RESISTANCE INDUCTION BY SILICON AGAINST BACTERIAL DISEASES OF TOMATO, EGGPLANT, CUCUMBER AND GERANIUM. T. Hartmann and K. Wydra
Leibniz Universität Hannover, Institute of Plant Diseases and Plant Protection. Herrenhäuser Str. 2. 30149 Hannover, Germany.

Abstract: To contribute to the development of new integrated practices for the control of bacterial diseases, root and/or foliar application of silicon to eggplant, geranium, tomato and cucumber were investigated. In eggplant and geranium, wilt incidence caused by Ralstonia solanacearum was reduced in silicon-treated plants, and initially delayed by two days. Bacterial numbers were significantly reduced in stems of eggplant and geranium. Immunohistochemical studies of possible molecular mechanisms of silicon-mediated resistance on cell wall level in eggplant and geranium showed a strong yellow autofluorescence of the xylem parenchyma and vessel walls, indicating the production of phenolic substances in inoculated plants without silicon application, but not in plants treated with silicon. In geranium, inoculation resulted in an increased staining for (1→5)-α-L-arabinan side chains of rhamnogalacturonan-I in cell walls, which was less in inoculated plants without silicon application. Foliar- and/or root-application with silicon to tomato genotypes with different levels of resistance, and to cucumber, inoculated with Pseudomonas syringae pv. tomato and Pseudomonas syringae pv. lachrymans causing bacterial speck in tomato and angular leaf spot in cucumber, respectively, resulted in slightly reduced bacterial speck in a moderately resistant tomato genotype. In cucumber, a weak retardation in the initial development of angular leaf spot was observed. A reduction in bacterial populations was observed in tomato, but not in cucumber. In tomato, the enzyme activity of guaiacol peroxidase was increased after inoculation, but no effect due to silicon treatment was observed, while in cucumber, the enzyme activity was also increased after inoculation, and was higher in silicon-treated plants. A major role of the genetically determined resistance of a genotype was decisive and, thus, silicon-induced resistance can most effectively be triggered in genotypes exhibiting a moderate resistance against a pathogen.