Isolation, characterization and effect of plant-growth-promoting rhizobacteria on pine seedlings (Pinus pseudostrobus Lindl.)

In this study, 10 bacterial strains were isolated from the rhizosphere of coniferous trees on Mount Tlaloc in Mexico. The strains were characterized by their capacity to produce auxins, solubilize phosphates and stimulate mycelial growth of the ectomycorrhizal fungus Suillus sp. All isolates were identified at the molecular level. Moreover, an experiment was established to evaluate the response of Pinus pseudostrobus seedlings to inoculation with the rhizobacteria strains. The isolated strains belonged to the species Cupriavidus basilensis, Rhodococcus qingshengii, R. erythropolis, Pseudomonas spp., P. gessardii, Stenotrophomonas rhizophila and Cohnella sp. All of the strains produced auxins; the best producer was R. erythropolis CPT9 (76.4 mu gmL(-1)). P. gessardii CPT6 solubilized phosphate at a significant level (443 mu gmL(-1)). The strain S. rhizophila CPT8 significantly increased the radial growth of the ectomycorrhizal fungus Suillus sp. by 18.8%. Five strains increased the dry mass of the shoots; R. qingshengii CPT4 and R. erythropolis CPT9 increased growth the most, by more than 20%. Inoculation with plant-growth-promoting rhizobacteria can be a very useful practice in a forest nursery to produce healthy, vigorous plants.