to the general public.

Nursery as a Helpful Source for the Improvement in Family Income

In the case of vegetables, flowers, and fruits, there are a number of advantages to using a modern nursery raising system.

1. It is entirely possible to raise virus-free seedlings.

2. There are no fungus or nematodes in the soil.

3. Possibility of raising a nursery in the off-season

4. Reduced seeding frequency

5. Seedlings with a strong root system,

6. There is no or very little seedling mortality.

7. There will be no transplant shock.

8. Establishment quickly,

9. In a small, protected area, a large number of seedlings can be raised.

10. Handling is simple.

11. Long-distance transportation is possible, and it can also function as a small-scale industry.

Because of the growing interest in vegetable gardening, fruit tree cultivation, social forestry, agro-forestry, and plantation crops, the demand for high quality planting material is steadily increasing. Small and marginal farmers, as well as gardeners and farm house owners, have recognised the need to establish plant nurseries to meet public demand. To meet this demand, there is plenty of room for small nurseries to be established, which will help to supplement the income of the poorest members of rural society.