Abstract
The wilting of rice seedlings appeared at high rate when inoculated at the four leaf stage in the nursery by immersed in bacterial suspension (105 cells/ml) for 16 hours. Most of the lower leaves of wilted seedlings showed ordinary yellow blight symptom and the sixth leaves wilted, whereas the fifth leaves did not show any symptoms.
Histological study revealed that the primary infection occurred only at the hydathode of the lower leaves which were already developed at the time of inoculation, and that the wilting of the upper leaves was due to the vessel embolisms caused by the secondary colonization of those infecting bacteria. The reason why the fifth leaf was not wilted, was that the vessels of this leaf are connected with those of the third leaf where bacterial multiplication was insufficient to induce the wilting. In general, the vessels of the even-numbered leaves did not connect with those of the uneven-numbered leaves. So far as this study, no direct invasion of the bacteria through the roots and the basal parts of the stems was found.
In several cases, the rupture of the infected vessels and bacterial exudation to the intercellar spaces of the parenchyma were observed. The vessels were always ruptured from the inside of the vessels and the infection of the healthy vessels by those exudated bacteria was never recognized.
