Abstract
In breeding programs, obtaining breeding lines was important, and first selfing selection generations is common. In addition, an analytic approach through mixed models can lead to more success in genotype selection because it lends flexibility in analysis of unbalanced data and provides more precise genotypic values in regard to progenies evaluated. The goal of this study was to make early selection (in the S2 generation) of progenies evaluated in top crosses, using a mixed-model approach. Five hundred S2 progenies were plant derived from three populations using selection intensity (40%), which were crossbreeding with three testers. The hybrids obtained, together with control treatments, were set up in five experiments in Brazil: three in Minas Gerais, one in Santa Catarina, and one in Parana, which evaluated grain yield. The REML method was used for calculation of variance components, and means were predicted through BLUP. The BLUPs of general combining ability (GCA) and specific combining ability (SCA) were also predicted, and the Spearman correlation coefficients among BLUPs were estimated. The dominance effects had a bigger influence on yield expression, as seen from wider amplitude in SCA values. There was an 86% coincidence considering strategy in which selection index was carried out within three populations, in relation to selection by the overall value of GCA. Considering superior hybrids, the progenies of population C exceeded the quantity of hybrids expected by 24.6%, whereas there was a reduction of 30.8% for A and 20% for B. The hybrids that exhibited the highest BLUP means were derived from crosses between progenies of population C together with the tester LE84. The low correlation among testers, both for SCA and for BLUPs, indicates that there is progeny per tester interaction. Key words: Zea mays, combining ability, mixed models, development of breeding lines.
Highlights
The Restricted Maximum Likelihood (REML) method was used for calculation of variance components, and means were predicted through BLUP
Considering superior hybrids, the progenies of population C exceeded the quantity of hybrids expected by 24.6%, whereas there was a reduction of 30.8% for A and 20% for B
Grain yield increase in the maize crop is directly related to the use of superior hybrids, associated with biotechnological events that contribute to taking better advantage of the genetic potential of these hybrids
Summary
Grain yield increase in the maize crop is directly related to the use of superior hybrids, associated with biotechnological events that contribute to taking better advantage of the genetic potential of these hybrids. The exploitation of heterosis makes the use of hybrids in the production system viable. Replacing current hybrids with even better ones is one of the big challenges facing breeders (Bison et al, 2003). Since this is an extremely important matter for the seed sector, breeding companies must adopt efficient breeding strategies to obtain new hybrids. In addition to its consequences for increasing crop yield, releasing new cultivars directly affects company profitability
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