Cultivable bacterial communities associated with roots of rose-scented geranium (Pelargonium graveolens) with the potential to contribute to plant growth

Rose-scented geranium (Pelargonium graveolens) is greatly used in ornamentation and in the production of geranium oil, which is used for medicinal purposes and in the perfumery and cosmetics industries. Frequently, rose-scented geranium cultivation is greatly affected by fungal diseases, mainly anthracnose. However, to date, no data is available on the bacteriome associated with rose-scented geranium plants, including for the bacteria that present characteristics indicative of a potential to promote plant growth. Isolation and characterization of such bacteria could result in future development of beneficial bacterial consortia for geranium. Here, two different media (Tryptic Soy Agar and King’s B) were used to isolate bacterial strains from the rhizosphere and roots of rose-scented geranium. A potential fungal pathogen, Colletotrichum acutatum, was also isolated and identified by morphological and molecular methods. We assessed the diversity and some plant growth-promoting characteristics (including antagonism against C. acutatum) of the plant-associated bacterial community. Bacterial isolates (n=169) were molecularly identified as belonging to the phyla Firmicutes, Actinobacteria, Proteobacteria and Bacteroidetes. The genus Bacillus predominated in the rhizosphere and roots. Several Bacillus strains were found to not only have antagonistic activity in vitro against C. acutatum, but were also able to produce siderophores, mineralize organic phosphate, solubilize inorganic phosphate and/or produce indolic compounds.