Benzothiadiazole (BTH)-induced resistance against Botrytis cinerea is inversely correlated with vegetative and generative growth in bean and cucumber, but not in tomato Zabihollah Azami-Sardooei & Hamed Soren Seifi & David De Vleesschauwer & Monica Höfte Received: 5 December 2012 / Accepted: 28 February 2013 / Published online: 21 March 2013 # Australasian Plant Pathology Society Inc. 2013 Abstract Greenhouse-cultivated tomato, bean and cucum- ber suffer great economic losses due to grey mould, caused by Botrytis cinerea. Benzothiadiazole (BTH) is a chemical analogue of salicylic acid that induces resistance in a variety of plants by activating the systemic acquired resistance (SAR) pathway. Here, we investigated the effects of foliar applications of different concentrations of BTH on resis- tance to B. cinerea in these plants and on plant vegetative and generative growth. Leaf treatments with 1 up to 50 mg/l BTH resulted in increased protection of tomato against B. cinerea. However, on bean and cucumber, only concentra- tions of 250 mg/l and higher, strongly reduced susceptibility against B. cinerea. Moreover, BTH concentrations above 100 mg/l had a significant negative effect on plant height, flower and fruit numbers in bean and cucumber plants under pathogen-free conditions, whereas in tomato only the highest BTH dose (1000 mg/l) resulted in a significant negative effect on vegetative and generative growth. We hypothesize that the protective effects observed on bean and cucumber plants treated with higher levels of BTH are due to a general stress response, which is distinctly different from the BTH-induced resistance observed in tomato at lower concentrations of the compound without negative effects on plant growth. Keywords Acibenzolar-S-methyl . Actigard . Bion . Grey mould . Phytotoxicity . Induced resistance . SAR . Solanum lycopersicum . Phaseolus vulgaris . Cucumis sativus The ascomycete Botrytis cinerea has been recently nomi- nated as the most scientifically/economically important necrotrophic fungal plant pathogen (Dean et al. 2012). The pathogen causes grey mould on flowers, leaves, fruits and stems of a wide range of important crops and vegetables. Tomato, bean and cucumber are amongst economically im- portant vegetables that are highly susceptible to the pathogen. The plant activator benzo(1,2,3)-thiadiazole- 7-carbothioic acid S-methyl ester (BTH, also called acibenzolar-S-methyl) is a functional analogue of salicylic acid that induces resis- tance against a broad spectrum of phytopathogens by activat- ing the systemic acquired resistance (SAR) pathway (Tally et al. 1999; Vallad and Goodman 2004). Although resistance to necrotrophic pathogens is usually controlled by the plant hormones jasmonic acid and ethylene (Thaler et al., 2012), BTH has repeatedly been shown to be effective against B. cinerea in various plants including tomato, Arabidopsis, grape and grapevine (Achuo et al. 2004; Zimmerli et al. 2001; Iriti et al., 2004, 2005). Interestingly, the effect of BTH treatment on plant defense activation strongly depends on the concentration used. At low concentrations, BTH does not induce defense responses directly, but rather sensitizes plants for a faster and/or stronger response to successive pathogen invasion, a phenomenon commonly referred to as priming (Conrath, 2011). High concentrations of BTH on the other hand, often result in direct activation of defenses and sometimes adverse effects on plant growth. Such growth defects trig- gered by high BTH doses are partly explained by the Electronic supplementary material The online version of this article (doi:10.1007/s13313-013-0207-1) contains supplementary material, which is available to authorized users. Z. Azami-Sardooei : H. S. Seifi : D. De Vleesschauwer : M. Höfte (*) Laboratory of Phytopathology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Gent, Belgium e-mail: Monica.Hofte@UGent.be Australasian Plant Pathol. (2013) 42:485–490 DOI 10.1007/s13313-013-0207-1