Using MAGIC against Tan Spot disease: How Multiparent Advanced Generation Intercross wheat lines respond to Pyrenophora tritici-repentis infection

Pyrenophora tritici-repentis (Ptr) causes the Tan Spot disease of wheat, a major foliar disease. It is mainly managed through chemical control due to the lack of reliable resistant cultivars. Herein we explore Multiparent Advanced Generation Intercross (MAGIC) wheat populations for new sources of resistance and to develop our understanding of the wheat-P. tritici-repentis pathosystem. Seedlings were inoculated with toxin toxA positive Ptr strains and disease progression was assessed over 14 days after inoculation (dai). The eight parental lines exhibited differential responses where “Robigus” and “Hereford” were the most resistant and susceptible, respectively. Fluorescence microscopy indicated Ptr penetrating through the epidermis and stomata at 1 dai, followed by intra-/intercellular mycelial growth and localized cell death (1-3 cells) in both genotypes. However, at 3 dai extensive superficial and subcuticular growth was seen in Hereford but not in Robigus. Our initial omic characterization focused on metabolomics, which indicated the mobilization ofglycerophospholipids, amino acids and sugars in Hereford after 3 dai. Resistance in Robigus was not associated with the production of phenylpropanoids or anti-microbial polyketides suggesting a novel defense mechanism may be being deployed. These results will be integrated into transcriptomics data in the near future. This program illustrates how genotypically varied populations such as MAGIC can be exploited to define new sources of resistance against important emerging diseases.