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Interpopulation genetic variances and hybrid breeding programs

Cláudio Lopes de Souza Jr.

Departamento de Genética, ESALQ/USP, Caixa Postal 83, 13400 Piracicaba, São Paulo, SP, Brasil

ABSTRACT

This paper reports the implications of interpopulation genetic variances (s²A12, s ²A21, and s ²D(12)) for the breeding programs of hybrids from inbred lines. The genetic variances of normal hybrids, hybrids from partly inbred lines, and of modified hybrids, were derived in the assumption of linkage equilibrium of the parental populations. Comparisons among several types of hybrids were made by comparing their genetic variances. The results showed that for the same inbreeding coefficient, the interpopulation genetic variances of single-crosses (SC), three-way crosses (TWC), and double crosses (DC) of normal hybrids follow the order s²SC > s²TWC > s²DC, with the response to selection following the same pattern. There were differences between the two possible types of three-way crosses, and the appropriate crosses should be made by taking into account the magnitudes of the additive variances that are related to the populations that gave rise to the inbred lines and to the single-crosses. The implications of the use of lines with lower inbreeding levels (F < 1.0) and of hybrids from full- and half-sib progenies were also included. The three types of modified single-crosses and two types of modified three-way crosses were compared with the normal hybrids, and with the hybrids produced from partly inbred lines. The results showed modified hybrids have some advantages over normal hybrids and over hybrids from partly inbred lines.

Keywords: Genetic variances; Hybrid.

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