Exploring the mycovirus SsHADV-1 as a biocontrol agent of Sclerotinia white mold

Authors: FU, MIN - Washington State University; QU, ZHENG - Washington State University; Pierre-Pierre, Nickisha; JIANG, DAOHONG - Huazhong Agricultural University; SOUZA, FERNANDA - Washington State University; Miklas, Phillip - Phil; Porter, Lyndon; Vandemark, George; Chen, Weidong

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: White mold caused by the fungal pathogen Sclerotinia sclerotiorum is a devastating disease on many economically important crops. The disease is difficult to control because the pathogen can persist in soil for several years as resting spores and there is a general lack of resistance in crop cultivars. Although effective fungicides are available, it is difficult to apply them to the infection site once the plant canopy is formed, and the application of fungicides increases production costs and contributes to environmental concerns. Sclerotinia is infected by numerous viruses, some of which are debilitating to the fungus. Some viruses have been demonstrated to be effective in controlling white mold disease, but this potential has not been fully exploited in the United States. This research utilizes the mycoviorus SsHADV-1 that was initially discovered in China. The virus can be readily transmitted from the Chinese isolate to and among US isolates and all strains carrying this virus showed significantly reduced ability to cause white mold disease (hypovirulence). The SsHADV-1 virus-carrying strains can be used as a biocontrol organisms to control white mold disease when applied either on seeds (bio-priming) or crop leaves. These fungal strains have been shown to grow inside plants without causing visible symptoms and this growth increases plant resistance to white mold disease and enhances expression of several plant defense-related genes. The results indicate that SsHADV-1-carrying strains can function as a vaccine, and that their growth in plants stimulate the expression of genes related to the plant immunity pathways, which help plants respond rapidly and strongly to fungal infection.

Technical Abstract: Sclerotinia sclerotiorum is a necrotrophic fungal pathogen that causes white mold disease on many important economic crops. Recently, some mycoviruses, such as Sclerotinia sclerotiorum hypovirulence-associated DNA virus 1 (SsHADV-1), have been shown to convert the pathogenic fungus into a beneficial symbiont that helps plants against pathogens and other stresses. To explore the potential use of SsHADV-1 as a biocontrol agent in the United States, we transferred the mycovirus SsHADV-1 from the Chinese strain DT-8 to US isolates of S. sclerotiorum and tested the efficacy of SsHADV-1-infected US isolates in managing white mold and other diseases. The mycovirus SsHADV-1 was readily transmitted horizontally among US strains of S. sclerotiorum and consistently conferred hypovirulence to its host strains. Bio-priming of dry bean seeds with hypovirulent S. sclerotiorum strains enhanced resistance to white mold and also to gray mold caused by Botrytis cinerea. To investigate the underlying mechanisms, we used PCR to confirm endophytic growth of the hypovirulent S. sclerotiorum in bean plants. Expression patterns of 12 defense-related genes were monitored in bean plants before and after infection by virulent S. sclerotiorum. Results indicated that SsHADV-1-infected strains function as a vaccine and that their endophytic growth in plants stimulate the expression of genes related to plant immunity, which help plants respond rapidly and effectively to fungal infection. Finally, the use of bio-priming technology on pea, sunflower and wheat was also examined.