First Observation of Xanthomonas campestris pv. vesicatoria Race T2P7 Isolated from Pepper in the Philippines

Abstract

Thirteen strains of Xanthomonas campestris pv. vesicatoria, causal agent of bacterial spot of pepper (Capsicum spp.) and tomato (Lycopersicum spp.), were isolated from six different pepper fields in the vicinity of Bongabon, Luzon, the Philippines. The strains were characterized based on sensitivity to copper and streptomycin, physiological tests, analysis of whole cell fatty acids (fatty acid methyl ester; FAME), serology, amplification of the 16S-23S rDNA spacer region, pathogenicity, and virulence on pepper and tomato differential genotypes as previously described (1,2). All of the Philippine strains were copper resistant (50 μg/ml), and streptomycin sensitive (20 μg /ml). None of the strains were pectolytic or amylolytic. FAME analysis showed that all strains had similar fatty acid profiles, and matched the strains to X. campestris (similarity indices [S.I.] = 0.186-0.455). With the universal primers 4F/7R, a DNA fragment (680 bp) was amplified from 16S-23S rDNA spacer regions of all Philippine strains. Serological fingerprints of the strains with a set of eight monoclonal antibodies (MAbs) in indirect enzyme-linked immunosorbent assay showed that all Philippine strains were serovar A1. Existence of the avrRxv gene in X. campestris pv. vesicatoria race T1 strains was also confirmed for all Philippine strains by amplifying a DNA fragment (approximately 0.7 kb) with the primer set RST 27/28. This is genetic evidence for race identity of the Philippine strains with T1. However, hypersensitive test results on pepper and tomato differential lines identified the Philippine strains as T2P7. These results showed that X. campestris pv. vesicatoria strains may contain the avrRxv gene, but it may not be functional. This is the first report of the observation of X. campestris pv. vesicatoria race T2P7 on pepper.