2,6-Dichloroisonicotinic Acid-Induced Resistance to Pathogens Without the Accumulation of Salicylic Acid. Bernard Vernooij. Agricultural Biotechnology, Ciba-Geigy Corporation, P.O. Box 12257, Research Triangle Park, NC 27709-2257. Leslie Friedrich, Patricia Ahl Goy(1),Theodor Staub(1), Helmut Kessmann(1), and John Ryals Agricultural Biotechnology, Ciba-Geigy Corporation, P.O. Box 12257, Research Triangle Park, NC 27709- 2257. (1)Crop Protection Division, Ciba-Geigy Limited, CH-4002 Basel, Switzerland. MPMI 8:228-234. Accepted 13 December 1994. Copyright 1995 The American Phytopathological Society.

Systemic acquired resistance (SAR) is a pathogen-induci-ble defense mechanism effective against a wide range of pathogens. Salicylic acid (SA) is an essential component of this pathway, as transgenic plants unable to accumulate salicylic acid are incapable of developing SAR. Here, we show that the synthetic chemical 2,6-dichloroisonicotinic acid (INA) acts via the SAR signal transduction pathway. However, it does not induce SA accumulation during the time required for the induction of SAR gene expression or resistance to TMV. Furthermore, INA can induce both resistance and SAR gene expression in transgenic tobacco and Arabidopsis plants that cannot accumulate SA. Thus, INA apparently activates a component of the SAR signaling pathway downstream of SA accumulation.