Role of VOCs in the interaction of rhizobacteria and plant pathogenic fungi

ROLE OF VOCS IN THE INTERACTION OF RHIZOBACTERIA AND PLANT PATHOGENIC FUNGI N. S. Iacobellis, A. Giorgio, D. Lamorte, , P. Lo Cantore. Scuola di Scienze Agrarie, Forestali, Alimentari ed Ambientali, Università degli Studi della Basilicata, Viale dell’Ateneo Lucano, 85100, Potenza, Italy; e- mail: nicola.iacobellis@unibas.it. Among 162 bacteria isolates obtained from bean plants rhizosphere 60 inhibited in dual plate assays the growth of bean fungal and bacterial pathogens. When the above 60 antagonistic bacteria were applied to bean seeds and the relative plants challenged with a highly virulent strain of X. campestris pv. phaseoli var. fuscans six isolates highly protected bacterized bean plants. The bean plant protection by the six bacterial strains, though at different level, was observed either in in vitro or in greenhouse cotyledon and trifoliate pathogenicity leaf assays, respectively. The Induced Systemic Resistance (ISR) is apparently involved and, in fact, ISR has been recently ascertained in parallel studies using the pathosystem Arapidopsis thaliana and X. c. pv. amoriaceae for 3 of the above rhizobacteria. On the basis of 16S rDNA sequence analysis the above antagonistic rhizobacteria were identified by as Pseudomonas brassicacearum subsp. brassicacearum (3 strains), P. putida (2 strains) and Bacillus megaterium (1 strains). The six antagonistic bacterial strains did produce an array of hydrolytic enzymes, diffusible antimicrobial substances and volatile substances which inhibit the growth of several plant pathogenic fungi as assessed either in dual plate and volatile assays. In particular, strains of Sclerotinia sclerotiorum resulted highly sensible to both diffusible and volatiles and for that selected for further studies. Pure synthetic volatiles such as 2-nonanone, 2-undecanone, m-cymene, limonene, dimethy disulfite, dimethyl trisulfide, produced by the above antagonistic bacteria as ascertained by Solid Phase MicroExtraction of the overhead cultures space of the bacterial cultures followed by GC-MS analysis, highly inhibited, though with different MIC, the growth of S. slerotiorum strains and showed haemolytic activity suggesting that membrane systems are the target of the above VOCs. Preliminary observation with optical and electron microscopes of S. sclerotiorum mycelia appear to confirm the membrane as target for the above VOCs.