Implications of additive × additive epistasis for common bean breeding

The presence of epistasis in complex traits can be significant and affect the selection of segregating populations undesirably. The purpose of this study was to determine the epistatic genetic components that influence root and shoot traits of common bean and identify their effect on the performance of segregating populations. The field experiment consisted of 49 treatments (backcross progenies, parents and segregating populations in the F₂ and F₃ generations). The cross P₁-BAF53 (Andean) × P₂-IPR 88 Uirapuru (Mesoamerican) as reference. Six traits were taken into consideration: root distribution (%), first pod length (cm), number of grains (plot), plant height (cm), reproductive cycle (days) and number of basal branches (plot). For root distribution, first pod length and number of grains, the additive and additive × additive components were significant. On the contrary, for plant height, reproductive cycle and number of basal branches, no interaction component was observed. These results can be explained by the magnitude of variance determined for these traits. The additive × additive epistasis had a negative influence on the mean performance of segregating progenies. Contrariwise, transgressive segregation effects on plant height were observed as a function of genetic dominance deviation. Thus, additive × additive epistasis can hamper the success of a breeding program, for being associated with low-variability traits. This fact may be related with the number of crosses and/or the choice of genetically more distant parents for the program, and possibly with the presence of linked genes.