Optimum prediction of three-way crosses from single crosses in forage maize (Zea mays L.)

Abstract

Three-way cross means were predicted with formulae involving linear functions of general (GCA) and specific combining ability (SCA) effects estimated from single-cross factorials between genetically divergent populations. Data from an experiment with 66 single-cross and 66 three-way cross forage maize (Zea mays L.) hybrids was used for comparing the prediction formulae. The genotypic correlation (r) between observed and predicted three-way crosses increased with increasing χ, the weighting factor of SCA effects, for plant height and ear dry matter (DM) content. It displayed slightly convex curves for total and stover DM yield, ear percentage, and metabolizable energy content of stover. For Jenkins' method B, r was considerably less than 1.0 for all traits, indicating the presence of epistasis. The square root of heritability (hĜ) of the predicted means decreased with increasing χ, the reduction being small with a greater number of test environments. Using the product r·hĜ as a criterion of efficiency, none of the prediction methods was consistently superior and the differences among them were rather small (< 7.5%) for all traits, irrespective of the number of test environments. We recommend evaluating the GCA of a greater number of lines from each parent population in testcrosses with a small number of elite lines from the opposite population. All possible three-way or double crosses between both sets of lines should be predicted by Jenkins's method C. This procedure allows one to select with a higher intensity among the predicted hybrids and thus should increase the genetic gain.

Genetic analysis of tropical maize inbred lines for resistance to maize lethal necrosis disease

“…Best linear unbiased prediction (BLUP) was investigated by Bernardo (1996) to predict performance of untested single crosses using phenotypic information of related single crosses and genetic relationships among their parental inbred lines. The GCA estimates of parental lines provide an established and simple approach to predict hybrid performance (Melchinger et al 1987). In this study, GCA based prediction of 28 9 28 maize inbred lines crosses was performed to predict single-cross performance for MLN resistance and GY.…”

Impact of Interpopulation Divergence on Additive and Dominance Variance in Hybrid Populations

“…Since the Hessian matrix (see appendix b) of F pp1;pp2 at the critical point is positive definite (due to positive eigenvalues), its determinant, detðH ðF pp1;pp2 ÞÞ, is also positive. Thus, F pp1;pp2 has a local minimum at (0, 0) (Price 1984 (Melchinger et al 1987). With predominance of s 2 GCA over s 2 SCA , early testing becomes more effective and superior hybrids can be identified and selected mainly on the basis of their prediction from GCA effects.…”

Concept of Heterotic Group and its Exploitation in Hybrid Breeding

“…An increased divergence between two populations of a heterotic pattern increases the probability to complementary select for favorable alleles at different loci. Melchinger et al, (1987) emphasized the importance of the variances due to general (σ 2 GCA) and specific combining ability (σ 2 SCA) and their ratio for predicting hybrid performance. MELCHINGER and GUMBER (1998) recommended the following criteria for the identification of new patterns: (i) high mean performance and large genetic variance in the hybrid population; (ii) high per se performance and good adaptation of the parent populations to the target environment; and (iii) low inbreeding depression, if hybrids are produced from inbreds.…”