Characterization of Ohio Strains ofXanthomonas campestrispv.vesicatoria,Causal Agent of Bacterial Spot of Pepper

Abstract

In 1993 and 1994, 105 samples from pepper (Capsicum annuum) plants exhibiting symptoms of bacterial spot were collected from commercial fields and home gardens throughout Ohio and neighboring states. Eighty-nine presumptive Xanthomonas campestris pv. vesicatoria strains were isolated on a semiselective medium and identified by a combination of biochemical tests and gas chromatographic analysis of fatty acid methyl esters (FAMEs). All 89 strains caused a hypersensitive response (HR) on tobacco (Nicotiana tabacum cv. Samsun), and 76 strains were virulent on the susceptible pepper cultivar Marengo. Most (89%) of these strains were also virulent on the susceptible processing tomato cultivar Ohio 8245. The majority of the strains (80%) were identified as pepper race 3. Among the remainder, 2.6, 12, and 4% were pepper races 0, 1, and 2, respectively. One strain was identified as pepper race 6. Of the 68 strains pathogenic on tomato, 96% (65 strains) were tomato race 1 and three strains were tomato race 2. Fifty-two of the 76 strains were nonamylolytic (Amy - ) and nonpectolytic (Per - ); the remaining 24 strains, including two pectolytic (Pec + ) and 22 Pec- strains, were amylolytic (Amy + ). Although the composition of fatty acids in amylolytic and nonamylolytic strains was similar, it differed between pathogenic X. campestris pv. vesicatoria strains and nonpathogenic X. campestris strains isolated from pepper. Six serogroups were identified among X. campestris pv. vesicatoria strains using monoclonal antibodies (MAbs) in an enzyme-linked immunosorbent assay. However, 39.5% of the strains did not react with any of the MAbs and could not be assigned to a serovar. Streptomycin-resistant strains (49%) were more prevalent than copper-resistant strains (13%).