Co-inoculation with tropical strains of Azospirillum and Bacillus is more efficient than single inoculation for improving plant growth and nutrient uptake in maize.

Ubiraci Gomes de Paula Lana,Sylvia Morais de Sousa,Antonio Marcos Coelho,Eliane Aparecida Gomes,Christiane Abreu de Oliveira-Paiva,Ivanildo Evódio Marriel,Vitória Palhares Ribeiro

doi:10.1007/s00203-022-02759-3

Abstract

Usage of Bacillus and Azospirillum as new eco-friendly microbial consortium inoculants is a promising strategy to increase plant growth and crop yield by improving nutrient availability in agricultural sustainable systems. In this study, we designed a multispecies inoculum containing B. thuringiensis (strain B116), B. subtillis (strain B2084) and Azospirillum sp. (strains A1626 and A2142) to investigate their individual or co-inoculated ability to solubilize and mineralize phosphate, produce indole acetic acid (IAA) and their effect on maize growth promotion in hydroponics and in a non-sterile soil. All strains showed significant IAA production, P mineralization (sodium phytate) and Ca-P, Fe-P (tricalcium phosphate and iron phosphate, respectively) solubilization. In hydroponics, co-inoculation with A1626 x A2142, B2084 x A2142, B2084 x A1626 resulted in higher root total length, total surface area, and surface area of roots with diameter between 0 and 1mm than other treatments with single inoculant, except B2084. In a greenhouse experiment, maize inoculated with the two Azospirillum strains exhibited enhanced shoot dry weight, shoot P and K content, root dry weight, root N and K content and acid and alkaline phosphatase activities than the other treatments. There was a significant correlation between soil P and P shoot, alkaline phosphatase and P shoot and between acid phosphatase and root dry weight. It may be concluded that co-inoculations are most effective than single inoculants strains, mainly between two selected Azospirillum strains. Thus, they could have synergistic interactions during maize growth, and be useful in the formulation of new inoculants to improve the tropical cropping systems sustainability.

Highlights

Synthetic fertilizers are among the basic principles of plant nutrition management and have been used for decades worldwide to increase the crop production
Two Azospirilum (A1626 and A2142) and two Bacillus strains (B116 and B2084) isolated from tropical maize and sorghum were selected based on plant growth promoting traits for a co-inoculation assay
The choice of the strains was based in our research group’s previous studies, considering that the individual inoculation of Bacillus strains B116 and B2084 significantly increased the dry weight of maize seedlings in hydroponics and maize yield in the field (36 and 12%, respectively) (Sousa et al 2021)

Summary

Introduction

Synthetic fertilizers are among the basic principles of plant nutrition management and have been used for decades worldwide to increase the crop production. Their systematic and uncontrolled use has undesirable effects on soil and water besides promoting CO2 emissions. Intensive investigations on microorganisms for better adaptation under biotic and abiotic stresses and their plant growth characteristics with fertilizer effects have been undertaken to reduce the use of synthetic nutrients. In this context, microbial inoculant or biofertilizers have received increasing attention, gaining prominence and market scale in agriculture. Research is needed to generate knowledge aiming the production of new formulations for commercial inoculants with combined bacteria (Cassán et al 2015)

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