Adaptability and stability of soybean genotypes evaluated using three backcrosses generations: BC4, BC5 and BC6

An adaptability and stability study by the traditional and Lin and Binns methods (1988) was carried out to assess the genotypic stem canker resistance of three backcross generations (BC4, BC5 and BC6) in three environments. The study consisted of genotype trials carried out in the towns of Florestal, Capinopolis and Rio Paranaiba, in Minas Gerais state during the 1997/98 growing season. The experiments assessed the recurrent (FT-Cristalina) and donor (Doko BC) parents and 13 derived lines, five from the BC6 generation (UFV95370A2156, UFV95-370A2142, UFV95-370A2133, UFV95-370A2121 and UFV95-370A2115); four from BC5 (UFV95-370A2022, UFV95-370A2021, UFV95-370A2020 and UFV95-370A2019); and four from BC4 (UFV95-370A667, UFV95-370A666, UFV95-370A65 and UFV95-370A661). The Lin and Binns (1988) method was more efficient in discriminating the genotypes. The UFV95-370A2021 line belonging to the BC5 generation showed the best genotypic performance among the studied genotypes, and also showed the second best yield mean in the experiments. The UFV95-370A665 line, belonging to the BC4 generation, had the poorest genotypic behavior and also presented the lowest mean yield in the experiments. As the backcross generation advanced, there was a simultaneous improvement in the genotypic performance of the individuals in these generations, most probably because of the greater recuperation of the recurrent parent in each generation. This suggests the need for at least five to six backcrosses to obtain genotypes as adapted as the recurrent parent.