Breeding for drought tolerance is a challenging task that requires costly, extensive, and precise phenotyping. Genomic selection (GS) can be used to maximize selection efficiency and the genetic gains in maize (Zea mays L.) breeding programs for drought tolerance. Here, we evaluated the accuracy of genomic selection (GS) using additive (A) and additive + dominance (AD) models to predict the performance of untested maize single-cross hybrids for drought tolerance in multi-environment trials. Phenotypic data of five drought tolerance traits were measured in 308 hybrids along eight trials under water-stressed (WS) and well-watered (WW) conditions over two years and two locations in Brazil. Hybrids' genotypes were inferred based on their parents' genotypes (inbred lines) using single-nucleotide polymorphism markers obtained via genotyping-by-sequencing. GS analyses were performed using genomic best linear unbiased prediction by fitting a factor analytic (FA) multiplicative mixed model. Two cross-validation (CV) schemes were tested: CV1 and CV2. The FA framework allowed for investigating the stability of additive and dominance effects across environments, as well as the additive-by-environment and the dominance-by-environment interactions, with interesting applications for parental and hybrid selection. Results showed differences in the predictive accuracy between A and AD models, using both CV1 and CV2, for the five traits in both water conditions. For grain yield (GY) under WS and using CV1, the AD model doubled the predictive accuracy in comparison to the A model. Through CV2, GS models benefit from borrowing information of correlated trials, resulting in an increase of 40% and 9% in the predictive accuracy of GY under WS for A and AD models, respectively. These results highlight the importance of multi-environment trial analyses using GS models that incorporate additive and dominance effects for genomic predictions of GY under drought in maize single-cross hybrids.

Water deficit is one of the most common causes of severe crop‐production losses worldwide in maize (Zea mays L.). The main goal of this study was to infer about genotype × environment interaction (G × E) and to estimate genetic correlations between drought tolerance traits in maize using factor analytic (FA) multiplicative mixed models in the context of multi‐environment trial (MET) and multi‐trait multi‐environment trial (MTMET) analyses. The traits measured were: grain yield (GY), ears per plot (EPP), anthesis‐silking interval (ASI), female flowering time (FFT), and male flowering time (MFT). Three‐hundred and eight hybrids were evaluated in a total of eight trials conducted under water‐stressed (WS) and well‐watered (WW) conditions across 2 yr and two locations in Brazil. For most of the traits (GY, ASI, and FFT), the magnitude of the genetic variances differed across WS and WW conditions. Genetic correlations between water conditions for FFT and MFT were 0.81 and 0.82, respectively, indicating that it might be unnecessary to measure these traits in both water conditions. Grain yield and EPP showed moderate to high G × E, with genetic correlations of 0.57 and 0.39 between WS and WW conditions, respectively, which suggested that gene expression was not consistent across different water regimes. Therefore, it is necessary to evaluate these traits under both water conditions. Genetic correlations between pairs of traits, in general, were higher under WS conditions compared with WW conditions. Grain yield exhibited moderate correlations with EPP (r = 0.62) and FFT (r = −0.42) under WS conditions. The FA models can be a useful tool for MET and MTMET analyses in maize breeding programs for drought tolerance.

Vitamin A deficiency causes xerophthalmia in preschool-aged children worldwide. The objective of this study was to estimate the genetic parameters that would be useful in selecting parent plants for developing productive hybrids with higher levels of provitamin A in the maize kernel. A complete 7 9 7 diallel mating scheme was used to generate 21 single-cross hybrids. The F 1 crosses and check hybrids were evaluated in complete block design across three different Brazilian environments, and carotenoid content was analyzed by high performance liquid chromatography. General combining ability effects were significant for all traits except a-carotene This result indicates that the contribution of the additive effect was more important for provitamin A and other carotenoids and, consequently that there is high chance of improving this trait through recurrent selection methods. Line 3 produced the highest level of kernel provitamin A among the inbred lines evaluated and also demonstrated the potential to contribute to the development of genetic materials with a good performance for provitamin A. Inbred lines 1, 6, and 7 showed a higher concentration of favorable alleles for grain yield, and inbred lines 3 and 6 exhibited a higher concentration of favorable alleles for b-carotene. Hybrid 1 9 3 performed well in terms of provitamin A and grain yield and combination 2 9 3 was the best performer in terms of lutein content.

2019. Variability in herbivore-induced defence signalling across different maize genotypes impacts significantly on natural enemy foraging behaviour.

e PAULO CÉSAR LEMOS DE CARVALHO 4 RESUMO -Três ciclos de seleção entre e dentro de progênies de meios-irmãos foram praticados na população de milho (Zea mays L.) de alta qualidade protéica CMS-52, nos tabuleiros costeiros dos estados de Sergipe e Bahia, no período de 1995 a 1997, visando à obtenção de uma população melhor adaptada às condições edafoclimáticas da região. As progênies foram avaliadas em látice simples 14 x 14, com recombinação das progênies superiores, dentro do mesmo ano agrícola, de modo a se obter um ciclo por ano. Os valores dos parâmetros genéticos decresceram do ciclo original para o ciclo I, mantendo-se no ciclo II com magnitudes semelhantes ao ciclo I. As altas magnitudes desses parâmetros genéticos, as altas médias de produtividades das progênies, e o ganho médio esperado com a seleção entre e dentro de progênies, por ciclo de seleção (12,3%), mostram o grande potencial da população em responder à seleção, o que permitirá a obtenção de uma população mais produtiva e melhor adaptada às condições edafoclimáticas da região. A magnitude da interação progênies x locais evidenciou a importância de se avaliarem as progênies em mais de um local, para melhorar a eficiência do processo seletivo e obter estimativas mais consistentes dos componentes da variância.Termos para indexação: Zea mays, parâmetros genéticos, variação genética, teste de progênie, seleção, métodos de melhoramento. THREE CYCLES SELECTION AMONG AND WITHIN HALF SIB PROGENIES IN THE MAIZE POPULATION CMS-52ABSTRACT -Three cycles of selection among and within half-sib progenies were carried out in the high quality protein maize (Zea mays L.) population CMS-52, at the tabuleiros costeiros of Sergipe and Bahia, Brazil, during the period of 1995 to 1997. The work aimed at obtaining a better adapted population for the regional environment. The progenies were evaluated on a 14 x 14 látice design. Recombination of the superior progenies was processed within the same year in order to get one cycle per year. The values of the genetic parameters decreased from the original cycle to cycle I, keeping at cycle II similar magnitudes of cycle I. The high magnitudes of the genetic parameters, the high productivity means of progenies, and the averaged gain expected from the selection among and within progenies per selection cycle (12.3%) show the high potential of the population to respond to selection, which will permit to attain a higher yielding population, better adapted to the regional environment. The high progeny x location interaction showed the importance for progeny evaluation in more than one location, to increase the efficiency of the selection process and to obtain more accurate estimates of variance components.

Resumo -O objetivo deste trabalho foi caracterizar e avaliar a variabilidade quanto ao teor e perfi l de carotenoides nos grãos de 134 genótipos de milho (Zea mays), com vistas à utilização em programas de biofortifi cação. Os materiais foram provenientes dos campos experimentais e do Banco Ativo de Germoplasma da Embrapa Milho e Sorgo, Sete Lagoas, MG. São cultivares e híbridos comerciais, linhagens-elite e outros acessos escolhidos com base na coloração amarelo-alaranjada do endosperma. A quantifi cação do teor de carotenoides totais, carotenos e xantofi las mono-hidroxilada e di-hidroxilada dos grãos foi realizada por método cromatográfi coespectrofotométrico. As médias encontradas nos grãos foram 22,34 µg g -1 de carotenoides totais, 2,55 µg g -1 de carotenos, 3,86 µg g -1 de xantofi las mono-hidroxiladas e 15,93 µg g -1 de xantofi las di-hidroxiladas. Os genótipos foram agrupados em 18 grupos pelo método de Tocher. O germoplasma da Embrapa possui potencial para ser usado em programas de desenvolvimento de linhagens de milho biofortifi cadas, quanto ao total de carotenoides pró-vitamina A.Termos para indexação: Zea mays, biofortifi cação, carotenoides, melhoramento, vitamina A. Variability of maize genotypes for grain carotenoid compositionAbstract -The objective of this work was to characterize 134 maize (Zea mays) genotypes, for carotenoids content and build a genetic profi le to facilitate future breeding to increase grain nutritional value (biofortifi cation). Seeds came from experimental fi elds and from the Banco Ativo de Germoplasma of Embrapa Milho e Sorgo, Sete Lagoas, MG, Brazil. The genotypes were commercial hybrids, varieties, and inbred lines developed by the Embrapa biofortifi cation program and other accessions, chosen for their yellow-orange endosperm color. Total grain carotenoids, carotenes, xanthophylls (monohydroxylates and dihydroxylates) were determined by chromatographic-spectrophotometric methods. The detected averages were: 22.34 µg g -1 for total carotenoids, 2.55 µg g -1 for carotenes, 3.86 μg g -1 for monohydroxylated xanthophylls, and 15.93 µg g -1 for dihydroxylated xanthophylls. The genotypes variability was divided into 18 groups by the method of Tocher. The Embrapa germplasm has variability and potential for development of maize lines biofortifi ed for total of provitamin A carotenoids.

The study of inbreeding depression is important for breeding strategies such as use of inbred progenies or extraction of inbreed lines. A diallel of 28 maize open-pollinated varieties was evaluated in 10 environments in the early 1990s. At the same time, S 1 populations for each of the 28 varieties were evaluated in the same 10 experiments (environments). Yield reductions of the populations from S 0 to S 1 (mean of the 10 environments), varied from 34.6% (CMS-01) to 59.2% (CMS-30), with an average of 49.1%. Inbreeding depression was greater in populations with a wider genetic base, which had never been exposed to inbreeding (CMS-30, BR-107, PH4, Cunha, Saracura, Nitrodent, and Nitroflint). Inbred lines with greater yield means should be obtained from the BR-105, BR-111, CMS-01, CMS-03, BR-106, CMS-14c, and CMS-28 populations. The use of parameter estimates generated by analysis of inbreeding depression, allow to make inferences about frequencies of deleterious alleles in the population. The frequencies of favorable alleles in the parents can be obtained by diallel analysis. The association of these two types of information, can provide a better interpretation of the genetic parameters and also can improve the process of selection of parents for either an intra-or an inter-populational breeding program.

Understanding the crop diversity is critical for a successful breeding program, helping to dissect the genetic relationship among lines, and to identify superior parents. This study aimed to investigate the genetic diversity of maize (Zea mays L.) inbred lines and to verify the relationship between genetic diversity and heterotic patterns based on hybrid yield performance. A total of 1,041 maize inbred lines were genotyped-by-sequencing, generating 32,840 quality-filtered single nucleotide polymorphisms (SNPs). Diversity analyses were performed using the neighbor-joining clustering method, which generated diversity groups. The clustering of lines based on the diversity groups was compared with the predefined heterotic groups using the additive genomic relationship matrix and unweighted pair group method with arithmetic mean. Additionally, the genetic diversity of lines was correlated with yield performance of their corresponding 591 single-cross hybrids. The SNP-based genetic diversity analysis was efficient and reliable to assign lines within predefined heterotic groups. However, these genetic distances among inbred lines were not good predictors of the hybrid performance for grain yield, once a low but significant Pearson's correlation (.22, p-value ≤ .01) was obtained between parental genetic distances and adjusted means of hybrids. Thus, SNP-based genetic distances provided important insights for effective parental selection, avoiding crosses between genetically similar tropical maize lines.