Effect of the inoculation of plant growth promoting bacteria on maize plants to improve their growth under drought stress

Abstract

Global warming and bad agricultural practices are affecting the environment, with animpact on food productivity. Applying sustainable practices in agriculture is essential to maintain soil fertility and to promote crop productivity. It has been demonstrated that plant growth promoting bacteria (PGPB) have positive effects on plants because of their ability to influence plant’s growth through direct and indirect effects, such as production of phytohormones, increase of nutrient availability and/or synthesis of biocontrol agents. From Escola Superior de Biotecnologia collection of PGPB, thirteen strains were screened in vitro for abilities such as osmotic tolerance and indole acetic acid production under different osmotic potentials. Two bacterial strains were selected, Pseudomonas fluorescens (S3X) and Ralstonia eutropha (1C2) for a greenhouse assay using maize (Zea mays) as target plant to assess their effect on plant productivity under water stress. Different inoculation treatments were applied (control, commercial inoculum, S3X, 1C2 and co-inoculation of both strains) as well as different inocula size (V1 and V2, 3.3x103and 2.5x106cell. g-1dry weight, respectively). Maize plants were subjected to different water regimes (80, 60 and 40% of water holding capacity (WHC)). The water regime at 40% of WHC affected to higher extent plant growth, such as elongation and biomass, as well as plant nutrient uptake and activity of soil enzymes. Application of the commercial inoculum proved to be the less effective treatment in enhancing plant growth under the water stress deficit.The highest improvement on plant growth was observed with the co-inoculation of strains S3X and 1C2 at 80 and 60% of WHC and no differences were observed between the two inocula size applied. The co-inoculation improved shoot biomass by 20 and 28% in V1 and by 16 and 47% in V2 at 80 and 60% of WHC, respectively. The consortia at 60% caused 11% increase in root biomass in V2. Nitrogen and phosphorous accumulation in shoot and root was also improved by the addition of both strains into the rhizosphere at 80 and 60%. Nutrient use efficiency was also calculated and the inoculation of both strains enhanced this parameter. Overall, the highest enhancement of plant performance occurred when the mixture of P. fluorescens S3X and R.eutropha 1C2 was used, with similar effects with the two inocula size. Combinations of PGPBs may prove to be of significant advantage for the design of bioinoculants for agriculture.

Date of Award	4 May 2018
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Paula M. L. Castro (Supervisor) & Sofia Pereira (Co-Supervisor)