Potential role of volatile organic compounds (vocs) in the interaction of Pseudomonas tolaasii and mushrooms

POTENTIAL ROLE OF VOLATILE ORGANIC COMPOUNDS (VOCS) IN THE INTERACTION OF PSEUDOMONAS TOLAASII AND MUSHROOMS Pietro Lo Cantore,1 Rocco Racioppi,2 Maurizio D’Auria2 and Nicola Sante Iacobellis1* 1Scuola di Scienze Agrarie, Forestali, Alimentari e Ambientali, 2Dipartimento di Scienze, Università degli Studi della Basilicata, viale dell’Ateneo Lucano 10, 85100, Potenza, Italy. e-mail: nicola.iacobellis@unibas.it Cultivated mushrooms are attacked by a series of parasites, including bacteria, which cause significant crop losses. Among them Pseudomonas tolaasii is recognized to cause serious diseases on several mushroom species including Agaricus and Pleurotus spp. . It is well recognized that the lipodepsipeptides tolaasins are the main virulence factor since they are responsible for symptoms development on mushrooms due to the ability to cause cell lysis through transmembrane ion channel formation. Our recent studies, following preliminary studies (Shirata A., 1996. Ann. Phytopathol. Soc. Jpn. 62:185-193), demonstrated that virulent strains of P. tolaasii produce in vitro an array of volatile substances which are apparently involved in the P. tolaasii/mushrooms interaction. In particular, SPME analysis (fiber coated with 100 µm of no grafted poly(dimethylsiloxane) (PDMS) phase) followed by GC-MS of the overhead cultures space of three virulent strains of Pseudomonas tolaasii, including the type strain, showed the production of methanethiol (MT), dimethyl disulfide (DMDS), p-cymene, 2,4-undecadiene, 1-undecene and 2-undecanone though the level among the strains was different. The volatile mixture produced by the pathogen strains and the main representative pure components of the volatile Organic Compounds (VOCs) mixture such as dimethyl sulfide and methanethiol caused brown discoloration of Agaricus bisporus and Pleurotus ostreatus tissue blocks and inhibited the growth of P. ostreatus and P. eryngii mycelia. These results indicate that VOCs may play a role in the virulence of the producer and in the mushroom pathogen interaction. Furthermore, the volatile mixture as well as pure MT and DMDS resulted toxic also against plants since interfered, though at different level of concentration, with the lettuce and broccoli seed germination and broccoli seedling growth features.