Investigations on the possible use of abiotic and biotic elicitors in defence-related responses in plants

Summary Experiments were conducted to determine the protective effect triggered by the plant growth retardant prohexadione-Ca (Regalis®), bacterial lipopolysaccharides (LPS) and oligosaccharides (OLS) in different host-pathogen systems. These molecules did not show any direct antibacterial activity in vitro. On tobacco leaves, LPS infiltration (100 µ gm l –1 ) prevented hypersensitive reaction (HR), whereas OLS at different concentrations did not give constant and reliable responses. On micropropagated pear plantlets in vials, only Regalis® and LPS (100 µ gm l –1 ) gave a significant defence-related response against fire blight (Erwinia amylovora): in particular, plant-derived antimicrobial compounds were related to flavan-3-ols and appeared to be newly synthesized after LPS application. Regalis®, applied at different concentrations, significantly lowered progression of bacterial wilt (Ralstonia solanacearum) and reduced leaf lesions of bacterial speck (Pseudomonas syringae pv. tomato) and spot (Xanthomonas vesicatoria) on tomato plants in the greenhouse. OLS application (100 µ gm l –1 ) significantly protected tomato leaves from bacterial speck, but not from bacterial spot. Two treatments with Regalis®, at a twelve-day interval and at different concentrations (75+50 ppm), gave a valuable protection of grapevine leaves to downy mildew (Plasmopara viticola) in the greenhouse. When Regalis® was sprayed at different concentrations and at different times on potted plum trees kept outdoors it was apparently ineffective against bacterial spot/canker (Xanthomonas arboricola pv. pruni). These findings further support the potential of prohexadione-Ca and of other biotic molecules as tools for plant defence responses against different pathogens, in the perspective of integrated, eco-friendly and sustainable control programmes. Zusammenfassung Untersuchungen uber eine mogliche Anwendung von biotischen und abiotischen Elizitoren von Schutzmechanismen in Pflanzen. Die Untersuchungen wurden durchgefuhrt, um die Schutzwirkung des Wuchshemmstoffs Prohexadion-Ca (Regalis®) und von bakteriellen Lipopolysacchariden (LPS) sowie Oligosacchariden (OLS) in unterschiedlichen Wirt-Pathogen-Beziehungen zu ermitteln. In vitro weisen diese Molekule keinerlei direkte antibakterielle Wirkung auf. Auf Tabakblattern verhindert die LPS-Infiltration (100 µ gm l –1 ) Hypersensitivitatsreaktionen (HR), wahrend OLS in unterschiedlichen Konzentrationen keine konstante und zuverlassige Reaktion hervorruft. Mikrovermehrte, getopfte Birnenpflanzchen zeigten nur bei Regalis® und LPS (100 µ gm l –1 ) signifikante Abwehrreaktionen gegen Feuerbrand (Erwinia amylovora): die von den Pflanzen gebildeten antimikrobiellen Verbindungen waren insbesondere mit Flavan-3-ol verwandt und wurden offenbar nach der LPS-Gabe neu synthetisiert. Regalis®, das in unterschiedlichen Konzentrationen angewendet wurde, verlangsamte bei Gewachshaustomaten die Entwicklung der bakteriellen Welkekrankheit (Ralstonia solanacearum) signifikant und reduzierte Blattlasionen, die durch Blattflecken- (Pseudomonas syringae pv. tomato) und Ringfleckenkrankheit (Xanthomonas vesicatoria) verursacht wurden. Die OLS-Gabe