Botrytis cinerea CCg11 is infected with several putative mycoviruses and exhibits a severe hypovirulence phenotype

The wild-type strain Botrytis cinerea CCg11 contains at least nine double-stranded RNA (dsRNA) molecules that are likely associated with multiple putative mycoviruses. This strain exhibits a hypovirulent phenotype compared with the virulent wild-type strain B. cinerea CCg55L, in which no dsRNA elements were detected using the dsRNA purification approach applied in this study. Sucrose-gradient purification revealed isometric virus-like particles of approximately 45, 40, 26, and 18 nm in diameter, suggesting a complex dsRNA-associated viral infection. To evaluate whether the hypovirulent phenotype of CCg11 was associated with the presence of these dsRNA elements, twelve monosporic clones showing differential loss of one or more dsRNA molecules were obtained and compared with the parental strain. The monosporic clones displayed changes in mycelial morphology, and most of them showed increased radial growth and conidiation. In addition, all clones exhibited increased virulence on grapevine leaves compared with the parental strain CCg11, with several clones reaching levels comparable to the virulent control strain CCg55L. These results support an association between the presence or loss of specific dsRNA elements and the hypovirulent phenotype of B. cinerea CCg11. However, because the viral elements were not molecularly characterized, their identity, novelty, and individual contribution to the observed phenotypes remain to be determined. Future high-throughput sequencing and virus-specific molecular analyses will be required to define the complete virome of CCg11 and establish direct virus-phenotype relationships.