Screening for ISR-inducing Trichoderma spp.

Abstract: The genus Trichoderma constitutes a promising collection of potential biocontrol organisms (BCOs), reducing plant disease either via direct interaction with plant pathogens and/or indirectly through induced systemic resistance (ISR). The ISR capacity is mostly investigated by performing classical disease assays in which physical contact between the BCO and pathogen is avoided, however, such disease assays are very labour‐, time‐ and space-consuming. The discovery of general ISR markers could therefore greatly facilitate the search for novel or more efficient BCOs. We reported that application of Trichoderma hamatum T382 to Arabidopsis thaliana roots resulted in ISR against leaf infection by the necrotrophic pathogen Botrytis cinerea and performed a genome-wide analysis of ISR-related leaf gene expression, both before and after B. cinerea infection. In addition, we recently completed a similar microarray analysis with tomato replacing A. thaliana in the tripartite interaction. Based on the comparison of the transcriptomic analyses in both plants, a series of orthologous genes up-regulated in both tripartite systems was selected for their potential as general markers for Trichoderma-induced ISR. We developed a screening system based on pMarker-GUS lines, allowing fast and effective visual detection of ISR-inducing Trichoderma spp. The potential of the pMarker-GUS lines as a screening tool is demonstrated by the clear correlation between the percentage of disease reduction and the degree of staining of the pMarker-GUS lines. In this presentation we will describe our screening assay and cover the most recent advances that we have made with this system. Hereby we will focus on our ongoing characterization of Trichoderma isolates with so-far unknown ISR capacity, as well as on the extrapolation of our discoveries to tomato. In addition, we will address the question whether the screening system can also be used for BCOs that do not belong to the genus Trichoderma.