Monitoring the occurrence of tomato bacterial spot and range of the causal agent Xanthomonas perforans in Iran.

A 2-year comprehensive field survey was conducted across major tomato-growing areas of Iran. Two hundred and thirty-four tomato fields and six tomato-producing greenhouses were surveyed for the potential presence of bacterial spot disease. Five hundred and ninety-six tomato samples with and without symptoms were analysed. While Xanthomonas spp. were found in association with tomato plants both with and without symptoms from five surveyed counties, the bacterial spot disease was observed only in plants from three of them. Only strains isolated from plants with symptoms induced disease symptoms on tomato, while those isolated from symptomless plants caused symptoms only on cabbage and common bean. None of the isolates caused disease symptoms on pepper and eggplant. Phylogenetic analysis showed that X. perforans is the causal agent of tomato bacterial spot in Iran, although X. campestris and X. axonopodis were also associated with symptomless tomato plants. All X. perforans isolates in this study were sensitive to streptomycin, copper sulphate and copper oxychloride at concentrations of 50 mg L⁻¹, 200 mg L⁻¹ and 0.8 g L⁻¹, respectively. Unlike the type strain of X. perforans, isolates in this study did not produce bacteriocin against other Xanthomonas spp., nor were they detected using the usual species-specific primer pair Bs-XpF/Bs-XpR. This suggests an atypical nature of X. perforans strains in Iran, which leads to the hypothesis that X. perforans strains in Iran may have a separate origin to those causing disease epidemics elsewhere. The aggregated dispersal pattern of the diseased tomato fields signifies the seedborne introduction of the pathogen into the country. [ABSTRACT FROM AUTHOR]