Propagation of Fruit Plants - Seeds by Parshant Bakshi

SEED PROPAGATION The propagation of fruit trees can be done either by seeds or by vegetative means such as grafting, budding, cuttings, layering and suckering. Seeds removed from fruit can be grown although the seedlings do not always come true and take longer time to fruit. Plants propagated vegetatively will be genetically identical to the plants from which the propagation material was taken and will usually bear fruit within 2 to 3 years. Seedlings are mainly used as rootstocks for the more desirable varieties of fruit, but some tropical and subtropical fruits are propagated by seed. Seed may be obtained from commercial suppliers, nurserymen, fruit packing houses or from plants maintained for seed production. The multiplication of plants by seed is known as sexual propagation. The fruit crops like papaya, phalsa, jackfruit and mangosteen are only being propagated by seed. Plants raised through seeds are called seedlings.

Flowchart of seed propagation Plant in containers or seedbed for rootstock raising

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Select and prepare seed

Sow seeds directly in the nursery

Improve cultivar by grafting, budding, topworking

Establishment of Improved cultivar in field

Advantages Ä Seedling trees are long lived, hardy and bear more heavily. Ä It is a simple and cheap method of propagation. Ä Apomixis exists in a number of apple species which gives rise to apomictic seedlings which are true to its mother plant. These species are thus commercially propagated through seed. Ä Sexually propagated plants are free from virus diseases and can tolerate biotic and abiotic stresses. Ä Fruits of mangosteen (Garcinia mangostana) are developed through parthogenesis. Seedlings obtained from seeds of such fruits are similar to its mother plant, thus the plants can be commercially raised by seed. Ä In-breeding for evolution of new varieties, the hybrid plant is first raised by seed. Ä It has been responsible for the production of some chance seedlings of highly superior qualities. Ä Polyembryony exists in some varieties of fruits like citrus and mango which give rise to more than one seedling from one seed. These Polyembryonic varieties can be propagated only by seeds. Ä Rootstocks upon which the fruit variety is budded or grafted are usually raised by seeds as they develop better root system.

Disadvantages Ä Seedlings have long juvenile phase which resulted in delay in fruiting. Ä There is no uniformity in growth, yield and quality of fruits. Ä Fruits obtained from seedlings are of inferior quality.

Unimproved/ungrafted fruit tree

Improved grafted fruit tree

Ä It is not possible to perpetuate the exact characters of any superior selection. Ä These trees are usually large in size and thus the cost of harvesting, pruning and crop protection is more. Ä As seed-borne viruses like psorosis and mosaic exist in citrus, peach, cherry and almond fruit plants. Thus, the multiplication of such plants by seed is not recommended.

Propagation by seed is recommended © for rootstock propagation in the nursery © for later top-working in the field © to propagate an indigenous or rare type of tree © if the fruits are required for domestic consumption or local market © if quality, yield and time are of minor importance © if one cannot get any improved cultivar propagation material

Fruit trees as seed sources: Select seed from ¶ healthy, outstanding mother trees ¶ typical and well-growing trees ¶ mature trees ¶ fresh, ripe fruits

Good quality seeds are: ¶ clean and free of disease ¶ fresh, for a good germination rate

of the desired cultivar

Propagation by seed Fruit crops like papaya, phalsa, kagzi lime and jamun are usually propagated by seeds. In citrus and mango, seeds are also used to raise rootstock seedlings. This method being the easiest and cheapest is generally employed on a commercial scale in these fruit crops. In mango and citrus, nucellar seedlings can be used to raise true-to-type plants. Seed propagation is essential for breeding new plant type and conserving genepools. For raising of a plant by seed, a thorough knowledge of seed viability, its storage, time of sowing, factors responsible for germination and care of germinated seedling is essential. The condition in which the seed can germinate immediately upon the absorption of water in the absence of any internal germination barrier, the embryo (or seed) is said to be quiescent, while those seeds which fail to germinate even though the embryo is alive, moisture is absorbed and favourable conditions are provided are known as dormant seeds. In most of the fruit crops, there may be natural or chemical dormancy. The dormancy in seeds of ber, guava and walnut is due to the presence of hard seed coat which inhibits penetration of water and oxygen required for germination. Presence of chemical inhibitors (abscisic acid) is responsible for dormancy in seeds of most of temperate fruits (apple, pear, peach and walnut). Besides ABA, higher concentration of pectin, gum, tannin and amino acids are also responsible for dormancy in seeds of temperate fruits.

How to overcome dormancy Seed dormancy due to hard seed coat can be overcome by softening the seed coat. It can easily be done either by scarification, stratification or by use of chemicals and hormones.

Scarification: It is the process of breaking, scratching, altering or softening the seed covering to make it permeable to water and gases. It can be achieved mechanically, or by hot water and acid. In mechanical scarification, cracking of seed with hammer, rubbing with sand paper or cutting with a file without injury to embryo is generally employed to break the dormancy (ber, peach, walnut). Impermeable seed coat of guava can be softened by hot water 0 scarification. Seeds are placed in hot water at 77-100 C. They are immediately removed from hot water and allowed to soak gradually in cool water for 12-24 hours. Acid scarification consists of treating guava seeds with concentrated sulphuric acid for 3 minutes, ber for 56 hrs and strawberry seeds with 0.25% nitric acid or hydrogen peroxide results in higher germination.

Stratification: It is the method of handling of dormant seeds, in which, the imbibed seeds are subjected to a period of chilling to after-ripen the embryo. This term originated as the nurserymen used to place seeds in stratified layers interspaced with a moist medium such as soil or sand out of door or in pits during winter. The term moist chilling has been used as synonym to stratification. Stratification can be achieved by refrigeration of dormant seed. Dormant seeds of temperate fruits like apple, cherry, pear and apricot are generally placed in layers of sand in a box 0 0 at a temperature of 1 -5 C. Depending upon the seed type, treatment time varies from 1-5 months for breaking dormancy of seeds. The seed dormancy due to presence of growth inhibitors can be broken by placing the seeds in running water. It results in leaching of inhibitors. The freshly extracted seeds of strawberry and grape if placed in running water for 7-12 days result in increased germination.

Chemical treatments: Many freshly harvested dormant seeds usually respond to soaking in potassium nitrate solution. This technique is largely used in seed testing laboratories where seeds are placed in petri-dishes containing 0.2% solution of potassium nitrate. The seeds of peach and grape, treated with 5,000 ppm (5 g/litre) of thiourea show enhancement in their germination.

Use of hormones: The seed dormancy can also be overcome by the treatment of growth regulators. Treatment of seeds of apple, cherry, peach, strawberry and hazelnut with 100-500 ppm of GA3 for 24-48 hrs improves germination and better growth of seedlings. Ethrel (5,000 ppm)-treated seeds of guava and strawberry also show better germination and growth of seedlings. Treatment of apple and peach seeds with 10-20 ppm solution of benzyl adenine (BA) is effective for higher seed germination.

Seed sowing The fruit seeds are sown in seed bed, polythene bags or in situ. Seeds of tropical and sub-tropical fruits are sown during monsoon (June-July) or in the beginning of spring (February-March). Generally, seeds of mango and jackfruit are sown during June-July, while those of guava, ber and aonla during February-March. Seeds of temperate fruits are generally available during June-October and their sowing should be done after the dormancy period is over. In citrus, mango, loquat, litchi and jackfruit, seed viability is very less, so these should be sown immediately after extraction. In north India, seeds of different citrus types are available during winter months. Germination of seeds is low due to prevailing low temperature. Hence, use of alkathene tent on seed beds during December-January is useful in increasing germination percentage and faster growth of seedlings. The seeds are usually sown at a depth 3-4 times of their size. It should be a little deep in light soils while shallow in heavy soils. Now-a-days, sowing of seeds in polythene bags, earthen pots and pans is becoming popular. It is usual practice to sow papaya seeds in polythene bags or earthern pots. For epicotyl grafting, mango stones are also sown in polythene bags. While raising the plants in polythene bags, care should be taken that root system develops properly. It has been observed a number of times that the roots get twisted and there is difficulty in establishment of the plants in field due to poor anchorage.

In-situ sowing In walnut, pecannut, jackfruit and ber, the tap-root system is very vigorous. So, during the process of transplanting, root system is disturbed which ultimately affects their establishment in the field. Therefore, for these fruits, sowing of seeds in-situ is recommended. In rocky soils (Orissa and Gujarat), in-situ sowing of mango seeds and grafting later on is recommended.

Seed storage Based on storage behaviour, seeds are classified as orthodox or recalcitrant. The orthodox seeds can tolerate loss of moisture and their longevity can be increased by preserving them at low temperature. These include the seeds of apple, ber, custard-apple, date palm, fig, grape, guava, lemon, lime, mandarin, papaya, passion fruit, peach, pineapple, plum, phalsa, pomegranate and sweet orange. Recalcitrant seeds do not withstand desiccation and need a critical level of moisture to survive. Such seeds can be stored for relatively short period ranging from a few weeks to a few months. Seeds of fruits which show recalcitrant behaviour are avocado, barbados cherry, carambola, breadfruit, durian, jackfruit, litchi, mango, mangosteen and rambutan. Seeds of most of the tropical and sub-tropical fruits cannot be stored for a long period. However, in controlled temperature and humidity, storage period can be prolonged. Cryopreservation: It is the method of storage of material in a liquid nitrogen maintained at a temperature of 196 C. Successful cryopreservation of material involves the application of chemicals known as cryoprotectants. The most commonly used chemicals are glycerol and DMSO (Dimethyl sulphoxide). This method has recently been used in preservation of embryos of coconut and jackfruits under in-vitro conditions. 0

Stepwise procedure for seed extraction and treatment 2. Wash it immediately and remove fruit flesh. Some seed, for example, citrus, can be planted immediately.

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4. Protect the seed from insects and birds.

5. Rub dried seed in your hands to remove remaining particles of flesh and husk.

3. Dry seeds in shade, do not expose them to the sun. Spread the seed widely on a cloth, paper or plank. Make sure that air and breeze can go through.

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1. Extract the seed from the fruit.

7. Store seed in a closed container or bag in a cool, dry and shady place. Plant as soon as possible in seedbed or container.

รฐ 6. To avoid fungus infection, mix the seed with fungicide, such as Bavistin, or use any locally available methods.

Seed germination test (Sinkers and floaters test) Put the seeds in a bucket of clean water. The floaters on the water surface will not germinate, the sinkers will. Plant the sinkers only. This method works well with small seeds, such as citrus. Use it especially if the seed has been stored for a long period.

the seeds floating on the surface of water should be discarded

Pre-treating the seed Some seeds are difficult to germinate because their coats are hard or they have other coverings on them. To get rid of these problems, try the following techniques: Scarify: manually break, cut or scratch the seed cover Shell: crack the seeds open so that water and gases can enter; for coconut, mango and macadamia Soak: put the seeds in water and leave overnight

Planting seed F Sow the seed in the already prepared seedbed. F Space small seeds: 3–5 cm from seed to seed, 10–15 cm from row to row. Sow the seed by distributing them

evenly in the rows. F Generally, cover large seeds with more soil than small seeds. F In general, the soil layer covering the seed should not be deeper than the size of the seed itself—mango, avocado: 2.5 cm; guava, citrus: 1 cm. F Water carefully with a watering can or a perforated tin. Do not use equipment that will wash away the soil or the seeds. F Press the soil down firmly to ensure good contact between soil and seed. F If possible, cover the seed with a transparent sheet of polythene to hold the moisture. As soon as the seeds germinate, remove the cover. F Water the seed twice a day. F Seeds will germinate in 1 to 4 weeks, depending on the type and quality of seed planted.

To avoid disease

For maintaining the planted seed © Weed once a week © Water twice a day © Prune roots once a month © Destroy diseased seedlings whenever they are

found

Seed rot

Root rot

Damping off

Transplanting and pricking out ¤ Prick out the germinated seedlings from a seedbed 6 weeks after sprouting to transplant in containers. The plants should have 5 to 6 leaves or about 5 cm in height. ¤ Transplant them carefully, using a small stick, do not damage the roots. ¤ If you raise the seedlings in a seedbed, allow a spacing of 30 cm (1 ft) between the plants and 30 cm (1 ft) between rows for bare-rooted propagation, such as for citrus, applicable on the standard width seedbed of 90 cm (3 ft). ¤ If you plant in containers, fill containers with soil mixture, make a hole in the middle of the container and place the roots straight down in the soil. ¤ Water the seedbed and containers after transplanting. ¤ Weeding should be done whenever required.

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Right sowing density

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Wrong: Too dense

Wetland Dryland

Wrong: Too thin

Correct: planting hole is large with sufficient room for roots to develop.

! " ! " Soil

Compost

Wrong: Planting hole too small. Roots are damaged or deformed. Seedlings develop slowly.

Sowing of seeds in polybags Sow extracted seed: v Water carefully v Weed and discard weak plants v Prune roots v Plant 1 large seed, such as mango, jackfruit per bag v Plant 2–3 small seeds, such as papaya, aonla and citrus, per bag

Seeds

Seed sown

Seedling

Authentic sources of seeds Seeds can be obtained from: ¯ Your extension worker ¯ Fruits from your farm or village ¯ Local nurseries ¯ Fruits from the local market ¯ Planting material from Agricultural University/Department of Horticulture

Sowing of Mango seeds Step 1: Dehusk with a knife. Participants can see the inner seed. Dehusk to ease germination. Seedling will germinate in 2 weeks instead of 3. The seed spoils after 2 weeks and will not germinate. To ease the dehusking, dry the slippery seed in the shade for 1 day. Step 2: Plant seed so as to ensure straight shoot development and cover the mango seed with 5 cm sandy soil.

Step 2

Step 3: Water and cover with mulch. S t e p 4 : Transplant the seed as soon as it germinates.

Step 1