VARIABILITY OF TRAITS ASSOCIATED WITH PHOSPHORUS EFFICIENCY IN WILD AND CULTIVATED GENOTYPES OF COMMON BEAN

Genetic variation in plant growth under limited phosphorus (P) supply is necessary to obtain more productive cultivars on low P-available so ils. Two pot experiments were conducted to evaluate the variability of some traits associated with efficiency of P absorption and utilizatio n in wild and cultivated genotypes of common bean (Phaseolus vulgaris L.) under biological N-2 fixation. At two P levels (20 and 80 mg P kg( -1) soil, P-1 and P-2, respectively), 20 wild and 6 cultivated genotyp es were grown in Experiment 1, and 4 wild and 27 cultivated genotypes were grown in Experiment 2. Plants were harvested at flowering, but in Experiment 1 wild accessions that did not flower were harvested at th e beginning of leaf senescence. In Experiment 1, part of the genotypic variability of wild accessions was attributed to a less homogeneous o ntogenetic stage at harvest, whereas in Experiment 2 some variation in biomass production was due to distinct phenologies of cultivated geno types. Wild lines did not seem more tolerant to low P conditions, but the genotypic variation observed suggests these materials as a source of genetic diversity. Part of the variation in the root area and root efficiency ratio (total P content:root area) was compensatory, resulti ng in narrow genotypic differences in the total P content. The total P content and root efficiency ratio presented a wider amplitude of vari ation at P-2 than at P-1, and P uptake was more influenced by P supply than root production. Since the genotype x P level interaction was no t significant for shoot biomass and shoot P concentration in Experimen t 2, P utilization efficiency may be a useful selection criterion for cultivars between limited and adequate P supply. Within the sample of genetic diversity evaluated herein, there was large genotypic variabil ity for traits related to P efficiency among wild and cultivated genot ypes of common bean.