Disease resistance to viral diseases

Plant viruses

Plant viruses represent a huge part of agricultural planning, crop losses and quality reduction around the world. Although simple biologically, the mechanisms they use to survive are complex and not yet well understood. Resistance to plant viruses is an important attribute that is widely prevalent in nature, and often the subject of any plant genetic engineering ventures.

Signs that this blueberry plant has been virally compromised.

Viral life cycle

• Entry, un-coating of nucleic acid, translation of viral proteins, replication of viral nucleic acid, assembly of progeny, cell-cell, systemic and plant-plant movement.
• Most viruses make it to un-coating viral nucleic acid, even in nonhost species.

What defenses do plants have against viruses?

• Genetic defenses- “R genes” are genes that allow a plant to be a less susceptible host.
• Resistance to most plant viruses is the norm, while the exception is plant susceptibility
• Non-host resistance is said to be the case when discussing a virus that cannot infect any genotype of a certain plant species, which is harder to study
• Host resistance refers to the appearance of a resistant genotype within a population previously susceptible to a particular virus. This phenomenon is easier to study in a genetic context.
• Pathogen resistance is a complex term- it is sometimes hard to tell whether the pathogen is still able to enter the plant and reproduce without the plant showing physical signs, or if the pathogen was stopped all together from entering the plant, as resistance may develop at any point in the pathway towards disease.
• 80% of genetic viral resistance has been shown to be monogenic, with the remainder polygenic or oligogenic

Mechanisms of resistance

Schematic of viral resistance from "Genetics of Plant Viral Resistance."

• Dominant resistance is most commonly associated with a “recognition” event.
• Most known resistance pathways target viral replication and movement

Previously described viral resistance genes

• Table (File:Table.pdf) of known viral resistance genes that show both dominant and recessive inheritance. (Supplementary materials from Genetics of Plant Viral Resistance Media:Annurev.phyto.43.011205.141140 (1).pdf.)