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A seleção de caracteres relacionados à tolerância à deficiência hídrica em milho tem sido objeto de interesse em programas de melhoramento, principalmente em virtude da ineficiência da seleção para produzir grãos nessas condições. O objetivo deste trabalho foi estimar parâmetros genéticos em duas populações de milho tropical. Foram avaliadas duas populações (denominadas D e U) com 256 progênies F 2:3 , no delineamento em látice 16 x 16 em sete ou nove ambientes e densidade populacional de 62.500 plantas ha -1 . Diferenças significativas foram constatadas entre progênies (P), ambientes (A) e para a interação P x A em ambas as populações. Os coeficientes de herdabilidade em nível de médias de progênies variaram entre 73,52% para prolificidade na população D e 95,88% para florescimento feminino (FF) na população U. No caráter produção de grãos (PG) houve correlação genética significativa nas populações U e D, respectivamente, com prolificidade (0,79 e 0,88) e florescimento feminino (-0,76 e -0,44); na população U com florescimento masculino (-0,74) e; na população D com stay-green (-0,50). Não foi constatada correlação genética significativa entre PG e intervalo entre florescimentos (IF). Os parâmetros genéticos estimados sugerem que a utilização de índices de seleção que incluam, além de PG, caracteres como prolificidade, FF e SG na seleção de progênies sob condições normais de umidade, poderia propiciar o desenvolvimento de material com alta produtividade e boa tolerância a estresses hídricos.Palavras-chave: Estresse hídrico, estresse abiótico, correlação, produção de grãos, stay-green. ABSTRACT GENETIC PARAMETERS OF DROUGHT TOLERANCE RELATED TRAITS IN TROPICAL MAIZEThe selection of drought tolerance related traits in maize has been object of interest in improvement programs, mainly in function of the selection inefficiency for grain yield on these conditions. The objective of this work was to estimate genetic parameters in two populations of tropical maize. Two populations (called D and U) with 256 F 2:3 progenies had been evaluated in a 16x16 simple lattice, in seven and nine environments with population density of 62,500 plants ha -1 . Significant differences were observed among line (P), environments (A) and for the P x A interaction in both populations. The heritability coefficients at progenies level average had varied between 73.52% for prolificacy in population D and 95.88% for female flowering (FF) in population U. Grain yield (PG) presented significant genetic correlation in populations U and D, respectively, with prolificacy (0,79 and 0.88) and female flowering (-0,76 and -0,44); in population U with male flowering (-0.74) and; in population D with stay-green (-0.50). No genetic correlation was observed between PG and anthesis-silking interval (IF). Estimated of genetic parameters suggest that the use of selection indices that include, besides PG, characters as prolificacy, FF and SG in the selection process under conditions of normal water supply, could lead to the development of cultivars with high ...

No abstract

Phaeosphaeria leaf spot (PLS) is an important disease in tropical and subtropical maize (Zea mays, L.) growing areas, but there is limited information on its inheritance. Thus, this research was conducted to study the inheritance of the PLS disease in tropical maize by using QTL mapping and to assess the feasibility of using marker-assisted selection aimed to develop genotypes resistance to this disease. Highly susceptible L14-04B and highly resistant L08-05F inbred lines were crossed to develop an F(2) population. Two-hundred and fifty six F(2) plants were genotyped with 143 microsatellite markers and their F(2:3) progenies were evaluated at seven environments. Ten plants per plot were evaluated 30 days after silk emergence following a rating scale, and the plot means were used for analyses. The heritability coefficient on a progeny mean basis was high (91.37%), and six QTL were mapped, with one QTL on chromosomes 1, 3, 4, and 6, and two QTL on chromosome 8. The gene action of the QTL ranged from additive to partial dominance, and the average level of dominance was partial dominance; also a dominance x dominance epistatic effect was detected between the QTL mapped on chromosome 8. The phenotypic variance explained by each QTL ranged from 2.91 to 11.86%, and the joint QTL effects explained 41.62% of the phenotypic variance. The alleles conditioning resistance to PLS disease of all mapped QTL were in the resistant parental inbred L08-05F. Thus, these alleles could be transferred to other elite maize inbreds by marker-assisted backcross selection to develop hybrids resistant to PLS disease.

Oil content and grain yield in maize are negatively correlated, and so far the development of high-oil high-yielding hybrids has not been accomplished. Then a fully understand of the inheritance of the kernel oil content is necessary to implement a breeding program to improve both traits simultaneously. Conventional and molecular marker analyses of the design III were carried out from a reference population developed from two tropical inbred lines divergent for kernel oil content. The results showed that additive variance was quite larger than the dominance variance, and the heritability coefficient was very high. Sixteen QTL were mapped, they were not evenly distributed along the chromosomes, and accounted for 30.91% of the genetic variance. The average level of dominance computed from both conventional and QTL analysis was partial dominance.The overall results indicated that the additive effects were more important than the dominance effects, the latter were not unidirectional and then heterosis could not be exploited in crosses. Most of the favorable alleles of the QTL were in the high-oil parental inbred, which could be transferred to other inbreds via markerassisted backcross selection. Our results coupled with reported information indicated that the development of high-oil hybrids with acceptable yields could be accomplished by using marker-assisted selection involving oil content, grain yield and its components. Finally, to exploit the xenia effect to increase even more the oil content, these hybrids should be used in the Top Cross TM procedure.