Self incompatibility in plants
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This document discusses self-incompatibility (SI) in plants. It describes three main types of SI - homomorphic and heteromorphic systems as well as gametophytic and sporophytic SI. It also outlines some methods that have been used to overcome SI, such as bud pollination, delayed pollination, irradiation and heat treatment. SI promotes outbreeding and maintains genetic diversity in plant populations.
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Self incompatibility in plants
- 1. T.C.B College of Agriculture and Research Station, Bilaspur Chattisgarh Presented To; Presented By; Dr.Roshan Parihar SHEKH ALISHA Dept.of Plant Breeding BSc Ag 2nd yr 2nd sem.. Self IncompatIbIlIty
- 2. • If a plant does not set seed when pollinated with its own functional pollen, but exhibits normal seed setting when cross pollinated,it indicates presence of SELF INCOMPATIBILITY. • SELF INCOMPATIBILITY refers to the inability of a plant with functional pollen to set seeds when self pollinated. • Term Self Incompatibility was originally coined by Stout in 1917.
- 3. Features of self-incompatibility It is an important outbreeding mechanism ,prevents autogamy & promotes allogamy Maintains high degree of heterozygosity due to outbreeding & reduce homozygosity due to elimination of inbreeding. SI results due to morphological,genetic,physiological & biological , chemical causes. Not under simple genetic control. SI has been reported in 70 angiospermes including several crop species.
- 4. 1.FLOWER MORPHOLOGY •HETEROMORPHIC: i.Distyly ii.Tristyly •HOMOMORPHIC: i.Sporophytic ii.Gametophytic 2.GENES INVOLVED: a.Monoallelic b.Diallelic c.Polyallelic 3.SITE OF EXPRESSION OF SI REACTION: a.Stigmatic b.Stylar c.Ovarian 4.POLLEN CYTOLOGY a.Binucleate b.Trinucleate
- 5. When SI is associated with differences in Floral Morphology ,it is known as Heteromorphic system. SI results due to differences in the length of style and stamen. System is again of two types: 1.DISTYLY 2.TRISTYLY 1.DISTYLY: It refers to two types of Styles (short& long) and Stamens (low & high). The crosses are compatible only between the style and stamen of matching length. EXAMPLE: Primulaceae Family 2.TRISTYLY: When style has three different positions in flower viz short, medium and long. EXAMPLE: Lythraceae Family
- 6. In Homomorphic system, Self incompatibility results due to physiological causes rather than differences in flower morphology. In this system ,the plant do not have differences in the length of style and stamens or other floral parts. 1.The pollen grains do not germinate on the stigma of same flower.If they germinate the pollen tube fails to penetrate the stigma as in Rye, Cabbage and Raddish. 2.The pollen grains may germinate but there in retardation of pollen tube growth. 3.In some cases, there is slow rate of pollen tube growth and it rarely reaches the ovary in time to effect self fertilization. 4.In some cases, pollen tube growth may be normal, but it does not release the male gamete.
- 7. HOMOMORPHIC SYSTEM IS Of TwO TYPES: 1.GAMETOPHYTIC SYSTEM 2.SPOROPHYTIC SYSTEM 1. GAMETOPHYTIC SYSTEM When SI is controlled by the genetic constitution of Gametes, it is known as Gametophytic self incompatibility system. FEATURES: •SI in majority of species is governed by a single gene S, which has large no. of multiple alleles. However, in rye SI reaction is governed by 2 loci. •In this system alleles have individual action in the style without interaction. •Pollen grains are unable to germinate or function on a pistil having similar allele as that of pollen. The pollen tube growth is usually inhibited in the style or ovary. •Plant species belonging to GSI system have binucleate pollen.
- 8. 2.SPOROPHYTIC SYSTEM When the SI is governed by the genotype of pollen producing plants (sporophytes), it is called sporophytic system. FEATURES: •In this system also SI is controlled by single gene S which has multiple alleles. •The alleles may show dominance, individual action or interaction in either pollen or style as per the allelic combinations involved. •This system exhibits inhibition of pollen germination or pollen tube growth on the stigma of same flower. •Pollen grains from both heterozygous or homozygous plants react in a similar fashion due to dominance effect of male parent. •Plant species of this system have trinucleate pollens.
- 9. GAMETOPHYTIC (GSI) outcome of the interaction between the pollen tube and the style is determined by the genotype of the pollen (gamete) S-locus products are synthesized after completion of meiosis growth of the pollen tube arrests in the style SPOROPHYTIC (SSI) outcome of the interaction between the pollen tube and the style is determined by the genotype of the sporophyte (diploid tissue) S-locus products are synthesized before completion of meiosis growth of the pollen tube arrests at the surface of the stigma
- 10. 1.BUDPOLLINATION 2.DELAYEDPOLLINATION 3.ENDSEASON POLLINATION 4.IRRADIATION 5.HIGHTEMPERATURE 6.MUTILATION OFSTYLE 7.IN VITRO FERTILIZATION
- 11. Pollination of immature buds with mature pollen has been successful in the production of large quantity of self seed both in gametophytic & sporophytic systems in Brassica,Nicotiana & Petunia.This method is now used for the development of inbred lines for hybrid seed production in Brassica species. This also leads to self fertilization in some species.Pollination of aged pistils several days after maturity with normal incompatible pollen resulted in some degree of self fertilization in Brassica , Linum.
- 12. Self pollination at the end of flowering season also leads to seed set in some species like Nicotiana, Petunia and Abutilon.This may be due to loss of capacity to produce active incompatibility substances at the end of flowering season. Irradiation of style with X- rays immediately before selfing resulted in breakdown of self incompatibility in Petunia. Gamma irradiation significantly increased seed setting upon selfing in Lycopersicon Peruvianum. However, these effects were observe in one generation & were lost in the next generation. Mutation plays an important role in overcoming self incompatibility.
- 13. Heat treatment inactivates he substance or enzyme which causes self incompatibility. Removal of stigma in species having stigmatic incompatibility results in certain amount f seed production in some crops. In this species, SI could be broken by mutilating the stigma with steel wire brush during pollination Placing of pollen grains in direct contact with ovules, resulted in breakdown of self incompatibility in many crop species.
- 14. Utilization 1.Production of Hybrids 2.Combining desirablegenes limitations 1.Difficult to producehomozygousinbred line 2.Affected by environmental factors Temperature,humidity 3.Sometimesbeesvisit only on oneparental linein theseed production plot resulting in sib mating
- 15. Summary ●SI is an important mechanism for preventing inbreeding in plants ●3 different mechanisms of SI have been described at the molecular level ●Sporophytic SI dependent on a kinase-mediated signaling cascade ●Gametophytic SI based on selective degradation of pollen rRNA by S-RNases ●Gametophytic SI based on a calcium-dependent (MAPK) signaling cascade leading to cell death in pollen