Induced systemic resistance in Arabidopsis thaliana elicited by bean (Phaseolus vulgaris) rhizobacteria and their volatiles against Xanthomonas campestris pv. armoraciae.

INDUCED SYSTEMIC RESISTANCE IN ARABIDOPSIS THALIANA ELICITED BY BEAN (PHASEOLUS VULGARIS) RHIZOBACTERIA AND THEIR VOLATILES AGAINST XANTHOMONAS CAMPESTRIS PV. ARMORACIAE A. Giorgio1, P.A.H.M. Bakker2, N.S. Iacobellis1 1Scuola di Scienze Agrarie, Forestali, Alimentari ed Ambientali, Università degli Studi della Basilicata, Viale dell’Ateneo Lucano 10, 85100, Potenza, Italy. 2Plant-Microbe Interactions, Institute of Environmental Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands. E-mail: iacobellis@unibas.it Bacteria that are naturally associated to the rhizosphere of Phaseolus vulgaris were isolated and evaluated for the production of diffusible and volatile antimicrobial metabolites and hydrolytic enzymes. Six strains of rhizobacteria that inhibited the growth of bean pathogens, were identified as Pseudomonas and Bacillus spp.. When applied to bean seeds, these stains reduced the disease caused by Xanthomonas campestris pv. phaseoli var. fuscans inoculated by injection in the leaves, suggesting the involvement of induced systemic resistance (ISR). Arabidopsis thaliana is a model plant for which ISR has been well documented, including signal transduction pathways involved, and we assessed whether three selected rhizobacteria were able to elicit ISR in the pathosystem A. thaliana / X.c.pv. armoraciae. Pseudomonas fluorescens WCS417 was used as a positive control for ISR in A. thaliana. Inducing plants by root colonization or exposing A. thaliana to volatiles produced by three selected rhizobacteria reduced X.c.s pv. armoraciae growth in plant tissues and disease symptoms after inoculation of the leaves by dipping. Expression analysis of the defense marker genes PR1, ERF1, PDF1.2, and VSP2 in A. thaliana Col-0 after pathogen infection showed that exposure to the volatiles resulted in priming. The involvement of specific defense-related pathways in ISR was investigated using A. thaliana mutants affected in salicylic acid, ethylene, or jasmonic acid signaling. These results provide new insights on plant defense responses through different signal transduction pathways, depending on the rhizobacterium used and on the involvement of rhizobacterial volatiles in eliciting ISR.