Abstract
ABSTRACT Plant growth-promoting bacteria (PGPB) comprise part of plant microbiome of biotechnological interest due to their potential to decrease the use of agrochemicals in agriculture. Among the commonly found PGPB species, the Pseudomonas genus is known for high competitiveness and efficiency in expressing growth-promotion traits. To increase the contribution of diazotrophic Pseudomonas sp. to the plant nitrogen nutrition, the strain AZM-01 was chemically mutagenized with methyl methanesulfonate (MMS), following the selection for resistance to ethylenediamine (EDA). From the 13 EDA-resistant mutant strains selected, four showed increased the ammonium excretion, with the highest value reaching up to 284% increase as compared to the wild strain, and six strains were found to produce significantly more auxins than the wild strain. Two independent inoculation trials with the wild and EDA-resistant Pseudomonas were performed on maize, with the objective to study the influence of bacteria on seed germination and its potential to promote maize growth under N-limiting condition. In general, Pseudomonas inoculation modified the root architecture of germinating seeds, and increased biomass of maize plants grown under N-limiting conditions. Shoot dry weight of maize was increased by inoculation with several EDA-resistant mutants as compared to the strain AZM-01, with emphasis on the EDA-5 strain which supports biomass accumulation at equivalent amount of plants grown under full N supply. Significant correlations between in vitro and in vivo parameters were found although low coefficient values predominate. The strategy of random mutagenesis was found suitable to develop PGPB strains with higher potential to supply maize plants with nitrogen.
Highlights
Representative strains of the plant microbiome with positive activity on growth and productivity of plants have been studied as alternative biological input able to decrease, at least partially, the use of agrochemicals (Pieterse et al 2016)
According RDP analyses, AZM-01 is a member of the genus Pseudomonas and had greater similarity to sequences of P. mosselii and P. guariconensis
The ability to fix atmospheric nitrogen is not common in species of Pseudomonas genus, which comprises more than 140 species with a great metabolic diversity (Venieraki et al 2014)
Summary
Representative strains of the plant microbiome with positive activity on growth and productivity of plants (called PGPB, or plant growth-promoting bacteria) have been studied as alternative biological input able to decrease, at least partially, the use of agrochemicals (Pieterse et al 2016). The growth promotion through PGPB inoculation can occur by direct mechanisms, such as the nutrient provision, or by indirect mechanisms, such as the mitigation of stresses imposed to the host plant When the beneficial effects of PGPB inoculation imprints a better development of root system, the plants are thought to present a higher capacity to absorb water and nutrients from the soil. If the promotion of root growth comes together with the biological nitrogen fixation (BNF). Ability, such microorganisms become extremely important for development of biofertilizers (Cassán et al 2014). The identification of diazotrophic bacteria in association with non-leguminous plants is common, the ability of these microorganisms to contribute effectively to nitrogen nutrition of the plant is still controversial (Santi et al 2013; Cassán and Diaz-Zorita 2016). While the transfer of N fixed by symbiotic bacteria to the legume plants is a well-documented event, the mechanisms for
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