Abstract

Common bean (Phaseolus vulgaris L.) production is severely limited by phosphorus (P) deficiency in tropical and subtropical regions. Plants are known to exudate organic acids in order to survive in low nutrient environment. However, little is documented on the effect of inoculation on organic acids exudation by plants as a strategy to adapt to low P stress. In this study, the organic acids exuded by two bean genotypes (known to have contrasting symbiotic nitrogen fixation capacities) inoculated with Rhizobium etli and subjected to P deficiency were compared. The results showed that, under P deficiency, the P efficient genotype (BAT477) secretes higher amounts of organic acids serving as nutrient for Rhizobacteria or involved in P solubilisation. Furthermore, inoculation with R. etli under P deficiency strongly enhanced the exudation of oxalate and citrate by the P-efficient genotype. These effects of P-level and inoculation on root exudation were much less observed for the P-inefficient genotype (DOR364). This study indicated the difference in organic acid exudation between the two bean genotypes, especially in combination withRhizobium inoculation which may contribute to the contrast in performance under P deficiency.

Key words: Phaseolus vulgaris, Rhizobia, root exudation, genotypic performance, phosphorus efficiency