Submitted to: Archives of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2013
Publication Date: 2/3/2014
Citation: Marvelli, R.A., Hobbs, H.A., Li, S., McCoppin, N.K., Domier, L.L., Hartman, G.L., Eastburn, D.M. 2014. Identification of novel double-stranded RNA mycoviruses of Fusarium virguliforme and evidence of their effects on virulence. Archives of Virology. 159(2):349-352. Interpretive Summary: Sudden death syndrome (SDS) of soybeans is caused by a fungal plant pathogen and can reduce soybean yields from 15% to over 80%. At present, no fungicides or seed treatments are available to manage the disease. Crop rotation, tilling, and delayed planting can reduce damage in some instances. Even though the use of resistant cultivars of soybean could provide better control, no soybean cultivars are commercially available with high levels of SDS resistance. Because none of these measures have provided acceptable levels of disease management, biological control may help mitigate the damage caused by SDS. Naturally occurring mycoviruses, which have been shown to reduce the virulence of other fungal pathogen, are potential biological control agents for SDS. In this study, isolates of the fungus that cause SDS were identified that appeared to be infected with mycoviruses. The SDS symptoms induced by fungi with mycoviruses were significantly less severe than those induced by fungal isolates without mycoviruses. Therefore, intentional infection of the fungus causing SDS with mycoviruses may reduce the severity of SDS-induced yield losses and increase the effectiveness of other management practices. This information will be useful to researchers who are interested in biological controls for fungal diseases of crop plants.
Technical Abstract: Virulence and double-stranded RNA (dsRNA) profiles of 44 isolates of Fusarium virguliforme were compared. Twenty three isolates (52%) had one or two large dsRNA segments; five (11%) contained both large and small segments; while sixteen (37%) had no detected dsRNA. Single large segments ranged from 9.5 to 12.5 kb in length, and the two small segments were 1.8 and 2.3 kb in length. Isolates differed significantly in virulence. When grouped according to dsRNA profiles, isolates with only large dsRNAs were significantly (P=0.05) less virulent than isolates without dsRNAs. High-through-put sequence analysis of total RNA prepared from cultures with large dsRNAs identified nearly complete genome sequences of approximately 9.3 kb for two novel viruses, which were named Fusarium virguliforme dsRNA mycovirus 1 and Fusarium virguliforme dsRNA mycovirus 2. The new viruses were most closely related to a group of unclassified viruses that included viruses of F. graminearum and Phlebiopsis gigantea and related to members of the family Totiviridae. The genomes of the viruses had two large overlapping open reading frames that could be translated by -1 frameshifting. Understanding how these dsRNA mycoviruses reduce the virulence of F. virguliforme may aid in developing biocontrol methods for sudden death syndrome of soybean.