Multiple stress response and belowground competition in multilines of common bean (Phaseolus vulgaris L.)

Multilines (genetic mixtures) composed of genotypes of contrasting root architecture were hypothesized to show improved growth and productivity in comparison with genetic monocultures in conditions of multiple edaphic stresses. To test this hypothesis, three multilines of common bean (Phaseolus vulgaris L.), each composed of two recombinant inbred lines having contrasting root architecture in previous studies, were evaluated at seven sites in Honduras with varying soil phosphorus and moisture availability. Molecular markers were used to quantify the presence of each genotype in both root and seed-yield samples. Root growth in competition was dependent on both soil treatment and genotype. In one of the multilines, the root zone was dominated by one genotype, especially in the high-P treatment. In contrast, the root zone of another multiline had equal representation from both genotypes. These results show that response to belowground competition can differ among genotypes of the same species. No tradeoff between root growth and plant performance (yield or shoot biomass) was observed. Contrary to expected results, profiles of root distribution did not differ significantly in the environments tested in this study. As a result, differences in uptake of resources (phosphorus and water) in divergent soil domains and yield advantage of multilines were observed in only a small number of cases. Multilines did not create any yield penalty. Future work with genotypes that are more contrasting in root architecture is necessary to assess this strategy for use by resource-poor farmers.