Pre-sowing recurrent inoculation with Pseudomonas fluorescens promotes maize growth

Despite the rapid development of microbial inoculants use, their effectiveness still lacks robustness, partly due to our limited understanding of the factors influencing their establishment in soil. Recurrent inoculation can temporarily increase their abundance, but the effect of this inoculation strategy on plant growth and on the resident microbial community is still poorly studied. Here, we investigated maize growth and soil bacterial community responses under recurrent inoculation of the plant-beneficial bacterium Pseudomonas fluorescens B177. We further assessed how the effect of recurrent inoculation was modulated by the inoculant dose, the application timing and the soil type. Recurrent inoculation at high dose transiently increased the abundance of P. fluorescens B177 and resulted in larger shifts in the resident bacterial community compared to a single inoculation event. Moreover, recurrent inoculation prior to sowing had the strongest effect on maize growth, with increased shoot dry weight by 47.4%, likely due to an indirect effect of the inoculant through early changes in the resident community. Altogether these findings highlight the significance of recurrent pre-sowing inoculations as an alternative strategy for promoting plant growth.