Biocontrol under salinated conditions using Stenotrophomonas strains

Abstract: The genus Stenotrophomonas is of high medical, ecological and biotechnologicalinterest due to the versatility of the different species. Root colonisation and plant growthpromotion by Stenotrophomonas rhizophila DSM14405T in different crop species and at differentsalinities were investigated. Plant growth promotion was most significant in solanaceous crops(tomato, sweet pepper). In non-sterile systems and ambient humidity, colonisation of abovegroundplant parts was strongly dependent on plant species; epiphyllic populations on tomatowere 4-5 orders of magnitude higher than epiphyllic populations on sweet pepper and cotton.Rhizosphere populations were uniformly high irrespective of plant species (104 CFU/g root freshweight). However, in sweet pepper they declined sharply from 104 to 101 CFU/g root freshweight with increasing soil salinity in non-sterile soil (0-1% NaCl). Rhizosphere populationswere higher (~108 CFU/g FW) and the decline with salinity less pronounced in sterile(autoclaved) soil. A similar decline with salinity could be observed in the above-groundpopulations. Although population sizes where lower, plant growth promotion by S. rhizophilaDSM14405T was more pronounced in non-sterile soil than in sterile soil. Only there the effectwas consistent across all salinities so that a linear regression model with S. rhizophilaDSM14405T as significant growth promoting factor could be fitted. The greater effect in nonsterilesoil points to an indirect plant growth promotion effect of S. rhizophila DSM14405T,possibly via the elimination of deleterious components of the rhizosphere flora.