Sustainable soil management systems, such as organic fertilization and reduced tillage, are increasingly adopted by farmers to protect soils and to decrease the application of mineral fertilizers. However, it is still not well known how these practices influence the presence and abundance of key groups of soil microorganisms, such as fluorescent pseudomonads. This group of bacteria can improve plant health by protecting roots against the attack of soil borne fungal pathogens through the production of antifungal metabolites and by activating plant defence mechanisms.
In this study, the abundance of fluorescent pseudomonads producing the antifungals 2,4-diacetylphloroglucinol (DAPG), phenazines and pyrrolnitrin was measured in soil and rhizosphere of wheat with a qPCR based approach in two long term trials that compare conventional to organic cultivation, reduced tillage to conventional tillage and monoculture to crop rotation.
DAPG and phenazine producers were significantly less abundant in unfertilized plots compared to plots under conventional or organic cultivation. Phenazine and pyrrolnitrin producers were less abundant in organic plots compared to conventional plots. Monoculture, which had been found to favour the build-up of pseudomonads populations in past studies, had no significant effect on the abundance of any of the three quantified pseudomonads groups. Our results indicate that the quantity of fertilization, rather than the form of fertilization, influences the abundance of plant beneficial pseudomonads in wheat cultivation systems. Further research is needed to identify soil management systems favouring the growth of plant beneficial pseudomonads populations in different cropping systems.