Abstract
The sustainable development of agriculture can be stimulated by the great market availability of bio-inputs, including phosphate-solubilizing microbial strains. However, these strains are currently selected using imprecise and questionable solubilization methodologies in solid or liquid media. We hypothesized that the hydroponic system could be a more efficient methodology for selecting phosphate-solubilizing strains as plant growth promoters. This methodology was tested using the plant Glycine max as a model. The growth-promoting potential of the strains was compared with that of the Biomaphos® commercial microbial mixture. The obtained calcium phosphate (CaHPO4) solubilization results using the hydroponic system were inconsistent with those observed in solid and liquid media. However, the tests in liquid medium demonstrated poor performances of Codinaeopsis sp. (328EF) and Hamigera insecticola (33EF) in reducing pH and solubilizing CaHPO4, which corroborates with the effects of biotic stress observed in G. max plants inoculated with these strains. Nevertheless, the hydroponic system allowed the characterization of Paenibacillus alvei (PA12), which is also efficient in solubilization in a liquid medium. The bacterium Lysinibacillus fusiformis (PA26) was the most effective in CaHPO4 solubilization owing to the higher phosphorus (P) absorption, growth promotion, and physiological performance observed in plants inoculated with this bacterium. The hydroponic method proved to be superior in selecting solubilizing strains, allowing the assessment of multiple patterns, such as nutritional level, growth, photosynthetic performance, and anatomical variation in plants, and even the detection of biotic stress responses to inoculation, obtaining strains with higher growth promotion potential than Biomaphos®. This study proposed a new approach to confirm the solubilizing activity of microorganisms previously selected in vitro and potentially intended for the bio-input market that are useful in P availability for important crops, such as soybeans.
Highlights
The world population is estimated to reach ∼9.735 billion people by 2050 (United Nations, 2019)
Electron microscopy analyses showed the formation of protein crystals in B. thuringiensis (SC10) colonies and bacterial spores in Lysinibacillus fusiformis (PA26) root colonies (Figures 1A–D)
In vivo analysis using the hydroponic system showed that P. alvei (PA12) and L. fusiformis (PA26), strains not shown to solubilize CaHPO4 in any of the in vitro tests were more efficient at promoting growth and providing free P to the plant, which was demonstrated by the higher total P content in G. max tissues
Summary
The world population is estimated to reach ∼9.735 billion people by 2050 (United Nations, 2019). Current agricultural practices use fertilizers to add P to the soil, the use of phosphate fertilizers is expensive and unsustainable (Situmorang et al, 2015). These fertilizers are precipitated with aluminum (Al), iron (Fe), and calcium (Ca), forming low-solubility complexes that are not used by plants (Penn and Camberato, 2019). In this context, the dissemination of more economical and ecologically appropriate technologies to improve P availability in soil has become urgent
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