Effect of techlofthalam [bactericide] spray on Xanthomonas oryzae [causal bacterium], the causal pathogen of rice bacterial leaf blight in the rice leaf [Oryza sativa]

Effects of a spray with techlofthalam [N-(2, 3-dichlorophenyl)-3, 4, 5, 6-tetrachlorophthalamic acid] at 100ppm on the population and aggressiveness of Xanthomonas oryzae, the causal organism of bacterial leaf blight of the rice plant, in rice leaf tissues were periodically studied. Change of bacterial populations after spraying showed a definite trend independent of application time, 1 day before and 3 days after hydathode inoculation, and after lesion formation. The bacterial population relatively decreased a few days after spraying and then it remained consistent at a much lower level, particularly at approximately 10% the level of unsprayed plants in case of spraying following lesion formation. Bacteria isolated from leaves 17 and 30 days after spraying produced smaller lesions on rice leaves free of techlofthalam than those from unsprayed leaves. This indicates the lower aggressiveness of the bacteria in sprayed leaves and retention of the property even after isolation from the host. The bacteria, however, recovered their original aggressiveness when grown on an agar medium or in rice leaves.