Dipartimento di Protezione delle Piante, Universita ` degli Studi della Tuscia, Viterbo, Italy Induced Resistance by b-Aminobutyric Acid in Artichoke against White Mould Caused by Sclerotinia sclerotiorum Emanuela manuela Marcucci arcucci, Maria aria Pia ia Aleandri leandri, Gabriele abriele Chilosi hilosi and and Paolo aolo Magro agro AuthorsÕ address: Dipartimento di Protezione delle Piante, Universita` degli Studi della Tuscia, Via S. Camillo de Lellis, 01100 Viterbo, Italy (correspondence to P. Magro. E-mail: magro@unitus.it) Received August 21, 2009; accepted December 10, 2009 Keywords: Cynara cardunculus subsp. scolymus, BABA, b-1,3-glucanase, chitinase, peroxidase, induced resistance Abstract b-aminobutyric acid (BABA) was assessed for the abil- ity to protect two artichoke cultivars, C3 and Exploter, against white mould caused by Sclerotinia sclerotiorum, which represents a major problem in the cultivation of this crop in many growing areas of Central Italy. Changes in the activity and isoenzymatic profiles of the pathogenesis-related (PR) proteins b-1,3-glucanase, chitinase and peroxidase in plantlets upon BABA treatment and following inoculation of the pathogen in plantlets and leaves detached from adult plants were also investigated as molecular markers of induced resistance and priming. BABA treatments by soil drenching induced a high level of resistance against S. sclerotiorum in artichoke plantlets of both cultivars C3 and Exploter with a similar level of protection and determined a consistent increase in peroxidase activity paralleled with the differential induction of alkaline isoenzyme with a pI 8.6. A consistent change was found in Exploter in the peroxidase activity following BABA treatments and pathogen inoculation and was paralleled with the expression of an anionic band in plantlets and both anionic and cationic bands in leaves. Our results showed a correlation between BABA- induced resistance (BABA-IR) and a augmented capacity to express basal defence responses, more pro- nounced in cultivar C3 and associated b-1,3-glucanase accumulation in both plantlets and leaves inoculated with the pathogen, whereas chitinase resulted affected only at plantlet stage. The present results represent the first one showing the effect of BABA in inducing resis- tance in artichoke and associated accumulation of selected PRs. If confirmed in field tests, the use of BABA at early plant stages may represent a promising approach to the control soilborne pathogens, such as the early infection of S. sclerotiorum. Introduction White mould caused by Sclerotinia sclerotiorum (Lib.) de Bary represents a major problem in the cultivation of artichoke [Cynara cardunculus L. subsp. scolymus (L.) Hegi] in many growing areas of Central Italy. The disease affects the leaves and crowns. The first symp- toms are brown, water-soaked lesions on outer leaves that enlarge rapidly under cool and moist conditions. Rots develop at the crown level comprising white, cot- tony mycelium, accompanied by the appearance of black sclerotia. Symptoms on crowns are often fol- lowed by wilt and death of the entire plant. Susceptible artichoke genotypes, the wide host range of the patho- gen and the ability of sclerotia to survive many years make the crop rotation an ineffective control strategy. Therefore, the development of alternative control strat- egy is essential. The use of chemical resistance inducers represents an additional opportunity in controlling plant diseases within an integrated crop protection sys- tem (Oostendorp et al. 2001; Walters et al. 2005). Induced resistance is a phenomenon extensively stud- ied in many plant–pathogen interactions, induced by localized infection or by treatments with microbial components or products or by a diverse group of structurally unrelated organic and inorganic com- pounds (Kuc´ 2001). Induced resistance by acibenzolar- S-methyl (benzo[1,2,3]thiadiazole-7-charbothioic acid S-methyl ester) (BTH), a synthetic compound consid- ered a salicylic acid (SA) functional analogue, is tightly associated with the expression and accumulation of a set of pathogenesis-related (PR) proteins (Vallad and Goodman 2004). Phosphate salts have shown to induce systemic resistance in several plant species against a broad spectrum of diseases by the activation of mechanisms resembling those initiated by necrotis- ing microbes and viruses that trigger SAR (Orober et al. 2002). In the case of resistance induced by non- pathogenic rhizobacteria (ISR) and the non-protein amino acid b-aminobutyric acid (BABA), resistance is not based on direct defence activation by the inducer, but on faster and stronger activation of inducible defence mechanisms once the plant is exposed to the pathogen (Zimmerli et al. 2000; Pieterse et al. 2003). J Phytopathol 158:659–667 (2010) doi: 10.1111/j.1439-0434.2010.01677.x Ó 2010 Blackwell Verlag GmbH