Salicylic Acid Mediates Elicitin-lnduced Systemic Acquired Resistance, but Not Necrosis in Tobacco. Harald Keller. INRA, Station de Botanique et de Pathologie Vegetale, BP 2078, 06606 Antibes-cedex, France. Philippe Bonnet(1), Eric Galiana(1), Laurence Pruvot(1), Leslie Friedrich(2), John Ryals(2), and Pierre Ricci(1). (1) INRA, Station de Botanique et de Pathologie Vegetale, BP 2078, 06606 Antibes-cedex, France and (2) Molecular Genetics, Ciba Geigy Corp., Agricultural Biotechnology Research, Research Triangle Park, NC 27709 U.S.A. MPMI 9:696-703. Accepted 11 July 1996. Copyright 1996 The American Phytopathological Society.

Elicitins are proteinaceous elicitors which are secreted by all Phytophthora species analyzed so far. When applied on tobacco they induce necrosis and systemic acquired resistance (SAR). Elicitin-treated tobacco plants that express the bacterial nahG gene coding for salicylate hydroxylase did not show SAR against infection with the black shank fungus, Phytophthora parasitica var. nicolianae. However, nahG-expressing plants still responded to a treatment with the basic elicitin cryptogein by formation of necrosis. Elicitin-induced expression of genes encoding PR-la, PR-2, PR-5, and basic class III chitinase was suppressed in NahG tobacco, while the induced mRNA accumulation of basic PR-1, PR-3, str-246 and str-319 appeared to be unchanged. NahG plants showed enhanced susceptibility to several Phytophthora species and isolates that produce elicitins, but were not affected in the necrosis response during interaction. While SA is involved in SAR and disease resistance to Phytophthora, our results suggest that it does not mediate the hypersensitive-like necrosis response.