Asymptomatic infection, and distribution of Ophiostoma mitovirus 3a (OMV3a), in populations of Sclerotinia homoeocarpa

Abstract

One hundred and sixteen isolates of Sclerotinia homoeocarpa from nine locations in southwestern Ontario and one location in Nova Scotia were assessed for the presence of a hypovirulence-associated mitovirus, Ophiostoma mitovirus 3a (OMV3a). Two detection methods, nucleic acid extraction with gel electrophoresis (NAE–GE) and reverse transcription – polymerase chain reaction (RT–PCR), were employed. Phenotype, growth rate, and virulence of isolates were also assessed. OMV3a was detected in four isolates (3.4%), using both the standard NAE–GE method and the RT–PCR method. The four isolates displayed reduced colony growth and virulence, and they were considered to be symptomatic, hypovirulent isolates infected by OMV3a. In the remaining 112 isolates, OMV3a was detected in 53 isolates by RT–PCR only. These isolates displayed typical colony growth and virulence, and they were considered to have asymptomatic infections by the virus. OMV3a was not detected by either method in 59 isolates that displayed typical colony growth and virulence; these isolates were considered to be free of infection by the virus. OMV3a was detected from 8 of 10 locations, all in Ontario, and in 17% to 100% of S. homoeocarpa isolates at these locations. Vegetative compatibility groups (VCGs) were previously determined for these isolates, and OMV3a was detected in 66%, 54%, and 19% of the isolates from VCGs B, A, and G, respectively, which were the three most prevalent. The results demonstrated that OMV3a was present in isolates with and without the characteristic symptoms of hypovirulence and that it was widely distributed in southwestern Ontario and in isolates from the three most prevalent VCGs detected among these isolates. This is the first report of widespread asymptomatic infections by a hypovirulence-related virus in populations of a fungal plant pathogen.