Identification of plant viruses in orchards affected by rapid apple decline disease in the Okanagan and Similkameen valleys
Citation
Hao, W., Xiao, H., Sanfacon, H. (2020) Identification of plant viruses in orchards affected by rapid apple decline disease in the Okanagan and Similkameen valleys. Virtual oral presentation, BC regional meeting of the Canadian Phytopathological Society, Dec 10 2020
Plain language summary
Rapid apple decline is an emerging disease that has devastated apple orchards in several regions in Canada, including the Okanagan valley in British Columbia. This work is aimed at identifying plant viruses present in affected orchards in the Okanagan valley and at evaluating their impact on the disease. Nineteen viruses and one viroid were detected in the orchards in 2019. Of those, five (including a putative new virus belonging to the genus ilarvirus) were more prevalent. Although no single virus showed a clear association with the disease, it is possible that several viruses contribute together to the disease severity.
Abstract
Rapid apple decline disease (RAD) has been increasingly reported over the last few years in North American orchards. Although the cause for RAD remains unknown, this investigation focuses on the potential contribution of plant viruses to the disease. During the course of the 2019 growing season, 71 samples were collected from apple trees that displayed a range of symptoms from eight orchards in the Okanagan and Similkameen valleys. Results from high-throughput sequencing of 12 samples suggested the presence of 18 known viruses, one known viroid, and one putative novel ilarvirus in these orchards. Field prevalence of 12 of these viruses and of the viroid was examined by conducting RT-PCR on the 71 individual samples. Although no single virus showed specific association with the disease, five viruses were more prevalent, including apple chlorotic leaf spot virus (ACLSV), apple stem grooving virus (ASGV), apple stem pitting virus (ASPV), citrus concave gum-associated virus (CCGaV) and the putative novel ilarvirus. Phylogenetic analysis of assembled NGS sequences revealed a high degree of diversity among BC isolates of ACLSV, ASGV and ASPV, and showed evidence for potential new strains. Viruses were frequently detected in mixed infections, raising the possibility of synergistic interactions, which could collaboratively weaken the tree and make it more vulnerable to other stressors. The relative prevalence of specific viruses was found to vary with the sampling time and geographical location. Ongoing experiments are aimed at re-examining these trends during further growing seasons and examining possible relationships between virus incidence and cultivar types.