-This study aimed to verify the relationship between breeding for tolerance to low levels of soil nutrients and for nutrient use efficiency in tropical maize. Fifteen inbred lines were evaluated in two greenhouse experiments under contrasting levels of N and P. The relationship between nutritional efficiency and tolerance to nutritional stress was estimated by the Spearman ranking correlation between the genotypes for the traits related to N and P use efficiency and phenotypic plasticity indices. The lack of relationship between the traits, in magnitude as

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ABSTRACT. This study had three objectives: i) to observe maize inbred lines response to nitrogen (N) and phosphorus (P) acquisition as well as their utilization efficiencies and traits of root morphology in contrasting levels of these nutrients, ii) to study the relationship between root morphology and nutrient use efficiencies for both nutrients, and iii) to identify contrasting parents with components N and P use efficiency for an inheritance study. We evaluated 15 inbred lines in two experiments conducted in contrasting conditions of N and P. We evaluated the shoot, root traits and nutritional efficiencies and observed the genetic variability for most traits. Selection can be practiced for most of these traits in specific environments. Under conditions of nutritional stress, average and heritability estimates were of lesser magnitude. In this study, the shoot and root morphology traits were shown to be associated with the acquisition efficiency of both N and P in all of the environments that were evaluated.Keywords: Zea mays, acquisition and utilization efficiencies, root morphology, abiotic stress, REML/BLUP.Respostas genéticas de caracteres relacionados aos componentes da eficiência no uso de nitrogênio e fósforo em milho RESUMO. Esse estudo teve três objetivos: i) observar a resposta de linhagens de milho quanto às eficiências de absorção e de utilização de N e P e de caracteres de morfologia de raiz em níveis contrastantes destes nutrientes; ii) estudar as relações entre caracteres de morfologia de raiz e as eficiências nutricionais para ambos os nutrientes e iii) identificar genitores contrastantes quanto aos componentes da eficiencia no uso de N e P para estudo de herança. Foram avaliadas 15 linhagens de milho em dois experimentos conduzidos em condições contrastantes de N e P. Avaliou-se parte aérea, caracteres de raiz e eficiências nutricionais e Observou-se variabilidade genética para a maioria dos caracteres avaliados. A seleção pode ser praticada para a maioria destes caracteres em ambientes específicos. Em condições de estresse nutricional, as médias e herdabilidades apresentaram estimativas de menor magnitude. Nesse estudo, os caracteres parte aérea e morfologia de raiz apresentaram elevada associação com a eficiência de absorção, tanto para N como para P, em todos os ambientes avaliados.Palavras-chave: Zea mays, eficiências de absorção e de utilização, morfologia radicular, estresse abiótico, REML/BLUP.

The objective of this study was to evaluate four maize testers for identification of superior inbreed lines in testcross. The four testers evaluated are cultivars with narrow or wide genetic base (single-cross hybrids and open pollinated varieties) and two kernel types (flint or dent

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