SEXUAL INCOMPATIBILITYSEXUAL INCOMPATIBILITY

• IntroductionIntroduction

• Types of incompatibilityTypes of incompatibility

• Genetic basis of Self-incompatibilityGenetic basis of Self-incompatibility

• Level of its occurrence Level of its occurrence

• Physiology and BiochemistryPhysiology and Biochemistry

• Biological significanceBiological significance

• Methods to overcome IncompatibilityMethods to overcome Incompatibility

1. INTERSPECIFIC1. INTERSPECIFIC – – # #Between individuals of different Species. Between individuals of different Species. # Heterogenic. # Heterogenic.

Controlled by more than one gene. Linskens(1975)Controlled by more than one gene. Linskens(1975) #Basis of new races & prevents free Cross-Pollination #Basis of new races & prevents free Cross-Pollination

1. INTERSPECIFIC1. INTERSPECIFIC – – # #Between individuals of different Species. Between individuals of different Species. # Heterogenic. # Heterogenic.

Controlled by more than one gene. Linskens(1975)Controlled by more than one gene. Linskens(1975) #Basis of new races & prevents free Cross-Pollination #Basis of new races & prevents free Cross-Pollination

2.SELF INCOMPATIBILITY –2.SELF INCOMPATIBILITY –#Inability of a plant producing functional male and female #Inability of a plant producing functional male and female gametes.gametes.#TWO TYPES- 1.Heteromorphic and 2.Homomorphic#TWO TYPES- 1.Heteromorphic and 2.Homomorphic

**Heteromorphic :Heteromorphic : - - Characterised by occurrence of two Characterised by occurrence of two (distyly) or three (tristyl) morphologically distinct mating type. (distyly) or three (tristyl) morphologically distinct mating type. -Due to inhibition of growth of pollen. -Due to inhibition of growth of pollen. -Features -Features *Homomorphic*Homomorphic :- :- Indistinguishable type. Indistinguishable type. Categorized into:-Categorized into:-(i)Gametophytic self-incompatibility(GSI):(i)Gametophytic self-incompatibility(GSI): Determined by Determined by genotype of male gametophyte itself. Eg.Graminaceae, Liliaceae, genotype of male gametophyte itself. Eg.Graminaceae, Liliaceae, Solanaceae &Trifolium. Solanaceae &Trifolium. (ii)Sporophytic self-incompability(SSI):(ii)Sporophytic self-incompability(SSI): Controlled by Controlled by genotype of the sporophytic tissue of the plant from which the genotype of the sporophytic tissue of the plant from which the pollen is derived. Eg,. Compositae & Cruciferae.pollen is derived. Eg,. Compositae & Cruciferae.

2.SELF INCOMPATIBILITY –2.SELF INCOMPATIBILITY –#Inability of a plant producing functional male and female #Inability of a plant producing functional male and female gametes.gametes.#TWO TYPES- 1.Heteromorphic and 2.Homomorphic#TWO TYPES- 1.Heteromorphic and 2.Homomorphic

**Heteromorphic :Heteromorphic : - - Characterised by occurrence of two Characterised by occurrence of two (distyly) or three (tristyl) morphologically distinct mating type. (distyly) or three (tristyl) morphologically distinct mating type. -Due to inhibition of growth of pollen. -Due to inhibition of growth of pollen. -Features -Features *Homomorphic*Homomorphic :- :- Indistinguishable type. Indistinguishable type. Categorized into:-Categorized into:-(i)Gametophytic self-incompatibility(GSI):(i)Gametophytic self-incompatibility(GSI): Determined by Determined by genotype of male gametophyte itself. Eg.Graminaceae, Liliaceae, genotype of male gametophyte itself. Eg.Graminaceae, Liliaceae, Solanaceae &Trifolium. Solanaceae &Trifolium. (ii)Sporophytic self-incompability(SSI):(ii)Sporophytic self-incompability(SSI): Controlled by Controlled by genotype of the sporophytic tissue of the plant from which the genotype of the sporophytic tissue of the plant from which the pollen is derived. Eg,. Compositae & Cruciferae.pollen is derived. Eg,. Compositae & Cruciferae.

GENETIC BASIS OF SELF - GENETIC BASIS OF SELF - INCOMPATIBILITY INCOMPATIBILITY Opposition S-alleles. East & Opposition S-alleles. East & Mangalsdorf(1925).Mangalsdorf(1925).Incompatible reaction are Incompatible reaction are controlled by S-gene having controlled by S-gene having several alleles.several alleles.

Pollen grain possessing S-Pollen grain possessing S-alleles common to anyone of alleles common to anyone of the two allele in the cells the two allele in the cells results in incompatibility.results in incompatibility.

Pollen with S-alleles other than Pollen with S-alleles other than any two alleles in the pistil will any two alleles in the pistil will effect Fertilization.effect Fertilization.

Fig;Fig; Response of pollen on Response of pollen on SS1SS22 plant showing plant showing gametophytic incompatibility. gametophytic incompatibility. A-A- No Pollen from No Pollen from SS11SS22 plant plant is able to effect fertilization. is able to effect fertilization. BB- Only S- Only S33 plant succeded in plant succeded in fertilizing ovules resulting into fertilizing ovules resulting into 50% fertilization.50% fertilization.

LEVEL OF OCCURANCE OF LEVEL OF OCCURANCE OF INCOMPATIBILITY INCOMPATIBILITY

POLLINATION- POLLINATION- Self-pollination is check in some plants Self-pollination is check in some plants through dichogamy, herkogamy&Unisexuality. Because of through dichogamy, herkogamy&Unisexuality. Because of this, Self incompability occur in some plant.this, Self incompability occur in some plant.

PROGAMIC PHASE- PROGAMIC PHASE- Inhibition occur at any stage Inhibition occur at any stage from pollen germination to the discharge of male gamete in from pollen germination to the discharge of male gamete in the incinity of the egg. the incinity of the egg.

(a)On the stigma- (a)On the stigma- Pollen fail to germinate. Pollen fail to germinate. eg,.Cruciferae & Graminae.eg,.Cruciferae & Graminae.

(b)In the style(b)In the style- Pollen tube fail to grow through the full - Pollen tube fail to grow through the full length of the style.length of the style.

SYNGAMY – SYNGAMY – In some plants like In some plants like Gasteri, HemerochallisGasteri, Hemerochallis, , fusion of male and female gametes fail to occur.fusion of male and female gametes fail to occur.

PHYSIOLOGY AND BIOCHEMISTRYPHYSIOLOGY AND BIOCHEMISTRY

Two reactions are recognised as given below :Two reactions are recognised as given below :

1.RECOGNITION REACTION-1.RECOGNITION REACTION- Occurs at the molecular level Occurs at the molecular level and by this the pistil recognises whether a particular and by this the pistil recognises whether a particular grain is to be accepted(Compatible) or Rejected grain is to be accepted(Compatible) or Rejected (Incompatible). In SSI system and certain GSI system the (Incompatible). In SSI system and certain GSI system the recognition reaction sets in almost immediately after the recognition reaction sets in almost immediately after the pollen comes in cintact with the stigma. Generally, in GSI pollen comes in cintact with the stigma. Generally, in GSI systems, the recognition reaction occur inside the pistil.systems, the recognition reaction occur inside the pistil.

2.REJECTION REACTION –2.REJECTION REACTION – It may occur in the stigma inhibiting It may occur in the stigma inhibiting pollen germination or preventing entry of pollen tubes into the pollen germination or preventing entry of pollen tubes into the stigma(SSI system) or it may occur in the style inhibiting pollen tube stigma(SSI system) or it may occur in the style inhibiting pollen tube growth or leading to bursting of the tube into style(GSI system).growth or leading to bursting of the tube into style(GSI system).

BIOLOGICAL SIGNIFICANCE BIOLOGICAL SIGNIFICANCE OF OF INCOMPATIBILITY INCOMPATIBILITY• A balance in breeding and outbreeding of plant is A balance in breeding and outbreeding of plant is

regulated by intraspecific and interspecific.regulated by intraspecific and interspecific.• Prevents extensive selfing of plant which leads to Prevents extensive selfing of plant which leads to

highly homozygous individual.highly homozygous individual.• Interspecific incompatibility brings about Interspecific incompatibility brings about

reproductive Isolation.reproductive Isolation.• Possess serious problem in order to maintain the Possess serious problem in order to maintain the

homozygosity of a species.homozygosity of a species.• In several plants where the anther has failed to In several plants where the anther has failed to

yield pollen, Self-Pollination is an important yield pollen, Self-Pollination is an important approach to achieve Homozygous individuals.approach to achieve Homozygous individuals.

• Interspecific incompatibility also prevent distinct Interspecific incompatibility also prevent distinct Hybridisation.Hybridisation.

METHODS TO OVERCOME METHODS TO OVERCOME INCOMPATIBILITY INCOMPATIBILITY• MIXED POPULATION : In this method, the stigma is disguised from

recognising the incompatible pollen by pollinating it with a mixture of live incompatible pollen, and killed(by chemical or radiation) compatible pollen(termed Mentor pollen or Recognition pollen). By employing recognisition pollens, self incompatibility has overcome in Cosmos (Howlett et al.,1975) andPetunia hybrida(Sastri and Shivanna.,1975) and interspecific incompability in genus Populus(Knox et al.,1972).

• BUD-POLLINATION : In some plants, pollination at an early bud stage has proceed very effective in overcoming intraspecific incompatibility. At the bud stage (before anthesis), the stigma lacks the exudate to inhibit pollens and by chance pollination at that stage may effect fertilization.

• STUB-POLLINATION : In some plants incompability may be restricted to the stigma or the style is too long and the pollen tube could not reach the ovary. In this case, removal of stigma and part of style before pollination may prove helpful in overcoming incompatibility.

• INTRA-OVARIAN POLLINATION : In this technique, the ovary surface is sterilised with ethanol and two punctures are made in the wall- one for introducing the pollen suspension and the other to permit the escape of of air in the ovarian cavity(Kanta et al.,1962). Variable seeds following intra-ovarian pollination have obtained in several members of Papaveraceae such as Argemone mexicana, A. ochroleuca, Papaver somniferum and P. rhoeas.

• HEAT TREATMENT OF STYLEHEAT TREATMENT OF STYLE : Moderately high temperature (up to 50 C) are known to reduce the self-incompability reaction in certain plants. e.g,. Lilium longiflorum (Hooper et al 1967).

• IRRADICATION : Induce temporary breakdown of incompatibility reaction (Pandey, 1963), or alteration of the inhibitory substances in the style(Kumar and Hecht,1965). Irradication helpful in those systems where process are controlled gametophytically.

• CHEMICAL TREATMENT :Application of certain chemicals may prolonged the life of flowers (Choudhury 1965). Oenothera species by the application of p-chloromercuribenzoate ..Hodgdon and Hetch(1975).

• PARASEXUAL HYBRIDISATION : In 1969 a new approach was proposed to raised such hybrid which could not be produced through the conventional method of hybridisation because of sexual incompatibility. This technique involves fusion of isolated protoplast of somatic cell and is described as parasexual hybridisation. This involves the following step :-

(a)Isolation of protoplasts. (b)Fusion of isolated protoplasts. (c)Cultured of hybrid protoplasts to regenerate whole plant.