A new method for mechanical virus transmission and factors affecting its sensitivity¹

Abstract

Efficient transmission of plant viruses has been achieved using specially designed and constructed compressed‐air guns. Minimal puncturing of indicator‐plant epidermal cells, with a silicon carbide particle gun, rendered them highly susceptible to infection with sap inoculum applied by a spray gun. Sensitivity was improved 500‐fold compared with finger rubbing transmissions, and 1000‐fold compared with ELISA methods, as assessed by serial dilutions of infected sap in water. Punctured epidermal cells were observed slowly to extrude beads of cytoplasm, which took some minutes to attain maximum size before gradual retraction was completed 40–60 min later. Leaf susceptibility related to surface area of cytoplasm exposed at any time after cell puncture, suggesting that virus particles were bound to cytoplasm or plasmalemma and were passively carried into the cell. Spray nozzle design and construction materials influenced the infectivity of applied inoculum due to electrostatic charging effects on sprayed droplets.