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Inbreeding can potentially be used for the development of inbred lines containing alleles of interest, but the genetic causes that control inbreeding depression are not completely known, and there are few studies found in the literature. The present study aimed to obtain estimates of inbreeding depression for eight traits in seven tropical maize populations, analyze the effects of inbreeding over generations and environments, and predict the behavior of inbred lines in future generation S? through linear regression methods. It was found that regardless of the base population used, prediction values could vary when the model was based on only 2 generations of inbreeding due to the environmental component. The influence of the environment in this type of study could be reduced when considering 3 generations of inbreeding, allowing greater precision in predicting the phenotypes of inbred lines. The use of linear regression was effective for inbred line prediction for the different agronomic traits evaluated. The use of 3 levels of inbreeding minimizes the effects of the environmental component in inbred line prediction for grain yield. GO-S was the most promising population for inbred line extraction.

In order to verify the genetic and agronomic value, yield potential and inbreeding depression of synthesized composites, as well as quantifying the population variability and incorporating new sources of semiexotic germplasm in maize genetic improvement programs, four populations, identified as NAP-FA x HG-71 (P1), NAP-FL x HG-49 (P2), NAP-FB x HG-49 (P3), and NAP-DB x HG-49 (P4), with two levels of inbreeding (S0 and S1), were evaluated in three locations. From the P1 and P4 populations, 100 full-sib progenies were evaluated in only one location. Plant and ear height, lodging, breakage, ear length and diameter, resistance to diseases, ears with chalky kernels and grain yield were evaluated. The grain yield of the S0 and S1 populations varied between 5.50 and 6.65 t ha-1 and 3.8 and 4.58 t ha-1, respectively, with an average inbreeding depression between 23.9% and 38.0%. Considering all the locations, the grain yields of the non-inbreeding populations varied between 64.4% and 78.0% in relation to commercial hybrids (witnesses), indicating a good yield potential for start of improvement program. In the P1 and P4 populations, sufficient genetic variability was identified in most of the characters, which accredits them for recurrent selection. Gains of 13.7% and 17.8% for grain yield and 31.64% and 29.9% for ears with chalky kernels were estimated.

The rapid expansion of corn in Brazil indicates the need to explore new sources of germplasm. Thus, the wider use of local germplasm, and the introduction of exotic ones seem to be an advisable strategy to achieve higher levels of yield and adaptability. The objective of this work was to generate information about the potential of two groups of populations (NAP - exotic; HG - local) and their heterotic pattern in hybrid combinations for the synthesis of new populations. Populations and hybrids were evaluated in complete randomized block designs with four replications, in two locations, and three yield traits were studied (GY - grain yield, EY - ear yield, SW - specific weight). The basic strategy was the selection of one HG population as base for the incorporation of each exotic population. The expected yield gain of the best combinations varied from 1 to 22%. Average heterosis for grain yield was 34.5%. Resumo A rápida expansão do milho no Brasil indica claramente a necessidade de explorar novas fontes de germoplasma. Assim, o uso mais amplo de germoplasma local e a introdução de germoplasma exótico parecem uma estratégia recomendável para atingir níveis mais elevados de produtividade e adaptabilidade. O objetivo deste trabalho foi gerar informação sobre o potencial de dois grupos de populações (NAP - exótico; HG - local) e seu potencial heterótico em combinações híbridas para a síntese de novas populações. Populações e híbridos foram avaliados em blocos casualizados com três repetições em dois locais e três caracteres de produção foram estudados (GY - produção de grãos, EY - produção de espigas, SW - peso específico). A estratégia básica foi a seleção de uma população HG como base para incorporação de cada população exótica. O ganho esperado na produção das melhores combinações variou de 1 a 22%. A heterose média para peso de grãos foi de 34,5%.

The rapid increase of the maize crop in the last decades in Brazil, mainly in the Central West region, has encouraged the second crop (usually maize after soybean) in the same year. For that reason the need for the exploitation of new sources of germplasm seems to be apparent to attend the challenge to create new cultivars (populations or hybrids) adapted to the extremely varying environments. Following this principle, the objective of the present work was directed to the study of genetic variability and yield potential of three semiexotic populations (CRE-01, CRE-02, CRE-03) under the condition of second crop in the Southwest region of the State of Goiás (Brazil). In addition, one cycle of recurrent selection with half-sib families was completed in each population. Half-sib families from each population (200, 180 and 180, respectively) were evaluated in completely randomized block experiments with three replications in Jataí (GO). Parameters estimates were obtained for ear yield (EY), grain yield (GY), plant height (PH), ear height (EH), ear length (EL) and ear diameter (ED). The population means for GY were 5.68 t/ha, 5.83 t/ha and 5.83 t/ha, which were around 70% of the hybrid check. The coefficients of heritability (family mean basis) varied from 0.36 to 0.70; 0.47 to 0.69; and 0.39 to 0.68 for the respective populations. Estimates of the additive genetic variance for grain yield (g/plant) were 316.1, 266.4 and 258.4; and the expected gain from selection were 11.8%, 10.1% and 9.3%, respectively.