Role of Viral Infections in Rapid Prunus Decline in the Niagara Region

Abstract

Plant diseases associated with viral infections are a serious issue for growers, causing significant reductions in yield and plant death. Rapid Prunus Decline (RPD) is an emerging disorder resulting in rapid and unexplained death of Prunus species in southern Ontario. In order to better understand RPD, disease symptoms in all major Prunus species in the Niagara region were surveyed, along with identification of major viruses in diseased Prunus trees. Our survey showed that diseased trees often showed symptoms of dehydration, leaf chlorosis, reduced new growth, and death. The average mortality rate in the Niagara region was 20% among all Prunus species with the highest site-specific mortality rate of 67%. In order to understand the contribution of viruses to RPD, RNA sequencing was employed to identify viruses in diseased trees and characterize viral sequence diversity. In total, 20 unique virus species and one viroid were identified in 42 diseased trees, demonstrating a wide diversity of viruses in diseased Prunus trees. Tomato ringspot virus (ToRSV) infection can result in similar symptoms to those observed in RPD trees. Based on these similar symptoms, a total of 507 Prunus trees were surveyed and the frequency of ToRSV infection was determined to be 13%. No direct correlation was identified between the presence of ToRSV and incidence of RPD, suggesting that other factors are involved. Multiple ilarviruses were identified in diseased trees including Grapevine associated ilarvirus (GaIV), Tobacco streak virus (TSV), Tomato necrotic spot virus (ToNSV), Prunus necrotic ringspot virus (PNRSV), and Prune dwarf virus (PDV). GaIV and ToNSV have never been previously reported in Prunus trees, or in Canada. GaIV was the most commonly detected virus and is an emerging concern for stone fruit production. Mixed infection of ilarviruses could have synergistic pathological effects, and the interactions between ilarviruses and other viruses are poorly understood. In summary, over the course of this study, many different viruses were identified in Prunus species exhibiting decline, yet no single virus was identified in all Prunus spp. or in all instances of the disease, suggesting RPD is a complex disease that could have multiple contributing factors.