Problems in Detection of Xanthomonas oryzae pv. oryzae in Rice Seed and Potential for Improvement Using Monoclonal Antibodies. S. S. GNANAMANICKAM, Centre for Advanced Studies in Botany, University of Madras, India 600025. T. SHIGAKI, Department of Plant Pathology, University of Hawaii, Honolulu 96822; E. S. MEDALLA and T. W. MEW, Department of Plant Pathology, International Rice Research Institute, Philippines; and A. M. ALVAREZ, Department of Plant Pathology, University of Hawaii, Honolulu 96822. Plant Dis. 78:173-178. Accepted for publication 19 October 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0173.

Four semiselective media that varied with respect to carbon source, amino acids, and antibiotics were evaluated for the growth of various strains of the rice bacterial blight pathogen, Xanthomonas oryzae pv. oryzae in pure and mixed culture. Plating efficiencies in pure culture ranged from 40 to 90% on these media, and colonies developed in 3-7 days, depending on the strain of X. o. oryzae. In mixtures with Erwinia herbicola and Pseudomonas putida (1:1:1), X. o. oryzae was recovered only on XOS medium. Recovery of a faster growing X. o. oryzae strain (X1-5) was improved by adding 50-100 mg/L of FeEDTA to XOS medium, but recovery of other strains was reduced or unaffected. Despite the semiselectivity of XOS medium, sensitivity of the seed assay remains inadequate because even the faster growing X. o. oryzae strains were not recovered unless present in relatively high populations (2 × 105 to 1 × 106 cfu/ ml) in the seed extract. When fluorescent pseudomonads were present at ratios greater than 60:1, X. o. oryzae was not detected. On plates crowded with rice seed contaminants, colonies of X. o. oryzae were identified by positive ELIS A or immunofluorescence reactions with pathovar-specific monoclonal antibodies. Reactivity with monoclonal antibodies correlated well with pathogenicity tests and shortened the assay time required for presumptive identification of X. o. oryzae