Abstract
Mesorhizobium contains species widely known as nitrogen-fixing bacteria with legumes, but their ability to promote the growth of non-legumes has been poorly studied. Here, we analyzed the production of indole acetic acid (IAA), siderophores and the solubilization of phosphate and potassium in a collection of 24 strains belonging to different Mesorhizobium species. All these strains produce IAA, 46% solubilized potassium, 33% solubilize phosphate and 17% produce siderophores. The highest production of IAA was found in the strains Mesorhizobium ciceri CCANP14 and Mesorhizobium tamadayense CCANP122, which were also able to solubilize potassium. Moreover, the strain CCANP14 showed the maximum phosphate solubilization index, and the strain CCANP122 was able to produce siderophores. These two strains were able to produce cellulases and cellulose and to originate biofilms in abiotic surfaces and tomato root surface. Tomato seedlings responded positively to the inoculation with these two strains, showing significantly higher plant growth traits than uninoculated seedlings. This is the first report about the potential of different Mesorhizobium species to promote the growth of a vegetable. Considering their use as safe for humans, animals and plants, they are an environmentally friendly alternative to chemical fertilizers for non-legume crops in the framework of sustainable agriculture.
Highlights
The plant growth promoting rhizobacteria (PGPR), named plant probiotic bacteria, are promising biofertilizers for sustainable and environmentally friendly agriculture since they allow the total or partial substitution of chemical fertilizers added to the crops alone or together with organic amendments [1,2,3]
We analyzed the atpD gene of 24 Mesorhizobium strains isolated in the Canary Islands from nodules of C. canariense, because this gene, which was not sequenced in our previous study [61], is commonly used for the differentiation of Mesorhizobium species
Some of them can be confirmed as belonging to already described species, namely, CCANP14, CCANP48, CCANP79 and CCANP82 to M. ciceri, CCANP3, CCANP99 and CCANP113 to M. opportunistum, CCANP1 to M. australicum and CCANP122 to M. tamadayense (Figure 1 and Table 1)
Summary
The plant growth promoting rhizobacteria (PGPR), named plant probiotic bacteria, are promising biofertilizers for sustainable and environmentally friendly agriculture since they allow the total or partial substitution of chemical fertilizers added to the crops alone or together with organic amendments [1,2,3]. These bacteria take part in the plant microbiome and can live in the rhizosphere or endosphere of plants [4,5]. Within the indirect mechanisms are included the synthesis of antibiotics, lytic enzymes or siderophores involved in the control of plant pathogens [7,9]
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