Tropical maize production represents 49% of the global maize harvested area. In terms of productivity, the annual increase rate in tropical regions is twice as higher as the increase rate in temperate regions. The increase in maize grain yield was expressive in the last 41 years in Brazil. Such achievement was possible due to the joint efforts of many areas of science, especially, plant breeding. Although maize breeding success, many are the challenges faced by the maize breeders to develop high-yielding maize hybrids. Tropical conditions provide more intense challenges in terms of pests and diseases pressures, and above all, water deficit conditions. In addition, the constant increase of breeding programs costs requires the development and application of new techniques to improve the genetic gain per time unit, increasing the maize breeding programs’ efficiency. This review discusses the main challenges faced by maize breeding programs under tropical conditions, highlighting topics related to the development of maize hybrids for first and second growing seasons; breeding for biotic and abiotic stresses conditions; specialty maize breeding; use of transgenic in maize; and genomic tools to maximize the efficiency of maize breeding programs under tropical conditions.

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The purpose of this study was to evaluate the effect of different combinations of products applied through seed treatment, associated with the inoculation, in the development of soybean plants. The experiment was conducted in a greenhouse at Federal University of Lavras (UFLA). The experimental design was a randomized complete block, with four repetitions in a factorial 4 × 11, being four soybean cultivars and 11 combinations of products associated with the inoculation in the treatment of seeds. At the stage (R 1 ) it was evaluated: plant height, leaf area, foliar chlorophyll content, number of trifoliate leaves, dry shoot mass, dry root mass, root length, root volume, nodules total number, viable nodules total number, nodules dry mass and foliar nitrogen content. The combination of products in the treatment of seeds, do not present phytotoxic effects in the characters related to the development, except for dry matter of aerial part and root volume. The combination of products in treatment of seeds influences negatively the nodulation, especially in the treatments with presence of nematicide. The inoculation performed in isolation or combined with fungicide and insecticide (I+FI) maintains nodule levels.

The choice of germplasm is one of the most important phases of a genetic improvement program to the fact that it is the initial development stage of superior hybrids. Hence, the objectives of this study were to obtain the estimates of m+a and d, and inbreeding depression for grain yield and plant height traits, for cultivars lacking this information, and thus to predict the potential of maize hybrids for the extraction of lines. The F1 and F2 generations of 12 maize hybrids were tested at two sites, during the crop years of 2017-18 and 2018-19, accounting for four environments. Both the generations were evaluated in contiguous experiments in randomized blocks design with three and two repetitions during the years 2017-18 and 2018-19, respectively. The data on plant height and grain yield were collected, per plot, from both the generations, utilizing which, the m+a and d mean components were estimated. The effects of dominance had greater importance for the character grain yield. The most promising hybrids for extraction of lines were AG1051, AG8025, BG7046, DKB455, and OMEGA due to their greater estimates of m+a. The hybrids AG8025 and BG7046 were associated with high values of m+a and grain yield. For the plant height trait, there was a greater contribution of additive effects. Therefore, greater inbreeding depression was observed for the grain yield trait when compared to the height of the plant.

The objective of this work was to estimate genotypic and phenotypic parameters associated with early maturity, and to select soybean (Glycine max) progenies that are high yielding and early maturing. F3:4 and F3:5 progenies were evaluated during the 2016/2017 and 2017/2018 crop years in five environments. Data on days to full maturity, days to flowering, and grain yield were collected and analyzed using the mixed model approach. Genotypic and phenotypic parameters, expected and achieved selection gains, and correlated responses were estimated. The components genetic variation and genotype x environment interaction were significant. Heritability fluctuated from 50.14%, for grain yield, to 90.37%, for full maturity. The achieved genetic gain for full maturity ranged from −0.17 to −2.57%. A positive correlation was observed among the three evaluated traits. The selection of 5.0% of the earliest-maturing soybean progenies would reduce mean grain yield by about 5.02%, but also reduce time to reach full maturity from 125 to 119 days, in detriment of 210.5 kg ha−1 potential yield. Five progenies reached full maturity up to 120 days. Progeny 51 overperformed the more productive parent (NK 7074 RR), with a grain yield of 4,975 kg ha−1 and 128 days to full maturity.