Abstract
Primary inoculation of an incompatible bacterium, Pseudomonas syringae pv. tabaci, to the loquat leaves, induced the growth inhibition of compatible strain B of P. syringae pv. eriobotryae inoculated 3 days after against to the same leaves. The growth inhibition of the parasitic bacterium was not observed when the sequence of inoculation was carryed in reverse order. Inoculated loquat leaves with the incompatible strain C of the pathogen or P. syringae pv. tabaci produced a phytoalexin (aucuparin) as early as 24hr post inoculation and its activity increased thereafter. Bacterial growth in the leaves was inhibited with the accumlation of aucuparin in the leaves. In contrast, when loquat leaves were inoculated with the compatible strain B, the bacterial population in the leaves increased gradually until 14 days when the lesion development was observed. Aucuparin activity was not detected before lesion development, but it increased rapidly thereafter and later reached a high level. A possible role of aucuparin in loquat leaves against P. syringae pv. eriobotryae was discussed in relation to the mechanism of disease resistance.
