Molecular Epidemiology of Pseudomonas syringae pv. tomato

Pseudomonas syringae pv. tomato (Pst) is the causal agent of bacterial speck of tomato. It grows as epiphyte on tomato leaves. When environmental conditions favourable to infection persist, bacteria penetrate in the leaves through stomata or in the fruits through lesions, developing disease. In this work, the genetic variability of a population of Pst, isolated in an unique field heavily infected in southern Italy, was characterized by M13-PCR. Bacteria were isolated from two tomato cultivars ('Alexa' and 'Talent'), so to have groups of isolates each obtained from a same fruit or from a same lesion. Strains from other countries were used as controls. Results showed a high genetic uniformity of this Pst population: in fact, only three haplotypes were observed. The most frequent haplotype included isolates from locations (France and Spain) far away from the field studied. From a same fruit, two haplotypes were frequently isolated and, sometime, the haplotypes isolated were three. From a same lesion, the haplotypes isolated were two or, sometimes, three.