The bioprotective effect of root endophytic Serendipita herbamans against Fusarium wilt in tomato and its impact on root traits are determined by temperature

Environmental conditions such as temperature can be important determinants for the success of biocontrol agents in field situations. On the one hand temperature affects biocontrol strains on the other plant-pathogen dynamics. In order to understand these dynamics, driving factors behind these interactions need to be fully characterized. Here, we i) investigated the effect of two temperature treatments on the biocontrol activity of the root endophyte Serendipita herbamans against the soil-borne pathogen Fusarium oxysporum f. sp. lycopersici (Fol) in tomato and ii) assessed the impact of this biocontrol system on root morphological traits. The results of this study indicate that inoculation with S. herbamans stimulated shoot length and enhanced the shoot and root dry mass in tomato plants across both temperatures. Furthermore, S. herbamans inoculation decreased disease incidence from 67% in the Fol only treatment to 22% at lower temperatures (24 degrees C). At 28 degrees C, disease incidence was around 41% and no reduction could be seen; however, root morphological traits such as root length, root surface area and root volume were not affected at 24 degrees C but severely reduced under 28 degrees C upon Fol inoculation. A reduction of root morphological parameters was not observed in S. herbamans + Fol treated plants at 28 degrees C indicating a protective effect against Fol. Moreover, root morphological traits appear to be more influenced by the different temperatures than root dry weights. In additional in-vitro experiments, growth promoting effects of S. herbamans on root traits without direct contact were evident indicating the involvement of volatile organic compounds in growth promotion. In conclusion, S. herbamans provides protection against the temperature-dependent damage Fol inflicts on the tomato plants by reducing disease development under 24 degrees C and by mitigating reduction in root morphological parameters under 28 degrees C in the early weeks of interaction.