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Suppressing Effects of Erwinia herbicola on Infection by Xanthomonas oryzae and on Symptom Development in Rice. S. P. Y. Hsieh, Graduate Student, Department of Plant Pathology, University of Hawaii, Honolulu 96822, Present address of senior author: National Chung Hsing University, Taichung, Taiwan; I. W. Buddenhagen, Professor, Department of Plant Pathology, University of Hawaii, Honolulu 96822. Phytopathology 64:1182-1185. Accepted for publication 27 March 1974. DOI: 10.1094/Phyto-64-1182.

Symptoms were reduced or prevented and the incubation period for symptom appearance was prolonged when rice plants were inoculated with Xanthomonas oryzae mixed with Erwinia herbicola by needle-prick or root-dip methods. Symptom development was retarded most when low concns of X. oryzae (10⁶/ml) were combined with high concns of E. herbicola (10⁸ or more/ml). However, no delay in symptom development was observed when rice leaves were inoculated with mixed inocula of X. oryzae and heat-killed E. herbicola or mixed inocula of streptomycin-resistant X. oryzae and viable E. herbicola suspended in streptomycin solution. E. herbicola lowered the pH of a liquid medium to inhibitory levels but otherwise did not produce substances antagonistic to X. oryzae in liquid or solid media.