Seed Propagation (Sexual Propagation)
It refers to multiplication of plants by seed. In sexual process male and female gametes are fused to produce seed. Meiosis division takes place in course of fusion and the chromosome numbers, as in parents is reduced to half, which after fertilization becomes normal.
In sexual propagation during meiosis segregation, reassortment or rearrangement of characters takes place. So, the plants thus produced may or may not be similar to their parents and the propagated plants may also be different from each other. It is called as seed propagation, since the propagation is through seed and also sexual propagation because sexes are involved Seed is the result of fusion of male and female gametes. Seeds are fertilized ovules, containing embryos resulting from the union of a male and a female gamete during fertilization. The embryo in the seed gives rise to a new plant on germination. Plants that are produced from seeds are called seedlings.
Advantages of Seed propagation
1) Seedling trees generally live longer, bear more heavily and are hardier than vegetatively propagated trees.
2) Seedlings are comparatively cheap, and can be more easily raised than vegetatively propagated materials.
3) Plants which are difficult to propagate, e.g., papaya and phalsa by vegetative method can only be propagated by seed.
4) In breeding for evolution of new varieties, the hybrids are first raised from the seed and it is, therefore, essential to employ this method in such cases.
5) Seed propagation, some times results in the production of Chance seedlings with superior characteristics, which may be of great benefit to the horticulture industry.
6) Rootstocks, on which desirable scion variety is budded or grafted, are usually raised from seeds.
7) Seeds of some fruits like citrus and mango varieties are capable of giving out more than one seedling from one seed. They arise from the cells of the nucellus and are called poyembyonic. The nucellar seedlings can be utilized for raising uniform plants, if they can be carefully detected at the nursery stage.
8) Since most virus diseases are usually not transmitted through seed propagation. Hence, it is useful in producing virus free plants.
9) Seeds also offer a convenient method for storing plants for a long time. Seeds when kept properly may remain viable for very long periods. Eg. Indian lotus remains viable for over 1000 years.
Disadvantages of seed propagation:
2) Seedling trees take more time to come to bearing than grafted plants. For example mango seedlings take 8 -10 years to come to bearing, compared with 3-4 years for grafted trees.
3) Seedling trees, being very large, pose problems for efficient management of orchard trees, i.e., harvesting, pruning spraying etc. become more difficult and expensive.
4) It is not possible to derive the benefits of rootstocks, if the plant is not propagated vegetatively by means of grafting or budding.
5) Continuous seed propagation leads to inferiority in the progeny.
6) Sexually propagated plants have long juvenile (pre-bearing) period.
7) Choice or chance tress or hybrid trees can not be multiplied true to type because of segregation of characters.
8) Seeds loose viability with in a short period. Eg.Citrus, mango, jack, papaya, jamun etc.
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