Abstract

                                The manifestations of increased size, vigour of development, productivity and similar beneficial effects have long been recognised in many first generation hybrids of plants and animals. This increase in size and vigour resulting from hybridisation has been designated variously as the "stimulating effects of hybridity", "hetero- zygosis" or "hybrid vigour" and Shuli (1914) first proposed the use of the term "heterosis" to denote such a phenomenon. "Heterosis" attracted the early attention of the plant breeders through its conspicuous effects on several economic characters of the crop plants studied, notably that of grain yields in maize (Zea Mays. L) a crop taken up for pioneer investigations by the American geneticists. With the advent of Mendelism after 1900, the subject of heterosis evoked considerable academic interest and the advancement of genetical knowledge provided practical applications The years that followed witnessed remarkable progress in the study of quantitative inheritance and applied genetics. In maize breeding in the United States of America, harnessing of heterosis became the main consideration and the achievements gradually revolutionised corn production and made economic history.

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