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.