Multitrophic Interactions in Soil IOBC/wprs Bulletin Vol. 71, 2011 pp. 47-51 47 Induced systemic resistance in strawberry (Fragaria × ananassa) to powdery mildew using various control agents Yael Meller Harel 1 , Max Kolton 2 , Yigal Elad 1 , Dalia Rav-David 1 , Eddie Cytryn 2 , David Ezra 1 , Menahem Borenstein 1 , Ran Shulchani 1 , Ellen R. Graber 2 1 Department of Plant Pathology and Weed Research, Institute of Plant Protection; 2 Department of Soil Chemistry, Plant Nutrition and Microbiology, Institute of Soil, Water and Environmental Sciences, The Volcani Center, Agricultural Research Organization, Bet Dagan 50250, Israel e-mail: yaelm@volcani.agri.gov.il Abstract: Powdery mildew, caused by Podosphaera aphanis, is one of the major fungal diseases of cultivated strawberry (Fragaria × ananassa Duchense) world-wide. In the present research we report the efficacy of various control agents in induced resistance in strawberry plants against Powdery mildew. Inducers tested are Trichoderma harzianum T39, acibenzolar-S-methyl (Bion), a new protein hydrolysate inducer, an isolate of a bacterium and one of a yeast, and biochar. These agents induced systemic resistance when applied to the root zone, while the disease was found and measured on the leaves. In addition, we studied the effect of T39, Bion and biochar on plant defense related gene expression. We show that while Bion induced Systemic Acquired Resistance (SAR) only, as expected, T39 as well as biochar induced SAR and Induced Systemic Resistance (ISR). Key words: Strawberry, powdery mildew, induced resistance, control agents, biochar, PR proteins, SAR, ISR Introduction Cultivated strawberry (Fragaria × ananassa Duchense) is widely grown worldwide. It is susceptible to the obligate parasite Podosphaera aphanis, causing powdery mildew, one of the major fungal diseases of this crop. The importance of reducing the use of fungicides makes the study of alternative means of control of plant diseases crucial. One promising alternative is the use of control agents that induce systemic resistance via the plants’ own natural defences. In the presence of biotic or abiotic inducing factors, plants respond by an increased level of systemic resistance (IR). Two major pathways leading to IR have been described. Systemic acquired resistance (SAR) involves synthesis of pathogenesis related (PR) proteins and is mediated by the phytohormone salicylic acid (SA). Induced systemic resistance (ISR) is generally triggered by growth-promoting rhizobacteria (PGPR) and fungi (PGPF) and depends on the phytohormones ethylene (E) and jasmonic acid (JA) (Vallad & Goodman, 2004). Few defence-related strawberry genes involved in these pathways are known. Among them, FaPR1(GenBank: AB462752.1) and Fraa3 (Munoz et al., 2010) encode PR proteins, lox (GenBank AJ578035) codes for the JA synthesis enzyme lipoxygenase, and FaWRKY is a trans acting factor involved in both SAR and ISR in strawberry (Encinas- Villarejo et al., 2009). In this study we were interested in comparing the relative efficacy of different control agents against strawberry powdery mildew. Acibenzolar-S-methyl (Bion), a chemical analogue of the plant hormone salicylic acid is the most commonly used chemical SAR inducer. T39 is a strain of Trichoderma harzianum which is an ISR inducer active against foliar pathogens on many crops (Perazzoli et al., 2009; De Meyer et al., 1998). Other lesser