Genetic selection of maize hybrids is often conducted using high N rates during the breeding cycle. This procedure may either lead to the release of genotypes that present nitrogen luxury consumption or require a stronger N input to accomplish their yield potential. This work was carried out to evaluate the effects of N rates on grain yield and N use efficiency of hybrids cultivated in different decades in Southern Brazil. The trial was performed in Lages, Santa Catarina State. A split plot design was used. Hybrids Ag 12, Ag 28, Ag 303 and Ag 9012, released during the 60 s, 70 s, 80 s and 90 s, respectively, were evaluated in the main plots. Nitrogen rates equivalent to 0, 50, 100 and 200 kg ha -1 were side-dressed in the split-plots when each hybrid had six fully expanded leaves. Modern-day hybrid Ag 9012 had higher grain yield than hybrids of earlier eras, regardless of N rates. Under high doses of N, the older hybrids Ag 12 and Ag 28 took up more N and presented higher values of shoot dry matter at flowering than Ag 9012. Nonetheless, they set less grains per ear which contributed to decrease their grain yield and N use efficiency.

The objective was to identify phenotypic and genotypic associations, and cause-and-effect relations of secondary components on primary components to establish criteria in the indirect

There is a need to strengthen maize (Zea mays L.) breeding strategies based on multivariate selection to obtain high-yielding hybrids that are more stable and resilient to contrasting environmental conditions. Here, we show how the multi-trait stability index (MTSI) can be used to select maize hybrids for mean performance and stability of multiple traits. A set of 10 traits, including grain yield (GY), yield components, and plant-related traits with negative and positive desired selection gains (SGs), were accessed in 90 F 1 hybrids conducted in multi-environment trials. Hybrid and hybrid × location interaction effects were significant (p ≤ .001) for all analyzed traits. The MTSI provided positive gains for all the four traits that were wanted to increase (2.52% ≤ SG ≤ 4.86; mean, 3.28%), including GY (SG, 4.86%), and negative gains for all the six traits that were wanted to decrease (-20.28% ≤ SG ≤ -0.09%; mean, -6.70%), including tassel branch number (SG, -20.28%) and plant height (SG, -1.2%). We also observed desired gains for the stability of all traits. Direct and univariate selection for GY solely was not efficient to provide desired gains for all traits. The MTSI provides a unique, robust, and easy-to-handle selection process that allows identifying the strengths and weaknesses of hybrids. The index was found to be a powerful tool to develop better selection strategies, optimizing the use of resources and time, thus contributing to the sustainability of maize breeding programs worldwide.Abbreviations: DFL, distance from the flag leaf to the first branch of the tassel; DLN, distance for the last node to the first branch of the tassel; EH, ear height; GTB, genotype-by-trait biplot; GY, grain yield; KD, kernel depth; MET, multi-environment trial; MPE, mean performance and stability; MTSI, multi-trait stability index; NKE, number of kernels per ear; PH, plant height; SG, selection gains; TBN, tassel branch number; TKW, thousand-kernel weight; TL, tassel length; WAASB, weighted average of absolute scores from the singular value decomposition of the matrix of best linear unbiased predictions for the genotype × environment interaction effects generated by a linear mixed-effect model; WAASBY, superiority index that weights between mean performance and stability.

Escala diagramática para avaliação de severidade da helmintosporiose comum em milho.Ciência Rural, v.42, n.12, dez, 2012. Ciência Rural, Santa Maria, v.42, n.12, p.2131-2137, dez, 2012 ISSN 0103-8478 0,5; 1,0; 2,5; 6,5; 15,5; 30,0; 54,0%. A validação 0,5; 1,0; 2,5; 6,5; 15,5; 30,0 and 54 Adriana

R E S U M OO objetivo deste trabalho foi caracterizar morfologicamente a dissimilaridade genética entre 25 genótipos de milho (Zea mays L.), visando a seleção dos mais divergentes e de maior potencial produtivo, por meio da análise multivariada, em cinco ambientes de cultivo do Sul do Brasil. As linhagens endogâmicas dos dois grupos heteróticos foram provenientes do banco de germoplasma da empresa KSP Sementes Ltda. Utilizaram-se 15 linhagens como genitores femininos e oito linhagens como genitores masculinos. Os ensaios foram conduzidos na safra agrícola 2011/2012 em cinco ambientes, com delineamento de blocos completos ao acaso com três repetições por local. Foram avaliados 15 caracteres de interesse agronômico. A divergência genética foi avaliada por meio do método de agrupamento de Tocher e UPGMA. As estimativas da D 2 indicam os pares de genótipos 6 e 22 como mais distantes geneticamente, e 1 e 14 os pares mais similares. Foram identificados nove grupos divergentes em ambos os métodos de agrupamento. Os caracteres profundidade de grãos, diâmetro do sabugo, massa de sabugo, diâmetro de espiga e peso de 100 grãos foram os principais determinantes na quantificação da divergência genética. Para o melhoramento de milho, os genótipos com maiores potenciais são 5, 15, 12, 20, 9, 25 e 10. Palavra-chave: Análise multivariada, dissimilaridade genética, desempenho agronômico A B S T R A C TThe aim of this study was to morphologically characterize the genetic dissimilarity among 25 maize (Zea mays L.) genotypes in order to select the most divergent and higher yield potential, by multivariate analysis, in five cultivation environments in southern Brazil. The inbred lines of the two heterotic groups were from the genebank company KSP Seeds Ltda. Fifteen inbred lines were used as female parents and eight inbred lines as male parents. The tests were conducted during the harvest 2011/2012 in five environments, in randomized complete block design with three replications per location. We evaluated 15 characters of agronomic interest. Genetic divergence was assessed by the clustering method of Tocher and UPGMA. Estimates of D 2 indicated genotype pairs 6 and 22 as genetically more distant, and 1 and 14 the most similar pairs. Nine different groups were identified in both clustering methods. The depth of grain, cob diameter, cob weight, ear diameter and weight of 100 grains characters were the main determinants in the quantification of genetic divergence. For breeding purposes, genotypes 5, 15, 12, 20, 9, 25 and 10 are those of higher potential.

The objective of this study was to estimate the correlation coefficients of phenotypic, genotypic and environment, and their consequences direct and indirectly on the yield of maize grains considering a set of environments. The experiments were conducted in randomized complete blocks with three replications in five locations in the season of 2011/2012. A thirteen morphological characters and grain yield were evaluated. Grain yield had positive but low correlation with the characters such as height of ear (r P =0.24; r G =0.26), plant height (r P =0.27; r G =0.29) and ear diameter (r P =0.59; r G =0.68). The prolificacy (r P =0.35; r G =0.43), mass on the ear (r P =0.49; r G =0.55), the grain depth (r P =0.39; r G =0.43), total mass of grains per ear (r P =0.47; r G =0.53) and mass of hundred grains (r P =0.47; r G =0.50) showed positive but medium correlation with yield. However, the ear diameter had the positive and strong correlation with grain yield. Path analysis revealed that the simultaneous selection for ear diameter and prolificacy can be a confident alternative to increase the gains in maize, considering the available variation of grain yield in maize.

The implementation of a network of maize trials is an onerous task, so breeding programs seek to eliminate redundant environments, remaining only contrasting ones. The objective was to perform the homogeneous environment grouping by studying the G×E interaction through different environmental stratification methods, as well as to compare the efficiency of these methods. Four methods were used: environmental dissimilarity (Djj); Decomposition of the genotype × environment interaction (G×E) into simple and complex parts by Cruz and Castoldi; Pearson correlation coefficient; and factor analysis. Twenty-five single-cross corn hybrids and three commercial cultivars were tested in eight cultivation environments in a randomized complete block design with three replicates in the evaluation of grain yield. Quedas do Iguaçu and Cascavel can be reduced into only one test environment by methods of factor analysis and Pearson correlation. The environments of Pato Branco and Ampére are grouped by two of the four methods employed. However, Clevelândia, Londrina, and Coxilha do not group with other environments in three of the four methods, and Itapiranga in two of the four methods. Cruz and Castoldi’s method and stratification by factor analysis are more rigorous in grouping criteria.

The present work aimed at evaluating the canonical correlations between traits of grain yield and morphological traits in maize, in order to verify the associations and interdependence among groups. The experiment was conducted in the agricultural year 2010/2011; consisted of 25 corn hybrids, allocated in five locations of the states of Paraná, Santa Catarina e Rio Grande do Sul. Settled two groups of traits, with Group I comprised agronomic characters of grain yield: grain yield plot, the total weight of grains and weight of hundred grains and the group II formed by morphology: stem diameter , leaf angle , tassel length , number of tassel branches , total leaf area , insertion of the ear , plant height in maize. The first, second and third canonical pair proved significant at the 1% level of probability, using the chi-square test, indicating that the groups are not independent. Hybrids with higher plant height, insertion of ear and leaf angle and fewer branches and tassel length are associated with the increase in weight of hundred grains in maize. To increase the grain weight, should be considered hybrids with greater insertion of the ear, leaf area and shorter length of the tassel. The increase in leaf area, as well as smaller tassel length is related positively to increase grain yield in maize.Additional keywords: associations between characters; multivariate analysis; Zea mays L. ResumoO presente trabalho objetivou avaliar as correlações canônicas entre caracteres que compõem o rendimento de grãos e caracteres morfológicos em milho, visando a verificar as associações e a interdependência entre os grupos. O experimento foi conduzido no ano agrícola de 2010/2011, compreendido por 25 híbridos simples de milho, alocados em cinco locais dos Estados do Paraná, Santa Catarina e Rio Grande do Sul, Brasil. Estabeleceram-se dois grupos de caracteres, sendo o grupo I formado por caracteres agronômicos que compõem o rendimento de grãos: rendimento de grãos da parcela (RG), massa total de grãos da espiga (MG) e massa de cem grãos (MCG), e o grupo II formado por caracteres morfológicos: diâmetro do colmo (DC), ângulo de folha (AF), comprimento do pendão (CP), número de ramificações do pendão (NR), área foliar total (AFT), altura da inserção da espiga (AE) e altura de planta (AP) em milho. O primeiro, o segundo e o terceiro pares canônicos revelaram-se significativos a nível de 1% de probabilidade, pelo teste qui-quadrado, indicando que os grupos não são independentes. Híbridos com maiores altura de plantas, de inserção de espiga e ângulo foliar e menor número de ramificações e comprimento do pendão estão associados com o incremento da massa de cem grãos em milho. Para incremento de massa de grãos, devem ser considerados híbridos com maior altura da inserção da espiga, área foliar e menor comprimento do pendão. O aumento da área foliar, assim como menor comprimento do pendão, está relacionado favoravelmente para o aumento do rendimento de grãos em milho.Palavras-chave adicionais: análise multivariada; associações ...