Introduction:

The rising demand for food worldwide required the development of sustainable production alternatives. Plant growth-promoting rhizobacteria (PGPR) is a group of rhizospheric bacteria with the ability to promote good plant health and growth, as well as to restore soil fertility. The objective of this study was to evaluate the growth promotion of wheat (Triticum turgidum L. subsp. durum) plants, by co-inoculation of native Bacillus strains isolated from the Yaqui Valley, Mexico, for their potential use as a microbial inoculant.

Methods:

Three bacterial strains obtained from the Collection of Edaphic Microorganisms and Native Endophytes (COLMENA), isolated from wheat commercial fields in the Yaqui Valley, were studied. First, the molecular identification of strains was performed by sequencing the 16S rRNA gene, by using the Sanger platform. In addition, bacterial strains were metabolically characterized by functional activities associated with the promotion of plant growth (production of indoles, solubilization of insoluble phosphorus, and production of siderophores). Finally, the impact of the inoculation of these individual strains, and in consortia was determined in durum wheat (Triticum turgidum L subsp. durum), simulating the edaphoclimatic conditions of the Yaqui Valley. The morphometric variables measured were aerial and root length, aerial and root dry weight, and biovolume index.

Results:

The strains TRQ8, TRQ65, and TE3T were taxonomically affiliated with B. megaterium, B. paralicheniformis, and B. cabrialesii, respectively. This classification was supported by its macro-microscopic characteristics such as its bacillary form and Gram-positive staining, which are characteristic of this bacterial genus. Those strains had the ability to produce indoles, strain B. paralicheniformis TRQ65 had the highest production with 39.29 µg/mL. All studied strains showed the ability to solubilize insoluble phosphorus, solubilization index ranged from 1.37 to 1.43. Finally, only B. megaterium TRQ8 showed a siderophore production index of 8.17. Inoculation of the B. megaterium TRQ8 + B. paralicheniformis TRQ65 consortium showed the greatest increases in the 5 variables measured, significant difference (p <0.05) vs. the un-inoculated treatment, aerial and radical length showed an increase of 6 and 10%, respectively, while aerial dry biomass increased 60%, and root dry weight increase 82%. This consortium showed an 18% higher biovolume index than the un-inoculated treatment.

Discussion or Conclusion:

The strains studied showed growth promotion traits in vitro and in vivo. However, co-inoculation of these strains increased their ability to promote growth in wheat plants. Therefore, the mechanisms associated with this effect, as well as their ecological functions and interaction with the biotic and abiotic factors of agro-systems must be further studied for extensive use as a microbial inoculant.

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