Exploring the Mycovirus Sclerotinia sclerotiorum Hypovirulence-Associated DNA Virus 1 as a Biocontrol Agent of White Mold Caused by <i>Sclerotinia sclerotiorum</i>

Abstract

<i>Sclerotinia sclerotiorum</i> is a necrotrophic fungal pathogen causing white mold on many important economic crops. Recently, some mycoviruses such as <i>S. sclerotiorum</i> hypovirulence-associated DNA virus 1 (SsHADV-1) converted <i>S. sclerotiorum</i> into a beneficial symbiont that helps plants manage pathogens and other stresses. To explore the potential use of SsHADV-1 as a biocontrol agent in the United States and to test the efficacy of SsHADV-1-infected United States isolates in managing white mold and other crop diseases, SsHADV-1 was transferred from the Chinese strain DT-8 to United States isolates of <i>S. sclerotiorum</i>. SsHADV-1 is readily transmitted horizontally among United States isolates of <i>S. sclerotiorum</i> and consistently conferred hypovirulence to its host strains. Biopriming of dry bean seeds with hypovirulent <i>S. sclerotiorum</i> strains enhanced resistance to white mold, gray mold, and Rhizoctonia root rot. To investigate the underlying mechanisms, endophytic growth of hypovirulent <i>S. sclerotiorum</i> in dry beans was confirmed using PCR, and the expression of 12 plant defense-related genes were monitored before and after infection. The results indicated that the endophytic growth of SsHADV-1-infected strains in plants stimulated the expression of plant immunity pathway genes that assisted a rapid response from the plant to fungal infection. Finally, application of the seed biopriming technology with SsHADV-1-infected hypervirulent strain has promise for the biological control of several diseases of wheat, pea, and sunflower.