Salicylic acid accumulates in the roots and hypocotyl after inoculation of cucumber leaves with Colletotrichum lagenarium

SummaryIncreased amounts of salicylic acid (SA) were detected in the roots and hypocotyl of cucumber plants (Cucumis sativus) using high-performance liquid chromatography following inoculation of the leaves with the anthracnose pathogen, Colletotrichum lagenarium. The concentrations of SA in the internodes immediately below the infected leaves increased to more than 1 μg/g fresh weight. In contrast, the concentrations of SA in stems distant from, or above the infected leaves increased to 100–300 ng/g. An increase in SA levels was observed in the upper stem 2 d after inoculation, followed by the hypocotyl with an increase detected 4 d after inoculation. An initial increase in the SA levels was detected in the stem, followed by an increase in SA levels in the root from a basal level of approximately 300 ng/g to more than 1 μg/g. The increased level of SA in the lower leaves was less than 100 ng/g. These results indicate that the levels of SA in the hypocotyl and root increased significantly following inoculation of the leaves with a microorganism capable of inducing SAR.