Co-infection of two mycoviruses confers hypovirulence and reduce the production of mycotoxin alternariol in Alternaria alternata f. sp. mali.

fungal disease that affects the production of apple worldwide. Mycoviruses harbored in plant pathogenic fungi can confer hypovirulence in their hosts and have attracted wide attention as potential biocontrol tools. In this study, two co-infection mycovieuses, named Alternaria altenata chrysovirus 2 (AaCV2) and Alternaria altenata ourmia-like virus 1 (AaOLV1), respectively, were isolated from A. alternata f. sp. mali strain QY21. Sequence analyses revealed that AaCV2 virus belonged to the genus Betachrysovirus and AaOLV1 virus belonged to the genus Magoulvirus. These two mycoviruses were found to be associated with hypovirulence in A. alternata, among which AaCV2 might play a relatively leading role. Because the elimination of AaOLV1 from the strain QY21 do not affect hypovirulence trait, it indicated that the virus AaCV2 could independently induce slow growth and reduced virulence of the host. Moreover, the presence of viruses decreased the accumulation of mycotoxin alternariol (AOH) in A. alternata strains. Intriguingly, AaCV2/AaOLV1 mycoviruses can be transmitted horizontally to other A. alternata strains, and co-infection can promote the interspecific transmission efficiency of AaCV2. To our knowledge, this study reports the first description of the member of Chrysovirus is related to hypovirulence in Alternaria spp., which facilitate the development of biocontrol measures of Alternaria mali Roberts.