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Transmissible mitochondrial hypovirulence in a natural population of Cryphonectria parasitica
D Baidyaroy1, D H Huber, D W Fulbright
1Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312, USA.
Abstract:
A cytoplasmically transmissible hypovirulence syndrome has been identified in virus-free strains of the chestnut blight fungus Cryphonectria parasitica isolated from healing cankers on American chestnut trees in southwestern Michigan. The syndrome is associated with symptoms of fungal senescence, including a progressive decline in the growth potential and abundance of conidia, and elevated levels of respiration through the cyanide-insensitive alternative oxidase pathway. Conidia from senescing mycelia exhibited varying degrees of senescence ranging from normal growth to death soon after germination. Cytoplasmic transmission of hypovirulence between mycelia occurred by hyphal contact and coincided with the transfer of a specific restriction fragment length polymorphism from the mitochondrial DNA (mtDNA) of the donor strains into the mtDNA of virulent recipients. The transmission of the senescence phenotype was observed not only among vegetatively compatible strains but also among incompatible strains. Hypovirulence was present in isolates from the same location with different nuclear genotypes as identified by DNA fingerprinting. This study confirms that mitochondrial hypovirulence can occur spontaneously and spread within a natural population of a phytopathogenic fungus.
Insights
A novel hypovirulence syndrome in chestnut blight fungus (Cryphonectria parasitica) spreads through mitochondrial DNA transfer. This fungal senescence phenomenon impacts conidia growth and is transmitted via hyphal contact, even between incompatible strains.
Area of Science:
- Mycology
- Plant Pathology
- Genetics
Background:
- Hypovirulence, a disease-reducing trait in fungi, can be cytoplasmically transmitted.
- Cryphonectria parasitica causes chestnut blight, a significant threat to American chestnut trees.
Purpose of the Study:
- To identify and characterize a cytoplasmically transmissible hypovirulence syndrome in Cryphonectria parasitica.
- To investigate the mechanism and spread of this hypovirulence within a natural fungal population.
Main Methods:
- Isolation of virus-free Cryphonectria parasitica strains from healing cankers.
- Assessment of fungal senescence symptoms, including growth potential and conidia abundance.
- Analysis of mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs) and transmission via hyphal contact.
Main Results:
- A hypovirulence syndrome associated with fungal senescence was identified, characterized by reduced growth and increased respiration via the alternative oxidase pathway.
- Hypovirulence was transmitted cytoplasmically through hyphal contact, involving the transfer of specific mtDNA RFLPs from donor to recipient strains.
- Transmission occurred between both compatible and incompatible strains, and hypovirulence was found in isolates with different nuclear genotypes.
Conclusions:
- Mitochondrial hypovirulence can spontaneously arise and spread within natural populations of the chestnut blight fungus.
- The study confirms the role of mtDNA in the transmission of hypovirulence, impacting fungal populations.
- This finding has implications for understanding and potentially managing chestnut blight through biological control mechanisms.