Figure 1.

Extreme resistance induces systemic acquired resistance (SAR) signals. (A) Tobacco plants expressing both the N and Rx genes were rub‐inoculated on three lower leaves with buffer (Mock), tobacco mosaic virus (TMV) or potato virus X (PVX). Representative leaves from this primary (1°) infection are shown 5 days post‐infection (dpi). (B) Three systemic leaves immediately above the 1° infections were challenged with TMV (2° infection) 5 days after the 1° infection. Five days after the 2° infection, leaves were photographed and lesion sizes were determined. (C) Lesions sizes in millimetres (±standard deviation) from the experiment shown in (B). Reduction (%) is the percentage reduction in the size of 2° lesions on plants that received a 1° infection of TMV or PVX vs. mock 1° infected plants. N/A, not applicable. Experiments were performed at least four times with similar results.