Transmission of apple stem grooving virus (Capillovirus mali) to apple from the soil-borne fungus Fusarium solani.

Abstract

<h4>Background</h4>Viruses can affect the growth, yield and fruit quality of apple trees. Apple viruses are primarily spread through grafting and pruning, with limited evidence of natural transmission. Notably, wild apple trees have also been reported to carry viruses found in orchards, but the source of infection remains unknown. Plants are frequently co-infected with fungi and viruses, and recent studies have shown cross-kingdom bidirectional transmission of viruses and viroids between plants and fungi, suggesting that fungi may serve as reservoirs for certain phytopathogenic viruses. These facts raise the question whether fungi can also acquire apple viruses and serve as their hosts or vectors.<h4>Results</h4>Tree roots and rhizospheric soil were collected from an old apple orchard to isolate fungi. Twelve fungal species were identified and subjected to apple virus detection. Fusarium solani was shown to be a natural host of apple stem grooving virus (ASGV) which was transmitted vertically to its asexually produced spores and horizontally to ASGV-free F. solani culture. The presence of ASGV in the F. solani root infection negatively affected apple plant growth and ASGV was systemically transmitted to the apple seedlings from the F. solani root infection.<h4>Conclusions</h4>This study identifies F. solani as a novel vector for the transmission of ASGV. This previously unreported mode of transmission for an apple virus provides new insights for the development of effective disease management practices in apple cultivation.