Use of Rhizobium leguminosarum as a potential biofertilizer for Lactuca sativa and Daucus carota crops

Microbial biofertilizers are becoming an effective tool for sustainable agriculture by means of the reduction of the use of chemical fertilizers. However, the knowledge of each specific plant–microorganism interaction is essential for a correct application. In this study, we analyzed the in vitro plant-growth-promotion mechanisms of a Rhizobium leguminosarum strain named PEPV16 isolated from Phaseolus vulgaris nodules. This strain was able to produce siderophores and indole acetic acid and to solubilize phosphate. Confocal microscopy showed that this strain was able to colonize the roots of two horticultural crops, Lactuca sativa L. (lettuce) and Daucus carota L. (carrot). Strain PEPV16 was also able to promote the plant growth of both plant species increasing the dry matter of shoots and roots of lettuce and carrots, respectively, as well as to increase the uptake of N and P in the edible parts of both plant species. These data confirmed the suitability of Rhizobium as biofertilizer for nonlegumes.