Microbial two front attack: elaborate root infections by Colletotrichum graminicola oval conidia during maize anthracnose

Most plant pathogenic microorganisms have evolved to infect distinct host tissues. The maize anthracnose fungus, Colletotrichum graminicola , is known for its ability to invade above-ground tissues with asexual falcate conidia. Besides, C. graminicola generates a second asexual spore type, oval conidia. We analyzed in this study specific adaptations making oval or falcate conidia prone for maize root infection, providing evidence that only oval conidia show characteristics of a root pathogen. This includes the ability to germinate in soil and to grow chemotropically toward root-secreted molecules. HPLC/MS analyses combined with biological assays revealed that diterpenoids like dihydrotanshinone I are most likely responsible for the chemical attraction of C. graminicola . A genetics approach identified the a-pheromone receptor CgSte3 as being responsible for the perception of diterpenoids by the fungal pathogen. In conclusion, the understanding of the maize anthracnose disease has to be expanded to include an elaborated root infection cycle by oval conidia.