Figure 2.

The systemic acquired resistance (SAR) signal induced by extreme resistance is dependent on salicylate (SA)‐mediated signalling. F1 progeny from the crossing of Rx transgenic tobacco with NahG (A) or RNAi::SABP2 (B) transgenic tobacco or wild‐type tobacco (C) were assessed for their ability to develop SAR. Plants were rub‐inoculated on three lower leaves with buffer (Mock), tobacco mosaic virus (TMV) or potato virus X (PVX). 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 (A and B) and lesion sizes were determined. Lesions sizes in millimetres (±standard deviation) are shown in table form (A–C). 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 three times with similar results.