PROBLEMS IN DETECTION OF XANTHOMONAS-ORYZAE PV ORYZAE IN RICE SEED AND POTENTIAL FOR IMPROVEMENT USING MONOCLONAL-ANTIBODIES

Four semiselective media that varied with respect to carbon source, am ino acids, and antibiotics were evaluated for the growth of various st rains of the rice bacterial blight pathogen, Xanthomonas oryzae pv. or yzae in pure and mixed culture. Plating efficiencies in pure culture r anged from 40 to 90% on these media, and colonies developed in 3-7 day s, depending on the strain of X. o. oryzae. In mixtures with Erwinia h erbicola and Pseudomonas putida (1:1:1), X. o. oryzae was recovered on ly 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 re covery of other strains was reduced or unaffected. Despite the semisel ectivity of XOS medium, sensitivity of the seed assay remains inadequa te because even the faster growing X. o. oryzae strains were not recov ered unless present in relatively high populations (2 X 10(5) to 1 X 1 0(6) cfu/ml) in the seed extract. When fluorescent pseudomonads were p resent at ratios greater than 60:1, X. o. oryzae was not detected. On plates crowded with rice seed contaminants, colonies of X. o. oryzae w ere identified by positive ELISA or immunofluorescence reactions with pathovar-specific monoclonal antibodies. Reactivity with monoclonal an tibodies correlated well with pathogenicity tests and shortened the as say time required for presumptive identification of X. o. oryzae.