Epigenetic polymorphisms could contribute to the genomic conflicts and gene flow barriers resulting to plant hybrid necrosis

The fundamental molecular basis for phenotypic and genetic similarities among many described cases of plant hybrid necrosis has not been fully described. Plants can be good models for studying the basis of such gene flow barriers which occur between species. Many studies in prezygotic barriers like stigma recognition of pollen, environmental adaptation differences and pollinator preferences which can reduce the chances of species  mating success have been done. Also studied are post zygotic barriers in gene flow like lack of ecosystem adaptation of hybrids which may include failure of pollinators from being attracted to floral parts due to   developmental changes and gene or chromosome incompatibility resulting in genetic isolation. Polyploidy has also been recognized as an isolating force although it might not be the only post zygotic genome isolating  force; other forces may also contribute hindrances in the gene flow after zygote formation. Here, papers which  have tended to pinpoint the increasing evidence of epigenetic polymorphisms as causes of genomic conflicts  which cause barriers to the gene flow resulting in hybrid necrosis in plants were reviewed. Explorations into  the mechanisms which unlock hybrid necrosis can help plant breeders to avoid genetic and epigenetic  incompatibilities during crop improvement programs. Key words: Hybrid necrosis, heterosis, epigenetic, hybrid sterility, RNAi.