Evaluation of Spray-Induced Gene Silencing of Blueberry Scorch and Shock Viruses

Title: Evaluation of Spray-Induced Gene Silencing of Blueberry Scorch and Shock Viruses as a Method to Reduce Virus Number and Symptoms of Infected Blueberry Plants

Principal Investigator: Dr. Jim Mattsson, Associate Professor, Simon Fraser University

Duration: April 1, 2019 to March 31, 2021

Two plant viruses, Blueberry Scorch Virus (BlScV) and Shock Virus (BlShV), are widespread in blueberry fields in BC and northwestern Washington.  Both viruses reduce productivity, and the damage is costly. BlScV is lethal to plants and is primarily spread by aphids, while BlShV is non-lethal to plants and spread primarily by pollen.  The disease symptoms caused by these viruses are initially similar, but differentiation via a lab-based test is necessary to differentiate between the two viruses to direct management practices.  Whereas BlShV-infected plants can recover, BlScV-infected plants must be removed to prevent spread within the field.

Ribonucleaic acid (RNA) is a non-toxic biomolecule, present in all living cells. RNA is rapidly degraded and oral toxicity studies indicate that it is not toxic to mammals.  A novel approach to controlling the spread of viruses is to spray double-stranded (ds) RNA onto infected plants to combat pathogens using their own genetic code. The dsRNA either enters pathogen cells or plant cells, triggering RNA interference (RNAi) of the pathogen’s messenger RNA (mRNA). This approach, known as Spray-Induced Gene Silencing (SIGS), has been shown to prevent disease caused by plant pathogenic insects, fungi and more than 20 different viruses, in a number of different plant species.

SIGS has the advantages over other sprays in that it can be developed rapidly, uses a non-toxic biodegradable RNA molecule, and can target pathogens with no previous method of treatment, in particular viruses. Until recently though, SIGS was not deemed commercially viable as the synthesis of RNA is costly and the RNA is quickly degraded.  This pilot project is testing the efficacy of spraying BlShV-infected blueberry plants with dsRNA matching viral genes to reduce virus number and symptom development.

Objectives

The primary objective of this project is to demonstrate that BlShV numbers can be reduced in infected plants by sprays with dsRNA.  Positive results will provide the proof of concept needed to obtain resources to pursue future objectives:

1. Use of SIGs for larger-scale treatment of diseased plants;
2. Use of SIGs to reduce or prevent the risk of viral spread to uninfected plants; and
3. Identification of commercially viable conditions for implementing SIGs via cost/benefit analysis.