Resistance to Tomato Bacterial Wilt Induced by Acibenzolar-S-Methyl J.S. de P. Araujo, K.S. Gonçalves, R. de L.D. Ribeiro and J.C. Polidoro Departamento de Fitotecnia Instituto de Agronomia Universidade Federal Rural do Rio de Janeiro Seropédica, Rio de Janeiro Brazil R. Rodrigues Lab. de Melhoramento Gen. Vegetal/ CCTA, Universidade Estadual do Norte Fluminense Campos dos Goytacazes Rio de Janeiro Brazil Keywords: Ralstonia solanacearum, Lycopersicon esculentum, systemic acquired resistance Abstract The present study was undertaken to evaluate the potential of acibenzolar-S- methyl as a plant resistance activator against tomato bacterial wilt caused by Ralstonia solanacearum. Plants of the cultivars Santa Clara, Diana and AF-2573 received seven weekly applications of acibenzolar-S-methyl (ASM, 2.5 g a.i./100 L water), by foliar sprays or soil drenches. The first application was carried out 14 days after sowing. Thirty-two day-old plants were transplanted into soil infested with R. solanacearum and four weekly applications of the activator were made after transplanting. Plants in control plots received plain water. Disease incidence was evaluated daily as the number of wilted leaves and plants. Data obtained allowed the estimation of the area under the disease progress curve (AUDPC). Wilt symptoms increased at a slower rate in the three cultivars when ASM was sprayed onto plants. This effect was significant up to four weeks after transplanting to R. solanacearum- infested soil. INTRODUCTION Bacterial wilt, caused by Ralstonia solanacearum E.F. Smith (Yabuuchi et al., 1995), is regarded one of the most important diseases that affect tomato (Lycopersicon esculentum Mill.). It occurs in great portions of tropical and subtropical regions (Martin et al., 1982), notably when air temperature is higher than 25°C (Lopes and Quezado-Soares, 1997). The bacteria infect roots, moving systemically through the xylem and causing wilt symptoms. The disease occurs throughout Brazil, limiting the production of tomato in warmer regions, including production areas in the north, northeast, central-west, and southeast. Studies involving pathogenicity and genetic variability of the pathogen, though not complete, provide information about the composition of prevalent populations in different agricultural areas. The identification of biovars, serovars, pathotypes, and their respective geographical distribution is highly desirable, especially to better understand the pathogen’s ecology and etiology, as well as to develop devise control methods including incorporation of genetic plant resistance. Ralstonia solanacearum race 1 (including biovars I, III, and IV) affects the greatest number of cultivated solanaceous plants (tomato, potato, eggplant, tobacco). Race 2 affects banana and heliconias, whereas race 3 (biovar II) is considered specific to potato, occurring in colder regions, although it may naturally infect other solanaceous plants. Its wide host range, high genetic variability, and ability to survive in the soil for long periods are the factors responsible to the failure of antibiotics, fungicides, fertilizers, and plant breeding programs tested to control bacterial wilt (Hartman and Elphinstone, 1994). Plant resistance to pathogens is mainly based on multiple barriers and defense mechanisms that exist regardless of the arrival of the pathogen to the infection site. These defenses are called constitutive, unspecific, or static. Higher plants possess other defense mechanisms, supposedly more efficient, which apparently remain inactive or latent, being triggered only after exposure to activators (abiotic or biotic). In these cases, the resistance 429 Proc. 1st IS on Tomato Diseases Eds. M.T. Momol, P. Ji and J.B. Jones Acta Hort 695, ISHS 2005