Plant pathogens do not operate alone but can form synergistic interactions in disease complexes. This has important implications for diagnosis, epidemiology and disease management. Here we use Fusarium/Sarocladium interactions in the rice sheath rot disease complex as a model to gain more insight into their within-host interplay and implications on virulence and in planta mycotoxin production. Our prior research has shown that in planta these fungi mainly produce the mycotoxins zearalenone and enniatin which pose risks for animal and human health. Moreover, co-infection has a strong influence on mycotoxin production. We will also use this model to study virulence evolution by investigating the effects of co-infection on horizontal and vertical pathogen transmission. Representative genomes from Saroclarium and Fusarium available in our culture collection will be sequenced and mined for mycotoxin biosynthetic gene clusters. Co-inoculation experiments will be done to investigate the effects on panicle formation and seed set. Plant colonization and toxin expression and production in planta will be assessed. Mycotoxin mutants will be generated to study their role in the interaction and pathogenicity. We will also test the effect of co-inoculations on other rice diseases, such as rice blast caused by Pyricularia oryzae.