Topic: Polyembryony B.Sc. Botany (Hons.) II Paper: IV Group

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Topic: Polyembryony B.Sc. Botany (Hons.) II Paper: IV Group

By Dr. Sanjeev Kumar Vidyarthi Department of Botany Dr. L.K.V.D. College, Tajpur, Samastipur L.N. Mithila University, Darbhanga The occurrence of more than one embryo in the seed is known as polyembryony. Polyembryony is quite common among conifers (gymnosperms), but many species both of dicots and monocots (angiosperms) exhibit this phenomenon. There are two main types of polyembryony - i. True polyembryony and ii. False polyembryony. i. True Polyembryony: The true polyembryony may be subdivided into two types: (i) Cleavage polyembryony, where the embryos arise within an embryo sac, either by a cleavage of the egg, or from the synergids, antipodals or endosperm; (ii) Adventive polyembryony, where the embryos arise from the tissues living outside the embryo sac, i.e., the cells of the nucellus or the integuments, but generally they come to lie within the embryo sac. ii. False Polyembryony: Sometimes the polyembryony occurs due to the presence of multiple embryo sacs within the ovule. They may arise from: The derivatives of the same megaspore mother cell; From two or more megaspore mother cells, or From nucellus cells (i.e., apospory). Importance of Polyembryony: This phenomenon plays an important role in plant breeding and horticulture. Nucellar adventive polyembryony is of great value in horticulture, where the nucellar seedlings of Citrus have been proved to be better clones of orchard stock than cuttings. On the other hand, the nucellar embryos are supposed to be free from disease, and the nucellar seedlings rejuvenate the vigour that is generally lost after continued cutting propagation. The adventive polyembryony is much useful in the propagation of the fruit trees, such as Citrus and Mango. The application of adventive embryos is also important for providing genetically uniform seedlings in fruit trees. The haploids can be used for the development of homozygous diploid, which are of much value. Due to the practical value of haploids in plant breeding, the methods have been recognized for the artificial production of these embryos from the eggs or synergids. .

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Topic: Apomixis - Definition and Types
Course Teacher: Dr. Rupendra Kumar Jhade, JNKVV, College of Horticulture,Chhindwara(M.P.) B.Sc.(Hons) Horticulture- 1st Year, II Semester 2019-20 Course: Plant Propagation and Nursery Management Lecture No. 12 Topic: Apomixis - Definition and types Apomixis, derived from two Greek word “APO” (away from) and “MIXIS” (act of mixing or mingling). The first discovery of this phenomenon is credited to Leuwen hock as early as 1719 in Citrus seeds. In apomixes, seeds are formed but the embryos develop without fertilization. The genotype of the embryo and resulting plant will be the same as the seed parent. Definition: “The process of development of diploid embryos without fertilization.” Or “Apomixis is a form of asexual reproduction that occurs via seeds, in which embryos develop without fertilization.” Or “Apomixis is a type of reproduction in which sexual organs of related structures take part but seeds are formed without union of gametes.” In some species of plants, an embryo develops from the diploid cells of the seed and not as a result of fertilization between ovule and pollen. This type of reproduction is known as apomixis and the seedlings produced in this manner are known as apomicts. Apomictic seedlings are identical to mother plant and similar to plants raised by other vegetative means, because such plants have the same genetic make-up as that of the mother plant. Such seedlings are completely free from viruses. In apomictic species, sexual reproduction is either suppressed or absent. When sexual reproduction also occurs, the apomixes is termed as facultative apomixis. But when sexual reproduction is absent, it is referred to as obligate apomixis.
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12.2% 122,000 135M Top 1% 154 4,800
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