FIG 6 .

Theoretical relationship between virus dilution and plaque numbers at different coinfection frequencies. Plaque assays are based on the dose-response curve of a one-hit model (calculation depicted by the dotted black line) where each plaque is formed by one infectious unit. Certain plant and fungal viruses have two-hit kinetics (calculation depicted by the dotted red line), where two viral genomes per cell are required for productive infection and plaque formation. Purple, blue, and green lines represent calculations using data obtained in Fig. 5 for G64S-RdRp, WT-RdRp, and WT-RdRp+RBV viruses, respectively. The solid orange line represents the theoretical curve for a coinfection frequency of 50%. At low coinfection frequencies (e.g., 3.2% and 7.3%), the curvatures of the lines are minimal, and therefore, the relationship between dilution and the number of plaques is nearly linear (see the inset).