The role as inoculum sources of Xanthomonas citri pv. citri surviving on the infected Satsuma mandarin fruits

Importing citrus fruits infected by Asiatic citrus canker caused by Xanthomonas citri pv. citri (Xcc) can act as an inoculum source for the disease epidemic in citrus canker-free countries. In this study, the pathogenicity of the causal agent of Asiatic citrus canker surviving on infected Satsuma mandarin fruits was evaluated. The washing solution of infected Satsuma mandarin fruits did not cause lesion formation on the citrus leaves. However, a typical citrus canker lesion was formed on the leaves after inoculation with higher concentrations of the inoculum from the washing solution (washing solution II). It indicated that the pathogenicity of the citrus canker surviving on the symptomatic Satsuma mandarin fruits was not changed. Scanning electron microscopic observation showed that the numbers of bacterial cells on the leaves of Satsuma mandarin which inoculated with the washing solution directly (washing solution I) was less compared to those of leaves inoculated with the washing solution II. This result spports that the pathogenicity of Xcc surviving on Satsuma mandarin fruits may not be changed but that the sucessful infection of citrus caker may depend on the concentration of the inoculum.