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Mushroom dry bubble disease: novel pathogens, and mycoviruses as potential biocontrol agents
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Abstract
Dry bubble disease, caused by Lecanicillium fungicola, seriously affects the production of button mushroom (Agaricus bisporus) at a global level. Due to the increasing limitations of chemical pest management, there is high demand for novel, biological means of disease control. Fungal viruses (mycoviruses)have been shown to cause reduced virulence (hypovirulence)in plant pathogenic fungi, as well as Mycogone perniciosa, causal agent of wet bubble disease. The objective of the project ‘Leca-VIR’ is the search for viruses in fungi associated with dry bubble disease and their
evaluation as potential agents to reduce the virulence of L. fungicola. Fifty seven fungal strains originating from dry bubble-affected mushroom crops were identified based on their ITS
(internal transcribed spacer) sequences and tested for the presence of virus-associated double-stranded (ds) RNA elements by cellulose column chromatography, which were subsequently identified by rRNA-depletion RNAsequencing analysis. The fungal cultures were treated with different antiviral agents to eliminate any detected viruses, then the growth and sporulation of the virus-cured derivatives - confirmed by one-step RT-PCR using primers targeting the viral RdRp (RNA-dependent RNA polymerase) sequences - were examined in comparison with the parent cultures.
Most of the examined fungi were confirmed as L. fungicola. However, additional strains belonging to the family Cordycipitaceae, including Simplicillium aogashimaense and Akanthomyces spp., were also identified, and whose association with dry bubble disease has not yet been reported. Viruses were detected in seven L. fungicola and three Akanthomyces strains and were identified as representatives of the viral families, Chrysoviridae (7), Polymycoviridae (3) and Partitiviridae (1). All were successfully eliminated from the fungal cultures. Virus curing was found not no affect fungal growth however, virus-free derivatives of a L. fungicola strain originally infected with a partitivirus and a polymycovirus, produced up to 32-fold higher amounts of conidia compared to the parent culture. The disappearance of the polymycovirus during sub-culturing did not result in altered phenotype therefore, the partitivirus is proposed to play a role in the substantial reduction of
conidium production. As abundant sporulation is essential for the infectivity of pathogenic fungi, these findings suggest that this partitivirus may reduce the virulence of L. fungicola, and therefore be of interest in future studies targeting the biological control of dry bubble disease. Lorant Hatvani has received funding from the Research Leaders 2025 programme co-funded by Teagasc and the
Eu-ropean Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agree-ment number 754380.