Majority of the species are in reproductive isolation, which is usually enforced by physical and biochemical or behavioural mechanisms. These restrictive mechanisms can be classified into two groups: prezygotic and postzygotic (includes inviability, sterility and breakdown). Clarification of reproductive isolating mechanisms will provide important information about biological speciation and genes that may be employed for targeted crop breeding. Post zygotic incompatibility in interspecific hybrids, such as sterility and lethality, are widely observed to cause reproductive isolation and thus contribute to speciation. However, hybrid incompatibilities are caused by divergence in each of the hybridizing species, they also reveal genomic changes occurring on short evolutionary time scales that have functional consequences2. Surprisingly, much of this divergence does not appear to be driven by ecological adaptation, but may instead result from responses to purely mutational mechanisms or due to internal genetic conflicts. Recent progress suggests that hybrid incompatibility is a by-product of co-evolution either with “parasitic” selfish elements in the genome or with invasive microbes in the natural environment. Different species have evolved distinct strategies to prevent invasion. Mismatch of regulation machineries is the cause of hybrid incompatibility per se1.

Study was conducted in cotton between G. hirsutum and G. barbadense cv. Coastland R4-4 (Interspecific). Genetic analysis and microsatellite mapping was done to identify the lethal genes, where they found that two dominant genes (Le3 and Le4) interacting complementarily are controlling the hybrid incompatibility, these are in accordance with the Dobzhansky–Muller model and are novel4.

Genetically divergent rice (Oryza sativa L.) cultivars ‘Sasanishiki’ (japonica) and ‘Habataki’ (indica) displayed hybrid breakdown. They identified the regions controlling the hybrid breakdown by QTL analysis and epistatic interactions for hybrid breakdown. Through which they detected the QTLs with epistatic interactions of genes governing hybrid breakdown which are located on chromosome 2 and 113.

The studies on hybrid incompatibilities have enabled our understanding the formation of genetic barriers leading to speciation. In plant breeding, employment of modern tools can aid in removing incompatibility barriers. This will be useful in introgression of economic traits from wide non-crossable relatives which are incompatible to hybridize.

REFERENCES:

1.CHEN, C., E, Z. AND LIN, H.X., 2016, Evolution and molecular control of hybrid incompatibility in plants. Front. Plant Sci., 7:1208.

2.MAHESHWARI, S. AND BARBASH, D. A., 2011, The genetics of hybrid incompatibilities. Annu. Rev. Genet., 45: 331-355.

3.MATSUBARA, K., ANDO, T., MIZUBAYASHI, T., ITO, S. AND YANO, M., 2007, Identification and linkage mapping of complementary recessive genes causing hybrid breakdown in an intraspecific rice cross. Theor. Appl. Genet., 115(2): 179-186.

4.SONG, L., GUO, W. AND ZHANG, T., 2009, Interaction of novel Dobzhansky–Muller type genes for the induction of hybrid lethality between G. hirsutum and G. barbadense cv. Coastland R4-4. Theor. Appl. Genet., 119(1): 33-41.