Genetic structure of root distribution in genotype crosses of Mesoamerican common bean
Knowledge of the genetic structure of a trait shapes the entire strategy of a breeding program. In this study, the purpose was to determine the additive and non-additive effects that affect the genetic control of common bean roots. A field experiment, with 75 treatments in a partially balanced incomplete block design, was carried out in the 2018/19 growing season. The treatments consisted of backcross progenies (L1 - P1 x F2, L2 - P2 x F2 and L3 - F1 x F2) resulting from a Triple Test Cross mating design, with the Mesoamerican parents P1-BAF50 (accession of the active germplasm bank) and P2-IPR Uirapuru (commercial cultivar). The trait root distribution was assessed based on the soil excavation method, in situ. To this end, trenches were opened under each plant (two plants per replication, in each treatment) and a grid was inserted in the open profile. Pictures were taken of the grid in the trench, based on which the root distribution (percentage) could be quantitatively assessed. To compare root and shoot biomass, the numbers of pods and grains were counted at harvest. The treatment factor was partitioned into genetic effects (additive, dominant and epistatic) by the establishment of predictive functions. The additive genetic effect was the most influential in the genetic trait control. On the other hand, additive × additive epistasis caused no significant deviation from the genotypic value of plants, neither for roots (P = 0.7941) nor grain yield components. Among the evaluated progenies, effects of dominance deviation and additive x dominant and dominant x dominant epistasis were observed least often, and the expression in the trait root distribution had opposite directions (positive and negative deviations), whereas for the yield components, the non-additive gene effects had one and the same pattern. In crosses between Mesoamerican genotypes, the genetic value of roots is based on the average genetic effects alone, while the genetic interactions are negligible.