Abstract The aims of this study were to evaluate the homology of the ZmMATE1 and ZmMATE2 gene sequences with those deposited in the international banks of sequences and quantify the differential expression of the genes ZmMATE1, ZmMATE2, and ZmNrat1 in germplasms of landrace and hybrid maize under aluminum (Al) stress in minimal solution. Fifty-two hybrids from different companies and 50 landrace varieties were genotyped for the genes ZmMATE1 and ZmMATE2. For studies of gene expression, the tolerant (H 44 and V 18) and the sensitive (H 22 and V 25) genotypes were exposed to minimal solution containing 4 mg L-1 of Al for different periods (0, 1, 3, 6, 9, 12, 24, and 48 h). The results showed greater differential expression in the tolerant V 18 landrace variety of the gene ZmMATE1, indicating that exudation of citrate may be the main mechanism of Al tolerance in this genotype.

RESUMO A resistência genética a doenças em plantas representa um importante pilar de sustentação na agricultura moderna. Objetivou-se determinar a herança genética da resistência à antracnose do colmo em milho tropical. Nove famílias segregantes foram obtidas a partir de cruzamentos de linhagens endogâmicas contrastantes. As linhagens parentais e as gerações filiais (F1, F2, BC1 e BC2) foram avaliadas quanto à resistência à antracnose do colmo em um experimento em blocos casualizados, com três repetições. Os tratamentos foram arranjados em delineamento de parcelas subdivididas, com efeito de famílias nas parcelas e de gerações nas subparcelas. Os resultados mostraram herança semelhante entre as famílias, com predominância de efeitos genéticos aditivos. As linhagens endogâmicas (LR 04-2, LR 03-2 e LR 23-1) foram muito eficazes na transmissão de genes de resistência a seus descendentes, pois permitiram diminuições acentuadas no comprimento das lesões nos colmos. Também observou-se uma herança oligogênica envolvida na resistência à antracnose do colmo nas famílias avaliadas. Pode-se inferir que os ganhos genéticos com a seleção artificial poderiam ter sucesso no desenvolvimento de linhagens endogâmicas de milho mais resistentes à antracnose do colmo.

ABSTRACT The genetic resistance to diseases in plants represents an important support pillar in modern agriculture. This study aimed to determine the genetic inheritance to anthracnose stalk rot resistance in tropical maize. Nine segregating families were obtained from contrasting inbred lines crosses. The parental lines and the filial generations (F1, F2, BC1 and BC2) were evaluated for antrachnose stalk rot resistance in an experiment in randomized blocks, with three replications. The treatments were arranged in a split-plot design, with family effect in the plots and generation effect in the split-plots. The results showed a similar inheritance among the families, with predominance of additive genetic effects. The inbreed lines (LR 04-2, LR 03-2 and LR 23-1) were very effective in transmitting resistance genes to their descendants because they allowed sharp decreases in the lesions length in the stalks. It was also possible to notice an oligogenic inheritance involved in the anthracnose stalk rot resistance for the evaluated families. It may be inferred that genetic gains from artificial selection could be successful for developing maize inbred lines more resistant to anthracnose stalk rot.

ABSTRACT Aluminum (Al) toxicity is the most limiting factor to maize crop productivity in acid soils. Therefore, the understanding of inheritance of Al tolerance in maize is important for the developmentof more adequate procedures for Al tolerant genotypes selection. In this sense, the objectives of this study were to determine the inheritance, and the general (GCA) and specific combining ability (SCA) for Al tolerance in tropical maize. First, we evaluated diallel crosses of maize from landrace and hybrid germplasms for Al tolerance through the minimal solution methodology. The DIF data (root growth difference) were analyzed by Griffing diallel model. Later the additive-dominant genetic model proposed by Mather and Jinks (1971) was used to estimate the genetic effects. The results of the diallel analysis showed greater variability associated with the estimates of the SCA for both germplasm. The diallel crosses involving the V 06 (Dente de Ouro 2) landrace stood out by high SCA and GCA for Al tolerance. The generation mean analysis indicated quantitative inheritance of Al tolerance in this germplasm, with most of the variance explained by the additive effects. The heritability in the narrow sense varied from 47% to 71%, indicating the possibility of genetic gain with the selection of tolerant genotypes in F2 generation. Additive gene action associated with intermediate heritability and quantitative inheritance demonstrates the possibility of genetic gains with artificial selection for Al tolerance in this maize germplasm.

Abstract The objectives of this study were to map genomic regions associated with QTL for aluminum (Al) tolerance in maize and determine the phenotypic effects of tolerance loci. QTL analysis for Al tolerance was carried out in a population of F2:3 progenies resulting from a cross between the contrasting lines LT 99-4 and LS 04-2. SSR (Simple Sequence Repeat) loci and AFLP (Amplified Fragment Length Polymorphism) were used to construct the linkage map and to detect QTL mapped by composite interval mapping analysis. Nine tolerance QTL among eight linkage groups (chromosomes 2, 4, 5, 6, 7, 8, 9, and 10) were mapped, which explained 70.3% of the phenotypic variance. The results confirmed three major QTL (bins 6.00, 8.05, and 10.01) that are described in the literature for Al tolerance, which accounted for most of the phenotypic variance (40.3%).

Abstract The objectives were to map genomic regions associated with quantitative trait loci (QTL) to anthracnose leaf blight (ALB) in tropical maize, and to determine the effects of the loci on resistance to the pathogenic fungus Colletotrichum graminicola (Ces.). QTL analysis to ALB was carried out in a population of F2:3 progenies resulting from the cross between the contrasting lines LR 04-2 and LS 95-1. Seventeen QTL were located by mapping analysis by composite interval on eight chromosomes. Four QTL mapped on chromosomes 9 (1 QTL) and 10 (3 QTL) were the most stable, detected in at least two experiments, and represented the most part of the phenotypic variation (27.7 to 54.3%) of resistance. The majority of QTL mapped were associated to specific severity evaluations/development stage of maize growth, and may explain the quantitative inheritance of resistance of tropical maize to ALB.

RESUMO O presente trabalho objetivou estimar a divergência genética entre progênies de meios-irmãos de milho visando direcionar a recombinação entre progênies contrastantes e superiores para a produção de milho-verde. Noventa e seis progênies foram avaliadas no delineamento de blocos casualizados com 3 repetições, sendo mensuradas 18 características associadas à adaptação agronômica e ao rendimento de milho-verde. A divergência genética foi estimada a partir da distância quadrada generalizada de Mahalanobis e as progênies agrupadas pelos métodos UPGMA e de Tocher. A análise de variância conjunta evidenciou variabilidade genética entre as progênies para as características. O método UPGMA foi mais sensível que o de Tocher, pois levou à formação de 11 grupos geneticamente dissimilares em comparação com os 5 de Tocher. O agrupamento identificou progênies superiores e contrastantes para a produção de milho-verde. A recombinação dessas progênies possibilitará incrementar a variabilidade genética e a frequência de alelos favoráveis à produção de milho-verde.

ABSTRACT The present study aimed to estimate the genetic divergence among corn half-sib progenies seeking to direct recombination between contrasting and superior progenies for green corn production. Ninety-six progenies were evaluated in a randomized block design with 3 replications, and 18 characteristics associated with agronomic adaptation and green corn yield were measured. The genetic divergence was estimated using generalized square Mahalanobis distance and the progenies grouped by UPGMA and Tocher’s methods. The joint analysis of variance showed genetic variability among the progenies for the characteristics evaluated. The UPGMA method was more sensitive than Tocher’s, since it led to the formation of 11 groups genetically dissimilar compared to the 5 ones of Tocher’s method. The grouping allowed to identify superior and contrasting progenies for green corn production. The recombination of these progenies allows increasing genetic variability and the frequency of alleles favorable to the green corn production.

Abstract The objectives of this study were to evaluate the resistance of maize inbred lines to anthracnose leaf blight (Colletotrichum graminicola Ces.), and to estimate genetic parameters associated with resistance. Sixteen lines (S5) were evaluated for resistance to anthracnose leaf blight in three experiments, in a randomized block design with four replications. From three evaluations of severity, it was estimated the area under the disease progress curve (AUDPC), and the genetic parameters associated with resistance. Results showed the existence of genetic variability for resistance to anthracnose leaf blight in the set of studied lines. Five lines stood out for the high resistance pattern to anthracnose leaf blight, presenting the lowest AUDPC values in the three experiments, and thus were considered important sources of C. graminicola resistance genes. Estimates of genetic parameters indicated low participation of the environment and highlighted the possibility of genetic gains with artificial selection for resistance in this pathosystem.