A New Detection Method for the Pathogen of Bacterial Leaf Blight of Rice (Xanthomonas oryzae) by Means of Bacterial Exudation

A new detection method for the pathogen of bacterial leaf blight of rice (Xanthomonas oryzae was devised and its accuracy was evaluated. The process of this method is as follows: using seedlings of susceptible variety (Jukkoku or Kinmaze) at 4.5-5.0 leafstage, the materials to be detected are inoculated on leaf blade of the seedling twice with a bundle of 100 needles (i.e., 200 needle prick inoculation). Younger leaves are more suitable for detection than older ones, and the test plant should be applied with nitrogenous fertilizer. Seven days after inoculation, bacterial exudation is to be observed from a section of about 1.5mm wide cut at an upper part of the inoculated point. The bacterial exudation indicates the presence and abundance of the pathogen. The lower limit of detection seems to lie at about 100 cells per ml. Bacterial exudation is observed in the case of inoculation with Pseudomonas glumae, P. setariae and Xanthomonas phaseoli respectively, only when they are inoculated at high bacterial density of more than 107 cells per ml. Therefore, these contaminants seem to be negligible under field conditions when the method is applied to detect X. oryzae from natural materials. The author proposes to name this method “bacterial exudation method”.