Symptomatic plant viroid infections in phytopathogenic fungi

Significance Viroids are the only known autonomously replicating pathogenic agents that do not encode proteins. As viroids are known only to naturally infect plants, their infectivity and pathogenicity in other eukaryotes are largely unexplored. Herein, we demonstrate the stable infection of three viroid species in different plant pathogenic filamentous fungi and show that viroid infection can reduce the growth and virulence of fungi. In addition to successful viroid RNA inoculation of fungal spheroplasts, viroid infection of fungus could occur through viroid transmission from the plant and when viroid RNAs are directly applied to fungal mycelia. These findings are relevant to our understanding of viroid replication, transmission, and pathogenicity.