Root characterization of bean genotypes (Phaseolus vulgaris) under drought stress

The morpho-agronomic characterization of gene banks is a key step in enabling breeding programs to efficiently exploit genetic resources. Several studies have evaluated the root system traits of the common bean to develop genotypes better adapted to drought. We examined the root systems of 1000 common bean accessions, from the Agronomic Institute of Campinas gene bank to: count the number of whorls and basal roots, estimate the divergence between accessions and evaluate the 47 most divergent genotypes under drought. The average numbers of whorl and basal roots for the 1,000 accessions were 2.07 and 8.09, respectively. Seven different clusters were identified using the Mahalanobis genetic divergence analysis and the Tocher optimization method, from which the 47 most divergent genotypes were selected. Both genotype and water treatments, in the pre-blooming period, significantly affected root length, root surface area, root volume, number of pods, seeds per plant and grain yield. However, only water treatment significantly affected stomatal conductance, with water treatment x genotype interaction only having a significant effect on this characteristic. Water deficit reduced the average grain yield by 52%; the most promising genotypes under water deficit considering both root growth and grain yield were: RAI 76, 56 Retinto Santa Rosa, SER 28, Bayo, IAC Una, IAC Bico de Ouro and 12-D.