Dose-dependent effects of Pseudomonas trivialis rhizobacteria and synergistic growth stimulation effect with earthworms on the common radish

Abstract

The complex interactions between soil microorganisms with earthworms and plants have the capability to change the plant growth and development. Pseudomonas trivialis is a broad-spectrum plant growth promoting rhizobacteria (PGPR) due to its indole-3-acetic acid (IAA) production, siderophore production, 1-aminocyclopropane-1- carboxylate (ACC) deaminase activity, and phosphate solubilization attributes. A study has been conducted to investigate the effect of P. trivialis concentration in the presence or absence of earthworms (Allolobophora caliginosa) on radish (Raphanus sativus) plants growth and development. The experiment tests the impact of three inoculation concentrations in the presence or absence of earthworms on radish growth and development. We show earthworms enhance the positive effects of P. trivialis (KF695047.1) on plant growth. P. trivialis displayed a stimulatory effect on plant growth with increasing the P. trivialis inoculum size. In the presence of P. trivialis (KF695047.1), earthworms induced a significant increase in the aboveground biomass and total biomass, but there was no effect belowground. The positive effect of earthworms increased with increasing the inoculum concentration of P. trivialis. Inoculating radish plants with a low concentration of P. trivialis led to a decrease in the root length in comparison with inoculated plants and treated with earthworms but no effect on the above-ground height. Therefore, this P. trivialis strain is a PGPR for radish at higher abundances but has a negative impact on IAA levels at lower abundances. There are synergistic effects of earthworms and P. trivialis at higher bacteria abundance when in combination, to enhance the stimulatory effect on the growth and development of R. sativus. In the presence of the earthworms, 108 CFU/mL is the threshold dose of P. trivialis at and above which a positive effect on R. sativus growth occurs.