Oligandrin, the elicitin-like protein produced by the mycoparasite Pythiumoligandrum, induces systemic resistance to Fusarium crown and root rot in tomato plants

Oligandrin, the elicitin-like protein produced by the mycoparasite Pythium oligandrum, crab shell chitosan and crude glucans, isolated from P. oligand rum cell walls were applied to decapitated tomato plants and evaluated for their potential to induce defence mechanisms in root tissues infected by Fu sarium oxysporum f. sp. radicis-lycopersici. A significant decrease in dise ase incidence was monitored in oligandrin- and chitosan-treated plants as c ompared to water-treated plants whereas glucans from P. oligandrum cell wal ls failed to induce a resistance response. Ultrastructural investigations o f the infected root tissues from water-treated (control) plants showed a ra pid colonization of all tissues including the vascular stele. In root tissu es from oligandrin-treated plants, restriction of fungal growth to the oute r root tissues, decrease in pathogen viability and formation of aggregated deposits, which often accumulated at the surface of invading hyphae, were t he most striking features of the reaction. In chitosan-treated plants, the main response was the formation of enlarged wall appositions at sites of at tempted penetration, These wall appositions were found to vary greatly in t heir appearance from multi-textured to multi-layered structures and to cont ain large amounts of callose. The use of the WGA/ovomucoid-gold complex pro vided evidence that the wall-bound chitin component in Fusarium cells colon izing roots of oligandrin-treated tomato plants was not substantially alter ed even over cell walls of hyphae showing obvious signs of degradation. Evi dence is provided in this study that oligandrin has the ability to induce s ystemic resistance in tomato. Exogenous, foliar applications of the fungal protein sensitize susceptible tomato plants to react more rapidly and more efficiently to F o. f. sp. radicis-lycopersici attack, mainly through the m assive accumulation of fungitoxic compounds at sites of attempted pathogen penetration. Although cell wall modifications do not represent the central core of the oligandrin- mediated host response in tomato, they are part of the multicomponent defence system elaborated to fend off Fusarium invasion. (C) 2001 Editions scientifiques et medicales Elsevier SAS.