Acurácia da seleção simultânea para caracteres de interesse em milho tropical de segunda safra

Accuracy of simultaneous selection for interest traits in second growing season tropical maize Second growing season maize, also known as winter maize, is the maize sowed in Brazil between January and March. This growing modality reached 9.18 million hectares in 2013/2014, higher than the area cultivated in first growing season that was 6.61 million hectares in the same period. In the second season, there is a high risk of climate instabilities, mainly due to low temperatures, frost, poor rainfall distribution and reduction of photoperiod. All these factors harm photosynthetic activity, reducing the maize yield. However, because of the recent plant area increasing, public, private companies and universities have sought increased yield and stability of the second growing season maize. For this, some traits are mainly in the selection process. With the high risk of yield loses due to environmental adversities, many farmers have done little investment in fertilizers, especially nitrogen fertilization. In this context, the development of plants that are nitrogen use efficient and nitrogen stress tolerant could result in a safer activity for the farmers. In addition, the earliness is highly important, since early materials reduce the risk of losses during this period. However, the earliness must always be associated with a high yield. This way, simultaneous selection of these traits can be made by per se responses indexes of stressed plants, graphical analysis and simultaneous selection indexes. Additionally, the genotypic values of the genotypes for the traits can be predicted not only by REML/BLUP single-trait (univariate analysis), but also by REML/BLUP multi-trait (multivariate analysis). In the second, the genotypic values are adjusted considering the covariance between the traits. This way, the objective of this study was to investigate the possibility of simultaneous selection for nitrogen use efficiency and nitrogen stress tolerance, as well as early and high yielding plants. For this, tropical maize lines were grown and evaluate. By these data, it was simulated several simultaneous selection sets. It was observed that Harmonic Mean of the Relative Performance (HMRP) is the most efficient in the selection for nitrogen use efficient and nitrogen stress tolerance. This probably occurs due to the strong unfavorable correlation between the indexes that estimate the efficiency and the tolerance, as well as the superiority in accuracy, heritability and selections gains of HMRP. In case of simultaneous selection for yield and earliness, the additive simultaneous selection index using the genotypic values predicted by REML/BLUP single-trait proved the most efficient selection, because it got satisfactory gains in all the traits and, this index allows the possibility to modulate the gains in each trait. It was concluded that the simultaneous selection for nitrogen use efficiency and nitrogen stress tolerance, as well as for yield and earliness are possible. Furthermore, the choice of the best simultaneous selection method depends on the magnitude and direction of the correlation between the traits.