apomixis - MASTER SEMINAR ON PROSPECTS OF APOMICTIC...

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MASTER SEMINAR ON PROSPECTS OF APOMICTIC BREEDING IN CROP IMPROVEMENT PRESENTED BY: E. UMARANI RAM/12-52
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Reproduction - by which living organisms give rise to offspring Plant reproduction - complex & diverse Mode of reproduction - genetic constitution of crop plants and breeding procedure to be followed. In crop plants mode of reproduction is of two types: Sexual reproduction Asexual reproduction
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Sexual reproduction - most common in flowering plants
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Our reliance on sexual reproduction in agricultural systems also presents vulnerabilities associated with crop losses related to the ‘mechanics’ of sexual reproduction, such as failure of pollination or fertilization.
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Asexual reproduction – Dose not involve fusion of male & female gametes Provides the advantages of absolute crop uniformity. The genetic make-up of the progeny is identical to the parent
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Mendel tried to explain his theory using Hieracium Both in F1 & F2 -Mother-like plants -Few highly variable plants MENDEL’S EXPERIENCE Segregation of morphological traits in rare F1 hybrids & preservation of morphological traits in the F2
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Rosenberg reported cytological evidence - Fertilization was not necessary for embryo formation. Embryos develop from unreduced (2n) egg cells - mother-like offspring
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APOMIXIS The term apomixis - WINKLER Apo - away from, Mixis – mingling It is a natural process that allows clonal reproduction through seed - genetically identical to the mother plant It is a substitution of sexual process by form of asexual reproduction which does not involve meiosis & syngamy
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Particulars Apomixis Amphimixis 1.Term first used by WINKLER WEISMANN 2.Union of male and female gamates Does not involve involved 3.Gene combinations or gene flow Not possible possible 4.Segregation Does not occur occurs 5.Rapid development of inbred lines Possible Not possible 6.Conservation of heterosis Possible Not possible 7.Type of reproduction Asexual sexual 8.Types many Autogamy Allogamy 9.Frequency in plants Low High Apomixis and Amphimixis
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Present in > 300 species, 35 families 75% - in Asteraceae, Rosaceae & Poaceae. More common in polyploids than diploids Not rare but relatively uncommon Absent in main crops Prevalence of Apomixis
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MECHANISM OF APOMIXIS There are three elements : Production of diploid female gamet failure of fertilization of such egg cell Capacity of such egg cells to develop into a viable embryo & endosperm
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CLASSIFICATION
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(STEBBI NS)
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Adventive embryony – Strasburgar Development of embryo directly from the diploid cells - nucellus or integument No other embryo sac is formed. Eg. Citrus , Mango. SPOROPHYTIC APOMIXIS
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GAMETOPHYTIC APOMIXIS Diplospory : Diploid embryo sac - from archesporial cell ( Asteraceae) Apospory: The embryo sac may develop from – nucellus or integument Two types Generative apospory : Embryo - from the embryo sac - originated from archesporial cell ( Parthenium) Somatic apospory : Embryo - from the embryo sac - originated from the cell of either nucellus or integument ( Malus, Rubus, Allium etc,)
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