Abstract
The hybrid vigor is one of the greatest practical contribution of genetics to the agricultural world and had its most significant expression in maize crops, being intensively explored by breeders and seed production companies. This review presents aspects of the genetic basis for heterosis, biometrical assessment, and improvement methods to obtain heterotic hybrids and reciprocal recurrent selection in maize. Contributions from Biotechnology and Molecular Genetics as tools for hybrid programs to diminish hand pollination work to obtain inbred lines and to form heterotic groups through molecular markers are also reported. Finally, the identification of QTLs to help select superior lines and confirm genetic hypotheses is presented to completely elucidate the heterosis phenomena.
Highlights
Heterosis is the genetic expression of the developmental differences among hybrids and their respective parents
The use of heterosis developed in such a unique way that hybridization was recommended as a valuable breeding method
Kolreuter (1761) apud Brewbaker (1969) reported heterosis on Nicotiana sp. hybrids and emphasized two aspects of the phenomenon: a)that the hybrid vigor was related with the parents degree of genetic dissimilarity and; b) that it was important in the evolution, because the plant reproduction system suggests that nature favored natural outcrossing outcrossing
Summary
Heterosis is the genetic expression of the developmental differences among hybrids and their respective parents. Prominent scientists, including Sprague and Eberhart (1975); Paterniani (1976); Jenkis (1978); Miranda Filho and Viégas (1987), Hallauer and Miranda Filho (1981); Paterniani and Campos (1999), have studied various aspects of maize hybridization The competence of these authors makes scientific innovation difficult to be achieved in this field and, this review aimed at collecting and compiling information and at reporting on heterosis studies and results recently published. Reduction and the need to search for lines with superior behavior in crosses rather than per se He designed a generic procedure to obtain maize single hybrids that is, in essence, still used today: auto-fecundation of a large number of plants to obtain inbred lines; crossing the lines to obtain the largest possible number of hybrids; and experimentally evaluating the hybrids to determine the pair of lines with better performance (Paterniani and Campos, 1999). He mentioned the following disadvantages: the best genotypes are very difficult to obtain; heterosis is random (a limit is reached and it is difficult to overcome); it can only be used in species where the process of obtaining hybrid seeds is practicable and has a low cost (or the commercial product is expensive); and the maize hybrid scheme requires a developed social structure for production, processing, transport and commercialization
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