It is inability of gametes to fuse and form viable offspring. Incompatibility is of two types, interspecific and self incompatibility.
Context
- Interspecific Incompatibilty
- Self incompatibility
1. Interspecific incompatibility
It is the inability of viable gametes of two different species to fuse and produce viable offspring. The gametes do not fuse because of the absence of suitable attractants and development of incompatibility reaction when the two gametes are brought together. In flowering plants, the pollen grains of another species fail to germinate over the stigma. Interspecific incompatibility prevents free cross pollination and fertilization. It is a natural barrier in the fusion of interspecific gametes which maintaining genetic individuality of the species. is helpful in
2. Self Incompatibility
Self incompatibility is the inability of an intersexual plant to produce viable seeds on self pollination despite producing functional male and female gametes. Self incompatibility is also called self sterility and intraspecific incompatibility. It is a device to prevent self pollination and promote outbreeding or cross pollination. Self incompatibility is genetically controlled (East and Mangelsdorf, 1925). It occurs in some 66 families of flowering plants (Mc Cubbin and Dickinson, 1997). Self incompatibility may
Morphological or Heteromorphic Incompatibility. It occurs in flowers having heterostyly.
Heterostyly is of two types. (a) Heterostyly or Dimorphic Heterostyly. There are two mating types, pin- eyed and thrum-eyed flowers. e... Primula, Jasminum. Self incompatibility is controlled by one gene having two alleles (Ssb) Tri Heterostyly or Trimorphic Heterostyly. There are three types of flowers and three mating types, e.g., Lythrum, Oxalis. Self incompatibility of this type is determined by two genes.
each with two allels (M and S, Shivanna and Johri, 1985).
Physiological or Homomorphic Incompatibility. Various mating types are morphologically similar.
Incompatibility is determined by an S-gene with multiple alleles. Depending upon the basis of origin of mating types, self incompatibility is of two types. (a) Gametophytic Self Incompatibility (GSI). Self incompatibility is determined by genotype of pollen or male gametophyte, e.g., Solanaceae, Liliaceae, Poaceae (Gramineae). The rejection reaction occurs in the style causing retardation of pollen tube growth, deorientation of pollen tube and at times failure of nuclear fusion. The allele present in the pollen shows incompatibility reaction if the same is also present in the style, e.g., S, in S S2 or SS3 style. (b) Sporophytic Self Incompatibility (SSI). The incompatibility is determined by genotype of sporophyte of the plant from which pollen is formed. Rejection of self pollen occurs over the stigma. All the pollen of a plant having even one similar allele, whether the allele is present or not in the pollen, will he incompatible. Pollen of a plant S2S3 (whether S, or S3) will be incompatible over the stigma of plants
S.S, S S3, S2S4, S2S5, S1S3 etc. Sporophytic incompatibility is found in families Brassicaceae and Asteraceae.
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