Harnessing PGPRs from Asparagus officinalis to Increase the Growth and Yield of Zea mays L

Abstract

Microbial biotechnology employs techniques that rely on the natural interactions that occur in ecosystems. Bacteria, including rhizobacteria, play an important role in plant growth, providing crops with an alternative that can mitigate the negative effects of abiotic stress, such as those caused by saline environments, and increase the excessive use of chemical fertilizers. The present study examined the promoting potential of bacterial isolates obtained from the rhizospheric soil and roots of the Asparagus officinalis cultivar UF-157 F2 in Viru, la Libertad, Peru. This region has high soil salinity levels. Seventeen strains were isolated, four of which are major potential plant growth-promoting traits, and were characterized based on their morphological and molecular characteristics. These salt-tolerant bacteria were screened for phosphate solubilization, indole acetic acid, deaminase activity, and molecular characterization by 16S rDNA sequencing. Fifteen samples were from saline soils of A. officinalis plants in the northern coastal desert of San Jose, Lambayeque, Peru. The bacterial isolates were screened in a range of salt tolerances from 3 to 6%. Isolates 05, 08, 09, and 11 presented maximum salt tolerance, ammonium quantification, phosphate solubilization, and IAA production. The four isolates were identified by sequencing the amplified 16S rRNA gene and were found to be Enterobacter sp. 05 (OQ885483), Enterobacter sp. 08 (OQ885484), Pseudomonas sp. 09 (OR398704) and Klebsiella sp. 11 (OR398705). These microorganisms promoted the germination of Zea mays L. plants, increased the germination rates in the treatments with chemical fertilizers at 100% and 50%, and the PGPRs increased the height and length of the roots 40 days after planting. The beneficial effects of salt-tolerant PGPR isolates isolated from saline environments may lead to new species that can be used to overcome the detrimental effects of salt stress on plants. The biochemical response and inoculation of the three isolates prove the potential of these strains as sources of products to develop new compounds, confirming their potential as biofertilizers for saline environments.

Keywords: Biofertilizer; Microbial organism; Plant growth promotion; Saline environments; Siderophore; Solubilization ammonium; Solubilization phosphate.

Fig. 1

Descriptive summary of the methodology used in this study

Fig. 2

Phylogenetic tree based on the 16S ARNr nucleotide sequences RB-AOV-05, RB-AOV-08 and RB-AOV-09 (a) and RB-AOV-11 (b) inferred via the neighbor‒joining method. Evolutionary distances were computed via the TN93 + G evolutionary model. The 16S rRNA sequence of Bacillus cereus ATCC 14579 ^T (NR_074540) was used as an outgroup. The analysis was performed in MEGA 11 software and visualization’s ITOL

Fig. 3

Evaluation of the growth-promoting effects of individual inoculum treatments of rhizobacterial isolates from A. officinalis L. on the height of Z. mays. Measurements were made at 10 days (a), 20 days (b), 30 days (c), and 40 days (d), and the root length (cm) was 40 days (e)

Fig. 4

Plant height (a–b), Root Length (c), Root volume (d), and Dry biomass (e). Data represent responses of Z. mays seedlings under the following treatments: Control (non-inoculated), RB-AOV-05 (Enterobacter sp. 05, OQ885483), strain RB-AOV-08 (Enterobacter sp. 08, OQ885484), strain RB-AOV-09 (Pseudomonas sp. 09, OR398704), strain RB-AOV-11 (Klebsiella sp. 11, OR398705), NPK 50% and NPK 100% fertilizers