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The soybean crop has a substantial importance for Brazil’s agribusiness and economy. Besides, breeding programs have contributed to the development of the crop in the country allowing grain yield increase and, at the same time, intensifying the production of new cultivars that show both yield predictability and wide adaptation. This study was aimed at evaluating the agronomic performance, adaptability, and stability of soybean genotypes in the states of Maranhao, Piaui, Tocantins, and Bahia. The genotypes were evaluated to the extent of grain yield in the municipalities of Chapadinha (MA), Balsas (MA), Bom Jesus (PI), Porto Nacional (TO), and Formoso do Rio Preto (BA) under complete randomized block design, with three repetitions. Data were submitted to joint analyses and to studies of adaptability and stability by Wricke (1965), Eberhart and Russel (1966), and Annicchiarico (1992) methods. The genotypes UFUS 504, UFU 506, UFU 508, UFU 512, UFU 514, UFU 516, UFU 518, UFU 519, UFU 520, UFU 521, UFU 523, and UFUS Imperial showed wide stability and adaptability, whereas UFU 503, UFU 505, and UFUS Impact were adapted to favorable conditions.

Defining selection criteria is important to obtain promising genotypes in a breeding program. The objective of this study was to estimate genetic parameters for agronomic traits and to perform soybean line selection using selection indices. The experiment was conducted at an experimental area located at Capim Branco farm, belonging to the Federal University of Uberlândia. A total of 37 soybean genotypes were evaluated in randomized complete block design with three replicates, in which twelve agronomic traits were evaluated. Analysis of variance, the Scott-Knott test at the 1 and 5% level of probability, and selection index analyses were performed. There was genetic variability for all agronomic traits, with medium to high levels of genotype determination coefficient. Twelve lines with a total cycle up to 110 days were observed and grouped with the cultivars MSOY 6101 and UFUS 7910. Three lines, UFUS FG 03, UFUS FG 20, and UFUS FG 31, were highlighted regarding grain yield with higher values than the national average of 3072 kg/ha. The direct selection enabled the highest trait individual gains. The Williams (1962) index and the Smith (1936) and Hazel (1943) index presented the highest selection gain for the grain yield character. The genotype-ideotype distance index and the index of the sum of ranks of Mulamba and Mock (1978) presented higher values of total selection gain. The lines UFUS FG 12, UFUS FG 14, UFUS FG 18, UFUS FG 25, and UFUS FG 31 were distinguished as superior genotypes by direct selection methods and selection indexes.

Precocious soybean cultivars enable crop rotation and low pressure to the biotic and abiotic factors. This study aimed to determinate the inheritance of characters related to precocity and agronomic characters in soybean segregating population, coming from contrasting genitors to cycle. The experiment was conducted at a greenhouse located at Capim Branco farm, belonging to Federal University of Uberlândia. The MG/BR 46 Conquista and UFUS 6901 cultivars were used to bi-parental crossing and acquirement of F1 and F2 populations. The individuals of the genitors, F1 and F2 populations were evaluated to eight characters and the phenotypic, genetic and environmental variances, broad-sense heritability, average degree of dominance and gene number were determined. The average for number of days for flowering and number of days to maturity in the F1 generation was 40.26 and 103.52 days and in the F2 generation was 37.85 and 105.88 days, respectively, which fits into the classification of semi-precocious. The heritability varied from 2.36% for number of grains per pod – controlled by 160 genes, to 85.39% for number of days for maturing – controlled by two genes. On the F2 population, the existence of transgressed segregates was found, except for number of days to maturity, number of nodes and intersection height of the first pod. It was concluded that the genetic variance and heritability of the agronomic characters of the F2 population, allows the acquirement of selection of superior individuals in terms of precocity, height, number of nodes and compounds of productivity, being promising genotypes in the soybean breeding program

The soybean cyst nematode (SCN) is a major cause of soybean yield reduction. The objective of this study was to evaluate the efficiency of marker-assisted selection to identify genotypes resistant to SCN race 3 infection, using Sat_168 and Sat-141 resistance quantitative trait loci. The experiment was carried out under greenhouse conditions, using soybean populations originated from crosses between susceptible and resistant parent stock: CD-201 (susceptible) and Foster IAC (resistant), Conquista (susceptible) and S83-30 (resistant), La-Suprema (susceptible) and S57-11 (resistant), and Parecis (susceptible) and S65-50 (resistant). Plants were inoculated with SCN and evaluated according to the female index (FI), those with FI < 10% were classified as resistant to nematode infection. Plants were genotyped for SCN resistance using microsatellite markers Sat-141 and Sat_168. Marker selection efficiency was analyzed by a contingency table, taking into account genotypic versus phenotypic evaluations for each line. These markers were shown to be useful tool for selection of SCN race 3.