Parâmetros genéticos, estratégias de seleção e diversidade genética em genótipos de soja

Abstract

This thesis is divided into three chapters. In the first chapter, the objective was to study the combinatorial capacity of three parental lines through diallel crosses, using Griffing's method I (1956). Additive effects were more significant than non-additive effects for all traits evaluated. The TMG 801 parent contributed to an increase in most of traits evaluated, while the BRSGO 7560 parent contributed to a decrease in those traits. The most promising cross for shortening the growing season was BRSGO 7560 x TMG 801, while the cross UFUS 7415 x TMG 801 stood out for increasing grain yield. The combination that presented the most favorable values for cycle reduction and increased grain production was TMG 801 x BRSGO 7560. In the second chapter, the objective was to develop three soybean populations and estimate genetic parameters and breeding gains, with the aim of shortening the growing season and increasing grain yield, through the analysis of generations. Overall, for each cross, the means for agronomic and production traits in the F2, RC1, and RC2 generations were intermediate between those of their parents, and the values for the backcrosses were close to those of their respective parent. The heritability estimates (%) for the BRSGO 7560 x TMG 801 cross were: NDF (114.66%), NNTo (78.92%), NTV (102.21%), and PG (69.02%); in the combination TMG 7161 RR x UFUS 7415 they were: NNTo (107.2%), NTV (94.06%), and PG (104.91%); and in the combination TMG 801 x UFUS 7415 they were: NDF (94.84%), NDM (168.40%), NTV (71.05%), and PG (70.69%). The greatest gains per selection for cycle reduction (NDM) were obtained in the TMG 801 x UFUS 7415 cross (-21.09%), while, for increased grain production (g), the greatest gains were observed in the TMG 7161 RR x UFUS 7415 cross (97.88%). In the third chapter, the objective was to evaluate different strategies for selecting early-cycle, high-grain-yielding progenies using direct and indirect selection indices, as well as to conduct studies of genetic diversity using different clustering techniques, with the aim to identify divergent parents. Thirty progenies, F6-F7 and F7-F8, were evaluated in two growing seasons, in addition to four control lines (UFUS 7415, UFUS Tupi, UFUS 7910, and UFUS MLX). Genetic variability was detected among the evaluated progenies at a 1% or 5% probability level using the F-test for all evaluated traits. Direct and indirect selection provided the greatest genetic gains. Among the selection índices, the highest total genetic gain were obtained using the Mulamba and Mock indices. The NDM and NDF traits contributed most to determining genetic diversity. The Tocher, UPGMA, and canonical variable analysis methods clusteres the genotypes in a similar manner, forming five groups in the summer crop and four groups in the winter crop. The S128P3 and S128P4 progenies presented short cycle and high yield, desirable characteristics for use in crossbreeding with divergent genotypes.