Self incompatibility and its role in hybrid seed production of vegetable crops

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Self-incompatibility

Definition:
It refers to the inability of a plant with functional pollen to set seeds when self pollinated. OR It is defined as the prevention of fusion of fertile (=functional) male and female gametes
after self-pollination.
The process of pollen germination, pollen
tube growth, ovule fertilization or embryo
 development is halted at one of its stages
and consequently no seeds are produced

Published in: Science

Self incompatibility and its role in hybrid seed production of vegetable crops

  1. 1. PRESENTATION ON Self-incompatibility and its Role in Hybrid Seed Production of Vegetable Crops Presented by- Sunidhi Mishra Deptt. of Vegetable Science IGKV, Raipur
  2. 2. Self-incompatibility Definition: It refers to the inability of a plant with functional pollen to set seeds when self pollinated. OR It is defined as the prevention of fusion of fertile (=functional) male and female gametes after self-pollination. The process of pollen germination, pollen tube growth, ovule fertilization or embryo development is halted at one of its stages and consequently no seeds are produced.
  3. 3. Hybrids  Hybrids are the F1 progenies obtained by crossing two genetically dissimilar parents. Why Self Incompatibility for the development of hybrids ?  Production of large scale of F1 seeds.  Reduced cost of hybrid seed production.  Speedup the hybridization programme.  Commercial exploitation of hybrid vigour.
  4. 4. General features of Self-incompatibility  Prevent self-fertilization and thus encourage out-crossing or allogamy.  Increases the probability of new gene combinations.  Normal seed set on cross pollination.  May operate at any stage between pollination and fertilization.  Reduces homozygosity (aa/AA) and increases heterozygosity (Aa)  In plants, self-incompatibility is often inherited by a single gene (S) with different alleles (e.g. S1, S2, S3 etc.) in the species population. AA X aa Aa
  5. 5.  First reported by Koelreuter in middle of eighteenth century.  First discussion on self-incompatibility by Darwin (1877).  The term self incompatibility was given by Stout (1917).  Bateman (1952, 1954, 1955) gave explanation on incompatibility in Brassicas plants namely Raphanus sativus L. and Brassica campestris L. History
  6. 6. Self- incompatibility Heteromorphic SI Distyly Tristyly Homomorphic SI Gametophytic SI Sporophytic SI Classification Given by Lewis, 1994
  7. 7. Heteromorphic self-incompatibility  Flowers of different incompatibility group are different in morphology. Distyly  In Primula, there are two types of flowers, pin and thrum.  Pin (ss) flowers have long styles and short stamens  Thrum(Ss) flowers have short styles and long stamens.  Pin and Thrum flowers are produced on different plants.  Flowers belonging to single incompatibility group do not set seeds when they are cross pollinated.  The only compatible mating is between pin and thrum flowers.
  8. 8. Thrum Pin Pin Thrum
  9. 9. Cross Result Ss (thrum) X Ss (thrum) Incompatible ss (pin) X ss (pin) Incompatible Ss (thrum) X ss (pin) 1 Thrum :1 Pin ss (pin) X Ss(thrum) 1 Thrum :1 Pin
  10. 10. Tristyly In tristyly, styles and stamens have three different positions. It is determined by two genes S and M, each with two alleles.  S gives rise to short style,  S and M to medium style and  s and m to long style. Flowers of same style length belong to same group.
  11. 11. Short Style Medium Style Long Style
  12. 12. Homomorphic System  The incompatibility reaction of pollen is controlled by the genotype of the plant on which it is produced or by its own genotype.  Incompatibility is not associated with morphological differences among flowers.  These mechanisms are based on protein-protein interactions, and are controlled by a single locus termed S, which has many different alleles in the population like S1, S2, S3 etc.  Found in majority of self incompatible species.
  13. 13. Gametophytic System  The incompatibility reaction of pollen is determined by its own genotype.  Pollen tube carrying a single allele is inhibited if the same allele is present in the style.  Fertilization is successful only if the S-allele carried by the pollen is different from either of the two carried by the diploid tissues of the pistil.  Two allele of S gene show co-dominance.  E.g., Lycoperscion, Solanum etc.
  14. 14. Cross Compatibility S1S2 X S1S2 Fully incompatible S1S2 X S1S3 Partially compatible ((i.e., 50% of the pollen) S1S2 X S3S4 Fully compatible The two alleles show Codominance
  15. 15. Sporophytic System  The SI reaction of pollen is governed by the genotype of the plant on which the pollen is produced, and not by the genotype of the pollen.  Governed by a single gene, S, with multiple alleles.  Example : Brassica oleracea, Raphanus sativus.  S alleles show dominance i.e., S1> S2>S3>S4  S1 S2= S1 S2S3 = S2  S1S3= S1 S2S4 = S2  S1S4 = S1 S3S4 = S3
  16. 16. The two alleles show Dominance- S1> S2>S3>S4
  17. 17. Gametophytic SI Sporophytic SI Governed by genotype of pollen Governed by genotype of pollen producing plant The stigma is smooth and wet The stigma is papilate (hairy) and dry Pollen tube inhibition in style Pollen germination, tube entry inhibited on the stigmatic surface. The pollen-pistil interaction govern by haploid genome of each male gametes and diploid genome of pistil tissue (Haplo-Diplo) The pollen-pistil interaction govern by genome of the plant on which the male and female gamete produced ( Diplo-Diplo) S alleles show codominance S alleles show dominance Difference between Gametophytic and Sporophytic Self incompatibility
  18. 18. S allele product is synthesised after completion of meiosis. S allele product is synthesised before completion of meiosis. Pollen grains in such species are binucleate. Pollen grains in such species are trinucleate. Does not permit production of homozygotes. Permits production of homozygotes. Pollen tube inhibition in style Pollen germination, tube entry inhibited on the stigmatic surface. Crosses may be sterile, partially fertile or fully fertile Crosses may be fully sterile or fully fertile Found in Potato, Tomato, Sweet potato. Present in Cabbage, Radish , Cauliflower, Broccoli, etc.
  19. 19. This system was confirmed :- Kale ( Thompson 1957) Radish ( Sampson 1957) Broccoli ( Sampson 1957 and Odland 1962) Cabbage ( Adamson 1965) Cauliflower ( Hoser-krauze 1979)
  20. 20. Use of self-incompatibility in hybrid seed production It can be done by following methods : 1.Two self-incompatible ,but cross compatible line are inter planted. Line A Line B SI but compatible with SI but compatible with line B line A Seeds obtained from both the lines would be hybrid seed.
  21. 21. 2. A self-incompatible line may be inter planted with a self compatible line.  Used in all the Brassica vegetables crops in Europe and Japan.  Example : Brussel sprouts and cabbage. Self-incompatible Self-compatible line line Seed from only the self-incompatible line would be hybrid seed, while that from self-compatible line will be mixture of hybrid and selfed seed.
  22. 22. 3. Schemes for the production of double cross and triple cross hybrids  demonstrated in the case of Brassicas.
  23. 23. Maintenance and Crossing of SI Lines
  24. 24. Characteristics of superior SI lines  Stable self incompatibility.  High seed set on self pollination at bud stage.  Favorable and uniform economic characters.  Desirable combining ability.  Easy to develope and maintain. Need to use SI for Hybrid seed production  To increase the productivity .  To reduce the cost of hybrid seed.  To develop hybrids easily.  To reduce the duration of hybrid development.
  25. 25. Problems in use of SI in hybrid seed production  Bud pollination for maintenance of SI- tedious and costly.  High cost of hybrid seed.  Continued selfing eliminates SI and self-fertility is developed.  Environmental factors like high humidity and high temperature reduce or even totally eliminates SI reaction leading to a high (30% or more) proportion of selfed seed.  Transfer of S alleles from one variety or species into another variety or species is tedious and complicated.  This has prevented the use of self-incompatibility in hybrid seed production in Solanaceae and Compositae.
  26. 26. Crop Name of Hybrid Parentage Developing Institution Cabbage KGMR-1 H-43, H-44, H-46 Self-Incompatibility (KGMR-1=83-1-621 x GA-111) (H- 43=S2S2 x Pusa Mukta) (H-44=S2S2 x Cornell 83-6) (H-46= Cornell 83-23 x Golden Acre) IARI regional station, Katrain Cauliflower Pusa Hybrid-2 , Pusa Kartik Sankar Self-Incompatibility (Pusa Hybrid-2=CC-35 x 18-19) (Pusa Kartik Sankar=CC 14 x 41-5) IARI, New Delhi Cauliflower Xiahua 6(heat- resistant) Self-incompatibility Xiamen Agricultural Research Institute of Sciences, China, 2006
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